A SIGNAL REGENERATION TECHNIQUE FOR LONG-RANGE PROPAGATION OF DISPERSIVE LAMB WAVES

A technique which enables a dispersive Lamb wave to be propagated over a considerable distance to give a simple waveform at the receiver position is described. The method works by launching a signal which, by superposition of its frequency components, will recombine to form a signal with a simple shape (a pulse or tone burst) at the measurement position. The technique has been tested on thin plates both numerically and experimentally, simple windowed tone bursts being received at the measurement position even though the propagating modes were grossly dispersive. The advantage of this method in NDE applications is that the simple form of the signal received on a good plate potentially makes it easy to detect any small changes due to defects along the propagation path, and also that the signal/noise ratio is maximized at the measurement position.