Optical Interferometric Detection Method of Ultrasound Waves for Biomedical Imaging and Non- Destructive Testing

Abstract

Ultrasound technology (UST) is one of the most widely used techniques in non-destructive testing across both industrial and biomedical fields. It offers the advantage of causing no damage to the sample, while still providing high resolution and the ability to measure at greater depths. However, its major limitation lies in the need to use electrical piezo-based transducers (PZT), which require direct contact with the sample. Because of this, UST cannot be used in cases where large surface areas need to be measured, where high temperatures could damage the PZT, where surface contamination must be avoided, or when operator safety is at risk due to the measurement environment. To overcome this limitation, various non-contact ultrasound techniques have been developed. However, most of these systems are large, complex, expensive, and difficult to miniaturize. To address these challenges, this doctoral dissertation proposes a simplified optical interferometry-based system for measuring ultrasound waves. This dissertation consists of six parts: The first chapter introduces the motivation and background of the research. The second chapter presents an interferometer based on a 3×3 optical fiber coupler, and mathematically proves the method for calculating nanometer-scale displacement. The third chapter details the development of a non-contact LUS system based on the 3×3 optical interferometer and demonstrates its ability to measure thickness variations in a PDMS phantom in real time at a single point. The fourth chapter describes the miniaturization of the LUS system’s probe to a few millimeters in diameter and presents results of 2D and 3D scans conducted on PDMS phantoms and biological samples. The fifth chapter applies the system to industrial scenarios, successfully measuring abnormal vibrations caused by equipment malfunctions from a distance of several meters, ensuring operator safety while maintaining high sensitivity. Finally, the sixth chapter provides a comprehensive summary of the research and outlines directions for future work.