Abstract:

In this paper a novel technique to generate and detect Lamb waves by use of cylindrical ultrasonic waveguides with off-shelf ultrasound transducers attached to the ends will be investigated. Due to the impedance mismatch between the transducer and the cylindrical rod waveguide, the energy transmission from an off-shelf transducer to the rod is not very efficient. An unique technique, which makes use of solid conical waveguide as an impedance transformer between the transducer and the rod waveguide, was investigated to solve the problem. Insertion loss measurements for two different waveguide systems, i.e., transducer rod and transducer-conical waveguide rod, were conducted to verify the improvement of the acoustic energy transmission of a transducer-conical waveguide-rod combination. Transient plate waves excited by Nelson--Hsu pencil lead breaks were detected and recorded on an aluminum plate by the as-developed waveguides. Dispersion analysis was conducted to verify the plate modes excited by pencil lead breaks at different locations of the plate. Excitation of Lamb waves was also exercised by use of the waveguides. Experimental measurement of the mode velocity was compared with the theoretical predication.