Prepared by:
Himani Patel

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Introduction
• Portable electronic devices are very popular now a days.
• As the usage of these portable electronic devices is increasing, the demands for longer battery life are also increasing. These batteries need to be recharged or replaced periodically.
• It is a hassle to charge or change the battery after a while, especially when there is no power outlet around. This wireless battery charger is expected to eliminate all the problems with today’s battery technology.
Abstract
• The wireless charger will convert the RF/ microwave signal at 900 MHz frequency into a DC signal, and then store the power into an AAA battery.
• The project is divided into 3 parts: transmitter, antenna, and charging circuit.
Design Overview
This wireless battery charger is designed to operate at 900 MHz In this project, a power transmitter acts as the power source. It will transmit power to the receiver side. And then, the rectifier circuit in the receiver will convert the RF/ microwave signal into DC signal. After the DC signal is produced, the charging circuit will store the power into the battery. Here is the block diagram of the overall design
Transmitter
It is a 900 MHz video/audio transmitter. Here’s the specification of the transmitter.
Antenna
The antenna plays a very important role. To charge a battery, a high DC power signal is needed. there are many considerations to choose the correct parts for the design. The considerations of choosing the appropriate antenna are:
1. Impedance of the antenna
2. Gain of the antenna
Taking the above design spec in consideration, the team found Yagi antennas that fit our spec. Above is a picture of the Yagi antenna
• The impedance of the antenna should match with the output impedance of the power transmitter and input impedance of the rectifier circuit.
• Non-matching impedance between circuits can cause a tremendous power loss due to signal distortion. Since the output impedance of the transmitter is 50 Ω, the antenna should also have 50 Ω impedance.
• The higher of the antenna gain yields a better result of the design. However, higher gain will also increase the cost and the size of the antenna.
Receiver
• The receiver’s main purpose is to charge an AAA battery.
A simple battery charging theory is to run current through the battery, and apply a voltage difference between the terminals of the battery to reverse the chemical process. By doing so, it recharges the battery