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 pos ition is described. The method works by launching a signal which, by s uperposition of its frequency components, will recombine to form a sig nal with a simple shape (a pulse or tone burst) at the measurement pos ition. The technique has been tested on thin plates both numerically a nd experimentally, simple windowed tone bursts being received at the m easurement position even though the propagating modes were grossly dis persive. The advantage of this method in NDE applications is that the simple form of the signal received on a good plate potentially makes i t easy to detect any small changes due to defects along the propagatio n path, and also that the signal/noise ratio is maximized at the measu rement position.