Dipole-Coil-Based Wide-Range Inductive Power Transfer Systems for Wireless Sensors

Abstract

A dipole-coil-based extremely loosely coupled inductive power transfer system (IPTS) for wireless sensors over a wide range is proposed. The overall superiority of dipole coils for a long-distance power delivery over loop coils with an identical configuration of a square core is verified by comparing the magnetizing inductance between primary and secondary coils. Series-parallel resonant circuits were used to achieve a higher load voltage than that of the series-series scheme. Contrary to conventional IPTSs or coupled magnetic resonance systems, the quality factor Q was set as low as 100, guaranteeing a frequency tolerance of 1%, where a prototype of narrow dipole coils with a length of 2 m was used to deliver 10.3 W of power up to 7 m away at a low frequency of 20 kHz. The powering capabilities of the proposed IPTS were experimentally compared inside and outside of a metal container 8 m x 4 m x 2.5 m in size at different frequencies ranging from 20 to 150 kHz, where the proposed IPTS is highly likely to be surrounded by arbitrary distributed conductors in most wireless sensor usage environments. The coupling coefficient. between the primary and secondary coils was measured over a long distance from 2 to 12 m for different secondary coil positions, where. is mostly much less than 0.01. A comparative analysis of the maximum amounts of load power among different core materials, i.e., two ferrite cores and an amorphous core, was conducted in relation to the design of a secondary coil. The results were verified by experiments at a given switching frequency of 20 kHz