Study On Acoustic Radiation Of Small Particles In Water

Tiny particles can be trapped by the radiation force in the sound field. The manipulation and capture of the tiny particles in the liquid can be realized using the radiation force of sound wave. Gaussian beam is very important in the industrial, biomedical and other fields. The research of acoustic radiation characteristics of the particles incidented by Gaussian beam is a hot research topic at home and abroad. Based on the series expansion theory, the incident Gaussian beam is expanded with finite series in this study.The acoustic radiation force characteristics of the tiny particles in water is studied using the radiation theory of sound wave. The main contents are as follows:(1) Based on acoustic scattering theory, the acoustic scattering coeffcient of spherical particles is deduced under the different boundary conditions for the plane wave, and the analytical expression for acoustic radiation force on spherical particles is given.(2) The incident Gaussian beam is expanded as spherical function using the serious expansion method and the beam factor of the Gaussian beam is calculated. According to the radiation theory of sound wave, the analytical expression for the acoustic radiation force of a spherical particle at the center of the Gaussian beam is deduced, and the acoustic radiation force function for different materials is calculated. Simulation results show that the beam width affects the acoustic radiation force. The acoustic radiation force of the spherical particles gradually increases as the beam width increases. When the beam width is much larger than the radius of the spherical particles, the values of the radiation force is close to those of the plane wave.(3) When the position of the particles deviating from the center of the beam, the Gaussian beam is expanded as a spherical function at the center of the particles and the expanded coefficients of the Gaussian beam is calculated. The analytical expression of the acoustic radiation force on spherical particles deviating from the Gaussian beam center is deduced. The acoustic radiation force affected by the acoustic frequency, the beam waist of the Gaussian beam and the offset distance from the Gaussian beam center is investigated. The results show that the value of the radiation force for a spherical particle gradually decreases with the offset distance when ka is small. When ka is large. the radiation force is almost free from the impact of the offset distance. When the beamwidth is larger than the wavelength, the change of the radiation force of the Gaussian beam with ka is consistent with that of the plane wave.(4) Based on series expansion theory, the incident Gaussian beam is expanded as cylindrical function at the center of the cylinder and the expanded coefficients of the Gaussian beam is calculated. The analytical expression of the acoustic radiation force on cylindrical particles deviating from the Gaussian beam center is deduced. The acoustic radiation force affected by the acoustic frequency, the beam waist and the offset distance from the Gaussian beam center is investigated by numerical simulations. The results show that the acoustic radiation force of a cylindrical particle in the Gaussian sound field is related to the position on the beam axis, the acoustic frequency and the beamwidth. The value of the radiation force for a cylindrical particle gradually decreases as the offset distance increases when ka is small. When ka is large, the acoustic radiation force fluctuates very small with the offset distance. When the beamwidth is much larger than the wavelength, the Gaussian beam can be seen as plane wave approximately, and the change of the radiation force of the Gaussian beam is basically consistent with that of the plane wave.