Research On The Low Frequency Transmittng Array With Passive Array Elements

When low frequency transducers are deployed in arrays,because of their low frequency and large wavelength,the space utilization of arrays will be greatly reduced if the arrays are deployed according to the traditional 1/2 wavelength spacing,so the close-packed structure is usually adopted.When the spacing of arrays reaches one hundredth or even one thousandth of the wavelength,the sound fields radiated by the arrays will interact and couple with each other.This effect is called mutual radiation.It will reduce the resonance frequency of the array,increase the response of the transmitting voltage,and different resonance frequencies can be obtained by adjusting the spacing of the arrays.The main work of this paper is based on the strong mutual radiation between elements in low frequency close array.It is assumed that passive elements are added to the array to excite its vibration through the sound field radiated by active elements and analyze the change of array performance.Firstly,the binary and ternary equivalent models of low-frequency close-array with passive elements are established,and the mutual radiation impedance formulas of active elements in different models are derived.The curve of mutual radiation impedance varying with the element spacing and wavelength ratio is simulated by using MATLAB software.Then,using the new bending disk transducer as the array element,the binary array with passive elements is simulated by ANSYS finite element software,and the influence of passive elements on the resonant frequency,transmission voltage response and directivity of the array is analyzed.The array is simulated by finite element method.Finally,a prototype transducer array is designed and manufactured.After assembly,the pool test is carried out.The resonance frequency of a single active element in water is 1.5 kHz,the transmission voltage response is 128.36 dB and the maximum sound source level is 172 dB.When passive elements are added to the upper and lower sides of the active element to form a ternary array,the whole array has three resonance peaks,which are 1.2 kHz,2.6 kHz,3.9 kHz in turn,and two adjacent ones.The maximum fluctuation between resonant peaks is 10 dB,which can realize broadband emission of low frequency multi-resonant peaks,and is basically consistent with the simulation results of finite element method.The results show that passive elements can play the same role as active elements when there are passive elements in low-frequency close-array.When the array structure is asymmetric,directional modes can also be excited.For ternary arrays,low-frequency broadband multi-resonance peak emission can be achieved by reasonable array arrangement.