Photoacoustic wave propagation simulations using the FDTD method with Berenger's perfectly matched layers

Abstract

ABSTRACT Several photoacoustic (PA) techniques, such as photoacoustic imaging, spectroscopy, and parameter sensing, measure quantities that are closely related to optical absorptio n, position detection, and laser irradiation parameters. The photoacoustic waves in biomedical applications are usually generated by elastic thermal expansion, which has advantages of nondestructiveness and relatively high conversion efficiency from optical to acoustic energy. Most investigations describe this process using a heuristic approximation, which is invalid when the underlying assumptions are not met. This study developed a numerical solution of the general photoacoustic generation equations involving the heat conduction theorem and the state, continuity, and Navier-Stokes equations in 2.5D axis-symmetric cylindrical coordinates using a finite-difference time-domain (FDTD) scheme. The numerical techniques included staggered grids and Berenger’s perfectly matched layers (PMLs), and linear-perturbation analytical solutions were used to validate the simulation results. The numerical results at different detection angles and durations of laser pulses agreed with the theoretical estimates to within an error of 3% in the absolute differences. In addition to accuracy, the flexibility of the FDTD method was demonstrated by simulating a photoacoustic wave in a homogeneous sphere. The performance of Berenger’s PMLs was also assessed by comparisons with the traditional first-order Mur’s boundary condition. At the edges of the simulation domain, a 10-layer PML medium with polynomial attenuation grading from zero to 5u 10