Proposal and verification of sensitivity calibration methods for miniature hydrophones in the high frequency range

采用两种方法对直径分别为0.6mm和1mm的两种小型PVDF水听器的灵敏度响应进行了标定。其中一种方法是基于传统的互易校准方法，另一种方法是基于声束的非线性传播。具体来说，有限振幅的超声波束由于介质固有的非线性而产生波形畸变，波束中出现大量明显的谐波。我们为精确描述非线性声束提出了一个模型方程，从理论上预测了各个谐波分量的大小。谐波压力在很大程度上依赖于源条件，如驱动频率和源压力水平。用互易法测量了基频下输出电压对压力的灵敏度响应。基频源条件的信息唯一地决定了所有高次谐波的压力大小。通过实验与理论谐波压力的详细比较，对两种不同的水听器进行了2.5 ~ 20MHz频率范围内的标定。结果表明，水听器的灵敏度响应总体上与所附数据表一致，误差在1.5dB以内。

Two different kinds of miniature PVDF hydrophones of 0.6mm and 1mm in diameter have been calibrated for their sensitivity responses using two methods. One of which is based on a conventional methodology, the reciprocity calibration, and the other is based on nonlinear propagation of sound beams. Specifically, ultrasound beams of finite amplitude generate waveform distortions due to the inherent nonlinearity of a medium, and plenty of harmonics appear significantly in the beam. The magnitudes of individual harmonic components are theoretically predicted by a model equation that we propose for precise description of nonlinear sound beams. The harmonic pressures are strongly dependent on source conditions such as driving frequency and source pressure level. The sensitivity response of output voltage to pressure at the fundamental frequency is measured by the reciprocity method. The information of the fundamental frequency source conditions uniquely determines all the pressure magnitudes of higher harmonics. By detailed comparison of harmonic pressures between experiment and theory, the calibration in the frequency range of 2.5 to 20MHz has been performed for the two different hydrophones. It has been concluded that the sensitivity responses for the hydrophones are overall in good agreement with the attached data sheets within 1.5dB differences.