The technique of direct electromagnetic generation of surface elastic waves eliminates the mechanical coupling bond required by piezoelectric transducers and thus offers many practical advantages in nondestructive testing and materials characterization. In this paper, some of these advantages are explored. The ease of measurement made possible by the noncontact coupling is demonstrated by phase velocity, group velocity, and diffraction loss data for 130 kHz flexural Lamb waves on 3/8 in. steel plate, all of which are in good agreement with theoretical models. Further data define the ability to detect discontinuities with these transducers either by the detection of reflected energy or the measurement of phase shifts when a transmitted wave is partially scattered by the discontinuity. Feasibility studies of the use of the noncontact transducers in the inspection of large pipes will be described, and other areas in which their application appears promising will be indicated.
Available at: http://works.bepress.com/rbruce_thompson/42/