Laser Doppler Interferometry as a receiver of the ultrasonic waves: An experimental study on Gosford sandstone

Nazanin Nourifard, Eduard Mashinskii, Maxim Lebedev

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The change of ultrasonic velocities and displacement on the core scale for the isotropic Gosford sandstone was studied using the Laser Doppler Interferometry (LDI) method. We observed that the P- and S-wave velocities and the corresponding surface displacement of the sample consist of multiple wavelets at the core scale. Ultrasonic wave velocity experiments usually measure the average wavelet recorded by two transducers (source and receiver). The recorded travel velocity varies as a function of the material's elastic properties; therefore, knowing the components of the averaged wavelet can be used to understand such behaviour in detail. LDI had been used to measure particle displacement for decades however its accuracy to measure precise ultrasonic velocity has not been studied in details. We designed an experiment to study the averaging wavelets by its components using LDI on isotropic Gosford sandstone to study the displacement pattern and the accuracy of the velocity recorded by LDI in porous media. By changing the monitoring system from a receiving transducer (which normally are 5 to 20 mm in diameter) to a laser beam receiver (diameter of about 0.2 mm) on the same surface area enables us to scan the behaviour of transmitted wave at much higher spatial resolution at different zones on the surface of the sample. A Laser Doppler Interferometer, as a receiver, benefits this experimental study over piezoelectric transducers because, (a) A much smaller area of measurement than the wavelength is covered, (b) it records the full particle-velocity wave field and displacement vector, and (c) strain in ultrasonic wave can be directly measured. This study plotted the displacement field within the boundaries of the source transducer and outer orbit of the transducer zone to show the effect of energy distribution when the wave passed through the porous media. We compared the displacement rate for the sample on the nanometre scale and observed that the averaging of the recorded wavelets by LDI show a resemblance to the waveform recorded by a pair of conventional transducers in terms of the velocity and waveform features. This verifies the accuracy of the component's wavelets and validity of such an experimental approach for future studies of ultrasonic measurements (velocity and displacement) at grain scale for porous media by LDI.

Original languageEnglish
Article number103062
JournalWave Motion
Publication statusPublished - Nov 2022

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