Pressure sensors used as bioimpedance plantar electrodes: a feasibility study

Diabetic Foot Ulcers are ominous consequence of Diabetic Foot. Only general preventive guidelines are available, and ulcers happen with no previous notice. To develop a multidimensional ulcer opening warning device: temperature, pressure, humidity and friction are usually considered. We use standard flexible Force Sensing Resistors FSR 402 to detect not only plantar pressure, but also plantar bioimpedance. Since FSR includes conductive electrodes covered by polymer films, the interface with the subject can be considered a capacitive electrode. A special bioimpedance detection circuit is required to inject current using two homologous FSR 402 contacts and measuring the resulting voltage from the other two contacts available. This circuit is able to detect the cardiac activity from the foot sole. For the first time, pressure sensors are used as bioimpedance electrodes.