Building a Real Time Plantar Force Measurement Sensor With LC Resonator

Abstract

The development of wearable equipment is posing new challenges to traditional sensors. Currently, it is important to reduce sensor size and improve sensor sensitivity so that data could be collected without interfering users’ common behavior. This article illustrates a new method for real time plantar force measurement. By paralleling planar inductive sensing coils with capacitors to form a LC resonant circuit and monitoring the change of resonant frequency or inductance, the occurrence of heel-strike and toe-off could be detected, because the change of the clearances between foot and insole triggers the simultaneous alternation of coil inductance. We conducted experiments on two different types of coils and compared them with force sensitive resistor (FSR). It is found that the Pearson correlation coefficients of these two coils’ inductance with the output voltage of FSR conversion circuit are −0.9780 and −0.7788, respectively. With smaller size and less expensive than traditional resistive sensors, this new sensing system could precisely reflect different gaits of walkers when tested in realistic situations.