Miniature Multiaxial Optoelectronic Shear Stress Sensing System Based on a Segmented Photodiode

Recording shear stresses is becoming relevant in an increasing number of applications, e.g., in rehabilitation sciences, where detecting foot-sole interaction is very important. This paper describes a portable and complete system to record multiaxial shear stresses. The sensing operation itself is based on the changing coupling of light between a vertical-cavity surface-emitting laser (VCSEL) and a segmented photodiode. Applying shear stress causes lateral displacement of both optoelectronic components leading to variation in the photocurrent. By combining signals from different photodiode segments, multiaxial shear stresses can be detected. A standalone system was designed to drive the VCSEL and to readout the signals from the different photodiode segments in order to measure shear stress as well as to evaluate the sensing system performance. Furthermore, the sensor signals can be efficiently monitored and visualized on a tablet or PC in real-time using dedicated software. The design presented in this article is optimized to measure shear forces with a magnitude up to 2 N and arbitrary direction. Yet, by changing the transducer material this range can be tuned for a specific application.