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Publication Detail
Analysis of the Directivity of Glass Etalon Fabry-Pérot Ultrasound Sensors.
Abstract
Planar glass-etalon Fabry-Pérot (FP) optical ultrasound sensors offer an alternative to piezoelectric sensors for measurements of high-intensity focused ultrasound (HIFU) fields and other metrological applications. In this work, a model of the frequency-dependent directional response of the Fabry-Pérot sensor was developed using the global matrix method, treating the sensor as a multilayered elastic structure. The model was validated against the experimentally measured directional response of an air-backed cover-slip Fabry-Pérot sensor with well-known material properties. Additionally, the model was compared with measurements of an all-hard-dielectric sensor suitable for HIFU measurements. The model was then used to calculate modal dispersion curves for both glass-etalon sensors, allowing the features of the directional response to be linked to specific wave phenomena. The features in the directivity of the air-backed cover-slip sensor are due to guided Lamb waves. Symmetric Lamb modes give rise to regions of high sensitivity whereas anti-symmetric modes cause regions of low sensitivity. For the all-hard-dielectric sensor, two features correspond to the water-substrate and water-spacer compressional and shear critical angles. A region of high sensitivity close to the shear critical angle is associated with a leaky-Rayleigh wave, which has a frequency-dependent phase speed. At higher frequencies, this feature is counteracted by a region of low sensitivity which occurs when there is no difference in the vertical displacement of the mirrors forming the Fabry-Pérot cavity. The model may be used to improve and optimize the design of Fabry-Pérot sensors, or could be used to assist with the accurate deconvolution of the directional response from array measurements in metrological and imaging applications.
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Dept of Med Phys & Biomedical Eng
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Dept of Med Phys & Biomedical Eng
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Dept of Med Phys & Biomedical Eng
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Dept of Med Phys & Biomedical Eng
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Dept of Med Phys & Biomedical Eng
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Dept of Med Phys & Biomedical Eng
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