Null-point cross-coupling for semi-remote sensing of resonant frequency of tuning circuit and its application for intra-corporeal sensing

Abstract

When two flat ring coils are layed on a plane in free space, overlapping about 20%, there can be found a null-coupling point where mutual flux coupling is cancelled to make zero transmission to each other. On such setup we can detect nearby interrupting magnetic material and/or LC-resonant tank circuit which causes extra transmission via cross-coupling to the interrupter. Such detection capabikity would depend on accuracy of null-point setup, driving signal design, gain and bandwidth of detecting amplifier and the size of the interrupter to be detected. Adequate design can detect a similar size tank circuit having Q0=70 or more at several times distance of interlogating coil pair diameter. In this study we aimed to use this for extrra corporeal sensing of intra corporeal passive sensing device. In our model experiment 5cm interlogating coil pair can steadily sense 1cm dia. x 1cm length ferrite cored LC tank circut, at 1 to 2 MHz frequency band.