Ultrasensitive and low-cost insole for gait analysis using piezoelectrets

The emerging need of wearable healthcare monitoring systems for e.g. predicting cognitive decline, necessitates practical requirements such as high sensor sensitivity and low fabrication costs. In this work, we present an ultrasensitive piezoelectric insole using 3D-printed flexible piezoelectret with a readout circuit that sends measurement data via WiFi. The insole is printed using pure polypropylene filament and consists of eight independent sensors, each with a piezoelectric d(33) coefficient of approximately 2000 pC/N. The active part of the insole is protected using a 3D-printed polylactic acid cover that features eight defined embossments on the bottom part, which focus the force on the sensors and act as overload protection against excessive stress. In addition to determining the gait pattern, an accelerometer is implemented to measure kinematic parameters and validate the sensor output signals. The combination of the high sensitivity of the sensors and the kinematic movement of the foot, opens new perspectives regarding diagnosis possibilities through gait analysis.