Multisensor piezoelectric polymer insole for pedobarography

Abstract

Abstract Analysis of the pressure distribution under the foot in walking and standing patients (pedobarography) can be used to detect orthopaedic as well as neurological defects. Sensorized insoles are increasingly used, at least for research purposes, because of the inherent advantages they offer compared to the force platforms presently available. We have developed and evaluated a piezoelectric polymer insole for pedobarography, using a 200 μm thick polyvinylidene fluoride (PVDF) film which had been uniaxially stretched and poled in selected areas. Sixteen circular aluminium disks, 6 mm diameter each, deposited onto the film by vacuum evaporation, served as the electrodes for the pressure sensors and were located so as to optimize the response of the five metatarsal transducers, which are particularly critical for a correct gait analysis. The 16 sensors were disposed on the ideal loading surface, the response of which identified incorrect foot conformation on loading. Sixteen conductive tracks, one for each transducer, converged toward a side of the insole, where 16 contact pads were provided to bond connecting wires, leading to an electronic unit conveniently attached to the leg of the patient. A system was designed to allow data acquisition and processing by a Digital MINC 11 minicomputer. This sensorized insole is currently evaluated for gait analysis, and tests on a normal subject are reported.