Research And Implementation Of Phased Parametric Array Based On Fractional Delay

The propagation of sound waves is nonlinear in medium,especially in water.The two sound waves with different frequencies which propagate in the same direction will produce a strong directional difference frequency wave,due to the interaction in medium.The ultrasonic wave can be demodulated to form a difference frequency wave with high directivity,due to the nonlinear effect in medium.The phased parametric array is composed by the parametric array and the phased array and it can realize the directional deflection of the difference frequency sound wave.The phased parametric array can take place of the mechanical deflection.Based on the previous research experience,the theoretical basis,design scheme and system architecture of phased parametric array are deeply studied and discussed in this paper.The main work is as follows:(1)The theoretical basis of parametric array is studied.The ‘Westervelt equation' and the ‘Berktay far-field solution' are analyzed and discussed in this paper.The knowledge of phased array is introduced,in order to change the traditional way of mechanical deflection.(2)The digital beam forming is the key of this system,and the basic theory of digital beam forming is studied and analyzed in this paper.We use MATLAB to simulate the directivity of the difference frequency beam in range from-30°to 30°generated by the linear parametric array which consists of 32 elements array.The time delay of each array element is calculated at each integer angle.(3)Due to the limitation of DAC sampling rate(the maximum frequency is 750K),the minimum deflection angle of phased parametric array can't be infinitesimal.In this paper,the method of fractional delay is used to design the appropriate filter to approximate the ideal fractional delay filter.(4)In order to ensure the accuracy of the system test,this paper introduces the testing methods used in the system,and describes the working environment and the angle of the phased parametric array.In order to verify the reliability and practicability of the system design,the amplitude of the main lobe is large enough and the minimum deviation angle is less than the error to meet once,these two aspects of the test,the measurement results show that the system meets the design requirements.The design of the parametric phased array is verified by the test results.The results show that the designed products meet the functional requirements of the system.