Paint Thickness Measurement Using Acoustic Interference

A novel method of determining the thickness of a paint coating over composites is presented. A sinusoidal ultrasonic wave modulated with a low-duty-cycle pulse train is interfered with its own reflection off the paint-composite interface. An amplitude profile periodic in frequency is observed after interference. Measurement is first made with the transducer facing air and then with the transducer facing the sample. The frequency shift of a chosen minimum is used to calculate the paint coating thickness. A method using two frequencies to increase the range of thickness measurement and improve the resolution is also presented. The method has been shown to yield an accuracy better than 3%