Low Frequency Wideband Transducer Based On Multi-mode Coupling Principle

Modal coupling technology is the most common method to realize broadband transmission of underwater acoustic transducer.However,the design method of modal coupling transducer is not mature enough and lacks theoretical support,which leads to some modal coupling problems in design work.This paper supplements the theory of modal coupling by exploring the influence of phase difference between modes on modal coupling.Using this method,a bender transducer with low frequency,wideband and small size characteristics and a flextensional transducer with wideband and small size characteristics are designed and manufactured.Firstly,the influence of phase relationship between adjacent modes on coupling is explored by method of equivalent circuit.A method of judging modal coupling by using the phase difference between modes is proposed,which can be used in the design of modal coupling transducers.Secondly,the traditional conformal drive mode of the bender transducer is replaced by the central drive mode,which improves the structural flexibility of the bender transducer.By changing the local stiffness of the radiation head,the phase difference between adjacent bending vibration modes is adjusted to make them successfully coupled.The coupling between the first-order bending vibration mode and the first-order longitudinal vibration mode of the transducer is optimized by using the method of additional cavity,which further reduces the fluctuation of the transmitting current voltage response curve.The voltage divider circuit reduces the response at high frequency and broadens the bandwidth of the bender transducer.Thirdly,the phase difference between the first-order and second-order flexural vibration modes of Class Ⅳ flextensional transducer is changed by using the method of additional cavity.The two modes are successfully coupled,which broadens the bandwidth of Class Ⅳflextensional transducer.Finally,a prototype of low-frequency wideband bender transducer is made,which is consistent with the simulation structure.The experiment results shows that the low-frequency wideband bender transducer has maximum transmitting current voltage response 138.5d B,frequency range 1k Hz-16 k Hz,fluctuation within the frequency range is less than 10 d B.A wideband Class Ⅳ flextensional transducer prototype consistent with the simulation structure and a traditional Class Ⅳ flextensional transducer prototype with the same size are made.The experiment results shows that the wideband Class Ⅳ flextensional transducer has maximum transmitting current voltage response 111 d B,frequency range 2k Hz-7k Hz,fluctuation within the frequency range is less than 7d B.The coupling between modes is effectively improved.The measured results of transducer prototypes show that by adjusting the phase of each vibration mode,the coupling between the modes can be effectively improved and the bandwidth of the transducer can be broadened.