Study of the compact fiber optic photoacoustic ultrasonic transducer

Recently, many studies have been exerted on developing ultrasonic transducers that can feature high frequencies for better resolutions and compact sizes for the limit space nondestructive testing applications. Conventional ultrasonic transducers, which are made by piezoelectric materials, suffer from issues such as low frequencies and bulky sizes due to the difficulty of dicing piezoelectric materials into smaller pieces. On the other hand, generating ultrasonic signals by photoacoustic principle is a promising way to generate a high frequency ultrasonic pulse. Optical fiber is a very compact material that can carry the light energy. By combining the photoacoustic principle and the optical fiber together, a novel ultrasonic transducer that features a high frequency and a compact size could be achieved. In this paper, an ultrasonic transducer using gold nanoparticles as the photoacoustic generation material is described. Gold nanoparticles are deposited on the end surface of an optical fiber acting as the ultrasonic generator. A cavity and a diaphragm are fabricated in the center of the fiber using as the ultrasonic receiver. A phase array technique is applied to the transducer to steer the direction of the acoustic beam. Simulation results demonstrated that the photoacoustic ultrasonic transducer is feasible.