Modelling of hysteresis and creep in SAW strain sensors

Shear strain transfer from a part surface to a SAW substrate is analyzed for a SAW strain sensor attached to the part by an elastic adhesive. An analytic expression for the strain transfer function is obtained. A viscoelasticity model for the adhesive is proposed that allows prediction of the shear strain sensor output as a function of time. The model gives good match of the theoretical values of creep/relaxation and hysteresis to those observed in SAW torque sensors.