Bioinspired Crocodile Skin-Based Flexible Piezoelectric Sensor for Three-Dimensional Force Detection

The demand for flexible pressure sensors is increasing with the rapid development of wearable smart devices, dexterous manipulators, and human–machine application interfaces. Despite the development of flexible sensors capable of effectively sensing multidimensional forces, the challenge of directly restoring information from objects in contact remains significant. Inspired by the tactile sensory organ of crocodile skin, this study reports a 3-D force sensing sensor, mainly composed of barium titanate polyvinylidene difluoride and silicone, to form a piezoelectric elastomer layer. Under normal and shear loads, the sensing mechanism relies on the change in output voltage between the semi-spherical electrodes and the piezoelastomer. An interlocking structure detects different directions of shear force. The sensor exhibits excellent directional resolution, with a normal force sensitivity of 20.42 ± 2 mvN−1 in the pressure range of 0.1–1.5 N and directional sensing sensitivity of 4.40, 5.29, 4.44, and 4.84 mVN−1 for the four faces, respectively. The sensor also exhibits high linearity. Further demonstrations included testing the sensor in molds over various rough surfaces. The sensor provided timely feedback to distinguish between different surface roughnesses and force directions—expected to be a self-powered wearable device for future human–computer interaction or personalized identification applications.