Research On Low-frequency Longitudinal-diameter Vibration Conversion Underwater Acoustic Transducer

Marine resources is an important factor affecting the development of countries in the world,and the sonic is the best carrier to obtain underwater information in detection of marine resources,and the hydro-acoustic transducer is a vital device,converting the electrical signal and the sound signal to each other in the ocean exploration.It can receive the underwater acoustic signal and transforms it to an electrical signal or switch an electrical signal to a sound signal,which can travel through water,to get the Information of underwater targets.In order to design the low frequency hydro-acoustic transducer used in low-frequency sonar system,the most effective way is increasing the volume of the transducer to enlarge radiation resistance of the transducer and reduce the frequency of the transducer,but this method will cause high cost of in the production process and the use of transducer.According to the characteristics of the composite rod transducer,which is high power radiation and stable,a longitudinal-radial vibration conversion transducer is presented in this paper using the coupled vibration of transducer and large size metal circular tubes.It can use the energy generated by the longitudinal vibration of composite rod transducers which installed at both ends to excite the radial vibration of metal circular tube,so that the transducer not only can radiate the energy to the longitudinal direction but also to the radial direction.Meanwhile,a proper number of vertical grooves are opened in the wall of the metal tube to reduce the resonant frequency of the longitudinal-radial vibration conversion transducer.The transducer proposed in this paper has the characteristics of small size,the structure and its fabrication process are simple and easy to install.The resonant characteristics and frequency response of the transducer are analyzed by using the equivalent circuit method and the finite element method.The specific contents are as follows:1.Based on the equivalent circuit of sandwich transducer and the equivalent circuit of the coupled vibration metal tube,the equivalent circuit of the longitudinal-radial vibration conversion transducer is obtained.The resonant frequency characteristic of transducer is analyzed by equivalent circuit.With the condition that ignoring the radiation impedance of the transducer in the surrounding medium,the resonant frequency of transducer in air is calculated using the equivalent circuit.In order to verify the rationality of the equivalent circuit,the resonant frequency of the transducer is also calculated by building the same size three-dimensional finite element model in air of the longitudinal-radial vibration conversion transducer,using the finite element simulation software COMSOL.2.An approach is proposed in this paper to decrease the resonance frequency of longitudinal-radial vibration conversion transducer by curving relevant number of vertical slots in the wall of the tube.The resonant frequency of the longitudinal-radial vibration conversion transducer with slotted circular tube in air is simulated by finite element software COMSOL.The result proved that in the wall of the metal tube can effectively reduce the resonant frequency of the transducer.In order to achieve the application of transducer in underwater sonar system,the three-dimensional model of the longitudinal-radial vibration conversion transducer with slotted circular tube in water is established by finite method software,the influence of the size parameters of the sandwich transducer and the size parameters of the slotted circular tube on the resonance frequency of transducer and the transmitting voltage response are studied by the control variable method,and a small-size longitudinal-radial vibration conversion transducer which resonance frequency lower than 1000Hz is designed.3.Periodic structure of the longitudinal-radial vibration conversion transducer with slotted circular tube can be gained by adding several slotted circular tubes and intermediate excitation units to the longitudinal-radial vibration conversion transducer with slotted circular tube.The resonance characteristics and the transmitting voltage response of three periodical structure transducers are studied using finite element method COMSOL.The simulation results indicated that adding a periodical structure to the longitudinal-radial vibration conversion transducer with slotted circular tube can decrease the resonance frequency in air and the first resonance frequency in water effectively,but the frequency decreases more slowly with the number of periodical structure increasing while the second resonant frequency of the transducer in water is remained.With the number of periodical structure increasing,the TVR of the transducer at the first resonant frequency shows a law of decreasing and then increasing while the TVR of transducer at the second resonant frequency shows the law of increasing monotonously.This kind of Periodic structure of the longitudinal-radial vibration conversion transducer with slotted circular tube is suitable for transmitting at one frequency due to the high TVR at the resonant frequency of the transducer.And it is suitable for broadband launch in the case of low emission power is required because of the flat TVR between the two resonant peaks.