Optical tactile sensor using scattering inside sol–gel-derived flexible macroporous monoliths

Tactile sensors are an essential technology for robots, and various types have been developed. This paper reports on a new optical tactile sensor based on multiple scattering in a porous material with a viscoelastic phase-separated structure fabricated by a sol–gel method. When a macroporous silicone monolith with a few micrometer diameter skeletons was compressed, the diffuse light intensity near the light source was reduced due to Mie multiple scattering. A simple tactile sensor using a macroporous monolith and a photo reflector was fabricated based on this finding. The skeleton diameter was an important factor for the sensor. In the case of macroporous silicones, the voltage-strain curve showed an almost hysteresis-free clear response. However, the response of macroporous polymethylmethacrylate monolith with a smaller skeleton diameter was weak due to low Mie scattering intensity. Using cell structure materials with a scale much larger than the optical wavelength, a decrease in light intensity with compression was not observed. Sensors using sol–gel-derived flexible macroporous monoliths could provide features such as thinness and improved surface tactility.