The influence of temperature on ultrasonic signals in online measurement of oil film thickness

Ultrasonic reflection provides a real-time way to monitor oil film thickness in a running machine with a non-destructive advantage. However, the influence mechanism of temperature on reference signals has not been clarified so far, which hinders the precise measurement of oil film thickness. Focusing on a common three-layer structure of sensor-adhesive-steel, a global propagation model is constructed to investigate variations in the reference signal with temperature. Through finite element simulations, distinct influence mechanisms are revealed for different components: For piezoelectric sensors and the adhesive layer, temperature may induce amplitude attenuation and wave extensions in the reference signal. In the steel component, only an overall time shift is observed in the reference signal. Subsequently, a compensation model is established and validated through temperature-controlled experiments. Within the effective bandwidth, the compensation model achieves a relative error of  and an absolute error of  radians for the amplitude and phase of the reference waves.