Effect of Platinum-Catalysed Silicone Elastomer Encapsulation on the Performance of Embedded Stretchable Capacitive Multimodal Sensor

This paper presents the study of the effect of Platinum-catalysed silicone elastomer encapsulation material on the performance of a stretchable multimodal sensor embedded inside it. The novel stretchable multimodal sensor is designed based on a parallel plate capacitor structure to measure strain, shear stress, and pressure. A prototype of the sensor is fabricated from thin copper-polyimide laminate and encapsulated inside Ecoflex 00-30 platinum-catalyzed silicone rubber and Polydimethylsiloxane (PDMS). Empirical tests are conducted on the prototype under different environment temperatures, which is known to affect the modulus of elasticity of silicone rubber encapsulation. For the temperature settings of 24, 30, and 37 °C, sensitivity values for strain sensor are recorded to be -18.2, -16.0, and -13.6 fF. %
^-1
respectively, whereas the sensitivities of the shear sensor are found to be 1.27, 1.24, and 1.16 fF.kPa
^-1
under the same temperature settings. The pressure sensor tested under the temperatures of 24, 30, and 37 °C shows an opposite trend with recorded sensitivity values of 0.087, 0.088, and 0.089 fF.kPa
^-1
respectively. In terms of cross-sensitivity performance, the pressure and shear sensors exhibit a small negative sensitivity to strain stimulus. Strain and pressure sensors also give slight negative sensitivities to the shear stimulus. Pressure stimulus, on the other hand, induces a significant positive response and small negative response by the shear and strain sensor respectively. The experimental results are validated using a series of finite element analysis (FEA). Simulation results confirm that the change in the embedded sensor sensitivity with temperature is due to the change in the stiffness of the encapsulation material. The cross-sensitivity performance on the other hand is due to the movement and deformation of the encapsulation material under mechanical stimuli.