An experimental method to measure the layer thickness and wave velocity of copper–steel composite board without interface echo

• The experiment is implemented by using the ultrasonic immersion coupling technique.
• The result shows a maximum relative error percentage of 0.2% with the actual value.
• The method is confirmed valid by both experiment and simulation tests.
• The method can also give same accuracy for another two-layer composite medium.

Thickness of each medium layer and velocity of ultrasonic wave propagation in each medium layer of the two-layer composite medium were measured simultaneously based on the method to collect phase information from continuous echo signals on front surface and undersurface. Such measurement was implemented under no interface echo and fixed total thickness of the testpiece. The method can be applied to any two kinds of two-layer composite medium. The paper only used a 35 mm thick copper–steel composite board as an experimental example. Calculated results demonstrated that measuring errors of both thickness and velocity of ultrasonic wave propagation are smaller than 0.2%, indicating the effectiveness of the proposed measurement method.