Table of Contents1. Introduction 1.1 Introduction1.2 Objectives of this Work 2. Inductance and Inductive Coupling2.1 Introduction 2.2 Magnetic field due to moving charges and electric currents 2.3 Inductive Coupling 2.4 Inductive Charging 2.5 Uses of Inductive Charging and Inductive Coupling2.6 Advantages and Drawbacks of Inductive Charging 2.7 Resonant frequency 2.8 Resonant Inductive Coupling 3. Inductance of Coil and Coil Design 3.1 Introduction 3.2 Single Layer Coil 3.3 Q factor of a Single layer Air Core Coil 3.4 Multi-Layer Coil 3.5 Advantages of Air Core Coil 3.6 Downfall of Air Core Coil 3.7 Losses in an Air Core Coil3.8 Applicaion of Inductor4. The Oscillator Circuit 4.1 Introduction 4.2 Harmonic Oscillator 4.3 Relaxation Oscillator 4.4 Working Principle of a Simple LC Oscillator 4.5 The Basic Royer Oscillator 4.6 The Crystal Oscillator 4.7 Basic RC Oscillator 5. Transmitter & Receiver Circuits 5.1 Introduction 5.2 Transmitter circuit and Working Principal5.3 Types of Transmitters 5.4 Block Diagram of Power Transmitter 5.5 Receiver Circuit and Working Principal5.6 Block Diagram of Power Receiver circuit

6. Design and Implementation of Our Project 6.1 Introduction 6.2 Transmitter Module

6.2.1 The D.C. Power Source 6.2.2 The Oscillator Circuit 6.2.3 Operation of the Oscillator Circuit 6.2.4 The Transmitter Coil 6.2.5 The Transmitter Circuit as a Whole 6.2.6 Components Used in the Transmitter Module 6.3 Receiver Module6.3.1 Receiver Coil6.3.2 Rectifier6.3.3 Operation of a Diode Bridge Rectifier6.3.4 Rectifier Used in the Receiver Module6.3.5 Voltage Regulator IC6.3.6 The Receiver Circuit as a Whole43 6.3.7 Components Used in the Receiver Module6.4 Performance and Analysis

7. Possible Applications of Project 7.1 Introduction 7.2 Installing the Receiver Circuit inside the Body of the Devices 7.3 Transmitter Circuit as the Charging Dock 7.4 Charging Mid-range Power Devices 7.5 Charging Electric Vehicles7.5.1 Benefits of the Technology 7.5.2 Safety Features 7.6 Commercial Possibility

8. Discussions and Conclusions 8.1 Discussions 8.2 Problems and Solutions 8.3 Suggestions for Future Work8.4 Conclusion

INTRODUCTION1.1IntroductionWireless Power Transmission (WPT) is the efficient transmission of electric power from one point to another trough vacuum or an atmosphere without the use of wire or any other substance. This can be used for applications where either an instantaneous amount or a continuous delivery of energy is needed, but where conventional wires are unaffordable, inconvenient, expensive, hazardous, unwanted or impossible. The power can be transmitted using Inductive coupling for short range, Resonant Induction for mid range and Electromagnetic wave power transfer for high range. WPT is a technology that can transport power to locations, which are otherwise not possible or impractical to reach. Charging low power devices and eventually mid power devices by means of inductive coupling could be the next big thing.The aim of the project WIRELESS ENERGY TRANSMISSION SYSTEM is to transmit electrical energy from a power source to an electrical load without interconnecting wires. Wireless transmission is useful in cases where instantaneous or continuous energy transfer is needed but interconnecting wires are inconvenient, hazardous, or impossible.This project as it is clear from the title is able to transmit wireless energy so it can also be used to perform switching of any switching circuit by transmitting pulses which can be received near switching circuit as firing pulse to switch on the devices. All the home appliance switches can be used as wireless switching device with some modifications. In future, with the use of this system cell phones, household robots, mp3 players, laptop computers and other portable electronics capable of charging themselves without ever being plugged in, freeing us from that final, ubiquitous power wire. Some of these devices might not even need their bulky batteries to operate.

1.2 ObjectiveThe objective of this project is to design and construct a method to transmit wireless electrical power through space and charge a designated low power device. The system will work by using resonant coils to transmit power from an AC line to a resistive load. Investigation of various geometrical and physical form factors evaluated in order to increase coupling between transmitter and receiver.

A success in doing so would eliminate the use of cables in the charging process thus making it simpler and easier to charge a low power device. It would also ensure the safety of the device since it would eliminate the risk of short circuit. The objective also includes the prospect of charging multiple low power devices simultaneously using a single source which would use a single power outlet.

2.INDUCTANCE AND INDUCTIVE COUPLING2.1 IntroductionInductance is the ability of an inductor to store energy in a magnetic field. Inductors generate an opposing voltage proportional to the rate of change in current in a circuit. This property is also called self-inductance to discriminate it from mutual inductance, describing the voltage induced in one electrical circuit by the rate of change of the electric current in another circuit.

The quantitative definition of the self-inductance L of an electrical circuit in SI units (Webers per ampere, known as Henries) is

v= L di/dt .. (2.1)

Where, v denotes the voltage in volts and i the current in amperes. The simplest solutions of this equation are a constant current with no voltage or a current changing linearly in time with a constant voltage.Inductance is caused by the magnetic field generated by electric currents according to Ampere's law. To add inductance to a circuit, electronic components called inductors are used, typically consisting of coils of wire to concentrate the magnetic field and to collect the induced voltage.

Mutual inductance occurs when the change in current in one inductor induces a voltage in another nearby inductor. It is important as the mechanism by which transformers work, but it can also cause unwanted coupling between conductors in a circuit.

The mutual inductance, M, is also a measure of the coupling between two inductors.

2.2 Inductive Coupling

Inductive or Magnetic coupling works on the principle of electromagnetism. When a wire is proximity to a magnetic field, it generates a magnetic field in that wire. Transferring energy between wires through magnetic fields is inductive coupling.

If a portion of the magnetic flux established by one circuit interlinks with the second circuit, then two circuits are coupled magnetically and the energy may be transferred from one circuit to the another circuit. In electrical engineering, two conductors are referred to as mutual-inductively coupled or magnetically coupled when they are configured such that change in current flow through one wire induces a voltage across the end of the other wire through electromagnetic induction. The amount of inductive coupling between two conductors is measured by their mutual inductance.Power transfer efficiency of inductive coupling can be increased by increasing the number of turns in the coil, the strength of the current, the area of cross-section of the coil and the strength of the radial magnetic field. Magnetic fields decay quickly, making inductive coupling effective at a very short range. 2.3 Inductive Charging

Inductive charging uses the electromagnetic field to transfer energy between two objects. A charging station sends energy through inductive coupling to an electrical device, which stores the energy in the batteries. Because there is a small gap between the two coils, inductive charging is one kind of short-distance wireless energy transfer.

Induction chargers typically use an induction coil to create an alternating electromagnetic field from within a charging base station, and a second induction coil in the portable device takes power from the electromagnetic field and converts it back into electrical current to charge the battery. The two induction coils in proximity combine to form an electrical transformer.

Greater distances can be achieved when the inductive charging system uses resonant inductive coupling.

2.4 Resonant frequency

Figure 1 Resonant Frequency Resonance is a phenomenon that causes an object to vibrate when energy of a certain frequency is applied. In physics, resonance is the tendency of a system (usually a linear system) to oscillate with larger amplitude at some frequencies than at others (figure 1). These are known as the systems resonant frequencies. At these frequencies, even small periodic driving forces can produce large amplitude oscillations.Resonance of a circuit involving capacitors and inductors occurs because the collapsing magnetic field of the inductor generates an electric current in its windings that charges the capacitor, and then the discharging capacitor provides an electric current that builds the magnetic field in the inductor.

2.5 Resonant Inductive Coupling

Resonant inductive coupling or electrodynamic induction is the near field wireless transmission of electrical energy between two coils that are tuned to resonate at the same frequency. The equipment to do this is sometimes called a resonant or resonance transformer. While many transformers employ resonance, this type has a high Q and is often air cored to avoid iron losses. The two coils may exist as a single piece of equipment or comprise two separate pieces of equipment.Using resonance can help efficiency dramatically. If resonant coupling is used, each coil is capacitively loaded so as to form a tuned LC circuit. If the primary and secondary coils are resonant at a common frequency, it turns out that significant power may be transmitted between the coils over a range of a few times the coil diameters at reasonable efficiency.

3. COIL DESIGN3.1 IntroductionAn inductor is usually constructed as a coil of conducting material, typically copper wire, wrapped around a core either of air or of ferromagnetic or ferrimagnetic material. Core materials with a higher permeability than air increase the magnetic field and confine it closely to the inductor, thereby increasing the inductance. Low frequency inductors are constructed like transformers, with cores of electrical steel laminated to prevent eddy currents. Soft ferrites are widely used for cores above audio frequencies, since they do not cause the large energy losses at high frequencies that ordinary iron alloys do. Inductors come in many shapes. Most are constructed as enamel coated wire (magnet wire) wrapped around a ferrite bobbin with wire exposed on the outside, while some enclose the wire completely in ferrite and are referred to as shielded. Some inductors have an adjustable core, which enables changing of the inductance. Inductors used to block very high frequencies are sometimes made by stringing a ferrite cylinder or bead on a wire. An ideal inductor has inductance, but no resistance or capacitance, and does not dissipate or radiate energy. However, real inductors have resistance (due to the resistance of the wire and losses in core material), and parasitic capacitance (due to the electric field between the turns of wire which are at slightly different potentials). At high frequencies the capacitance begins to affect the inductor's behavior; at some frequency, real inductors behave as resonant circuits, becoming self-resonant.3.2 Types of air CoilAir core coil is an inductor that does not depend upon a ferromagnetic material to achieve its specified inductance. The term refers to coils wound on plastic, ceramic, or other nonmagnetic forms, as well as those that actually have air inside the windings. Air core coils have lower inductance than ferromagnetic core coils.

Air core coil could be of two types; (a) Single Layer Coil and (b) Multi-Layer Coil

(a) Single Layer Coil

Figure 3.1 Single layer CoilA single layer coil, as shown in figure 3.1, has two advantages. Firstly, like all air core coils, it is free from iron losses and the non-linearity mentioned above. Secondly, single layer coils have the additional advantage of low self-capacitance and thus high self-resonant frequency.In the simple case of a single layer solenoidal coil the inductance may be estimated as follows: L = 0.001 N 2 (a/2) 2 / (114a + 254l) (3.1)Where L is the inductance in henrys, a is the coil diameter in meters, l is the coil length in meters and N is the number of turns.The Q factor of an inductor is the ratio of its inductive reactance XL to its series resonance RS. The larger the ratio, the better the inductor is.

Q = X L /RS.(3.2)X L = 2fL (3.3)Where f is the frequency in Hertz (Hz) and L is the inductance in henries (H)

RS is determined by multiplying the length of the wire, used to wind the coil, with the D.C. resistance per unit length for the wire gage used.

Q changes dramatically as a function of frequency. At lower frequencies, Q is very good because only the D.C. resistance of the windings (which is very low) has an effect. As frequency goes up, Q will increase up to about the point where the skin effect and the combined distributed capacitance begin to dominate.

(b) Multi-Layer Coil

Figure 3.2 Multi layer CoilFigure 3.2 above, shows a multi-layer air cored coil wound on a circular coil former or bobbin. This type of winding is very common because it's simple to construct with a winding machine and a mandrel.

Figure 3.3 Cross-sectional View of Multi-Layer CoilThe ratio of the winding depth to length, which is (b-a)/l, needs to be close to unity; so the winding should have a square cross section. This makes sense because only with the square is the average distance between turns at a minimum (a circular cross section would be even better, but that is hard to construct). Keeping the turns close together maintains a high level of magnetic coupling between them, and so the general rule that the inductance of a coil increases with the square of the number of turn is maintained. In the simple case of a multi-layer coil the inductance may be estimated as follows: L=0.008D 2 N 2 /(3D+9h+10g) . (3.4)Where D is the average diameter of the coil; h is the height of the coil; and g is the depth of the coilall in millimeters.

3.8 Applications of Inductor

Inductors are used extensively in analog circuits and signal processing. Inductors in conjunction with capacitors and other components form tuned circuits which can emphasize or filter out specific signal frequencies. Applications range from the use of large inductors in power supplies, which in conjunction with filter capacitors remove residual hums known as the mains hum or other fluctuations from the direct current output, to the small inductance of the ferrite bead or torus installed around a cable to prevent radio frequency interference from being transmitted down the wire. Smaller inductor/capacitor combinations provide tuned circuits used in radio reception and broadcasting, for instance.

Two (or more) inductors that have coupled magnetic flux form a transformer, which is a fundamental component of every electric utility power grid. The efficiency of a transformer may decrease as the frequency increases due to eddy currents in the core material and skin effect on the windings. The size of the core can be decreased at higher frequencies and, for this reason aircraft use 400 hertz alternating current rather than the usual 50 or 60 hertz, allowing a great saving in weight from the use of smaller transformers. The principle of coupled magnetic fluxes between a stationary and a rotating inductor coil is also used to produce mechanical torque in induction motors, which are widely used in appliances and industry. The energy efficiency of induction motors is greatly influenced by the conductivity of the winding material.

An inductor is used as the energy storage device in some switched-mode power supplies. The inductor is energized for a specific fraction of the regulator's switching frequency, and de-energized for the remainder of the cycle. This energy transfer ratio determines the input-voltage to output-voltage ratio. This XL is used in complement with an active semiconductor device to maintain very accurate voltage control.

Inductors are also employed in electrical transmission systems, where they are used to depress voltages from lightning strikes and to limit switching currents and fault current. In this field, they are more commonly referred to as reactors.

4. OSCILLATOR4.1 Introduction

An oscillator is a mechanical or electronic device that works on the principles of oscillation: a periodic fluctuation between two things based on changes in energy. Computers, clocks, watches, radios, and metal detectors are among the many devices that use oscillators. A clock pendulum is a simple type of mechanical oscillator. The most accurate timepiece in the world, the atomic clock, keeps time according to the oscillation within atoms. Electronic oscillators are used to generate signals in computers, wireless receivers and transmitters, and audio-frequency equipment, particularly music synthesizers.

An electronic oscillator is an electronic circuit that produces a repetitive electronic signal, often a sine wave or a square wave. They are widely used in many electronic devices. Common examples of signals generated by oscillators include signals broadcast by radio and television transmitters, clock signals that regulate computers and quartz clocks, and the sounds produced by electronic beepers and video games.

Oscillators are often characterized by the frequency of their output signal: an audio oscillator produces frequencies in the audio range, about 16 Hz to 20 kHz. An RF oscillator produces signals in the radio frequency (RF) range of about 100 kHz to 100 GHz. A low-frequency oscillator (LFO) is an electronic oscillator that generates a frequency below 20 Hz. This term is typically used in the field of audio synthesizers, to distinguish it from an audio frequency oscillator.

There are two main types of electronic oscillator: (a) harmonic oscillator and (b)relaxation oscillator.4.2 Harmonic OscillatorThe harmonic, or linear, oscillator produces a sinusoidal output. The basic form of a harmonic oscillator is an electronic amplifier connected in a feedback loop with its output fed back into its input through a frequency selective electronic filter to provide positive feedback. When the power supply to the amplifier is first switched on, the amplifier's output consists only of noise. The noise travels around the loop and is filtered and re-amplified until it increasingly resembles a sine wave at a single frequency.

Harmonic oscillator circuits can be classified according to the type of frequency selective filter they use in the feedback loop:RC oscillator : In an RC oscillator circuit, the filter is a network of resistors and capacitors. RC oscillators are mostly used to generate lower frequencies, for example in the audio range. Common types of RC oscillator circuits are the phase shift oscillator and the Wien bridge oscillator.LC oscillator : In an LC oscillator circuit, the filter is a tuned circuit (often called a tank circuit) consisting of an inductor (L) and capacitor (C) connected together. Charge flows back and forth between the capacitor's plates through the inductor, so the tuned circuit can store electrical energy oscillating at its resonant frequency. There are small losses in the tank circuit, but the amplifier compensates for those losses and supplies the power for the output signal. LC oscillators are often used at radio frequencies, when a tunable frequency source is necessary, such as in signal generators, tunable radio transmitters and the local oscillators in radio receivers. Typical LC oscillator circuits are the Hartley, Colpitts and Clapp circuits.Crystal Oscillator : A crystal oscillator is a circuit that uses a piezoelectric crystal (commonly a quartz crystal) as a frequency selective element. The crystal mechanically vibrates as a resonator, and its frequency of vibration determines the oscillation frequency. Crystals have very high Q-factor and also better temperature stability than tuned circuits, so crystal oscillators have much better frequency stability than LC or RC oscillators. They are used to stabilize the frequency of most radio transmitters, and to generate the clock signal in computers and quartz clocks. Crystal oscillators often use the same circuits as LC oscillators, with the crystal replacing the tuned circuit; the Pierce oscillator circuit is commonly used. Surface acoustic wave (SAW) devices are another kind of piezoelectric resonator used in crystal oscillators, which can achieve much higher frequencies. They are used in specialized applications which require a high frequency reference, for example, in cellular telephones.

In addition to the feedback oscillators described above, which use two-port amplifying active elements such as transistors and op amps, oscillators can also be built using one-port devices with negative resistance, such as magnetron tubes, tunnel diodes and Gunn diodes. In these oscillators, a resonator, such as an LC circuit, crystal, or cavity resonator, is connected across the negative resistance device, and a DC bias voltage is applied to supply energy. The negative resistance of the active device can be thought of as cancelling the (positive) effective loss resistance of the resonator and permitting a sustained oscillation. These circuits are frequently used for oscillators at microwave frequencies.

4.3 Relaxation Oscillator A relaxation oscillator produces a non-sinusoidal output, such as a square, saw tooth or triangle wave. It contains an energy-storing element (a capacitor or, more rarely, an inductor) and a nonlinear trigger circuit (a latch, Schmitt trigger, or negative resistance element) that periodically charges and discharges the energy stored in the storage element thus causing abrupt changes in the output waveform. Square-wave relaxation oscillators are used to provide the clock signal for sequential logic circuits such as timers and counters, although crystal oscillators are often preferred for their greater stability. Triangle wave or saw tooth oscillators are used in the time base circuits that generate the horizontal deflection signals for cathode ray tubes in analogue oscilloscopes and television sets. In function generators, this triangle wave may then be further shaped into a close approximation of a sine wave. Ring oscillators are built of a ring of active delay stages. Generally the ring has an odd number of inverting stages, so that there is no single stable state for the internal ring voltages. Instead, a single transition propagates endlessly around the ring.4.4 Working Principle of a Simple LC Oscillator Energy needs to move back and forth from one form to another for an oscillator to work. We can make a very simple oscillator by connecting a capacitor and an inductor together. A capacitor stores energy in the form of an electrostatic field, while an inductor uses a magnetic field. Imagine the following circuit (figure 4.1):

Figure 4.1 LC circuitIf we charge up the capacitor with a battery and then insert the inductor into the circuit, the following will happen: 1. The capacitor will start to discharge through the inductor. As it does, the inductor will create a magnetic field.2. Once the capacitor discharges, the inductor will try to keep the current in the circuit moving, so it will charge up the other plate of the capacitor.3. Once the inductor's field collapses, the capacitor has been recharged (but with the opposite polarity), so it discharges again through the inductor.

This oscillation will continue until the circuit runs out of energy due to resistance in the wire. It will oscillate at a frequency that depends on the size of the inductor and the capacitor.4.5 The Basic Royer OscillatorA Royer oscillator is an electronic oscillator which has the advantages of simplicity, low component count, sinusoidal waveforms and easy transformer isolation. It was first described by George H. Royer in December 1954 in Electrical Manufacturing. The Basic Royer Oscillator is shown in Figure 4.2.

Figure 4.2Royer OscillatorThe diagram shows the basic Royer oscillator. It consists of a transformer with a center-tapped primary, a choke labeled L1, two semiconductors (here shown as IGBTs though they could just as well be FETs or bipolar transistors) labeled Q1 and Q2, a resonating capacitor labeled C1 and cross-coupled feedback illustrated by the crossed lines. In a real world oscillator there will be other components such as steering diodes, bias resistors and so on but this simplified drawing shows all that is necessary for the basic Royer oscillator.