Fiber-optic multipoint laser-ultrasonic excitation transducer using coreless fibers

Photoacoustic ultrasound excitation has great potential in structural nondestructive testing and applications for medical treatments as a promising alternative to electrical ultrasound. This study proposes and demonstrates a multipoint optical fiber laser-ultrasonic transducer system, wherein the fiber-optic ultrasonic transducer is fabricated by a coreless fiber segment's fusion with single-mode fibers at each end. Simulation and experiment results show that the transducer coupling ratio is dependent on the coreless fiber's length. The structure of such an ultrasonic transducer is easily manufactured. Thus, the structures of these optical fiber ultrasonic transducers with different coupling ratios are connected in the order of small to large coupling ratios. In this manner, multipoint ultrasonic excitation with equal intensities at each excitation point can be obtained using this simple and low-cost method. Using laser guidance through the optical fiber to generate ultrasound can efficiently solve some shortcomings of traditional ultrasonic transducers, such as large volume, small bandwidth, and electromagnetic interference. Moreover, this type of fiber-optic ultrasound transducer has higher mechanical strength than other fiber-optic ultrasound transducers and is expected to be useful in structural health-monitoring of buildings.