WIRELESS BATTERY CHARGING SYSTEM USING RADIO FREQUENCY ENERGY HARVESTING



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INTRODUCTION AND MOTIVATION

Cellular telephone technology became commercially available in the 1980’s. Since then, it has been like a snowball rolling downhill, ever increasing in the number of users and the speed at which the technology advances. When the cellular phone was first implemented, it was enormous in size by today’s standards. This reason is two-fold; the battery had to be large, and the circuits themselves were large. The circuits of that time used in electronic devices were made from off the shelf integrated circuits (IC), meaning that usually every part of the circuit had its own package. These packages were also very large. These large circuit boards required large amounts of power, which meant bigger batteries. This reliance on power was a major contributor to the reason these phones were so big.


PROBLEM STATEMENT

The goal of this thesis is to determine if is possible to capture enough power in a cellular phone in order to charge the battery. The requirements for the system to be presented are that it be incorporated into a base station and the operating frequency is set. The design of the board and choice of antenna for the stand are the focal point of the experiments that are to be performed. In order to prove the concept, power needs to be supplied to the energy harvesting circuit by an external transmitter. This transmitter will send a signal at the set frequency. Our test system will then receive this signal through the energy havesting circuit. This circuit is the fundamental design problem of this thesis.


THE TRANSMITTER

The most basic transmitter setup consists of a piece of equipment that generates a signal whose output is then fed into an amplifier that is finally output through a radiating antenna – the air interface.


THE PHONES

The design aspect of this project is focused on the receiving side. For this stage of research, of which the goal is to prove that the wireless battery charger idea is feasible, it was decided to incorporate the energy harvesting circuitry and antenna in some sort of base station or charging

stand. It is necessary to hide the components for demonstration purposes.


THE STANDS
Before starting the design of the circuitry for charging the phones, it is beneficial to know the space available for the board. The Nokia DCV-15 desktop stand and Motorola SYN8610 hands free speakerphone have commercially available accessories for holding the phones.