Proceedings Article | 13 March 2008
Proc. SPIE. 6920, Medical Imaging 2008: Ultrasonic Imaging and Signal Processing
KEYWORDS: Waveguides, Ultrasonography, Wavelets, Ultrasonics, Bone, Wave propagation, Transducers, Vibrometry, Signal detection, In vitro testing
Most of the techniques for generating and detecting ultrasonic Lamb waves (e.g. angle-beam piezoelectric transducers,
micro-electro mechanical systems (MEMS), comb and interdigital transducers, phased array transducers, and
piezoceramic transducers) require a firm physical contact with the measured objects. For objects with highly irregular
surfaces such as bones, it will be very difficult to produce a good contact. Thus, a non-contact Lamb wave measurement
technique, the scanning laser vibrometry, is proposed in this paper to examine a bovine cortical tibia <i>in vitro</i>. The
ultrasonic Lamb waves used had the center frequency of <i>84KHz</i>. The waves were generated using a planar transducer
which was coupled with a cone-shaped resonant vibrator. Only the fundamental modes of <i>a<sub>0</sub></i> and <i>s<sub>0</sub></i> were expected to
occur. 2-Dimensional images of the Lamb waves traveling in the bone were recorded. The scan results represent out-of-plane
vibration of the surface of the bone. Lamb wave modes were verified with further post-processing analyses. In
time-domain, time-history prediction of the modes is fitted onto the original detected signal as to confirm their common
rising time for each mode. A frequency-domain method, i.e. wavelet analysis, is also employed to define the traveling
modes and their group velocity. The expected modes can be clearly defined at the center frequency. Additionally, what
seemed to be a new mode, <i>a<sub>1</sub></i>, was generated and detected at the higher frequency of the responses.
