Characterization of a new flexible pressure sensor for body sensor networks

Pressure sensors are generally used in body sensor networks to measure physical forces exerted by our limbs. Popular sensors include the force sensitive resistor and the piezoelectric sensors, both made of rigid semiconductor technology. However, the application of these sensors to human movement monitoring necessitates that these sensors be made flexible. This paper focuses on the design of flexible pressure sensors, in particular on the effect of electrode composition and thin film carbon infused conductive layers on a force sensitive resistor based pressure sensor. Fourteen pressure sensor designs with Velostat as a piezo resistive layer were developed with a variety of electrode materials i.e. silver, copper and tin. These sensors were characterized into three types, according to the properties of the conducting material placed with respect to insulating material in the pressure sensor. Our force versus resistance and deformation experiments reveal similar trends to popular semiconductor based force sensitive resistors (FSRs) i.e. Tekscan and Novel sensors. The best sensor design achieved a resistance range of 4000Ω over a force range of 0 to 20N. The design consisted of silver-nylon conducting thread stitched into a neoprene insulator layer. Tests demonstrated that the developed sensor was reliable and the performance was repeatable.