An Optoelectronics-Based Sensor For Measuring Multi-Axial Shear Stresses

Abstract

Tactile shear force sensors are increasingly popular for medical applications especially for orthopedic rehabilitation such as measuring interfacial shear stresses between a residual limb and prosthetic socket to manage socket fit and residual limb tissue health, or measuring shearing between a foot sole and shoe for assessing performance in athletes. However, there are considerable challenges in implementing shear force sensors for orthopedic applications due to the requirements for noninvasiveness, light weight, low power, and robustness against motion artifacts, normal force, or electromagnetic fields. To address these challenges, this paper describes the design, fabrication, and characterization of a simple, low-cost, optoelectronic sensor that can measure multi-axial shear stresses. The sensor is based on a red, green, and blue (RGB) light-emitting diode (LED) cycling among red, green, and blue lights onto a color pattern surface. As shear strain causes a displacement between the LED and the color pattern, the relative intensities of reflected lights among the different colors change. A photodiode is used to capture the reflected light intensity at each color illumination, allowing the determination of the color pattern surface displacement, and in turn the shear, along two axes. In this paper, the efficacy of the sensor under benchtop testing conditions is reported, confirming the potential of this technology for shear monitoring at orthopedic devices such as protheses or shoes. Future efforts will focus on miniaturization and packaging of the sensors, and characterizing their performance for more medical and other types of applications.