Modeling of ultrasound generation by a polymer composite based fiber-optic photoacoustic transducer

Various types of ultrasound transducers have been developed for use in structural health monitoring, nondestructive testing, medical imaging and diagnostics applications. Recently, research efforts have been focused on development of optical ultrasonic transducers due to certain advantages that they possess over the traditional transducers, e.g. compact size, ability to be permanently integrated into structural components, safety in 1 volatile environments, and immunity to electromagnetic interference. Optical transducers generate ultrasound using a photoacoustic effect, where the absorbed light is turned into heat, which causes rapid expansion of the absorber material creating an elastic wave. In this work we develop a numerical model for analysis of a fiber-optic based transducer with the absorbing composite material made of polydimethylsiloxane (PDMS) with gold nanoparticles. Previous numerical and experimental studies have demonstrated effective generation of ultrasound by such transducers in mediums that have acoustic properties that are very well matched to those of PDMS (e.g. water and biological tissues). Here, we investigate the effects of laser pulse parameters and the absorbing layer thickness on the generation of acoustic pressure waves when coupled into carbon steel. We attempt to get insight into the formation of the temporal function of the pressure wave transferred from the absorber layer into steel. This study also aids in evaluating the feasibility of developing optoacoustic transducers for structural health monitoring applications. The obtained results are useful for development of designs for experimental transducers.