Simulation on photoacoustic conversion efficiency of optical fiber-based ultrasound generator using different absorbing film materials

Kai Sun; Nan Wu; Ye Tian; Xingwei Wang

doi:10.1117/12.880505

15 April 2011 Simulation on photoacoustic conversion efficiency of optical fiber-based ultrasound generator using different absorbing film materials

Kai Sun, Nan Wu, Ye Tian, Xingwei Wang

Author Affiliations +

Proceedings Volume 7982, Smart Sensor Phenomena, Technology, Networks, and Systems 2011; 798213 (2011) https://doi.org/10.1117/12.880505
Event: SPIE Smart Structures and Materials + Nondestructive Evaluation and Health Monitoring, 2011, San Diego, California, United States

Abstract

The low energy-conversion efficiency in photoacoustic generation is the most critical hurdle preventing its wide applications. In recent studies, it was found that the selection of the energy-absorbing layer material and design of the acoustic generator structure both determine the photoacoustic conversion efficiency. The selection of the absorbing material is based on its optical, thermal, and mechanical properties. In this research, we calculated and compared the conversion efficiencies of six different absorbing film materials: bulk aluminum, bulk gold, graphite foil, graphite powder-resin mixture, gold nanospheres, and gold nanorods. The calculations were carried out by a finite element modeling (FEM) software, COMSOL Multiphysics. A 2D-axisymmetric model in COMSOL was built up to simulate a 3-layer structure: optical fiber tip, light absorbing film, and surrounding water. Three equations governed the thermo-elastic generation of ultrasonic waves: the heat conduction, thermal expansion and acoustic wave equations. In "thick-film" generation regime, majority of the laser energy is absorbed by the film and converted to high-frequency film vibration, and the vibration excites the ultrasound wave in the adjacent water, while the water would not be heated directly by the laser. From the results of this FEM simulation, the acoustic signal generated by gold nanosphere (or nanorod) film is over two times stronger than that generated by graphite powder-resin film of the same thickness. This simulation provides a strong support to the absorbing material selection for our proposed fiber ultrasound generator.

Citation Download Citation

Kai Sun, Nan Wu, Ye Tian, and Xingwei Wang "Simulation on photoacoustic conversion efficiency of optical fiber-based ultrasound generator using different absorbing film materials", Proc. SPIE 7982, Smart Sensor Phenomena, Technology, Networks, and Systems 2011, 798213 (15 April 2011); https://doi.org/10.1117/12.880505

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