Research On Hydrophone Calibration Method Based On Laser Heterodyne Interferometry

Acoustic waves are currently a common carrier for long-distance underwater information transmission.As the basic unit for measuring underwater acoustic signals,hydrophones have been widely used in the fields of underwater acoustic detection,identification,communication,and ocean noise measurement.Therefore,in order to ensure the accuracy and uniformity of the acoustic signal measured by the hydrophone,it is necessary to periodically calibrate the sensitivity of the hydrophone.Aiming at the defects of optical calibration of hydrophones and insufficient calibration capabilities,this paper studies the calibration method of intermediate frequency hydrophones based on laser heterodyne interference,and conducts a preliminary analysis of the system effects such as membrane vibration modes in sound pressure measurement.This paper has carried out the following work:1.A hydrophone calibration method based on laser heterodyne interference is studied,which is different from using the vibration velocity directly output by the laser vibrometer to calibrate the hydrophone in the literature.Instead,it studies the two methods recommended in the international standard ISO 16063 that are suitable for demodulating laser Doppler signals.The signal demodulation method is verified by simulation experiments and actual data.The comparison experiment results confirm that the zero-crossing demodulation algorithm is used as the demodulation method in the experiment,and the amplitude of the non-uniform vibration velocity sequence obtained by the zero-crossing demodulation is calculated.2.The experimental system of hydrophone sensitivity measurement based on laser heterodyne interferometry is established,and the sensitivity measurement and uncertainty analysis of the intermediate frequency(IF)hydrophone are carried out.First,determine the components of the calibration system,such as the underwater sound field and measurement system,the internal optical path of the laser heterodyne interferometer,etc.then,carry out the hydrophone sensitivity calibration experiment in a 3m×2m×2 m anechoic pool and in the frequency range of 10-200 kHz give some measures to improve the calibration accuracy;finally,the various components that affect the calibration uncertainty are analyzed,and the expanded uncertainty is evaluated in detail,the expanded uncertainty is calculated to be lower than 0.6 dB(k=2).3.The influence of factors such as film width and film material on the sensitivity measurement results of hydrophones is explored.First,on the basis of the simplified measurement model,the film vibration simulation based on the finite element method analyzes the followability of the film;then,chooses different film widths(5 mm,8mm,11 mm)and different materials of film(tape,PET polyester film)to conduct an experimental analysis on the sensitivity calibration results of the hydrophone.The experimental results show that the different widths of the thin film with flat edges in a certain range have little effect on the hydrophone calibration results,except for the intersection of a few frequency points,the sensitivity measurement results of the hydrophone at most frequency points are relatively close.