Hybrid Sensor Insole for Wearable Ballistocardiography in Remote Health Monitoring

Remote health monitoring improves the quality of life by enabling an early condition detection. The human heartbeat qualifies as physiological measure for body vitality and can be acquired through unobtrusive ballistocardiography (BCG). Current wearable BCG devices lack customizability and posture detection of the wearer. In this work, we present a hybrid insole concept with piezoelectric ferroelectrets and piezoresistive Velostat sensors to complement their properties. The Velostat sensor is evaluated in a universal testing machine with an applied load up to 50 N, resulting in a sensitivity of 200 Ohm/N and 80% resistance change. It reliably activates the BCG once the insole wearer maintains a stable posture. The experiment involves three participants in upright posture on the smart insole, at resting pulse and after physical activity. We apply a continuous wavelet transform to the ferroelectret sensor data to enhance feature detection. The heart rate is extracted from the peak distance and, for resting pulse, aligns with the reference heartbeat acquired from a chest strap. Thus, our hybrid insole system proves suitable as a wearable heart rate detector for health monitoring.