Abstract
The fundamental flexural guided wave (FFGW) permits ultrasonic assessment of the wall thickness of solid waveguides, such as tubes or, e.g., long cortical bones. Recently, an optical non-contact method was proposed for ultrasound excitation and detection with the aim of facilitating the FFGW reception by suppressing the interfering modes from the soft coating. This technique suffers from low SNR and requires iterative physical scanning across the source-receiver distance for 2D-FFT analysis. This means that SNR improvement achieved by temporal averaging becomes time-consuming (several minutes) which reduces the applicability of the technique, especially in time-critical applications such as clinical quantitative ultrasound. To achieve sufficient SNR faster, an ultrasonic excitation by a base-sequence-modulated Golay code (BSGC, 64-bit code pair) on coated tube samples (1-5 mm wall thickness and 5 mm soft coating layer) was used. This approach improved SNR by 21 dB and speeded up the measurement by a factor of 100 compared to using a classical pulse excitation with temporal averaging. The measurement now took seconds instead of minutes, while the ability to determine the wall thickness of the phantoms was maintained. The technique thus allows rapid noncontacting assessment of the wall thickness in coated solid tubes, such as the human bone.
Highlights
Guided waves (GW) are widely used for non-destructive testing.[1]
An optical non-contact method was proposed for ultrasound excitation and detection with the aim of facilitating the fundamental flexural guided wave (FFGW) reception by suppressing the interfering modes from the soft coating
A method that employs a fundamental flexural guided wave (FFGW), consistent with the fundamental antisymmetric Lamb mode (A0), which corresponds to the case of the “free plate”, permits an inference of the wall thickness of tubes, e.g. the cortical thickness.[6]
Summary
Guided waves (GW) are widely used for non-destructive testing.[1]. These mechanical stress waves propagate along elongated structures and are sensitive to the structural and elastic properties of the inspected bodies.[2].
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