Calibration of hydrophones using a frequency domain filter processing method: theory and experiment

Abstract

To eliminate the interferences coming from the boundaries of a water tank and extend its low frequency calibration limit, a frequency domain filter processing (FDFP) method is proposed for hydrophone calibration measurements. The frequency domain filter function is designed according to the a priori spatial position of projector and hydrophone pair in a water tank. A simultaneous comparison method is used for calibration, and a wideband pink noise pulse signal is transmitted. After application of the FDFP method, the transfer impedances of projector and hydrophone pairs in a quasi-free-field are obtained, and interferences reflected from the boundaries of the water tank are effectively eliminated. To verify the FDFP method, an experimental system is established for calibration of the free-field sensitivity of a TC 4033 hydrophone. For a non-anechoic water tank of 1.5 m × 0.88 m × 0.90 m, the lowest calibration frequency is extended from 20 kHz to 3.15 kHz, and the calibration result is consistent with the free-field reciprocity calibration result obtained in an anechoic water tank of 50 m × 15 m × 10 m in the frequency range 3.15 kHz to 31.5 kHz.

Method for measuring the low-frequency sound power from a complex sound source based on sound-field correction in a non-anechoic tank

“…Blake and Maga [5] were the first to demonstrate through experiments that a nonanechoic water tank satisfies the diffuse-field conditions in the frequency band above the Schroeder cutoff frequency; they also demonstrated that the diffusion field theory commonly used in a reverberation chamber in air is also applicable to a non-anechoic water tank. On the basis of their research work, after decades of development, non-anechoic tanks have been widely used in many fields, including the calibration of underwater transducers, [6][7][8] measurement of the acoustic parameters of underwater acoustic materials, [9,10] and measurement of the sound power radiated from complex structures. [11][12][13][14] The premise of using diffuse-field measurement methods in a non-anechoic water tank is that the modal density in the tank will be sufficiently high that the measurement of the reverberation time will have very good consistency.…”