Calibration Of High-frequency Hydrophone By Heterodyne Interferometer And The Research Of Several Influcing Factors

High frequency hydrophone has been applied widely in the filed of clinical application and non-destructive testing areas. To determine the hydrophone sensitivity precisely is necerassary for keeping safty of the medical ultrasound equipments and has vital importance on the evaluation of ultrasonic transducers and making evaluation on measurement results.This research systematically analyzed several common calibration techniques and established the optical calibration sytem based on heterodyne interferometer. The frequency range has been extended to40MHz compared to ordinary reciprocity calibration technique. The main text of the research is as follows:1. Systematically analyzed the development of hydrophone calibration, together with the advantages and disadvantages of several demodulation techniques.2. The pellicle is mounted at the surface of water to avoid acousto-optical interaction which is a major uncertainty source in homodyne type interferometer in some other national measurement institutes; The phase modulated carrier signal is digitized and transferred to the computer, then processed by digital phase demodulation which can avoid the drawbacks in anglog electronics, such as thermal drifts, aging and limits in linearity for demodulation; The digital demodulation technique can decrease the dependence on frequency response of the photodiode; A5MHz focusing transducer is used to generate fields with significant high-frequency harmonic content; Pellicle displacement and voltage output of the hydrophone in focused ultrasonic field are processed by DFT to determine the amplitudes of the fundamental and harmonic components. The Harming-window is used to suppress the spectral leakage considering its coherent gain and the scalloping losses3. The diffraction effects in wave propagation is systematically studied. The estimation methods for both plane piston transducers and focusing transducers are described; The diffraction correction model in Two Samples Substitution Method (TSM) is proposed and transmission coefficient of different sample thickness and pulse duration is analyzed. Comparison experiment with Single Sample Substitution Mehthod (SSM) illustrates that the proposed diffraction correction model is sound in theory and feasible in practice.4. The calculation formula of hydrophone sensitivity for different experimental arrangenmts is deduced based on two-transudcer reciprocity theorem; The misunderstanding of transmiting current response is cleared and the ultrasonic power measurement method based on self-reciprocity is corrected; The measurement accuracy has been improved by40log rav, where rav is the average pressure reflection coefficient; A novel measurement method using the open-circuit volage of the driving source and first echo current instead is deduced and validated, which is advantageous over measuring the short-circuit current since the output of driving source like power amplifier are not recommended to be used in short-circuit. High short-circuit current may permanently damage the unit.