Flexible eddy current sensor array for proximity sensing

This paper presents a new flexible eddy current sensor array and its measurement system that used for conformable proximity sensing, for instance, the gap between curved surfaces. The sensor probe, designed to consist of a forked coils array and a long flat cable, is manufactured on a thin flexible substrate by the flexible printed circuit board (FPCB) technology. The probe is very thin and flexible, so that it can conform to the surface geometries of the measured objects. Time division multiplexing (TDM) technology has been introduced to scan and sample all the sensing elements. Some reforms are also implemented to the conventional LC oscillator to solve the problem of the coils having a low Q-factor. Experimental results show that, to a steel target, the measurement accuracy of the sensor system can reach ±0.5% for a 2 mm full scale. The practice for real-time inspection of the small gaps between large curved surfaces is also considered.