Surface Texture Detection With a New Sub-mm Resolution Flexible Tactile Capacitive Sensor Array for Multimodal Artificial Finger

This work presents a flexible polyimide-based capacitive tactile sensing array with sub-millimeter spatial resolution. The sensor is conceived to be embedded in a multimodal artificial finger to detect and classify the texture morphology of an object’s surface. The proposed tactile sensor comprises a <inline-formula> <tex-math notation="LaTeX">$16\times 16$ </tex-math></inline-formula> array of capacitive sensing units. Each unit is composed of a parallel square electrode pairs (<inline-formula> <tex-math notation="LaTeX">$340~ {\mu }\text{m}\,\,\times 340~ {\mu }\text{m}$ </tex-math></inline-formula>) separated by a compressible air cavity and embedded into a flexible polyimide substrate. Standard MEMS microfabrication techniques were used to develop the sensor. The polyimide device was covered with a thin compressible PDMS layer to tune the normal pressure sensitivity and dynamic range (225–430 <inline-formula> <tex-math notation="LaTeX">${\mu }\text{m}$ </tex-math></inline-formula> thin PDMS layer resulting in 0.23–0.14 fF/kPa). The detection of the surface morphologies of a regular grating stamp for different orientation and a small metallic nut placed on the sensor is demonstrated, showing a 420 <inline-formula> <tex-math notation="LaTeX">${\mu }\text{m}$ </tex-math></inline-formula> spatial resolution. The proposed sensor represents a novel capacitive tactile sensing device with a sub-mm resolution of human fingertip sensitivity.