Mode mixing in shear horizontal ultrasonic guided waves
ABSTRACT
SH guided waves are used increasingly for non-destructive testing
(NDT) applications, particularly for pipes and pipe supports using
circumferentially guided wave modes. In practical implementations,
it is not always straightforward to ensure single-mode operation and
this requires consideration when interpreting results. During shear
horizontal (SH) wave generation or SH guided wave interaction
with geometrical changes or defects, multiple SH guided wave
modes may be produced, depending on the shear wave speed,
the frequency of operation, the thickness of the sample and the
transducer characteristics. This paper discusses the interference
patterns created as the multiple SH modes mix (for both continuous
tone generation and short bursts), and the problems caused by the
interference patterns on applications such as NDT. In particular, the
patterns can lead to defects being missed during an NDT inspection
using SH waves, and a way to circumvent this problem is suggested.
