Optical ultrasonic imaging of geological structure models

Geological structure models are seismic physical models constructed based on geological structures and formations according to specific similarity ratios. In laboratory settings, ultrasonic or laser-ultrasonic techniques are utilized to perform model imaging for field exploration activities. Experiments with seismic physical models have found extensive applications in petroleum and gas exploration. These applications include studying the fundamental laws of wave propagation and seismic response of typical geological structures. The ultrasonic signals transmitted within these complex physical models generally display weak intensities. Therefore, it is necessary to excite high-intensity broadband ultrasonic waves as sources and, at the same time, use high-performance ultrasonic sensors to collect the model echoes.

Traditional piezoelectric transducers have been extensively utilized in the ultrasonic detection and imaging of seismic physical models. In contrast, laser ultrasonic technology possesses the ability to excite ultrasonic fields on the surfaces of objects with various scales and morphologies. These ultrasonic fields possess remarkable characteristics, including a wide bandwidth, multiple modes, and high intensity. In addition, optical fiber ultrasonic sensors are micro-acoustic sensors that employ optical fibers as the sensitive detection elements. Relative to electromagnetic transducers, these sensors demonstrate a superior sensitivity, a broadband frequency response, a compact size, and resistance to electromagnetic interference.

This work mainly presents the sensing mechanism and research status of laser ultrasound transducers and optical fiber ultrasonic sensors developed by our group. In the context of ultrasonic imaging technology for geological structural models, comparative analyses have been carried out on the research progress of conventional electroacoustic transducers, novel fiber-optic ultrasonic sensors, and emerging laser ultrasonic technology, as well as the technological issues and challenges involved.