Laser generated ultrasound sources using polymer nanocomposites for high frequency metrology
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AbstractAccurate characterization of ultrasound fields generated by diagnostic and therapeutic transducers is critical for patient safety. This requires hydrophones calibrated to a traceable standard and currently the upper calibration frequency range available to the user community is limited to a frequency of 40 MHz. However, the increasing use of high frequencies for both imaging and therapy necessitates calibrations to frequencies well beyond this range. For this to be possible, a source of high amplitude, broadband, quasi-planar and stable ultrasound fields is required. This is difficult to achieve using conventional piezoelectric sources, but laser generated ultrasound is a promising technique in this regard. In this study, various polymer-carbon nanotube nanocomposites (PNC) were fabricated and tested for their suitability for such an application by varying the polymer type, carbon nanotubes weight content in the polymer, and PNC thickness. A broadband hydrophone was used to measure the peak pressure and bandwidth of the laser generated ultrasound pulse. Peak-positive pressures of up to 8 MPa and −6dB bandwidths of up to 40 MHz were recorded. There is a nonlinear dependence of the peak pressure on the laser fluence and the bandwidth scales inversely proportionally to the peak pressure. The high-pressure plane waves generated from this preliminary investigation has demonstrated that laser generated ultrasound sources are a promising technique for high frequency calibration of hydrophones.
CitationRajagopal S, Sainsbury T, Treeby BE, Cox BT (2017) Laser generated ultrasound sources using polymer nanocomposites for high frequency metrology. 2017 IEEE International Ultrasonics Symposium (IUS). Available: http://dx.doi.org/10.1109/ultsym.2017.8092019.
SponsorsThe UK Department for Business, Energy & Industrial Strategy’s funding of the National Measurement System is gratefully acknowledged. S.R. thanks National Physical Laboratory (NPL) for supporting his PhD with University College London and Composites, Adhesives and Polymeric Materials Group at NPL for providing access to laboratory facilities to undertake the nanocomposite work.