Multipoint fiber-optic laser-ultrasonic actuator based on fiber core-opened tapers

Multipoint Energy-Balanced Laser-Ultrasonic Transducer Based on a Thin-Cladding Fiber

This study proposes a novel multipoint transducer system by utilizing the single-mode-multimode-thin-cladding fiber (SMTC) structure. This structure leverages the disparity in mode field diameter between the multimode fiber (MMF) and thin-cladding fiber (TCF) to generate high-amplitude ultrasonic signals safely and efficiently. The fabricated transducer exhibits signal amplitudes 2-3-fold higher compared to conventional laser-ultrasonic transducers. Simulation analysis investigates the impact of the length of the MMF and the diameter of the TCF on coupling efficiency. The coupling efficiency of individual transducer units can be accurately controlled by adjusting the length of the MMF. A three-point energy-balanced laser-ultrasonic transducer system was achieved, with improved energy conversion efficiencies, and the optimal thickness of candle soot nanoparticles (CSNPs) is experimentally determined. Additionally, we carried out experiments to compare the performance of the proposed SMTC-based transducer system under different material conditions using two different photoacoustic materials: graphite-epoxy resin and candle soot nanoparticle-polydimethylsiloxane (CSNP-PDMS) composite. CSNPs, as a cost-effective and easy-to-prepare composite material, exhibit higher photoacoustic conversion efficiency compared to graphite-epoxy resin. The proposed system demonstrates the potential for applications in non-destructive testing techniques.

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.