The Study On The Feasibility Of The Non-diffracting Beams In Acoustic Field

This paper has studied the feasibility of non-diffracting beams applied in the acoustic wave fields. First, a general theoretical approach is presented to investigate the feasibility of the non-diffracting beams. The thesis focuses on the normal theoretical model of the Bessel arbitrary weight function approach to investigate the space-time properties of the non-diffracting acoustic wave fields, which take some baseband and modulated carrier single as an arbitrary weight function. The distribution of acoustic source amplitude and closed form expressions for radiant acoustic wave field to generate Acoustic Directed-Energy Pulse Trains (ADEPT) in planar source are then developed. The fields of the acoustic transient Bessel beams has been calculated out and analysis the feasibility of the non-diffracting acoustic wave beams ideally has been analysed. From the theoretical analysis, in ideal medium, the stimulating acoustic wave fields have the properties of non-diffracting beams like in optics to some distribution of the acoustic source. But the nonlinear absorption and possibly accompanied sock wave of the high amplitude destroy the effect. The theory is obtained from the scalar wave equation in ideal medium. The theoretical analysis studied the infinite planar apertures source limitedly. It should use numerical simulating methods to get the properties of the non-diffracting acoustic wave fields from the limited planar apertures sources in real medium. This paper discuss the numerical simulating methods primarily accounting to the thermo viscous absorption effects, the diffraction effects and the nonlinear effects of the medium. The non-diffracting acoustic wave field is simulated using time domain nonlinearity acoustics calculating model based on enhanced KZK equation developed by Hamilton M.F. et al. in 1990s. Taking into account that this model can be used to simulate the radiating acoustic wave field in real medium of planar piston and focus piston acoustic sources with random amplitude and phase distribution. The nonlinearity, diffraction, relaxation and thermo viscous absorption effects are included in the calculation. In view of the complication of the acoustic distribution corresponding to the non-diffracting sound beams, the time and space step setting must accord to the evaluated scale of sound and medium parameters. Compared to the theoretical methods, the numerical simulating methods expands the research range. At last, the non-diffracting beams is feasible in acoustic.