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.　This light intensity change was opposite to the behavior of conventional polymer foams (cellular structures), which have a large structural scale. 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. Sensors using sol–gel derived macroporous materials have the potential to be thinner and provide improved surface tactile sensation compared to foam materials.