Ultrasonics: Part 9. Compression wave techniques

摘要

The important thing to remember when calibrating the timebase for compression waves is that the left-hand end of the timebase (Zero) must exactly correspond to the entry surface of the beam and the right-hand end represents a known thickness in the material being tested. The exceptions to this rule are those occasions when you are using delay to expand some distant portion of the material, or when you are using a multiple echo technique and only noting the decay pattern. For single-crystal probes, the initial pulse contains two elements; the applied square-wave voltage pulse and the ringing of the crystal. The end of the applied voltage pulse represents the top surface at which time the crystal ringing starts. Unfortunately, the amplitude of this part of the initial pulse is so large that it is not possible to identify the point at which the ringing starts, nor is it possible to tell from the timebase line.