Abstract: By increasing the initial time and time step in analysis of heat conduction, an ultrasonic model under steady heat conduction condition is established to simultaneously sense thickness and internal temperature field based on thermo-acoustic coupling analysis. By using ultrasonic echo method and inverse heat conduction analysis, the estimation of internal temperature field of structure is transformed into the inversion of equivalent heat boundary condition and the calculation of normal heat conduction problem. This not only avoids the matrix singularity problem caused by insufficient input information in parameter identification, but also reflects the accumulation characteristics of ultrasonic transition time caused by different temperature in the wave propagation path, which can effectively improve the accuracy of simultaneous temperature and thickness measurement under steady heat conduction conditions. The feasibility and reliability of the presented method are verified by experiments. An extensive parametric analysis of different sampling points, thermal boundary conditions and specimen thickness also shows that the method has good noise resistance.

Key words: ultrasonic, simultaneous measurement of temperature and thickness, thermo-acoustic coupling, inverse heat conduction problem, steady heat conduction problem