The Effect of a Ferrite-Core Relay Vs. an Air-Core Relay on the Output Power Characteristics of a Three-Coil Wireless Power Transfer System

Abstract

The purpose of this thesis is to determine the effect of using a ferrite-core relay on the output power characteristics of a three-coil, parallel-tuned, domino-resonator wireless power transfer (WPT) system in comparison to the effect of using an air-core relay in such a system. First, a general mathematical model is presented to describe both the ferrite-core-relay system and the air-core-relay system and to calculate their output power characteristics for seven different resistive loads at each of five different distance configurations between the coils. Next, experimental results are analyzed and compared to the mathematical results to confirm model accuracy. Finally, the output power characteristics of the two systems are compared and contrasted. The results of this thesis show that the model is most accurate when working with loads around 1000 Ohms, exhibiting an error of about 25%. More importantly, maximum power output is achieved when working with loads around 1000 Ohms, at which the average improvement to output power when using a ferrite core instead of an air core is about 87%. Therefore, it can be concluded that, with coil geometries and operating frequencies being held constant, the inclusion of a ferrite core in relay coils can noticeably improve output power characteristics at a given distance between coils. The reason for this improvement is most probably the result of magnetic flux concentration by the ferrite core, which in turn increases induced current and therefore output power.