Low Frequency Calibration System Of Hydrophone Sensitivity Based On Coupled Cavity Reciprocity Method

In ocean exploration activities,transducers acting on deep-water areas are necessary equipment.In order to accurately understand the changes of the acoustic performance of the transducer in the deep sea and improve the accuracy of detection,the acoustic performance of the transducer under high hydrostatic pressure has been tested at home and abroad.In view of the limitations of the current hydrophone sensitivity test methods and equipment under high hydrostatic pressure,a hydrophone sensitivity test system with a maximum pressure of 20 MPa and an overflow ring transducer cavity as the calibration site is established in this paper.Aiming at the problem that the traditional coupling cavity has high requirements for the shape and size of the test hydrophone due to the size,a coupling cavity system with built-in overflow ring is established in this paper.Firstly,this paper proposes a test method using the liquid cavity of overflow ring transducer as the low-frequency calibration place,and analyzes the signal-to-noise ratio in the liquid cavity.Then it focuses on the derivation of the reciprocity constant,error source and compensation in the coupled cavity reciprocity method with built-in overflow ring transducer.A high-pressure device with a diameter of 140 mm,a height of 130 mm and a working pressure of 0 ～ 20 MPa is designed and built as the measuring equipment.In this paper,two kinds of experimental studies are carried out.For the measurement experiment of sound field in the cavity,the axial sound field and radial sound field of the cavity are measured by using a standard hydrophone.The sound pressure of the axial sound field in the middle of the cavity is large,and the change rate of radial sound pressure at the center of the middle circle is small.For the sensitivity measurement experiment,the sensitivity changes of standard hydrophone,circular tube hydrophone and small ball hydrophone at 100-1000 Hz are tested respectively.By comparing the sensitivity data of standard hydrophone at 3 Mpa with the standard data,it is found that there is an error in the measurement frequency range system,and the possible sources of the error are analyzed.The measurement uncertainty is about 1 d B.The changes of the sensitivity of the three hydrophones under pressure are analyzed.It is found that the sensitivity of the hydrophone increases gradually with the increase of pressure.When the pressure reaches a certain threshold,the sensitivity begins to decrease gradually.