A Wireless Flexible Pressure Sensor for Human Motion Detection

Abstract

This paper presents a flexible wireless pressure sensor with a high sensitivity and quality factor which exhibits a great potential application in tactile sensing, health monitoring and smart electronics. Our flexible wireless pressure sensor is built on a three-layer structure: the bottom layer is a planar antenna consisting of an inductor and an inner-digit capacitor, which are patterned on two opposite-side of polyimide substrate, connected in serious; The middle layer is a layer of compressible flexible sponge with a thickness of 4.4mm; The top layer is a ferrite film with a thin layer of adhesive. Under external pressure, the flexible sponge layer is mechanically deformed, leading to the distance between the ferrite film and the antenna layer decreases. Consequently, the magnetic permeability increases, resulting in an increase in inductance, and further resonant frequency decreases. This study sets a special space to research the impact of the environment on the sensor (from indoor temperature to high temperature and from indoor humidity to high humidity). It turns out that environmental factors have little effect on the sensor, reflecting the environmental stability of the sensor. The cyclic and bending experiments have also been performed. Our sensor exhibits excellent stability when pressed and released periodically or bent repeatedly. Finally, we demonstrate the utility by attaching the sensor to an elastic leg straps to measure the compression force of the strap under different leg motions.