Research On Radiation Characteristics Of Gaussian Beams Based On Time - Domain Finite Difference Method

It is well known that acoustic waves carrying energy. Microparticle in sound field that absorbs or reflects sound energy is subjected to the acoustic radiation force by exchanging energy with sound wave. Acoustic radiation force is used to manipulate the microparticle, which is called acoustic manipulation. This technique can be applied widely in cell biology, biomedical and material science. It is a popular research subject in acoustic field. About the computation of acoustic radiation force, the analytical method, acoustic line method, finite element method and the finite difference time domain method are the mainly methods. In these methods, the finite difference time domain method (FDTD) is a simple numerical method whose simulation process is visual, and has no special requirements on the media. It also can be used to simulate the non-uniformity anisotropic and the dispersion characteristic of the media. In this paper, the finite difference time domain method is used in computation of sound field. The simulation details related to calculating the characteristics of acoustic radiation force of single rigid particle model and two rigid particles model in the acoustic field by FDTD method.The main conclusions are as follows:(1) The finite difference time domain method is introduced into the acoustic field by discretizing and gridding each parameter of the acoustic wave equation in time and space. The 3D and 2D Yee cellular of acoustic is set up and the iteration of pressure and velocity in the time domain are completed.(2) This paper will not only derive two differential formulas of the Mur and perfectly matched layer absorbing boundary condition (PML) in detail, which are used commonly and make good effects, but also verify the PML perfectly matched layer absorbing boundary conditions with the three different excitation sources, which are the sine wave, the rising cosine wave and the Gaussian pulse modulation cosine wave.(3) The finite difference time domain method can simulate the physical process of the acoustic scattering by setting up the scattering body model and setting the parameters, including geometry parameters, internal structure parameters, material parameters and acoustic characteristic parameters, to the specific selected grid points. In this paper, we have established the geometric models which include a rigid block, rigid spherical particle, sheet, ellipsoid, two rigid blocks, two rigid spherical particles and multiple difference geometry scattering bodies. The physical process of interaction between acoustic wave and different scattering bodies are simulated.(4) For the two-dimensional acoustic field, the acoustic radiation force of single particle and two particles in water is computed using finite difference time domain method. Firstly, we deduce the equations of acoustic radiation force for micro-particles in water by combing the FDTD method with momentum-flux tensor. The figure obtained from the former computation simulate the transverse and axial acoustic radiation force of a rigid spherical particle in Gaussian pulse wave. Then, by adding another rigid small particle into the computation field, the affection on acoustic radiation force of the rigid spherical particle are studied and the effects from different sizes of the rigid small particles are simulated. Simulation results show that the bigger radius of the rigid small particle, the more effect it will make on the acoustic radiation force of the rigid spherical particle. The position of the rigid small particle also has influence on acoustic radiation force. The acoustic radiation force of rigid spherical particle appeared the trend of the periodic oscillation when the position of the small rigid sphere is changed.