Strain transfer analysis of surface-bonded MEMS strain sensors

Surface-bonded MEMS strain sensors have been widely applied to the strain measurement and monitoring in many fields such as aerospace, automotive industry, civil engineering and etc. The MEMS strain sensors are bonded on host structures using adhesives, due to the influence of the adhesive layer, the strain of the structure cannot be fully transferred from the host structure to the strain sensor accurately, which makes certain error exist between the measurement value of the sensor and the real strain of the structure. To analyse the strain transfer mechanism of the surface-bonded MEMS strain sensors, based on the shear lag theory, a mechanical analysis model of the surface-bonded MEMS strain sensor is proposed. The strain distributions of the host structure and the substrate of the MEMS strain sensor, the shear stress distribution in the adhesive layer and the strain transmission rate characterizing the strain transfer effect of the MEMS strain sensor are deduced, and the results are compared with the numerical simulation results of finite element method. In particular, the effects of the geometric parameters and physical characteristic parameters of the adhesive layer and the substrate of the MEMS strain sensor on the strain transmission rate are analysed in detail. The results show that the strain transmission rate of metal adhesive material is higher than that of organic adhesive obviously; and the thinner the adhesive layer is, the better the strain transfer effect is. In addition, while manufacturing MEMS strain sensor, adopting thin Si or SiC substrate can ensure high strain transmission rate.