Wireless zero-power small displacement sensors

Power consumption, flexibility, cost effectiveness and dimension reductions are the most important parameters to consider in many applications of the biomedical field and particularly implant devices. Echoing this trend, we present a passive, flexible and low cost wireless microsensor based on a LC tank circuit whose capacity varies with the deformation as a result of the area change shared between the interdigitated parallel plates capacitor. As a result, two types of micro-sensor are defined, simulated, fabricated and tested. The capacitors constitute a set of interdigitated gold plates laid on a COP (Cyclo Olefin Polymer) substrate and the planar microcoils are designed to take into account the spacing between the turns, the width and the number of turns over the COP substrate. The system is completed by an inductive reading subsystem and testing results show the scalability of the system. Using the fabricated demonstrator, we detect displacements in the range of tens of micrometers and resonance frequency variations 200 to 350MHz.