Ultrasonic characterization of ultra-thin elastic layer using retrieve function

Using frequency domain retrieve function, a method is presented for characterizing ultra-thin plate by low frequency ultrasound. "Ultra-thin" means that the thickness of specimen is much less than the wavlength. The throughtransmission retrieve function is examined in detail. In conjunction with the method of least squares, the amplitude spectrum, phase spectrum and complex spectrum are all used to determine the best estimation. An analysis of some typical sources of the estimate deviation is presented. The sensitivities of the retrieve function to acoustical parameters and its significance in the propagation of errors have been derived and well discussed.In experimental study the technique is employed to characterize the brass sheets ranging from 25.4μm to 152.4 pm with a broadba-nd 2 MHz transducer. It is observed that the agreement between the nominal value and the estimation is excellent.