Design and fabrication of microstructures for reliable spatiotemporal pressure sensing under sensory interference

Abstract

Electronic skin are devices that mimic the functionalities of human skin, which require high sensitivity, large dynamic range, high spatial uniformity, low-cost and large area processability, and the capacity to differentiate various external inputs. Moreover, to accurately probe the tactile information on soft skin, it is critical for the pressure sensing array to be free of noise and inter-taxel crosstalk, irrespective of the measurement condition. However, on dynamically moving and soft surfaces, which are common conditions for on-skin and robotic applications, obtaining precise measurement without compromising the sensing performance is a significant challenge due to mechanical coupling between the sensors and with the moving surface. In this work, a versatile droplet-based microfluidic-assisted emulsion self-assembly process were firstly introduced to generate 3-dimensional microstructure based high-performance capacitive and piezoresistive pressure sensors for electronic skin applications. The technique can generate uniformly sized micropores that are self-assembled in an orderly close-packed manner over a large area, which results in high spatial uniformity. The size of the micropores can easily be tuned from 100-500 μm, through which sensitivity and dynamic range were controlled to as high as 0.86 $kPa^-1$ and up to 100 kPa. This microporous structure can be printed on curvilinear surfaces and be molded into various shapes. Furthermore, by simultaneously utilizing capacitive and piezoresistive pressure sensors, the device can distinguish between pressure and temperature, or between pressure and proximity. In addition to this, multi-level architectural design of micro-pyramids and trapezoid-shaped mechanical barrier array was implemented to enable accurate spatiotemporal tactile sensing on soft surfaces under dynamic deformations. Trade-off relationship between limit of detection and bending insensitivity was discovered, which was overcome by employing micropores in barrier structures. Finally, in-situ pressure mapping on dynamically moving soft surfaces without signal distortion is demonstrated while human skin and/or soft robots are performing complicated tasks such as reading Braille and handling the artificial organs.