Research On Technology Of Acoustic Parametric Array

Acoustic parametric array is a sound transmitting device which uses nonlinear effect of medium. It can generate difference frequency, sum frequency and other second harmonics by using two high frequency ultrasonic primary sound waves propagating in the same direction. Along with the development of nonlinear acoustics in recent decades ,as well as in the early 1960s Westervelt proposed the acoustic parametric array theory, acoustic research had a great breakthrough that changed the conception of low-frequency sound waves can not form sharp directivity, The acoustic parametric array not only has a good directivity, but also penetrativity. Through the previous study of the parametric array, it has been applied underwater and in the air. This dissertation is going to make a deep research of acoustic parametric array based on the previous research. Some key technologies of parametric array have been discussed. The System of parametric array has been designed.The acoustic parametric array has been realized in air and some characteristics are researched.(1) This dissertation has studied the theory of nonlinear acoustic. The principles of the parametric array's can be introduced, and the theory of parametric array has been researched deeply and systematically. This dissertation introduces the parametric array's proposal, as well as the history and the development. The relevant principles were more in-depth explanation and a numerical simulation. It also compares the performance of directivity between the parametric array and the conventional array. The superiority of parametric array's directivity has been manifested intuitively.(2) Some characteristics of the acoustic parametric array have been researched. When parametric array is been applied to underwater detection, difference-frequency waves generating by parametric array have a sharp directivity performance and as well as penetrativity performance. There is a great significance for distinguishing seabed properties and detecting buried object. Therefore, the directivity is very important factor of the low-frequency sound waves. According to the transducer selection, this paper studies the directivity of parametric transmitting array, as well as the width of the beam, the minimum beam angle, side-lobe level, and other parameters. To discuss the energy conversion efficiency of parametric array, as the conversion of original wave energy to the difference-frequency waves belong to the second effect, the energy conversion efficiency is very low. This dissertation from the derivation formula of parametric array power conversion efficiency, analyzes the relevant parameters of parametric array conversion efficiency. Some improvement measures are proposed.(3) Designing the system of parametric array. It is particularly important to design the transducer of parametric transmitting array for realizing the parametric array. According to the experimental task, this paper has designed the transducer (or array), pointed out the key factor in the design of transmitting array transducer (or array), as well as designed a circular piston transducer square array which is 3×3. At the same time, the ultrasound transmitting circuits and echo receiving circuits are designed. The drive circuits of transducer are designed basing on PA85. Some relevant experiments have been done. The DAQ system is programmed by LabVIEW, and the experiment data has been acquired, analyzed and storaged by using NI6024E data acquisition device.This dissertation systematically studies the relevant theories of acoustic parametric array, completes the design of acoustic parametric array system. In the course of the study, the mathematical tools such as MATLAB have been used, and the results of the study carry out for two to three-dimensional digital simulation and calculation.