Photoacoustic Signal Waveform Numerical Simulation

In this paper, we numerically simulate the photoacoustic signal waveforms based on the Huygens-Fresnel principle. In this model, laser absorption medium which is the source of generating photoacoustic signal is divided into microspheres. A N-shaped carrier ultrasonic spherical wave is generated by each microsphere due to the absorption of short laser pulse and propagates outwards from the sphere center. The N-shaped waves reach the detection point through the direct propagation and the reflection from the medium interface. The photoacoustic signal generated by the overall absorption medium detected in the observation point is calculated as the summation of all these individual N-shaped photoacoustic waves including the original and reflected waves by considering the temporal delay and attenuation induced by the propagation distance. The envelope of the resulted summation is the transducer-detectable photoacoustic signal waveform. The photoacoustic signal profiles and spectra under different media interface boundary conditions and propagation distances are studied. The effect of optical absorption to photoacoustic signal bandwidth is studied as well. This numerical investigation demonstrates the formation of the detected photoacoustic signals and improves the understanding of the mechanism of the photoacoustic signal generation.