Submitted By:
Aarti M. Sathe
Varsha B.Patil
Mayuri Y.Kande
Sonali Gaikwad

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INTRODUCTION
“Need is the mother of all inventions”
We live in a world that is rapidly progressing toward newer and greater levels of convenience, connectivity and freedom. This is the age of the wireless and communications revolution, where everything from handheld consumer electronics to home appliances to transportation is incorporating wireless technologies to create new levels of convenience, interaction and monitoring. While tremendous progress has been made because of technologies including Bluetooth, Wi-Fi, radio frequency (RF), Ultra Wide Band (UWB) and global positioning systems (GPS), one last tether has kept consumers from making the leap to a completely wireless lifestyle – the power cord.
The next generation in portable devices is a device that receives power wirelessly.
The first step in wireless power is providing power to a computer charging pad wirelessly. The market for this device would be businesses with large conference rooms.
The device would allow users to plug their phones and computers into the conference room table without large power bricks and cords running everywhere. The pads can conveniently be placed under the table and inside the ceiling so there are no visible wires that could ruin the aesthetic feel of the room. If the efficiency of coupling could be increased slightly further, wireless power transmission could become a standard means for charging a mobile device.
The prospect of simplifying the method in which any device receives power will have a large impact on the technology.
CONCEPT
Wireless energy transfer or wireless power transmission is the process that takes place in any system where electrical energy is transmitted from a power source to an electrical load without interconnecting wires.
The action of an electrical transformer is the simplest instance of wireless energy transfer. The primary and secondary circuits of a primary voltage either up or down.) The electric toothbrush charger is an example of
how this principle can be used. The main drawback to induction, however, is the short range. If resonant coupling is used, where inductors are tuned to a mutual frequency, significant power may be transmitted over a range of many meters. transformer are electrically isolated
from each other. The transfer of energy takes place by electromagnetic coupling through a process known as mutual induction. (An added benefit is the capability to step the primary voltage either up or down.) The electric toothbrush charger is an example of how this principle can be used. The main drawback to induction, however, is the short range. If resonant coupling is used, where inductors are tuned to a mutual frequency, significant power may be transmitted over a range of many meter
PRINCIPLE OF OPERATION
In 1825 William Sturgeon invented the electromagnet, a conducting wire
wrapped around an iron core. The principle of EM induction — that a changing magnetic field can induce an electrical current in an adjacent wire — was discovered by Michael Faraday in 1831. Combining these two discoveries, Nicholas Joseph Callan was the first to demonstrate the transmission and reception of electrical energy without wires. Callan’s 1836 induction coil apparatus consisted of two insulated coils called the primary and secondary windings both placed around a common iron core. A battery intermittently connected to the primary would ‘induce’ a voltage in the longer secondary causing a spark to jump across its free terminals.
In an induction coil or electrical transformer, which can have either an iron core or an air core, the transmission of energy takes place by simple electromagnetic coupling through a process known as mutual induction. With this method it is possible to transmit and receive energy over a considerable distance. However, to draw significant power in that way, the two inductors must be placed fairly close together. If resonant coupling is used, where inductors are tuned to a mutual frequency, significant power may be transmitted over a range of many meters.
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 & is illustrated below
Resonant Coupling
From the beginning of inductive power transmission, resonant circuits are used to enhance the inductive power transmission. Already NiKola Tesla used resonances in his first experiments about inductive power transmission more than hundred years ago.
Especially for systems with a low coupling factor, a resonant receiver can improve the power transfer. Resonant power transmission is a special, but widely used method of inductive power transmission and is limited by the same constraints of magnetic fields emissions and efficiency.
To understand the effect, it can be compared to mechanical resonances. Consider a string tuned to a certain tone as mechanical resonator. Even a far away and low level sound generator can excite the string to vibration, if the tone pitch is matched.
Here, the resonator in the receiver consists of the receiver i and a capacitor. Also the transmitter can have a resonator. The transmitter and receiver coils can be considered as weakly coupled transformer. For this, an equivalent circuit diagram consisting of magnetizing and stray inductance can be derived. In this, also the resistances of the windings are shown. The diagram shows clearly, that the resonant capacitors cancel out the stray inductance in the receiver and the magnetizing inductance in the transmitter. Now, the only remaining limit for the power transmission is the winding resistances of the coils, which impedance is one or two orders of magnitude lower than that of the inductances. Therefore, for a given generator source,much more power can be received.
Basic Principle Of Inductive Power Transmission
The basic principle of an inductively coupled power transfer system is shown in
Figure 1. It consist of a transmitter coil L1 and a receiver coil L2. Both coils form a system of magnetically coupled inductors. An alternating current in the transmitter coil generates a magnetic field which induces a voltage in the receiver coil. This voltage can be used to power a mobile device or charge a battery.
The efficiency of the power transfer depends on the coupling (k) between the inductors and their quality (Q). (See also Figure of merit)
The coupling is determined by the distance between the inductors (z) and the relative size (D2 /D). The coupling is further determined by the shape of the coils and the angle between them (not shown).
• A circuit [A] attached to the wall socket converts the standard 50-hertz current to 10 megahertz and feeds it to the transmitting coil . The oscillating current inside the transmitting coil causes the coil to emit a 10-megahertz magnetic field.
• The receiving coil [C] has the exact same dimensions as the sending coil and thus resonates at the same frequency and, in a process called magnetic induction, picks up the energy of the first coil's magnetic field.
• The energy of the oscillating magnetic field induces an electrical current in the receiving coil, lighting the bulb [D].
[b]Block Diagram
Referring to the block diagram, operation of system is as follows :
• Single phase 230V, 50Hz is given to the power supply which converts 230V AC input to 5V DC output.
• 5V DC supply is given to drive the Oscillator circuit. Oscillator gives high
frequency alternating (10-100 KHz) AC output which is given to the Amplifier.
• Amplifier converts low level power output of oscillator (nearly 5-10mA) to the higher level (nearly 500mA).
• Alternating output (5V,~500mA AC, 50-75KHz) is fed to the parallel LC tank circuit. LC tank circuit is basically air cored inductor with capacitor across it.
• Since high frequency AC input is given to LC tank circuit, high frequency
oscillating magnetic field is produced. The energy will transfer back and forth between the magnetic field in the inductor and the electric field across the capacitor at the resonant frequency. This oscillation will die away at a rate determined by the Q factor which is high is our case.
• Because the Q is high, even when low power is fed into the transmitter coil, a relatively intense field builds up over multiple cycles, which increases the power that can be received—at resonance far more power is in the oscillating field than is being fed into the coil, and the receiver coil receives a percentage of that.
• On the receiving end, we have another LC tank circuit which is designed to resonate/Oscillate at the same frequency as transmitter LC tank circuit i.e. 50-75kHz.
• Since there is a resonant inductive coupling between transmitter & receiver LC tank circuits, significant power gets transferred.
• High frequency AC output of receiver tank circuit then converted to 5V DC by means of rectifier circuit.
• 5V DC output is then given to the load (can be mobile battery/LED module etc)
• From above, we have seen that power gets effectively transferred from
transmitter to receiver without any connection of wires i.e power gets transferred
wirelessly.