| Title |
Signal technologies for ultrasound / |
| Authors |
Svilainis, Linas ; Chaziachmetovas, Andrius ; Alvarez-Arenas, Tomas Gomez ; Camacho, Jorge ; Rodriguez-Martinez, Alberto |
| Full Text |
|
| Is Part of |
International ultrasonic testing conference 2021 (UT-online 2021) "Novel methods and applications in ultrasonic testing": 1-30 November 2021: UT-online 2021 preface & abstract book.. Bad Breisig : NDT.net. 2021, p. 7-8 |
| Keywords [eng] |
ultrasonic testing (UT) ; laser ultrasound ; time of flight (TOF) ; resonant spectroscopy ; spread spectrum signals |
| Abstract [eng] |
Ultrasound is widely used in NDT. Main advantages are direct physical interaction with material properties, equipment safety, inspection speed, portable equipment and acceptable cost. Yet, bandwidth and SNR are limiting the results attainable. Going noncontact ultrasound is always confronted with signal coupling losses and the requirement for contact or immersion is sometimes a limiting factor. Here we present the signal technologies that help to solve these issues. Essential for good signal are the ultrasonic transducers. Developments in the air-coupled ultrasound allowed for significant air transduction losses reduction: sensitivities of -30dB can be obtained at more than 70% bandwidth for frequencies up to MHz. This means that 3V signal can be obtained on receiving transducer without any gain at 200V excitation voltage in air. However, insertion of the test sample significantly reduces the signal obtained due to impedance mismatch: losses can reach 100dB. Simple gain increase in such case in not enough because the noise floor is the limiting factor. Noise figure reduction of the receiving electronics is important and such examples are presented, but large gain is possible with only extremely narrowband electronics. Then developments in excitation come to help: excitation up to few kV is possible. Developments in both reception and excitation electronics are presented. Still, bandwidth and SNR will suffer. Resonant spectroscopy is the tool to maintain low frequency but keep the resolution. Examples of spectroscopy working in reflection will be given. Further bandwidth and SNR improvement is possible when spread spectrum signals are used, which already received acknowledgment in biomedical imaging and radars. Examples presented indicate, that spectral content can be matched to transducer or even compensate the spectral losses for bandwidth improvement. Time delay errors and their sources are discussed. Best results are achieved when generation of the spread spectrum signals is accompanied by the proper signal processing. Significant signal quality improvement can be achieved when combined with adaptive correlation, split spectrum, phase coherent imaging, SAFT or iterative/reiterative deconvolution processing. Finally, spread spectrum signal can be used to solve the problems of ther low power (thermoelastic) laser ultrasound. |
| Published |
Bad Breisig : NDT.net |
| Type |
Conference paper |
| Language |
English |
| Publication date |
2021 |
| CC license |
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