高频宽带水声换能器的背衬参数设计

Design of the backing for high-frequency underwater broadband transducers

为了扩展高频水声换能器带宽,添加背衬是方法之一,然而针对水声换能器的激励信号形式和工作状态,当前缺少针对水声换能器背衬设计的准则,本文开展了水声换能器背衬参数的作用机制研究工作。基于KLM (krimholtz leedom and matthaei)传输线模型研究了背衬厚度、衰减系数及特征阻抗对水声换能器性能的影响。研究结果表明:背衬在水声换能器中作为谐振体的一部分参与振动并形成了若干阶纵向振动模态,其作用是增加系统阻尼,而不是吸收声波。从扩展带宽的角度出发,背衬的衰减系数应尽量大,此时,发送电压响应波动减弱且对响应幅值影响很小;背衬特征阻抗能够调节两响应峰的相对幅值,阻抗过高或者过低都不利于宽带的形成,因此选择中等特征阻抗的背衬较为适宜。最后,基于上述的背衬优化方法,制备了水声换能器样机,其测试带宽为102%,与理论吻合较好。

Adding a backing layer is one of the methods for broadening the bandwidth of a high-frequency underwater acoustic transducer. However, in light of the form of excitation signals and the working state of the underwater transducer, no specific design principle is available for the backing of an underwater acoustic transducer. In this paper, the action mechanism of backing parameters of the underwater acoustic transducer is studied. The influence of thickness, attenuation coefficient, and characteristic impedance of the backing layer on the performance of underwater acoustic transducer is studied based on the Krimholtz-Leedom-Matthaei transmission line model. Results show that the backing layer is a component of the resonator, which exerts several-order longitudinal modes, and the function of backing is to increase transducer damping instead of absorbing the acoustic wave from the piezoelectric element. From the point of view of expanding bandwidth, the attenuation coefficient of the backing layer should be as large as possible. In this case, the fluctuation of the transmitting voltage response is weak, thus having little influence on the response amplitude. The characteristic impedance of the backing layer can tune the relative amplitude of the two peak amplitudes of the transmitting voltage response. Too big or too small characteristic impedance is detrimental to the formation of broadband. Therefore, the medium characteristic impedance is favorable. Finally, a transducer prototype is fabricated based on the optimization method of the backing mentioned above, and the tested bandwidth is 102%, which agrees well with the theoretical result.