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he further signal processing for wave signal extraction as in displacement-based detection systems. However, due to both interfering lights coming from sample surface, the collected light in a fiber-optic-based Sagnac interferometer system is very weak when applied to biological tissue, where the refractive index of tissue and air are close. The objective of this paper is to study the feasibility using a compact fiber-optic Sagnac interferometer to detect vibrational waves on a biological tissue surface. An actuator made with a 10mm x 10mm x 3mm piezoelectric chip loaded on a 3D-printed polymer-made prism-shaped wedge (1cm x1cm x1cm) was used for ultrasound surface wave excitation. A bulk copolymer-in-oil phantom (100mm diameter with 27mm height) was used to mimic biological tissues. A compact fiber-optic-based interferometer was used to detect the propagation of surface waves in the tissue mimicking phantom and the wave propagation speeds were determined based on the wave detection. Young’s modulus was calculated based on the measured wave speed on the phantom surface. A tensile testing machine was used to measure the Young’s modulus in a compression mode as a comparison. The results were compared. 

The Sagnac interferometer offers distinct advantages in vibrational wave detection. In this study, an air-coupled transducer and a compact fiber-optic Sagnac interferometer were developed for non-contact elasticity characterization in biological tissues. Given the challenge of limited light collection by a compact fiber optic Sagnac interferometer in biological tissues, this study aims to explore the potential of using a compact Sagnac interferometer to measure vibrational waves in biological tissues. The speeds of the generated vibrational surface waves in tissue-mimic phantoms were measured. Measurement errors caused by cross-correlation wave tracking were analyzed, and the performance of the integrated system was characterized. The results demonstrated the effectiveness of the integrated system and the cross-correlation algorithm in tracing the speed of vibrational surface waves in tissue-mimicking phantoms. They suggested potential applications for the non-invasive, contactless characterization of the mechanical properties in soft biological tissues.