A Textile Based Capacitive Pressure Sensor

Background. As interest on wearable computing [1] increases, researchers are looking for new materials to use as a support for electronics. A fabric substrate is very appealing: it is elastic and extensible [2], supported by a well known technology and produced at low-cost. State of the art. Some smart pressure-sensors interfacing with a flexible substrate have been developed, but they are either based on electro-optical fabric ([3]) which is not suitable for the low cost market, or they need expensive and cumbersome PCB electronics ([4]). Our contribution. This paper introduces an approach for decoding the pressure information exerted over a broad piece of fabric by means of capacitive sensing. The system is composed of a distributed passive array of capacitors (i.e. an array where no active elements like transistors are involved), whose capacitance varies according to the pressure exerted over a surface, as well as an electronic system that collects and computes the subsequent capacitance variations. Capacitors can be realized in different ways, though, in our demonstrator they have been implemented between rows and columns of conductive fibers patterned on the two opposite sides of an elastic synthetic foam. When the dielectric layer between a given row and column electrodes is squeezed, as a pressure is exerted over the corresponding fabric area, the coupling capacitance between the two is increased. The principle of sensing the capacitor array is displayed in Fig.1.