Study On The Directivity Of Ultrasonic In The Air

Ultrasonic has the excellent directivity. It can be widely used in many fields, such as the exploration and exploitation of the sea, non destructive testing and assessment and medical diagnosis. Based on the nonlinear acoustics and KZK equation, the diffraction, nonlinear and absorption effects are included in simulation. The research is about the directivity of ultrasonic in the air. The main studies and achieved results are as follows:(1) The ultrasonic theory is based on nonlinear acoustics. Using the discrete form of KZK equation, the directivity of ultrasonic can be calculated. The simulation includes the diffraction effects. The results display that harmonic directivity is superior to the fundamental directivity when they have the same pressure in the boundary. The existence of harmonics can improve the directivity of the synthesis sound field. The numerical results also display that change of the sound source's radius can change the directivity of the synthesis sound field, and increasing the sound source's radius can improve the directivity of ultrasonic.(2) The air can absorb the sound energy, so ultrasonic in the air will attenuate in the propagation direction. The absorption coefficient is proportional to the square of the ultrasonic frequency. With the increase of harmonic orders, the absorption effects can be more significant, which result in more attenuation of harmonics.(3) Based on KZK equation, the simulations are performed in the frequency domain. In this model, the harmonics are separated from the fundamental and the diffraction, nonlinear and absorption effects are included. The numerical simulation is performed to describe the sound field characteristic and the directivity of ultrasonic in the air. In the effect of nonlinearity, the fundamental and harmonics interact in the air. The research shows that the harmonic energy accumulates and will peak within a certain distance. The air absorption effects are more and more significant with the distance, which result in the decrease of sound pressure.The ultrasonic field characteristic in the air is studied systematically. The directivity and propagation distance of fundamental and harmonics are analyzed. MATLAB and other mathematical tools have been used in the research of the numerical results and simulation. The main results provide the reference for the directivity of ultrasonic in the air.