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In the preface of his book Switching Power Converters, Wood introduces the concept of a unified converter theory. There he states: “Most traditional views of the field have seemed somewhat disjointed; converters were largely regarded as related only because they all use semiconductor switches and have certain topological similarities. . . . the view expounded herein (is that) switching power converters are related by function and behavior; their basic characteristics do not in any way depend on the types of switches used, nor on the applications to which they are put, nor on the topologies in which they are realized.”. According to this unified theory, any power electronic converter can be viewed as a matrix of switches which connects its input nodes to its output nodes. These nodes may be either DC or AC, and either inductive or capacitive; and the power flow may be in either direction. Two obvious restrictions are enforced by some basic laws of electricity.

 

• If one set of nodes (input or output) is inductive, the other set must be capacitive, so as not to create a cut set of voltage or current sources when the switches are closed.

• The combination of open and closed switches should never open circuit an inductor, or short circuit a capacitor.

 

This unified set of converters is generally broken into a number of subsets. The term rectifier is used when the power flow is predominately from the AC port to the DC port and the term inverter is used when power flow is predominately from the DC port to the AC port. The term converter is used either when there is no predominant direction of power flow or as a general term to encompass both rectifiers and inverters. In a Voltage Source Converter (VSC), the DC port is the capacitive port and is voltage stiff (i.e. a large DC bus capacitor). The voltages in such a converter are well defined by this port and are generally considered independent of the converter’s operation. The value of the AC side inductance is comparatively small and modulation of the converter controls these AC side inductor currents. Should the voltage source converter be responsible for the control of the DC bus capacitor voltage, then this voltage is indirectly controlled by controlling the net current flow in the capacitor.

 

The switches in such a converter must block a unidirectional voltage, but be able to conduct current in either direction if bidirectional power flow is desired. The converse is true in a Current Source Converter (CSC) — the DC port is inductive and current stiff. The current in this port (and hence the converter) is well defined and slow to change. The voltage (particularly at the AC port) is considered the variable directly controlled by the converter modulation. Since the AC port usually has significant line or load inductance, line to line capacitors must be placed on the AC port. The switches must block either voltage polarity, but are only required to conduct current in one direction. This naturally suits thyristors and symmetrical GTOs.

Figure 2.1. A voltage source rectifier – inverter cascade (top) and a current source rectifier – inverter cascade

 

Since the AC line and AC motor loads are both inductive, Voltage Source Rectifier – Inverter cascades (Fig. 2.1) are usually used for small and now increasingly for large motor drives and similar applications, as GTOs and IGBTs have matured. Larger converters have traditionally been current source converters, both because this best suits the characteristics of the thyristors and because it requires a large DC bus inductor, which was preferred to a large capacitor. Some converters do not easily fall, or cannot be placed into either category. The matrix or Venturini converter [1] is one example (Fig. 2.2). Both input and output ports are AC, and the definition of voltage stiff or current stiff (and hence voltage or current source) becomes somewhat arbitrary. Both input and output ports are

 

Figure 2.2. The matrix converter, with one possible implementation of the bidirectional switches.

 

The next refinement is to define the meaning of multilevel. The following definition of a multilevel converter is offered:

A multilevel converter can switch either its input or output nodes (or both) between multiple (more than two) levels of voltage or current. The term “two-level” will be used where it is necessary to refer specifically to a converter which is not multilevel. This simple definition is deliberately quite broad and inclusive, in keeping with the spirit of the unified converter theory. For example, the multi-phase matrix converter (Fig. 2.2) is, strictly speaking, a multilevel converter, according to this definition. Consider the three phase to three phase matrix converter, with voltage source inputs and an inductive load. Any single output can be switched to one of three different voltage levels (the voltages of the three input phases) and similarly, any input can be switched to one of four current levels (including zero). In this preceding example, both the input and the output nodes are AC periodic varying quantities and so these levels can only be considered stationary for an interval much shorter than their AC period.

Figure 2.3. The current source converter (top right), voltage source converter (bottom left) and a simple three level voltage source converter (bottom right) can all be derived from the general topology of the matrix converter

 

                Both the voltage source and current source converters can be derived from the general matrix converter by setting one port to be either a two terminal DC voltage stiff or DC current stiff port [70, 30]. Retaining the third terminal leads to a simple and more conventional multilevel converter (Fig. 2.3). Note that now one of the ports has been made DC and voltage or current stiff, only one port will experience the multilevel stepped waveforms. The other will still have a continuous waveform similar to that of an equivalent two level converter.

 

For example, a converter with an appropriate structure may create a stepped multilevel voltage waveform at the inductive nodes, but will always have a continuous voltage waveform at its capacitive nodes. Similarly a different converter may create a stepped multilevel current waveform at its capacitive nodes, but must have a continuous current waveform at its inductive nodes.

The traditional understanding of what constitutes a multilevel converter follows this more narrow definition. One of the ports has multiple (more than two) voltage or current stiff DC nodes or terminals, while the second port has a conventional single or three phase set of terminals which are switched to these multiple levels.

Most multilevel converters discussed in the literature step between multiple voltage levels. This is usually the most useful configuration for a high power converter, as reducing conduction losses in both converter and machines will always favour increasing the voltage rating rather than the current rating of the converter. Also as power levels increase, the input and output voltage levels presented to the converter increase. The structures of these multilevel converters place the switches in series to share the duty of blocking these higher voltages. Equally however, for high current applications, many switches can be placed in parallel, with their current summed by inductors. When switched separately, multilevel current waveforms result. As expected, multilevel converters can be DC-DC, DC-AC and as explained, in the broadest sense, even AC-AC.

 

Generally multilevel topologies can be divided into two groups, although in some cases the dividing line is indistinct. The first approach relies on summing the outputs of a number of conventional two-level converters, to produce a resultant multilevel output. The second grou
p replaces the two-level switch structure with a multilevel switch topology within an otherwise conventional converter. These two groups will be distinguished by the terms multi-bridge converter and multilevel converter respectively. Any of the basic DC-DC converters (buck, boost, buck-boost, Cuk) can be extended to a multilevel topology. Often these are not called or perhaps even recognized as multilevel converters, but rather simply described as, for example, paralleled converters with interleaved switching instants. Two recent examples cited are multilevel boost converters used for power factor correction. In both of these examples, the switches are effectively placed in parallel and their contributions summed by separate boost inductors. They present multilevel current waveforms to the input and reduced voltage ripple at the output. Multilevel DC-AC converters range from the simplest single phase, full bridge driven with unipolar voltage switching to complex multi-phase converters. These are the most commonly recognized and reported multilevel converters and will be further categorized and referenced in the next section. Even multilevel AC-AC matrix converters have been shown to be at least theoretically possible.

At this point in the chapter, we will narrow the focus to that of three phase voltage source multilevel converters. Although this may seem somewhat limiting, it encompasses most of the higher power multilevel converters both in the published literature and in actual use. There are some examples of single phase converters functioning as AC-DC switching rectifiers, either in traction, computer or telecommunications power supplies. These Power Factor Correction rectifiers have lower inherent distortion and require less filtering because of their multilevel topology. There are four main voltage source DC-AC multilevel topologies which have been distinguished here and in the literature.

 

 

These are:

Ø       Multiple bridge using transformer or inductor summing;

Ø       Multiple bridge using direct series connection;

Ø       Multilevel diode-clamped converter; and

Ø       Multilevel flying capacitor converter.

 

Each of these will be examined in turn. Each of the diagrams presented are of a five-level converter, which can produce a nine-level phase to phase voltage waveform.

 

As the title suggests, these multilevel converters are simply a number of conventional two-level bridges, whose inputs or outputs are summed using transformers or inductors. The multiple transformer secondary’s force voltage sharing between the switches (Fig. 2.4). The most common and well known example of a multi-bridge converter is the twelve pulse thyristor converter, well covered in most power electronic textbooks [49]. Harmonic cancellation in these converters is achieved through the phase displacement of the voltage waveforms of the star and delta transformer secondary’s.

Figure 2.4. A five-level Transformer coupled multiple bridges, which produces nine level phase-phase waveforms on the transformer primary.

 

This 30? phase shift between transformer secondaries allows identical secondary switching instants and current waveforms to appear interleaved on the transformer primary. A series connection is used for HVDC; a parallel connection for high current applications such as electrolysis and electro-plating. The technique can and is extended to many bridges each with a transformer secondary connection of the appropriate phase shift to achieve cancellation of the further low order harmonics in the primary. By clever connection of the transformer primaries, current as well as voltage sharing can be ensured.

 

A good example of the next degree of complexity and flexibility is seen in a 10 MW battery energy storage plant. The GTO converters operate in square wave mode and still rely on the transformer phasing for harmonic cancellation. However because forced commutation is used; now both the magnitude and the phase (real and reactive power) can be separately controlled. An extension of this approach to 48 pulse operation is achieved by eight GTO bridges operating in square wave mode, with reliance on the transformer for harmonic cancellation. The cancellation of switching harmonics can also be achieved by switching strategies, rather than relying on the transformer secondary’s for the necessary phase shifting. The simplest case — the series or parallel connection of two PWM bridges — has been investigated by a number of researchers. By the use of appropriate PWM modulation for each bridge, the odd multiples of the PWM carrier and sidebands, including the first cluster, were entirely removed from the output spectrum. This improvement is better than can be achieved by merely doubling the carrier frequency as the carrier which remains has lower amplitude. A particularly good example of a six bridge, transformer summed multilevel converter is used as an active filter for arc furnace static flicker compensation [71].

The AC connections of these bridges are summed by separate transformer secondaries, which allow either a series or parallel DC connection. Since the transformer no longer provides phase shifting, it may seem possible to remove the transformer entirely and place the converters directly in parallel (for a parallel connection). However, while no difference exists between the desired input and output components of the two converters, the undesired switching components are by definition exactly out of phase. Kirchhoff’s laws would be violated if the converters were directly connected.

 

The solution is to use inter-phase reactors (current sharing reactors) or interphase transformers on either the input or output of the converters. Although these reactors see the full combined converter current (and so have similar copper volume and copper losses), they only experience the difference in voltage between the converters. The volts-second component of this voltage is smaller and so the iron content of these reactors can be reduced in comparison to the transformers which would be required for full isolation. Normally the inductors are placed on the AC side, which is already the inductive port of a voltage source converter. Research on a five level three-phase motor drive which used this technique was conducted by Matsui et al . The outputs of two half bridge legs were summed with a current sharing reactor to form a three level intermediate output. This and another similarly formed three level output were summed by a third reactor to form the final five level phase output. One further solution is to sum the outputs of two converters across a bridge connected source or load. Both ends of the transformer or motor winding are brought out and the winding must be fully floating. One converter is driven with a phase inverted signal, so that twice the desired converter output is impressed across the floating load. If the carriers are appropriately phased, part of the undesired carrier component will appear as a common mode component to the load. Of course, this technique can only be applied for two converters.

 

To summarize, the transformer or inductor summed approach has the following advantages:

 

• The voltages within the individual converters and thus across the switches are well defined by the stiff voltage source output of the transformer secondaries.

• Should a converter module fail, or be removed for service, the converter may continue operating at full voltage, but at reduced current. • Other than the transformer (inductors), the structure is modular, which allows easier maintenance and reduced spares.

• Its mode of operation is easily understood and, again because of its modular structure, control is more easily applied. but also the following disadvantages:

• The transformer itself, if not needed for isolation, adds significantly to the cost of the converter
and is one more item to maintain and potentially, to fail.

• The transformer requires multiple secondary windings, which must be isolated from one another and from ground. This is a significant problem at high voltages. This also increases the cost of the transformer.

 

A second topology, which is really only a variation on the first, is that of series connected bridge converters        (Fig. 2.5). Each phase leg consists of series connected single phase full bridges, the series connection being made directly (not by transformer as in the first case) on the AC side. A three phase converter can be constructed by connecting three of these single phase series strings to form a star or delta. Since this topology requires each full bridge to have an isolated DC bus, this connection has not been considered useful until recently re-examined. Now this topology is being considered for applications where no real power transfer is involved, such as for active power filtering and VAR correction. Then only a floating DC bus capacitor is required on each floating DC bus.

 

Some other sources of power which could easily be made modular and floating are batteries for battery energy storage systems (BESS) used for load leveling, or alternative energy sources such as solar panels. It is of course possible to power the isolated bridges from multiple isolated transformer secondaries, each with their own rectifier . By appropriate phase shifting of the transformer secondary windings, harmonic cancellation can be achieved on the primary side, as described previously, as well as at the multilevel output of the multi-bridge converter. However the disadvantages of a transformer with multiple isolated secondaries return. This multilevel converter structure has some very significant advantages, if its limitations are acceptable.

 

Its advantage is it has perhaps the simplest architecture and the lowest component count. No transformer is needed, so capital costs are low.

 

At this point it should be clear that one of the major advantages of a multilevel converter, regardless of topology, is increased power rating. A converter need not be limited in size by the prevailing semiconductor technology, since a multilevel converter allows the voltage and/or the current to be shared among a number of switches. This advantage has traditionally justified the extra complexity of multilevel converters only at very high power levels, for large motor drives and utility applications. As the understanding and acceptance of multilevel converters has increased, these converters are being used at all power levels to extend the useful power range of semiconductor switches. For example, using multilevel topologies, IGBTs are challenging traditional GTO converters in motor drive and traction applications and MOSFETs are displacing IGBTs in some larger Switch Mode Power Supplies. The more stringent harmonic standards now being legislated also advantage multilevel converters, since they produce lower switching harmonic spectral components for a given switching frequency limit.

 

The aim of this chapter has been to demonstrate the diversity of possible multilevel converter topologies. Each has its own mixture of advantages and disadvantages and for any one particular application, one topology will be more appropriate than the others. Often, topologies are chosen based on what has gone before, even if that topology may not be the best choice for the application. The advantages of the body of research and familiarity within the engineering community may outweigh other technical disadvantages. Despite the diversity, these different topologies contain common underlying links. Usually the modulation and, to a lesser extent, control strategies can be developed independently of the converter’s topology and then subsequently applied with little or no modification. In subsequent chapters, the simplest case of the transformer connected multi-bridge converter will be used as the implied default multilevel converter topology. Required variations on modulation and control strategies will be explained after the general technique has been presented.

 

Capacitance-voltage (C-V) testing is widely used to determine semiconductor parameters, particularly in MOSCAP and MOSFET structures. However, other types of semiconductor devices and technologies can also be characterized with C-V measure­ments, including bipolar junction transistors (BJTs), JFETs, III-V compound devices, photovoltaic cells, MEMs devices, organic TFT displays, photodiodes, carbon nano­tubes (CNTs), and many others.

The fundamental nature of these meas­urements makes them useful in a wide range of applications and disciplines. They are used in the research labs of universities and semiconductor manufacturers to evalu­ate new materials, processes, devices, and circuits. C-V measurements are extremely important to product and yield enhancement engineers, who are responsible for improv­ing processes and device performance. Reliability engineers use these measure­ments to qualify material suppliers, monitor process parameters, and analyze failure mechanisms.

With appropriate methodologies, instru­mentation, and software, a multitude of semiconductor device and material parame­ters can be derived. This information is used all along the production chain beginning with evaluation of epitaxially grown crys­tals, including parameters such as average doping concentration, doping profiles, and carrier lifetimes. In wafer processes, C-V measurements can reveal oxide thickness, oxide charges, mobile ions (contamination), and interface trap density. These measure­ments continue to be used after other process steps, such as lithography, etching, cleaning, dielectric and polysilicon depositions, and metallization. After devices are fully fabri­cated on the wafer, C-V is used to character­ize threshold voltages and other parameters during reliability and basic device testing and to model the performance of these devices.

A MOSCAP structure is a fundamental device formed during semiconductor fabri­cation. Although these devices may be used in actual circuits, they are typi­cally integrated into fabrication processes as a test structure. Since they are simple struc­tures and their fabrication is easy to control, they are a convenient way to evaluate the underlying processes.

The metal/polysilicon layer is one plate of the capacitor, and silicon dioxide is the insulator. Since the substrate below the insulating layer is a semiconducting material, it is not by itself the other plate of the capacitor. In effect, the majority charge carriers become the other plate. Physically, capacitance, C, is deter­mined from the variables in the following equation:

C = A (?/d), where

A is the area of the capacitor,

? is the dielectric constant of the insulator, and

d is the separation of the two plates.

Therefore, the larger A and ? are, and the thinner the insulator is, the higher the capacitance will be. Typically, semiconduc­tor capacitance values range from nanofar­ads to picofarads, or smaller.

The procedure for taking C-V measure­ments involves the application of DC bias voltages across the capacitor while mak­ing the measurements with an AC signal. Commonly, AC frequencies from about 10kHz to 10MHz are used for these measurements. The bias is applied as a DC voltage sweep that drives the MOSCAP structure from its accumulation region into the depletion region, and then into inversion

A strong DC bias causes majority car­riers in the substrate to accumulate near the insulator interface. Since they can’t get through the insulating layer, capacitance is at a maximum in the accumulation region as the charges stack up near that interface (i.e., d is at a minimum). One of the fundamental parameters that can be derived from C-V accumulation measurements is the silicon dioxide thick­ness, tox.

As bias voltage is decreased, majority carriers get pushed away from the oxide interface and the depletion region forms. When the bias voltage is reversed, charge carriers move the greatest distance from the oxide layer, and capacitance is at a minimum (i.e., d is at a maximum). From this inversion region capacitance, the number of majority carriers can be derived. The same basic concepts apply to MOSFET transistors, even though their physical structure and dop­ing is more complex.

Many other parameters can be derived from the three regions as the bias voltage is swept through them. Different AC signal frequencies can reveal additional details. Low frequen­cies reveal what are called quasistatic characteristics, whereas high frequency testing is more indicative of dynamic performance. Both types of C-V testing are often required.

Because C-V measurements are actually made at AC frequencies, the capacitance for the device under test (DUT) is calculated with the following:

CDUT = IDUT / 2?fVAC, where

IDUT is the magnitude of the AC current through the DUT,

f is the test frequency, and

VAC is the magnitude and phase angle of the measured AC voltage

In other words, the test measures the AC impedance of the DUT by applying an AC voltage and measuring the resulting AC current, AC voltage, and impedance phase angle between them.

These measurements take into account series and parallel resist­ance associated with the capacitance, as well as the dissipation factor (leakage).

Certain challenges are associated with this testing. Typically, test personnel have problems in the following areas:

Low capacitance measurements (picofarads and smaller values)

C-V instrument connections (through a prober) to the • wafer device

Leaky (high D) capacitance measurements

Using hardware and software to acquire the data

Parameter extractions

Overcoming these challenges requires careful attention to the techniques used along with appropriate hardware and software.

Low Capacitance Measurements. If C is small, the DUT’s AC response current is small and hard to measure. However, at higher frequencies, the DUT impedance is reduced, so the current increases and is easier to measure. Often semiconductor capacitance is very low (less than 1pF), which is below the capabilities of many LCR meters. Even those claiming to measure these small capacitance val­ues may have confusing specifications that make it difficult to deter­mine the final accuracy in the measurement. If accuracy over the instrument’s full measurement range is not explicitly stated, the user needs to clarify this with the manufacturer.

High D (Leaky) Capacitors. In addition to having a low C value, a semiconductor capacitor may also be leaky. That is the case when the equivalent R in parallel with C is too low. This results in resis­tive impedance overwhelming the capacitive impedance, and the C value gets lost in the noise. For devices with ultra-thin oxide layers, D values can be greater than five. In general, as D increases, the accu­racy of a C measurement is rapidly degraded, so high D is a limiting factor in the practical use of a C meter. Again, higher frequencies can help solve the problem. At higher frequencies the capacitive impedance is lower, resulting in a C current that is higher and more easily measured.

C-V Measurement Connections. In most test environments, the DUT is a test structure on a wafer: It is connected to the C-V instru­ment through a prober, a probe card adapter, and a switch matrix. Even if no switch is involved, there is still a prober and significant cabling. At high frequencies, special cor­rections and compensation must be applied. Usually, this is achieved with some combina­tion of an open, short, or calibration device. Because of the complexity of the hardware, cabling, and compensation techniques, it is a good idea to confer with C-V test application engineers. They are skilled at working with various probe systems to overcome many types of interconnection problems.

Obtaining Useful Data. In addition to the accuracy issues mentioned earlier, practical considerations in C-V data collection include the instrumentation’s range of test variables, versatility of parameter extraction software, and ease of hardware usage. Traditionally, C-V testing has been limited to about 30V and 10mA DC bias. However, many appli­cations, such as characterizing LD MOS structures, low-kinterlayer dielectrics, MEMs devices, organic TFT displays, and photodiodes, require tests at higher voltage or current. For these applications, a separate high voltage DC power supply and C meter are required; DC bias up to 400V differen­tial (0 to ±400V) and a current output up to 300mA are very useful. Being able to apply differential DC bias on both the HI and LO terminals of the C-V instrument offers more flexible control over electric fields within the DUT, which is very helpful in the research and modeling of novel devices, such as nano­scale components.

The instrumentation software should include ready-to-run test routines that do not require user programming. These should be available for the most widely used device technologies and test regimens, which were mentioned in the first three paragraphs of this article. Some researchers may also be interested in less common tests, such as performing both a C?V and C?f sweep on a Metal?Insulator?Metal (MIM) capacitor, measuring small interconnect capacitance on a wafer, or doing a C?V sweep on a two-terminal nanowire device. The parameter extractions should be easily obtained, with automated curve plotting.

Often, engineers and researchers are expected to perform C-V measurements with little experience and training on the instrumentation. A test system with an intui­tive user interface and easy-to-use features makes this practical. That includes simple test setup, sequence control, and data analy­sis. Otherwise, the user spends more time learning the system than collecting and using the data. Other considerations are a test system with:

Tightly integrated source-measure units, digital oscilloscope and C-V meter
Easy integration with other external  instruments
High resolution and precise measure­ments at the probe tips (DC biasing down to millivolts and capacitance measure­ments down to femtofarads)
Test setups and libraries that can be eas­ily modified
Diagnostic/troubleshooting tools that let users know whether or not the system is performing correctly.

is a soft light  that is effective and popular in all of the world .It can use in not only many different place ,such as room , shops , offices ,schools ,super markets ,cinemas but also can be used in the Light box , metro station , subway , night markets etc . Anyway it will be used in anywhere where needed .
It is not so ideal of the traditional fluorecsent’ power utilization:The power of extra ballast is too  high , need high voltage when start , the mercury that built in the fluorescent lamp can’t deal when it stop working and  becomes to hazards of environmental pollution .  Phosphor fluorescent tube fluorescent tube in the filling into the process, contain higher amounts of mercury (mercury), so the breakdown of fluorescent tubes, mercury vapor came out great harm to human body. Authoritative sources: mercury vapor up from 0.04 to 3 mg when will people in 2 to 3 months of chronic poisoning, up from 1.2 to 8.5 mg will induce acute mercury poisoning, should the the amount of 20 mg, will directly lead to animal death.
As the fourth and new light source ?The Led panel light  sources is used in many different area when it start.?The leds quantity in every  different LED panel light are not the same ,it is  about 840-1200 leds depend on the different power and lumen .and the color also not the same cause the different color temperature and the different color light ,for example ,white ,warm white etc ..
Energy saving is the most special point  of the Led panel light. Foe example , one T8 traditiona fluorescent tube ,the standard power is 36W ,and the extballast power is 8W , so total power is 44W when it’s working and the lumen is 420lm ,the serve life is 30,000 hours .But if you use a same features  led panel light , the working power is only 16W and the lumen is 815W and the serve life is even more than 50,000 hours .
PWM LED panel light driver PT4107
There many different  solution of the led panel light driver. The current program because of its high efficiency non-isolated and the mainstream though, and with PWM LED panel light  driver controller to do another drive power LED fluorescent is majority.
PT4107 Is a typical PWM LED driver controller, its internal topology shown in Figure 1.

PT4107 is a high voltage step-down type PWM LED led panel light-driven controller, through the external resistor and the internal zener diode that can be rectified 110V or 220V AC voltage clamp at 20V. When the voltage Vin on over-voltage lockout threshold of 18V, the chips began to work, in accordance with the peak current control mode to drive the external MOSFET. The external MOSFET’s source and to the current sampling resistor indirectly, the resistor voltage directly to the PT4107 chip CS side. When the CS terminal voltage exceeds the internal threshold voltage the current sample, GATE-side drive signal termination of the external MOSFET off. Threshold voltage can be internally set, or by applying a voltage to control the LD side. If the required soft-start, end in LD parallel capacitor voltage needs to be increased speed and increased speed and consistent LED current.
PT4107 main technical characteristics: from 18V to 450V wide voltage input range, constant current output; Frequency jitter to reduce electromagnetic interference, use of random source to modulate the oscillation frequency, it can extend the audio power spectrum, the energy spectrum can be expanded effectively reduce small band of electromagnetic interference, reducing system-level design difficulty; available linear and PWM dimming to support hundreds of 0.06W LED driving applications, operating frequency of 25kHz-300kHz, can be set by external resistors.
PT4107 package shown in Figure 2, the pin function as follows:

1. Chip ground terminal GND;
2. CS LED peak current input sample;
3. LD linear dimming access terminal;
4. RI Rosc access terminal;
5. ROTP over-temperature protection setting end;
6. PWMD PWM dimming input and enable the chip internal 100K pull-up resistors;
7. VIN-chip power supply terminal;
8. GATE drive external MOSFET gate;
Design full voltage 20W Led panel light switch current source
To AC 85V ~ 245V wide voltage input, for example, with PT4107 PWM LED panel light drive controller to do Led panel light-driven power of the main chip, the design of a better program application circuit (Figure 3). The program consists of the whole circuit by the anti-surge protection, EMC filter, full-bridge rectifier, passive power factor correction (PFC), buck regulators, PWM LED panel light-driven controller, extended flow constant current circuit.

Click philosophy, designed to switch the entire voltage 20W fluorescent lamp power constant current source schematic diagram shown in Figure 4. From the look into AC 220V, AC power entry has had 1A fuse FS1 and anti-surge of negative temperature coefficient thermistor NTC, EMI filter followed by the L1, L2, and CX1 composition. BD1 is a full-bridge rectifier, the internal pressure is four silicon diode. C1, C2, R1, D1 ~ D3 composition of passive power factor correction circuit. PT4107 chip from the T1, D4, C4, R2 ~ R4 formed after the power supply step-down regulator electronic filter, the filter input impedance is high, the output impedance is very small, close to 300V DC high voltage after rectification by the step-down to the transistor PT4107 Vin of about 18 ~ 20V voltage, to ensure that chip in the whole voltage range in stability.
Unlike the previous program that the resistance of the circuit step-down circuit as energy and hot. PWM control chip U1 (PT4107) and the power MOS tube Q1, ballast power inductor L3, diode D5 form continued buck regulator circuit, U1 collect current sampling resistor R6 ~ R9 on the peak current, the internal logic in a single cycle GATE pin control signal pulse duty cycle for constant current control. Output constant current and D5, L3 of the continued flow of the circuit to the LED light source combined constant current power supply, change the resistance of resistor R6 ~ R9 can change the circuit’s output current, but the D5, L3 changes have followed. R5 is a part of chip oscillator, the oscillation frequency can be adjusted to change it. Potentiometer RT in this circuit is not used for dimming, but to fine-tune the current source of current design of the circuit to power. As the dispersion device, a power board for each batch when the output current will be slightly different from the production line can use this potentiometer to adjust the power board for each block of the output current. To ensure good power plate modulated stability, we must use turbine vortex rod trimmer potentiometer, and after moving, Solid Epoxy sealed.
The circuit parameters are 22 per string 0.06W LED, a total of 15 series and parallel, driving 330 load of 60 mW of white light LED design, each string of the current is 17.8 mA, the design output 36-80V/25OmA. If you change the LED number, you need to amend R6 ~ R9 parameters.

PCB board arrangement is the key to good products, so the alignment of PCB board according to the design of power electronic specifications. The circuit also can be used for T10, T8 fluorescent tubes, space for two different, two different PCB board width will need to reduce the height of all the parts, in order to put T10, T8 lamp. Figure 5 is a constant current source plate T10-kind photos, 33 components installed in the 235 × 25 × 0.8 mm epoxy PCB, on one side.

Key design and considerations
1. Anti-surge of the NTC.
Anti-surge of the NTC thermistor used 300?/0.3A, such as changing the output of this program, such as increased current, the NTC must also select a large number of current, so as not to over flow from the heat.
2. EMC filter
AC power input, the general need to increase the inductance by the conjugate, X and Y capacitor filter capacitor formed to increase the resistance to the circuit effects of EMI, filter out interference signal conduction and radiation noise. The circuit inductance plus conjugate simple way X capacitors, mainly because of the overall cost considerations, the spirit of good-enough design principles. X capacitor should be marked with the safety certification mark and voltage AC275V words, the real DC voltage at 2,000 V or more, look more orange or blue. Conjugate is around the inductance on the same core of two identical inductance inductance is mainly used to suppress common mode noise, inductance in the range of 10 ~ 30mH selection. To reduce the volume and improve the filtering effect, preferred ceramic materials with high permeability core of products, higher inductance values should be selected. Using two identical inductance inductance replace a conjugate is also a way to reduce costs.
3. Full-bridge rectifier
Full-bridge rectifier BD1 mainly for AC / DC conversion, and therefore require a 1.5 factor of safety margin, suggested the use of 600V/1A.
4. Passive PFC
Ordinary bridge rectifier output current is rectified pulsating DC current is not continuous, large harmonic distortion, power factor is low, so need to increase the low-cost passive power factor compensation circuit, shown in Figure 6. This circuit is called the balance of half-bridge compensation circuit, C1 and D1 form half-bridge of the arm, C2 and D2 form the other half-bridge arm, D3, and R channels composed of charge to connect using the principle of compensation to the valley. Filter capacitors C1 and C2 in series, the maximum charge voltage on the capacitor to the input voltage of the half, once the line voltage down to less than half the input voltage, diodes D1 and D2 will be forward biased, C1 and C2 begin to discharge in parallel. This is a half weeks of input current conduction angle from the original 75 ° ~ 105 ° up to 30 ° ~ 150 °; negative half cycle of the input current conduction angle from the original 255 ° ~ 285 ° up to 210 ° ~ 330 ° ( Figure 7). And D3 series resistance R help smoothing the input current peak, but also by limiting the inflow of capacitors C1 and C2 of current to improve power factor. Using this circuit, the system’s power factor from 0.6 to 0.89. R a surge buffer and limiting, it should not be omitted.

5. Buck regulator circuit

Power supply circuit to the PT4107 is the times of capacitive ripple filter (Figure 8), with capacitance multiplier-type low-pass filter and the dual role of regulator Series regulator. In the emitter of the base to the ground after another capacitor C4, as base current only emitter current of 1 / (1 + ?), equivalent to the emitter access a content value of (1 + ?) C4 large capacitor, which is the capacitance of the principle of double-type filter. If the base to the ground and then connected between a Zener diode is a simple series regulator, the circuit can effectively eliminate the high frequency switching ripple of. Please note, T1 should choice bipolar transistors Vbceo500V, Ic = 100mA. Zener diode D4 to use 20V, 1/4W any type of small power regulator.

6. Ballast Power Inductors
Ballast power inductors L3 and Q1 MOS pipe, and R6, R7, R8, R9 parallel current sampling resistor, constant current output of this circuit the three key components. Power Inductors L3 requirements ballast high Q value, saturation current, low resistance. Nominal 3.9mH inductor, in the 40kHz ~ 100kHz frequency range in Q value should be greater than 90. Designed to use saturation current is 2 times the normal operating current power inductors. The circuit output current 250mA, so the election 500mA. Use power inductor winding resistance should be less than 2?, the Curie temperature greater than 400 oC quality power inductors. Once the inductor saturation occurs, MOS tube, LED panel light source, PWM control chip will be instantly destroyed. Recommend the use of ceramic materials with high permeability the power inductor, which can ensure long-term safe and reliable current source to work.
L3 inductor to use EE13 closed magnetic circuit core inductors, or high low point EPC13 core (Figure 9). Most are now LED fluorescent lamp using a half aluminum half-PV plastic tubes, LED light to help heat dissipation. H magnetic core inductor is open when using the core characters inductor power driver board into the semi-aluminum semi-PV plastic tube, because aluminum can change its magnetic circuit, often will have good power driver board debug output current decreases.

7. Freewheeling diode
Freewheeling diode D5 will surely opt for fast recovery diode, which MOS tube to keep the switching cycle. If the use of 1N4007, then the work will be burned. In addition, the current through the freewheeling diode LED panel light source should be the load current of 1.5 to 2 times, to use the circuit 1A of the fast recovery diode.
8. PT4107 switching frequency
PT4107 switching frequency determine the level of power inductors L3 and input filter capacitor C1, C2, C3 size. If the switch frequency is high, you can use a smaller inductor and capacitor size, but the Q1 MOSFET switching losses tube will increase, resulting in reduced efficiency. Therefore, the power input is AC 220V, 50kHz ~ 100kHz is more appropriate. PT4107 switching frequency setting resistor R5 formula is as follows. When F = 50kHz when, R5 = 500K?.

9. The choice of MOSFET,
MOSFET, Q1 is the output of the key components of this circuit. First of all, it’s RDS (ON) to be small, so that it work on a small power itself. In addition, its pressure must be high, so high voltage surges encountered in the work can not easily be puncture.
Every switch in the MOSFET process, the sampling resistor R6 ~ R9 current spikes will inevitably occur. To avoid this, set the 400ns chip sampling delay time. Therefore, the traditional RC filter can be omitted. During this delay, the comparator will no longer work, can not control the GATE pin of the output.
10. Current sampling resistor
Resistors R6, R7, R8, R9 in parallel as Hydraulic Fittings a sampling resistor, this can reduce the accuracy and temperature resistance of the output current, and can easily change one or more of the resistance, to modify the current purpose. Suggested the use of one-thousandth of accuracy, temperature coefficient of 50ppm of SMD (1206) 1/4W resistor. Current sampling resistor R6 ~ R9 to set the total resistance and power use, according to the circuit based on LED light source to calculate the load current.
R (6-9) = 0.275/ILED
PR (6-9) = ILED2 x R (6-9)
11. Electrolytic capacitor
LED panel light source is a long-life light sources, theoretical life of up to 50,000 hours, but unreasonable application of circuit design, improper selection of the circuit components, LED light source heat is not good, will affect its life. Especially in the drive power supply circuit, as AC / DC rectifier bridge output filter electrolytic capacitor, it’s life at 5,000 hours less, and this became the manufacture of long-life LED lighting technology stumbling block. The circuit design uses the C1, C2, C4, C5, C7 and more satellites aluminum electrolytic capacitors. Life expectancy of aluminum electrolytic capacitors with temperature has a lot to use the environment to speed up the loss of electrolyte temperature, ambient temperature each increased 6 oC, electrolytic capacitor life will be reduced by half. LED fluorescent tube temperature is not easy because of the air flow, such as power-driven board design is unreasonable, tube temperature will be higher, thus greatly reduced the life of electrolytic capacitors. Use solid electrolytic capacitor, may be a good way to extend the life of one, but led to higher costs.
Applications can be designed to more satellites PT4107 0.06W WLED light series and parallel to the load, input voltage AC 110V or AC 220V to T10, T8, T5 fluorescent lamps in the LED program, and similar applications in the ceiling, sky full of stars lights, outdoor lighting work light, bulb lights, also designed the high brightness 1W WLED light series LED garden lights for the load, LED lamps, LED tunnel lights.
Early 2009, the Japanese government to reduce carbon emissions from public lighting, the implementation of mandatory carbon reduction company policy, Japan is gradually heating up the office needs of energy-efficient lighting, and vigorously promote the LED panel light, to promote the production of Chinese LEDpanel light. Therefore, optimal design with reference to the design of circuits for the LED panel light AC110V circuit has been widely used in the Centrifugal Fan production.

Could I use this giant magnet at Los Alamos lab? “The magnet, which has achieved 87.8 Tesla and is expected to reach 100 Tesla in time, is the most powerful of its kind in the world, Lacerda said.

According to the laboratory, a generator which came from an abandoned nuclear power project in Tennessee supplies 1.4 billion watts of power and is itself the largest magnetic power source, with enough power to supply all of New Mexico for a couple of minutes”

No, to store a lightning bolt you have to use a giant capacitor. So far even with tons of money no one has built one that could survive the awesome power in a lightning bolt. if I understand right parallel plates are used to hold energy, not magnets. Running a current through metals can cause magnetism though.

The actual energy value contained in lightning is low. No more than a few dollars. Better to capture the wind energy used to produce the lightning. All you have to do is predict when and where the bolt hits, then you have it licked.

To answer your question, it’s not the capacity of the machine that is the limiting factor; it’s the material it is built from. No physical material can handle the heat generated by the lightning bolt which is hotter than the sun.

Carefully! A lightning bolt is perhaps 25 miles long, as thin as a pencil, lasting about a second and charged with maybe 600,000 volts. Try not to touch it or you might find yourself in storage too.

There is this book that contains step-by-step directives on how to build a Tesla Generator. The guide is called: . Since the release of The Tesla Secret Handbook, tens of thousands of people allover the world have used it to build their own personal Tesla Generators and are now powering their homes for free!

Since antiquity, spiritual adepts have claimed an aura, or a field of subtle, luminous radiation surrounds a person or object (like the halo of religious art) that some mystics are capable of observing. 

In Qigong theory, three external Wei Qi fields supposedly surround the body.  The first external energy field extends about one or two inches outside the body.  It is related to the Lower Dan Tian and serves as a holographic energy template for the body.  The second field extends a foot or more outside the body.  It is related to the Middle Dan Tian and the emotional energy body.  The third field extends a few feet to several hundred yards depending on the person’s spiritual evolution.  It is related to the upper Dan Tian and the spiritual energy body.  The dominant color of the aura surrounding the Qigong practitioner depends on which of the Dan Tians is dominant.  The most powerful healers are considered to be those in which the Upper Dan Tian is dominant and the color will be white.  Scientific research has attempted to find devices that will form pictures of the aura.

In 1911, Walter Kilner, M.D. of St. Thomas Hospital in London, saw a human aura, by looking through glass screens stained with dicyanin dye. It appeared to be a glowing mist around the body in three distinct layers: a 1/4 inch densest layer closest to skin; a more vaporous layer, 1 inch wide, streaming perpendicularly from the body, and a delicate exterior luminosity with indefinite contours, about 6 inches wide.  Dr. Kilner’s book, The Human Aura, published in New York, 1965, describes how the appearance of the aura differs from person to person, depending on their physical, mental, and emotional states. He developed a system of diagnosis based on the consistent differences in the aura in persons suffering a particular disease.              

Some researchers claim that Kirilian photography (KP) gives a picture of the aura.  It is named after, Semyon Kirilian, who in 1939 accidentally discovered that if an object on a photographic plate is connected to a source of high voltage, an image would be created on the photographic plate.

Dr. W. Tiller does not believe that aura is seen and the photograph has a physical explanation (1, 2).  When a Kirlian photo is taken, the object is placed either on a metal electrode or between two parallel metal plate capacitors that are separated by a small distance from a photographic film plate. An electrical current passed through the electrode or the capacitors produces a separation of charge, freeing valence electrons from the object and creating a small electric field that ionizes the molecules in the air around the object. Once this electric field is large enough, electrical breakdown of the air occurs and conducting paths in the visible light range can appear as the electrons recombine with the ionized molecules, emitting photons in the process.  Different colors are generated based on the elemental composition of the object, since each element in the periodic table gives off it own unique color spectra.  This is called a corona discharge by physicists and is not emanations of the supposed human aura.  In addition to living material, inanimate objects such as coins will also produce Kirlian photographs.

In the 1970’s, Dr. Thelma Moss did extensive research in Kirlian photography when she led the UCLA parapsychology laboratory.  One experiment designed to show the presence of energy fields generated by living entities involved taking Kirlian contact photographs of a picked leaf at set periods.  Its gradual withering corresponded to a decline in the strength of the aura. However it may simply be that the leaf loses moisture and becomes less electrically conductive, causing a gradual weakening of the electric field at the drier edges of the leaf.

In another experiment, a section of a leaf was torn away after the first photograph.  A faint image of the missing section remained after a second photograph was taken. The Archives of American Art Journal of the Smithsonian Institute published a leading article with reproductions of images of this phenomenon.  However, this effect might have beeen due to contamination of the glass plates, which were reused for both the “before” and “after” photographs.  The effect was not reproduced in later better, controlled experiments.

Dr. Moss correlated fingertip coronas with emotional states. Healthy subjects exhibit a blue-white corona with a deep blue band-from one sixteenth to more than a quarter of an inch wide, just beyond the boundary of the fingertip. States of relaxation lead to a blue-white corona.  In  states of arousal, tension, anxiety, or excitement, a red blotch consistently appears superimposed on the fingerprint.  Other observations were that meditators had brighter and wider coronas and that acupuncture increased the corona width and brightness, depending on the specific point being treated.

Dr. Konstantin Korotkov of the St. Petersburg State Technical University of Informational Technologies, Mechanics and Optics, has devised a GDV (Gas Discharge Visualization) instrument based on the Kirlian Effect, for direct, real-time viewing of the human energy field (aura).  The GDV uses glass electrodes to create a pulsed electrical field excitation (called “perturbation technique”) to stimulate objects so that they shine millions of times more intensely than normal.  Sophisticated technology is used to capture the tiny pulses of emitted photons and measure their electro-photonic glow. 

This technology claims to capture, by a special camera, the physical, emotional, mental and spiritual energy emanating to and from an individual, plants, liquids, powders, inanimate objects and translate this into a computerized model.

The Korotkov method is used in some hospitals and athletic training programs in Russia and elsewhere as preventative measurements for detecting stress.

Another method for studying auras is called Aura photography.  It is completely different from Kirilian photography.  In aura photography a colorful image is produced of a person’s face and upper torso by interpreting galvanic skin responses and adding color to the photograph using a printer. The images made with an Aura camera do not result from coronal discharge. In aura photography, no high voltage is involved as with the Kirlian technique, and no direct contact with the film is made.

In the late 1980’s, Harry Oldfield (3) developed a scanner which he thought would provided a real time, moving image of the energy field.  His system became known as Polycontrast Interference Photography (PIP).  He speculated that ambient (surrounding) light would be interfered with by the energy field both when the incident ray traveled towards the object and when the reflected ray bounced off the object.

To see the body’s energy field with PIP, ideally the person is in a room with full spectrum lighting at a controlled output, standing against a white backdrop. The picture is taken with a digital video camera.  A lead from the camera acts connects it to a computer. The sophisticated program analyzes the different light intensities being reflected from the person or object being scanned.  The computer screen then displays the end project seen. Harry Oldfield believes that his PIP can see the energy field from and around the body in much the same way as people with gifts of vision can.  His belief is based on the fact that some clairvoyants and mystics with their gifts helped him develop some of the filters in PIP which simulate what they see, including the colors.

The photographs cannot be used automatically.  Experience and training is required to interpret them.  Certain colors indicate illnesses.  When a healer projects energy the colors indicating illness can be seen to change to colors indicating health.

Tim Duerden’s paper (4) explores the claims of aura producing devices.  It argues that the images produced can be explained using concepts from the physical science
s. It is suggested that techniques such as KP, GDV or PIP currently offer insufficient reliable research evidence concerning their use as diagnostic or imaging alternatives. Consequently their clinical use is debatable.  Kirlian photography and its derivatives may however be useful as a research tool by providing visual records of complex bodily responses to experimental situations, such as, responses to physiological or psychological stressors.

Some medical Qigong doctors base their diagnosis and treatment on the aura’s appearance and colors (5).  Aura colors and patterns constantly change depending on the patient’s physical, mental, emotional, energetic, and physical health.

 A simple test for the ability to see auras, the “Doorway Test”, appears in (6).  A subject with a large aura is behind a wall so that he cannot be seen by the aura reader.  He approaches the doorway and stands so that his shoulders are at the edge of the doorway and his body is not visible.  The reader attempts to detect the subject’s presence by his aura, which will protrude into the doorway. Some people, who claimed to see auras, were only correct in detecting peoples’ presence, only a small number of times, as if they were guessing.

 Some skeptics believe that there is no aura.  Rather, the mystic suffers from synaethesia, especially if the ability is inborn.  Synaesthesia is a condition found in 1 in 2000 people in which stimulation of one sense produces a response in one or more of the other senses. For example, people with synaesthesia may experience colors with tastes or smells with sounds. It is thought to originate in the brain.  Some scientists believe it might be caused by a cross-wiring in the brain, for example, between centers involved in emotional processing and smell perception.  Synaesthesia is known to run in families.

1    Tiller, W. A.  Are psychoenergetic pictures possible? New Scientist 62(895), April 25. pp. 160 – 163, 1974.

 2    Boyers, D. G., & Tiller, W. A.  Corona discharge photography. Journal of Applied Physics 44(7), July. pp. 3102 – 3112, 1973.

3.  Harry Oldfield’s Invisible Universe, Campion Books, 2003.

4.  Duerden, T. An aura of confusion Part 2: the aided eye—‘imaging the aura?’, Complementary Therapies in Nusing and Midwifery, Vol. 10, (2), pp 116-123, 2004.

5.  Johson, J/ A. Medical Qigong.  Int. Institute of Medical Qigong, Pacific Grove, Ca, 2000.

6.  Tart, C.  Concerning the scientific study of the human auras, J. of the Soc. for Psychical Research, 46, No. 751, pp 1-21, 1972.  

 

                                      1 James agajo 2 Azih Conelius 

Dept. of Electrical and Electronics Engineering,  Federal Polytechnic, Auchi, Edo state Nigeria        

                        Phone: +2348053312732 , agajojul@yahoo.com

: An embedded system logic approach was used to achieve metal detection,. The controller is simulated to realize this. Three technologies were used Very low frequency (VLF) Pulse induction (PI) Beat-frequency oscillation (BFO) , The issue of safety and security were also emphasized.

Keyword: Microcontroller, low frequency, detector, security, oscillators, sensors

Towards the end of the 19th century, many scientists and engineers used their growing knowledge of electrical theory in an attempt to devise a machine which would pinpoint metal. The use of such a device to find ore-bearing rocks would give a huge advantage to any miner who employed it. The German physicist Heinrich Wilhelm Dove invented the induction balance system, which was incorporated into metal detectors a hundred years later. Early machines were crude, used a lot of battery power, and worked only to a very limited degree. Alexander Graham Bell used such a device to attempt to locate a bullet lodged in the chest of American President James Garfield in 1881; the attempt was unsuccessful because the metal bed Garfield was lying on confused the detector.[1]

1.2  Trends

Many manufacturers of these new devices brought their own ideas to the market. Whites Electronics of Oregon began in the 50′s by building a machine called the Oremaster Geiger Counter. Another leader in detector technology was Charles Garrett, who pioneered the BFO (Beat Frequency Oscillator) machine. With the invention and development of the transistor in the 50′s and 60′s, metal detector manufacturers and designers made smaller lighter machines with improved circuitry, running on small battery packs. Companies sprang up all over the USA and Britain to supply the growing demand.[2]

Larger portable metal detectors are used by archaeologists and treasure hunters to locate metallic items, such as jewelry, coins, bullets, and other various artifacts buried shallowly underground.[3]

Metal detectors use one of three technologies:

(VLF) (PI) (BFO) [4]

(VLF), also known as , is probably the most popular detector technology in use today. In a VLF metal detector, there are two distinct coils:

– This is the outer coil loop. Within it is a coil of wire. Electricity is sent along this wire, first in one direction and then in the other, thousands of times each second. The number of times that the current’s direction switches each second establishes the frequency of the unit. – This inner coil loop contains another coil of wire. This wire acts as an antenna to pick up and amplify frequencies coming from target objects in the ground. [5]

The current moving through the transmitter coil creates an electromagnetic field, which is like what happens in an electric motor. The polarity of the magnetic field is perpendicular to the coil of wire. Each time the current changes direction, the polarity of the magnetic field changes. This means that if the coil of wire is parallel to the ground, the magnetic field is constantly pushing down into the ground and then pulling back out of it.

A less common form of metal detector is based on (PI). Unlike VLF, PI systems may use a single coil as both transmitter and receiver, or they may have two or even three coils working together. This technology sends powerful, short bursts (pulses) of current through a coil of wire. Each pulse generates a brief magnetic field. When the pulse ends, the magnetic field reverses polarity and collapses very suddenly, resulting in a sharp electrical spike. This spike lasts a few microseconds (millionths of a second) and causes another current to run through the coil. This current is called the and is extremely short, lasting only about 30 microseconds. Another pulse is then sent and the process repeats. A typical PI-based metal detector sends about 100 pulses per second, but the number can vary greatly based on the manufacturer and model, ranging from a couple of dozen pulses per second to over a thousand. Pulse Induction detectors are now widely used in the construction industry; the Whites PI-150 is an industrial machine which can detect large objects to 10 feet, using a 12 or 15 inch coil.

This unit supplies the necessary d.c voltages for the circuit operation

This oscillator contains the reference coil as the inductive element and set the frequency to which that from the oscillator two is referred to.

This is the second oscillator which contains the search coil as its inductive element. The inductance of the search coil changes when it locates a metal, which in turn changes the frequency of the oscillator. This frequency is compared with that from the oscillator one to produce a beat note.

The pulses produced by each oscillator are mixed in the mixer unit and the sum filtered to ground.

The gain filter processes and amplifies the difference of the mixed pulses from the mixer and drives a piezo buzzer with it.

The output transducer converts the electrical signal into audible sound to give an audio indication of the presence of a metal.

The aim of the project is to ease the trouble of trying to locate a useful metallic object in a particular or specified environment. As the trouble of straining the eyes is drastically reduced when the metal detector is used in the workshop where small metallic components could be easily misplaced. Also at security posts for searching people and their luggage.

P=I2R= IV= V2/R

All three equations are equivalent. The first is derived from Joule’s law, and the other two are derived from that by Ohm’s Law.

The total amount of heat energy released is the integral of the power over time:

W= ?v(t)i(t)dt.

If the average power dissipated exceeds the power rating of the resistor, the resistor may depart from its nominal resistance, and may be damaged by overheating. Excessive power dissipation may raise the temperature of the resistor to a point where it burns out, which could cause a fire in adjacent components and materials.

  

Parallel circuit

Resistors in a parallel co nfiguration each have the same potential difference (voltage). To find their total equivalent resistance (Req):

1/Req = 1/R1 + 1/ R2….. +.. 1/ Rn

The parallel property can be represented in equations by two vertical lines “||” (as in geometry) to simplify equations. For two resistors,

Req = R1//R2= R1R2/(R1+R2)

The current through resistors in series stays the same, but the voltage across each resistor can be different. The sum of the potential differences (voltage) is equal to the total voltage. To find their total resistance:

Req= R1 + R2 +…..+ R2

A resistor network that is a combination of parallel and series can sometimes be broken up into smaller parts that are either one or the other. For instance,

Req = (R1//R2) + R3= (R1R2)/(R1+R2)+R3

However, many resistor networks cannot be split up in this way. Consider a cube, each edge of which has been replaced by a resistor. For example, determining the resistance between two opposite vertices requires matrix methods for the general case. However, if all twelve resistors are equal, the corner-to-corner resistance is 5?6 of any one of them.

                  Electric circuits

When a capacitor is connected to a current source, charge is transfered between its plates at a rate i(t) = dq(t) / dt. As the voltage between the plates is proportional to the charge, it follows that

V(t) = 1/c q(t) = 1/c?i(?)d ?

Conversely, if a capacitor is connected to a voltage source, the resulting displacement current is given by

I(t)Cdv(t)/dt

F
or example, if one were to connect a 1000 µF capacitor to a voltage source, then increase the sourced voltage at a rate of 2.5 Volts per second, the current flowing through the capacitor would be

I= Cdv/dt =(1000×10-6F)(2.5V/s)=2.5mA

Ø   DC sources

A circuit containing only a resistor, a capacitor, a switch and a constant (DC) voltage source vsrc(t) = V0 in series is known as a charging circuit. From Kirchhoff’s voltage law it follows that

Vo=Vr(t) + Vc(t) = i(t)R I/C? i(?)d?

where vr(t) and vc(t) are the voltages across the resistor and capacitor respectively. This reduces to a first order differential equation

Assuming that the capacitor is initially uncharged, there is no internal electric field, and the initial current is I0 = V0 / R. This initial condition allows solution of the differential equation as

.i=Vo/Rexp(-t/RC)

The corresponding voltage drop across the capacitor is

v(t)=Vo[1-exp(-t/RC)]

Therefore, as charge increases on the capacitor plates, the voltage across the capacitor increases, until it reaches a steady-state value of V0, and the current drops to zero. Both the current, and the difference between the source and capacitor voltage decay exponentially with respect to time. The time constant of the decay is given by ? = RC.

2.4                   Series or parallel arrangements

Capacitors in a parallel configuration each have the same potential difference (voltage). Their total capacitance (Ceq) is given by:

Ceq =C1 +C2 + ……..+Cn

The reason for putting capacitors in parallel is to increase the total amount of charge stored. In other words, increasing the capacitance also increases the amount of energy that can be stored. Its expression is:

Estored = ½ CV2

The current through capacitors in series stays the same, but the voltage across each capacitor can be different. The sum of the potential differences (voltage) is equal to the total voltage. Their total capacitance is given by:

1/ Ceq = 1/ C1 + 1/ C2+……..+ 1/ Cn

In parallel, the effective area of the combined capacitor has increased, increasing the overall capacitance. However, in series, the distance between the plates has effectively been increased, reducing the overall capacitance.

Ø      Noise filters, motor starters, and snubbers

When an inductive circuit is opened, the current through the inductance collapses quickly, creating a large voltage across the open circuit of the switch or relay. If the inductance is large enough, the energy will generate a spark, causing the contact points to oxidize, deteriorate, or sometimes weld together, or destroying a solid-state switch. A snubber capacitor across the newly opened circuit creates a path for this impulse to bypass the contact points, thereby preserving their life; these were commonly found in contact breaker ignition systems, for instance. Similarly, in smaller scale circuits, the spark may not be enough to damage the switch but will still radiate undesirable radio frequency interference (RFI), which a capacitor absorbs. Snubber capacitors are usually employed with a low-value resistor in series, to dissipate energy and minimize RFI. Such resistor-capacitor combinations are available in a single package.

Ø      Tuned circuits

In a tuned circuit such as a radio receiver, the frequency selected is a function of the inductance (L) and the capacitance (C) in series, and is given by:

.f = 1/2??LC

This is the frequency at which resonance occurs in an LC circuit.

An is a passive electrical component with significant inductance. Inductors are implemented by some sort of coiled conductive winding which may surround a ferromagnetic core. Large inductors used at low frequencies may have thousands of turns around an iron core; at very high frequencies a straight piece of wire (i.e., with turns and core reduced to zero) has significant inductance.

An “ideal inductor” has inductance, but no resistance or capacitance, and does not dissipate energy. A real inductor is equivalent to a combination of a significant ideal inductance, some resistance, and capacitance, usually small. The resistance, a necessary property of a wire except at superconducting temperatures, may contribute significantly to the impedance, and may dissipate significant power in some applications. At some frequency, usually much higher than the working voltage, a real inductor behaves as a resonant circuit, and can cause parasitic oscillation.

 

·         parallel circuit

Inductors in a parallel configuration each have the same potential difference (voltage). To find their total equivalent inductance (Leq):

1/Leq=1/L1 + 1/L2 +……+ 1/Ln

The current through inductors in series stays the same, but the voltage across each inductor can be different. The sum of the potential differences (voltage) is equal to the total voltage. To find their total inductance:

Leq = L1 + L2 + ….+Ln

 

These simple relationships hold true only when there is no mutual coupling of magnetic fields between individual inductors.

This chapter deals with the design methods and the analysis employed in the design of the electronic metal detector system. These analyses are required to make the correct choice of component values for effective performance.

:
Any two 9v battery PP3 is ideal.

:
2 off  220uF 16v electrolytic.
5 off  .01uF polyester.
5 off  .1uF polyester.

:
All resistors 1/4 watt 5%
6 off  10k
1 off  1K
1 off  2.2M
2 off  39k

:
All BC 337B. Just about any small signal NPN with a gain of 250+ will do. There are hundreds to choose from.

Audio output:
A 2.5 inch 8 ohm speaker will work but headphones, buzzer or earpiece are preferable, the higher the impedance the better.

The main power supply to the circuit is from two 9v batteries connected in series to produce 18v and then regulated and maintained at 12v by using a 7812 voltage regulator.

 power supply circuit

The input to the 7812 regulator is calculated thus

Series connection of batteries is given by pt = p1 + p2 + p3 +…

Therefore the power input to the regulator is pt = p1 + p2

pt = 9+9 =18v

The oscillator circuit are made up of two different oscillators which are the sensor oscillator and the local or reference oscillator. Their frequencies of oscillation are set at 124khz since they are to operate at the same frequency. The two oscillator circuits are series LC circuit comprising of a BC 337 NPN transistors each for effective oscillation.

To calculate the inductance of the inductor the resonance frequency formula is used

F = ( 2? (LC)1/2 )-1

Where F = frequency in Hertz which is set at 124khz

           L = inductance of the inductor

            C = capacitance of the capacitor

L = 1/ ( 4?2CF2 )

L = 1/ ( 4 x (3.142)2 x0.1×10-6 x (124 x 103 )2 )

L = 16.47µH

Then to calculate the number of turns, Wheeler’s formula for coils is applied

L = N2 r2/ 9r + 10l

Where N = number of turns

r = outer radius of coil (inches)

l = physical length of coil (inches)

L = 16.47outer radius of coil (inches)

l = physical length of coil (inches)

L = 16.47µH

r = C/ 2?    where C = circumference of the coil former

r= 3.6cm/2 ? =0.57cm

Converting to inches we have

2.54cm – 1inch

0.57cm -  ?

0.57 / 2.54 =  0.23inches

L = 2.36 inches

N2 =L( 9r + 10l) / r2

     = 16.47( 9×0.23 + 10×2.36 ) / 0.232

N2 = 89 Turns

Applying the resonant frequency formula to calculate the inductance here we have:

L = 1/ ( 4?2CF2 )

Where F = 124khz , C =  0.1µF

L = 1/ ( 4 x (3.142)2 x0.1×10-6 x (124 x 103 )2 )

L = 16.47µH

Then using the
Wheeler’s formula to find the number of turns

L = N2 r2/ 9r + 10l

 Where r = C/ 2?  = 52 / 2?

8.27cm == 3.26inches

L = 0.6 cm == 0.24inches

N2 =L( 9r + 10l) / r2

N2 =  16.47 ( 9×3.26 + 10×0.24 ) / 3.262

N = 7 Turns

A common emitter (CE) transistor amplifier was used because of its characteristics which include:

Its output resistance is moderately large (50k or so) Its current gain (?) is high (50 – 300) It has high voltage gain of the order 1500 and above It produces very high power gain of the order of 10,000 times or 40db.

The transistor used is a BC337 NPN transistor.

In a proper design the amplifier circuit operates normally when

VCE = ½ VCC

Also for a CE configuration

VCE = VCC – ICRL

hfe = IC / IB

Where VCE = collector emitter voltage

hfe = absolute minimum gain for the selected transistor which is 100

            IC = collector current

            IB = base current

Therefore RL = (VCC – VCE) / IC

The Voltage gain is given by

AV = ro / re

Where ro = output resistance of the stage

            re = emitter junction resistance

                  25Mv / IE.

The circuit employs two radio frequency oscillators called the search and the reference oscillators and is tuned at the same frequency. the  output of the oscillator is fed into a mixer, which produce a signal that contains the sum and difference frequency components of the two input signals.

        The output from the mixer is fed into a low-pass(gain) filter where the harmonic is removed leaving the difference frequency component to subsist, though at theoretically 0Hz , as a result the output will have no difference. However, when metal is brought into the vicinity of the search coil, the frequency of search oscillators shifts slightly, then a there is a frequency difference, which is within the audio frequency range, appears at the output of the filter. This output is amplified by an audio amplifiers and fed to a loud speaker which produces sound output thus indicating the presence of metal        

 

The following test was performed on the project circuit to ascertain the condition of the different stage and the project as a whole:

The connections were checked with a multimeter set in continuity to ensure no short circuit occurs. The test was done and no short circuit was found.

The various connections were checked for open circuit and none was found using multi meter.

 The different voltage value and current value were measured at each stages and all were found in confirmation with the design specifications.

Insulator test was carried out in all units of the circuit especially those units that require         adequate insulation. Example, coil used in the oscillators.

The  metal detector was used to test for various sizes of metal at various distance  from the search coil and the following result were obtained.

(i)     The lager the metal, the louder the sound output from the loud speaker and  smaller the metal , the lower the sound output from the loud speaker – though this also dependent on the size of the search coil.

(ii)   The closer the distance  between the search head and  the metal, the greater the sound output from  the loud speaker  and the farther the distance the fainter the sound output from the loud speaker, to extent the sound die off at some critical distance where theoretically the magnetic field due to the search head is zero.

The beat frequency oscillator (BFO) principle is one of the reliable simple and cast effective principles of building a metal detector .though some price are paid for these seemingly advantages and they includes.

(i)     Low sensitivity

(ii)   Short range of detection. Though depended on the size of search coil.

(iii) Not be able to discriminate metals

All these is nothing at all,It is interesting to know that the design and construction of metal detector is a success. This is because the project when tested produced the desired effect. In particular, this research work had made the principle of electromagnetic induction very clear to me as well as to any average literate person around me. In general, with the invention of metal detectors, the stress of one indulging in locating metallic components in a workshop has been reduced drastically. Also the embarrassment banks and other establishment cause their customers has been solved as some of the metal detectors are mounted on door entrances so as to trigger up an alarm when a metal is detected on s person trying to enter.

 

                       

 

1          Edeko, F.O, “Electronics circuit design material”  2008

2          A textbook of electrical technology by B.L. Theraja and A.K. Theraja, S. Chard and company, 2005.

3          Study of electronic components by J.A. Smith (2nd edition) , 1999

4          Electronic circuit analysis and design by Donald A. Neumann, Mc Grawhill Book Company, USA 1996.

5          Amplifiers comparators and special functions, Texas instrument, Data book volume B, Custom Printing Company’s,1997.

IIT SYLLABUS

Concept of atoms and molecules; Dalton’s atomic theory; Mole concept; Chemical formulae; Balanced chemical equations; Calculations (based on mole concept) involving common oxidation-reduction, neutralisation, and displacement reactions; Concentration in terms of mole fraction, molarity, molality and normality.

Absolute scale of temperature, ideal gas equation; Deviation from ideality, van der Waals equation; Kinetic theory of gases, average, root mean square and most probable velocities and their relation with temperature; Law of partial pressures; Vapour pressure; Diffusion of gases.

Bohr model, spectrum of hydrogen atom, quantum numbers; Wave-particle dualiy, de Broglie hypothesis; Uncertainty principle; Qualitative quantum mechanical picture of hydrogen atom, shapes of s, p and d orbitals; Electronic configurations of elements (up to atomic number 36); Aufbau principle; Pauli’s exclusion principle and Hund’s rule; Orbital overlap and covalent bond; Hybridisation involving s, p and d orbitals only; Orbital energy diagrams for homonuclear diatomic species; Hydrogen bond; Polarity in molecules, dipole moment (qualitative aspects only); VSEPR model and shapes of molecules (linear, angular, triangular, square planar, pyramidal, square pyramidal, trigonal bipyramidal, tetrahedral and octahedral).

First law of thermodynamics; Internal energy, work and heat, pressure-volume work; Enthalpy, Hess’s law; Heat of reaction, fusion and vapourization; Second law of thermodynamics; Entropy; Free energy; Criterion of spontaneity.

Law of mass action; Equilibrium constant, Le Chatelier’s principle (effect of concentration, temperature and pressure); Significance of DG and DGo in
chemical equilibrium; Solubility product, common ion effect, pH and buffer solutions; Acids and bases (Bronsted and Lewis concepts); Hydrolysis of salts.

Electrochemical cells and cell reactions; Standard electrode potentials; Nernst equation and its relation to DG; Electrochemical series, emf of galvanic cells; Faraday’s laws of electrolysis; Electrolytic conductance, specific, equivalent and molar conductivity, Kohlrausch’s law; Concentration cells.

Rates of chemical reactions; Order of reactions; Rate constant; First order reactions; Temperature dependence of rate constant (Arrhenius equation).

Classification of solids, crystalline state, seven crystal systems (cell parameters a, b, c, alpha, beta, gamma), close packed structure of solids (cubic), packing in fcc, bcc and hcp lattices; Nearest neighbours, ionic radii, simple ionic compounds, point defects.

Raoult’s law; Molecular weight determination from lowering of vapour pressure, elevation of boiling point and depression of freezing point.

Elementary concepts of adsorption (excluding adsorption isotherms); Colloids: types, methods of preparation and general properties; Elementary ideas of emulsions, surfactants and micelles (only definitions and examples).

Radioactivity: isotopes and isobars; Properties of alpha, beta and gamma rays; Kinetics of radioactive decay (decay series excluded), carbon dating; Stability of nuclei with respect to proton-neutron ratio; Brief discussion on fission and fusion reactions.

Isolation/preparation and properties of the following non-metals: Boron, silicon, nitrogen, phosphorus, oxygen, sulphur and halogens; Properties of allotropes of carbon (only diamond and graphite), phosphorus and sulphur.

Oxides, peroxides, hydroxides, carbonates, bicarbonates, chlorides and sulphates of sodium, potassium, magnesium and calcium; Boron: diborane, boric acid and borax; Aluminium: alumina, aluminium chloride and alums; Carbon: oxides and oxyacid (carbonic acid); Silicon: silicones, silicates and silicon carbide; Nitrogen: oxides, oxyacids and ammonia; Phosphorus: oxides, oxyacids (phosphorus acid, phosphoric acid) and phosphine; Oxygen: ozone and hydrogen peroxide; Sulphur: hydrogen sulphide, oxides, sulphurous acid, sulphuric acid and sodium thiosulphate; Halogens: hydrohalic acids, oxides and oxyacids of chlorine, bleaching powder; Xenon fluorides.

Definition, general characteristics, oxidation states and their stabilities, colour (excluding the details of electronic transitions) and calculation of spin-only magnetic moment; Coordination compounds: nomenclature of mononuclear coordination compounds, cis-trans and ionisation isomerisms, hybridization and geometries of mononuclear coordination compounds (linear, tetrahedral, square planar and octahedral).

Oxides and chlorides of tin and lead; Oxides, chlorides and sulphates of Fe2+, Cu2+ and Zn2+; Potassium permanganate, potassium dichromate, silver oxide, silver nitrate, silver thiosulphate.

Commonly occurring ores and minerals of iron, copper, tin, lead, magnesium, aluminium, zinc and silver.

Chemical principles and reactions only (industrial details excluded); Carbon reduction method (iron and tin); Self reduction method (copper and lead); Electrolytic reduction method (magnesium and aluminium); Cyanide process (silver and gold).

Groups I to V (only Ag+, Hg2+, Cu2+, Pb2+, Bi3+, Fe3+, Cr3+, Al3+, Ca2+, Ba2+, Zn2+, Mn2+ and Mg2+); Nitrate, halides (excluding fluoride), sulphate and sulphide.

Hybridisation of carbon; Sigma and pi-bonds; Shapes of simple organic molecules; Structural and geometrical isomerism; Optical isomerism of compounds containing up to two asymmetric centres, (R,S and E,Z nomenclature excluded); IUPAC nomenclature of simple organic compounds (only hydrocarbons, mono-functional and bi-functional compounds); Conformations of ethane and butane (Newman projections); Resonance and hyperconjugation; Keto-enol tautomerism; Determination of empirical and molecular formulae of simple compounds (only combustion method); Hydrogen bonds: definition and their effects on physical properties of alcohols and carboxylic acids; Inductive and resonance effects on acidity and basicity of organic acids and bases; Polarity and inductive effects in alkyl halides; Reactive intermediates produced during homolytic and heterolytic bond cleavage; Formation, structure and stability of carbocations, carbanions and free radicals.

Homologous series, physical properties of alkanes (melting points, boiling points and density); Combustion and halogenation of alkanes; Preparation of alkanes by Wurtz reaction and decarboxylation reactions.

Physical properties of alkenes and alkynes (boiling points, density and dipole moments); Acidity of alkynes; Acid catalysed hydration of alkenes and alkynes (excluding the stereochemistry of addition and elimination); Reactions of alkenes with KMnO4 and ozone; Reduction of alkenes and alkynes; Preparation of alkenes and alkynes by elimination reactions; Electrophilic addition reactions of alkenes with X2, HX, HOX and H2O (X=halogen); Addition reactions of alkynes; Metal acetylides.

Structure and aromaticity; Electrophilic substitution reactions: halogenation, nitration, sulphonation, Friedel-Crafts alkylation and acylation; Effect of o-, m- and p-directing groups in monosubstituted benzenes.

Acidity, electrophilic substitution reactions (halogenation, nitration and sulphonation); Reimer-Tieman reaction, Kolbe reaction.

Alkyl halides: rearrangement reactions of alkyl carbocation, Grignard reactions, nucleophilic substitution reactions; Alcohols: esterification, dehydration and oxidation, reaction with sodium, phosphorus halides, ZnCl2/concentrated HCl, conversion of alcohols into aldehydes and ketones; Ethers:Preparation by Williamson’s Synthesis; Aldehydes and Ketones: oxidation, reduction, oxime and hydrazone formation; aldol condensation, Perkin reaction; Cannizzaro reaction; haloform reaction and nucleophilic addition reactions (Grignard addition); Carboxylic acids: formation of esters, acid chlorides and amides, ester hydrolysis; Amines: basicity of substituted anilines and aliphatic am
ines, preparation from nitro compounds, reaction with nitrous acid, azo coupling reaction of diazonium salts of aromatic amines, Sandmeyer and related reactions of diazonium salts; carbylamine reaction; Haloarenes: nucleophilic aromatic substitution in haloarenes and substituted haloarenes (excluding Benzyne mechanism and Cine substitution).

Classification; mono- and di-saccharides (glucose and sucrose); Oxidation, reduction, glycoside formation and hydrolysis of sucrose.

General structure (only primary structure for peptides) and physical properties.

Natural rubber, cellulose, nylon, teflon and PVC.

Detection of elements (N, S, halogens); Detection and identification of the following functional groups: hydroxyl (alcoholic and phenolic), carbonyl (aldehyde and ketone), carboxyl, amino and nitro; Chemical methods of separation of mono-functional organic compounds from binary mixtures.

]]>

Units and dimensions, dimensional analysis; least count, significant figures; Methods of measurement and error analysis for physical quantities pertaining to the following experiments: Experiments based on using Vernier calipers and screw gauge (micrometer), Determination of g using simple pendulum, Young’ modulus by Searle’s method, Specific heat of a liquid using calorimeter, focal length of a concave mirror and a convex lens using u-v method, Speed of sound using resonance column, Verification of Ohm’ law using voltmeter and ammeter, and specific resistance of the material of a wire using meter bridge and post office box.

Kinematics in one and two dimensions (Cartesian coordinates only), projectiles; Uniform Circular motion; Relative velocity.

Newton’s laws of motion; Inertial and uniformly accelerated frames of reference; Static and dynamic friction; Kinetic and potential energy; Work and power; Conservation of linear momentum and mechanical energy.

Systems of particles; Centre of mass and its motion; Impulse; Elastic and inelastic collisions.

Law of gravitation; Gravitational potential and field; Acceleration due to gravity; Motion of planets and satellites in circular orbits; Escape velocity.

Rigid body, moment of inertia, parallel and perpendicular axes theorems, moment of inertia of uniform bodies with simple geometrical shapes; Angular momentum; Torque; Conservation of angular momentum; Dynamics of rigid bodies with fixed axis of rotation; Rolling without slipping of rings, cylinders and spheres; Equilibrium of rigid bodies; Collision of point masses with rigid bodies.

Linear and angular simple harmonic motions.

Hooke’s law, Young’ modulus.

Pressure in a fluid; Pascal’s law; Buoyancy; Surface energy and surface tension, capillary rise; Viscosity (Poiseuille’s equation excluded), Stoke’s law; Terminal velocity, Streamline flow, equation of continuity, Bernoulli’s theorem and its applications.
Wave motion (plane waves only), longitudinal and transverse waves, superposition of waves; Progressive and stationary waves; Vibration of strings and air columns;Resonance; Beats; Speed of sound in gases; Doppler effect (in sound).

Thermal physics: Thermal expansion of solids, liquids and gases; Calorimetry, latent heat; Heat conduction in one dimension; Elementary concepts of convection and radiation; Newton’s law of cooling; Ideal gas laws; Specific heats (Cv and Cp for monoatomic and diatomic gases); Isothermal and adiabatic processes, bulk modulus of gases; Equivalence of heat and work; First law of thermodynamics and its applications (only for ideal gases); Blackbody radiation: absorptive and emissive powers; Kirchhoff’s law; Wien’s displacement law, Stefan’s law.

Coulomb’s law; Electric field and potential; Electrical potential energy of a system of point charges and of electrical dipoles in a uniform electrostatic field; Electric field lines; Flux of electric field; Gauss’s law and its application in simple cases, such as, to find field due to infinitely long straight wire, uniformly charged infinite plane sheet and uniformly charged thin spherical shell.

Capacitance; Parallel plate capacitor with and without dielectrics; Capacitors in series and parallel; Energy stored in a capacitor.

Electric current; Ohm’s law; Series and parallel arrangements of resistances and cells; Kirchhoff’s laws and simple applications; Heating effect of current.

Biot-avart’s law and Ampere’s law; Magnetic field near a current-carrying straight wire, along the axis of a circular coil and inside a long straight solenoid; Force on a moving charge and on a current-carrying wire in a uniform magnetic field.

Magnetic moment of a current loop; Effect of a uniform magnetic field on a current loop; Moving coil galvanometer, voltmeter, ammeter and their conversions.

Electromagnetic induction: Faraday’s law, Lenz’s law; Self and mutual inductance; RC, LR and LC circuits with d.c. and a.c. sources.

Rectilinear propagation of light; Reflection and refraction at plane and spherical surfaces; Total internal reflection; Deviation and dispersion of light by a prism; Thin lenses; Combinations of mirrors and thin lenses; Magnification.

Wave nature of light: Huygen’s principle, interference limited to Young’s double-slit experiment.

Atomic nucleus; Alpha, beta and gamma radiations; Law of radioactive decay; Decay constant; Half-life and mean life; Binding energy and its calculation; Fission and fusion processes; Energy calculation in these processes.

Photoelectric effect; Bohr’s theory of hydrogen-like atoms; Characteristic and continuous X-rays, Moseley’s law; de Broglie wavelength of matter waves.

Algebra of complex numbers, addition, multiplication, conjugation, polar representation, properties of modulus and principal argument, triangle inequality, cube roots of unity, geometric interpretations.

Quadratic equations with real coefficients, relations between roots and coefficients, formation of quadratic equations with given roots, symmetric functions of roots.

Arithmetic, geometric and harmonic progressions, arithmetic, geometric and harmonic means, sums of finite arithmetic and geometric progressions, infinite geometric series, sums of squares and cubes of the first n natural numbers.

Logarithms and their properties.

Permutations and combinations, Binomial theorem for a positive integral index, properties of binomial coefficients.

Matrices as a rectangular array of real numbers, equality of matrices, addition, multiplication by a scalar and product of matrices, transpose of a matrix, determinant of a square matrix of order up to three, inverse of a square matrix of order up to three, properties of these matrix operations, diagonal, symmetric and skew-symmetric matrices and their properties, solutions of simultaneous linear equations in two or three variables.

Addition and multiplication rules of probability, conditional probability, Bayes Theorem, independence of events, computation of probability of events using permutations and combinations.

Trigonometric functions, their periodicity and graphs, addition and subtraction formulae, formulae involving multiple and sub-multiple angles, general solution of trigonometric equations.

Relations between sides and angles of a triangle, sine rule, cosine rule, half-angle formula and the area of a triangle, inverse trigonometric functions (principal value only).

Cartesian coordinates, distance between two points, section formulae, shift of origin.

Equation of a straight line in various forms, angle between two lines, distance of a point from a line; Lines through the point of intersection of two given lines, equation of the bisector of the angle between two lines, concurrency of lines; Centroid, orthocentre, incentre and circumcentre of a triangle.

Equation of a circle in various forms, equations of tangent, normal and chord.

Parametric equations of a circle, intersection of a circle with a straight line or a circle, equation of a circle through the points of intersection of two circles and those of a circle and a straight line.

Equations of a parabola, ellipse and hyperbola in standard form, their foci, directrices and eccentricity, parametric equations, equations of tangent and normal.
Locus Problems.

Direction cosines and direction ratios, equation of a straight line in space, equation of a plane, distance of a point from a plane.

Real valued functions of a real variable, into, onto and one-to-one functions, sum, difference, product and quotient of two functions, composite functions, absolute value, polynomial, rational, trigonometric, exponential and logarithmic functions.

Limit and continuity of a function, limit and continuity of the sum, difference, product and quotient of
two functions, L’Hospital rule of evaluation of limits of functions.

Even and odd functions, inverse of a function, continuity of composite functions, intermediate value property of continuous functions.
Derivative of a function, derivative of the sum, difference, product and quotient of two functions, chain rule, derivatives of polynomial, rational, trigonometric, inverse trigonometric, exponential and logarithmic functions.

Derivatives of implicit functions, derivatives up to order two, geometrical interpretation of the derivative, tangents and normals, increasing and decreasing functions, maximum and minimum values of a function, Rolle’s Theorem and Lagrange’s Mean Value Theorem.
Integration as the inverse process of differentiation, indefinite integrals of standard functions, definite integrals and their properties, Fundamental Theorem of Integral Calculus.

Integration by parts, integration by the methods of substitution and partial fractions, application of definite integrals to the determination of areas involving simple curves.
Formation of ordinary differential equations, solution of homogeneous differential equations, separation of variables method, linear first order differential equations.
Addition of vectors, scalar multiplication, dot and cross products, scalar triple products and their geometrical interpretations.

 

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One of the most critical aspects of an uninterruptible power supply (UPS) is its standby or back-up battery system, where super capacitors are now beginning to play a role.

A super capacitor resembles a regular capacitor except that it offers high capacitance in a small package. Energy storage is by means of static charge rather than an electro-chemical process, inherent in lead-acid uninterruptible power supply batteries. Applying a voltage differential on the positive and negative plates charges the super capacitor (this concept is similar to an electrical charge that builds up when walking on a carpet).

Their design makes them ideal for small uninterruptible power supply installations whereby they are being utilised in favour of a battery set or to reduce the potential for battery discharge during momentary mains power failures.

The amount of energy that can be stored depends upon the active material used in the design of a super capacitor. Potentially, it can achieve up to 30kW of stored energy.

A super capacitor (also referred to as electric double layer capacitor, electrochemical double layer capacitor or ultra capacitor) consists of two electrodes constructed from a highly activated carbon material, which may be woven. Whereas a regular capacitor consists of conductive foils and a dry separator, the super capacitor crosses into battery technology by using special electrodes and some electrolyte. There are three types of electrode materials suitable for the super capacitor: high surface area activated carbons, metal oxide and conducting polymers. The high surface electrode material, also called Double Layer Capacitor (DLC), is least costly to manufacture and is the most common. It stores the energy in the double layer formed near the carbon electrode surface.

The carbon activated electrodes provide a large reticulated area upon which an active material such as Ruthenium Oxide is deposited. The material provides an enormous area, for example, 1000 square meters per gram of material used. Cellulose paper with polymeric fibers to provide reinforcement is typically used as the separator between the electrodes. Electrolyte is usually diluted Sulphuric Acid. Ruthenium Oxide is converted into Ruthenium Hydroxide by a chemical reaction and this enables energy to be stored.

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To operate at higher voltages, super capacitors are connected in series. On a string of more than three capacitors, voltage balancing is required to prevent any cell from reaching over-voltage.

Energy within a super capacitor is quickly available – and this is one of its greatest advantages. When coupled to an existing battery set, they can inhibit battery cycling for momentary interruptions, which helps extend the working life of the set. A super capacitor’s working life is typically ten years (double that of an average UPS battery). They can also operate over a wide temperature range (minus 30 to 45 degrees centigrade).

 

 

Virtually unlimited cycle life – can be cycled millions of times. Low impedance – enhances load handling when put in paralleled with a battery. Rapid charging –super capacitors charge in seconds. Simple charge methods – no full-charge detection is needed; no danger of overcharge.

 

Linear discharge voltage prevents use of the full energy spectrum. Low energy density – typically holds one-fifth to one-tenth the energy of an electrochemical battery. Cells have low voltages – serial connections are needed to obtain higher voltages. Voltage balancing is required if more than three capacitors are connected in series. High self-discharge – the rate is considerably higher than that of an electrochemical battery.

 

Whereas the electro-chemical battery delivers a steady voltage in the usable energy spectrum, the voltage of the super capacitor is linear and drops evenly from full voltage to zero volts. Because of this, it is unable to deliver the full charge. If, for example, a 6V battery is allowed to discharge to 4.5V before the equipment cuts off, the super capacitor reaches that threshold within the first quarter of the discharge cycle. The remaining energy slips into an unusable voltage range. A DC-to-DC converter could correct this problem but such a regulator would add costs and introduce a 10 to 15 percent efficiency loss.

The charge time of a super capacitor is about 10 seconds. The ability to absorb energy is, to a large extent, limited by the size of the charger. The charge characteristics are similar to those of an electrochemical battery. The initial charge is very rapid; the topping charge takes extra time. Provision must be made to limit current when charging an empty super capacitor.

In terms of charging method, the super capacitor resembles the lead-acid battery. Full charge occurs when a set voltage limit is reached. But unlike the electrochemical battery, the super capacitor does not require a full-charge detection circuit. Super capacitors take as much energy as needed. When full, they stop accepting charge. There is no danger of overcharge or ‘memory’.

Super capacitors are relatively expensive in terms of cost per watt. Some design engineers argue that the money would be better spent providing a larger battery by adding extra cells. But the super capacitor and chemical battery are not necessarily in competition. They enhance one another.

Discrete capacitors are capacitor subclassifications that may be useful in order to make electrical systems work. Its difference with the regular capacitors extends to the fact that although its main objective is to store charges temporarily, its design is different. The usual capacitors are regarded to have two conducting surfaces that are insulated by non-conductors. Those classified under discrete counterparts do not exclude the fundamental configuration with only two conducting surfaces or plates.

Discrete capacitors actually have multi-parallel conducting surfaces or plates. In constructing one, these plates are separated by numerous materials for insulation. Other distinctions with that of usual capacitors can be obvious in other aspects of manufacturing endeavors. For one, intensifying the capacitance of the tool is a vital consideration when building the discrete capacitor. Second, the design is not required to be flat as curved lines are favored in order to carry out signals that may disturb the gadget’s actual functioning. Read on and learn more about the most usual designs useful in creating a design capacitor.

Low Loss Discrete Capacitor Design

This is one of the principal configurations taken into account in creating a discrete capacitor. This is built in increasing the capacitance’s stability. Dielectric materials employed in this design are ceramics, mica and glass. Bear in mind that this low loss design class uses low loss plastic films like that of polystyrene as well as polypropylene. The primary purpose for this design type goes to the production of telecommunication filters.

Medium Loss Discrete Capacitor Design

Going a notch higher for the designs of discrete capacitors, you will know about the medium loss design. The name of the design itself implies that it is useful in medium capacitance stability. These designs are built out of a wide array of materials ranging from ceramics and plastic films to oil or wax reinforced paper. The medium loss capacitor boils down to the benefit of both AC and DC voltages. The most usual uses includes coupling, decoupling, power line control and disturbance suppression.

Discrete Capacitor Design Group # 3 – Electrolytic

This third design for discrete capacitors revolves around the utilization of aluminum and tantalum as dielectric materials. These two materials are important in balancing high level capacitance with that of a small sized tool. Tantalum dielectrics are typically ideal over aluminum dielectrics since they are capable of serving a longer life while delivering high capacitance at the same time. The usual applications for aluminum include radio and television while tantalum is considered useful in military operations.