Three-layer-stacked pressure sensor with a liquid metal-embedded elastomer

This paper reports the fabrication of a hyper-elastic pressure transducer by embedding silicone rubber with micro-channels of conductive liquid metal eGaIn. Micro-channels with dimensions being as small as 300 µm are fabricated by a maskless soft lithography technique. The core of the sensor consists of three layers: the buffer area (top layer), the PDMS membrane layer (middle layer), and the microfluidic layer (bottom layer). Pressures applied on the surface of the elastomer deform the underlying channels and change the electrical resistance. Owing to the arrangement of the buffer strip, stress concentration in the vicinity of micro-channels is eliminated or distinctly reduced compared to the previous studies. At the same time, the stress tends to be more uniform and a certain degree of reduction is emerged at the microfluidic layer. The effects of the buffer zone are well validated by ANSYS workbench. Meanwhile, by adopting trapezoid geometry of micro-channels and the segmented statistical calibration method, the calibration curves and equations are obtained with better linearity and lower hysteresis. Besides, the spring steel shell (50CrVA) with high yield strength is used to bear the primary pressure together with peripheral parts composed of silica gel with good elastic property, which increases effectively the range of the flexible pressure sensor. Finally, theoretical predictions are conducted based on elasticity and contact mechanics. The experimental measured data are in good agreement with the theoretical results.