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			<titleStmt><title level='a'>Air-Coupled Whispering Gallery Mode On-Chip Microspherical Shell Resonator for High-Frequency Ultrasound Detection</title></titleStmt>
			<publicationStmt>
				<publisher>IEEExplore</publisher>
				<date>09/01/2024</date>
			</publicationStmt>
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				<bibl> 
					<idno type="par_id">10629042</idno>
					<idno type="doi">10.1109/LSENS.2024.3433472</idno>
					<title level='j'>IEEE Sensors Letters</title>
<idno>2475-1472</idno>
<biblScope unit="volume">8</biblScope>
<biblScope unit="issue">9</biblScope>					

					<author>Chichen Huang</author><author>Jiayuan Zhang</author><author>Srinivas Tadigadapa</author><author>Giacomo Langfelder</author><author>IEEE</author>
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			<abstract><ab><![CDATA[In this letter, we report on a high-sensitivity whispering gallery mode(WGM) resonator-based air-coupled ultrasound sensor capable of detectingminute pressure variations across an ultrasound frequency spectrum of0.6–3.5 MHz. The sensor comprises a microspherical glass shell of approximately450 μm in radius and nonuniform shell thickness of 7–15 μm, which is opticallycoupled to a tunable laser for resonance excitation. The setup allows forthe precise measurement of acoustic signals, benefiting from the high opticalQ-factor of ∼2 million of the blown glass microspherical shells. A noise equivalentpressure as low as 40 μPa/√Hz was obtained at 1.72-MHz ultrasound frequency.A very good correspondence between the simulated axisymmetric resonance frequencies measured using the WGMresonator and a 3D finite-element analysis model in COMSOL was established. The sensor showed an expectedlinear dependence on the drive voltage of the ultrasound transducer. The distortion of the microspherical shell underacoustic pressure was also independently confirmed using a laser Doppler vibrometer. The sensor’s capability tohandle high-frequency ultrasonic waves with significantly better signal-to-noise ratio than conventional piezoelectric- ormicrophone-based systems is demonstrated, highlighting its suitability for advanced photoacoustic applications.]]></ab></abstract>
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