Design, development, and characteristics of an in-shoe triaxial pressure measurement transducer utilizing a single element of piezoelectric copolymer film

In gait analysis, there is growing awareness of the need to simultaneously measure shear and vertical forces for the diagnosis and treatment assessment of pathological foot disorders. This is especially the case in the measurement of the forces between the plantar surface of the foot and the shoe. Although clinical awareness of the need to simultaneously measure shear and vertical forces under the foot has increased little has been done to provide the technology. This is mainly due to the difficulty in constructing devices capable of carrying out this task in the in-shoe environment. The aim of this paper is to describe the development and characteristics of a miniature triaxial transducer measuring 10 × 10 × 2.7 mm and a weight of only 2 g. This transducer is capable of simultaneously measuring three orthogonal forces under any location of the plantar surface of the foot utilizing a single element piezoelectric copolymer P(VDF-TrFE). Transducer sensitivity, linearity, hysteresis, crosstalk and temperature dependence is presented. As well as in-shoe force measurement, this triaxial transducer could have other biomedical and general engineering applications, e.g., prosthetic interface forces, handgrip forces, sport, robotics, etc.