  Structural health monitoring (SHM) has become more and more important in
modern industries as it can monitor the safety of structures during the full
service life and prevent possible losses of life and economics. Shear
horizontal wave in plate-like structures is very useful for long distance
defects inspection since its fundamental mode (SH0) is totally non-dispersive.
However, all the currently available SH wave transducers are not suitable for
practical SHM. In this work, we firstly investigated via finite element
simulations the performances of thickness-poled d15 PZT ring based
omni-directional SH wave piezoelectric transducers (OSH-PT) consisting of
different number of elements. Results show that the two half-rings based OSH-PT
can have perfect omni-directivity and acceptable performances in
excitation/reception of SH0 waves, and its performances can be fairly enhanced
by reducing the outer and inner diameters. Experimental results on a 2mm-thick,
21mm outer-diameter, 9mm inner-diameter two-half-ring OSH-PT shows that it has
good omni-directional properties with the maximum deviation of ~14% in both
excitation and reception of SH0 wave. The signal to noise ratio (SNR) of the
OSH-PT in the case of self-excitation and self-reception is over 15dB from
145kHz to 200kHz, which is acceptable for most applications. The proposed
two-half-ring OSH-PT is expected to be widely used in SH0 wave based SHM due to
its simple structure, easy fabrication/assembling, low cost and acceptable
performances.
