Calibration of hydrophones based on reciprocity and time delay spectrometry

Abstract

A brief survey is given of the calibration methods for hydrophones in the ultrasonic frequency range. The methods presently used in the Physikalisch-Technische Bundesanstalt (PTB), Braunschweig, West Germany, for hydrophone calibrations in the frequency range from 1 to 15 MHz are the primary subject of concern. These methods are the two-transducer reciprocity method for the calibration at discrete frequencies, the time-delay-spectrometry substitution method for quasifrequency continuous calibrations, and the two-transducer reciprocity method with time-delay spectrometry, also for quasi-frequency continuous calibration. Compared with the calibration at discrete frequencies, the expenditure of time for a calibration is considerably reduced in the case of the last-mentioned method. The influencing parameters which affect the evaluation of the measurement uncertainty are briefly discussed for the calibration methods applied at the PTB.

Detection and Measurement of Acoustic Fields

“…Its systematic application to the calibration of hydrophones has been described by Ludwig and Brendel (1988) and, for present purposes, it can be stated in the following terms.…”

Electromechanical characterization of ultrasonic NDE systems

“…However, the open circuit, blocked force receiving sensitivity is not so easily obtained since its definition involves both mechanical and electrical terms. In the acoustics literature [MacLean, 1940, Wathen-Dunn, 1949, Diestel, 1961, Beatty, 1966, Beatty, Bobber and Phillips, 1966, Bobber, 1966, 1970, Rudnick, 1978, Garrett, 1979, Hill and Egle, 1980, Ludwig and Brendel, 1988, Ge, 1989 An important contribution of Chapter 6 is to show that the generalized transducer sensitivity can also be obtained using purely electrical measurements and that having this generalized sensitivity one can then use it to obtain the open circuit, blocked force sensitivity parameter that appears in the transfer functions for both the generation and reception processes.…”

Signal-modelling methods applied to the free-field calibration of hydrophones and projectors in laboratory test tanks

“…Examples of such techniques include the time-delayed spectrometry method, which uses swept sinusoidal signals and a narrowband swept filter synchronised to the drive signal but with a delay to accommodate the acoustic propagation delay. The tracking filter enables the isolation of the direct arrival signals from the reflections (the reflected signals arriving at a later time and at frequencies outside the pass band of the tracking filter) [14,15]. Other methods reported in the literature have utilised noise or pseudo-random noise signals to undertake measurements in a diffuse-field in a reverberant tank [7,13,[16][17][18], with recently reported methods successfully conducting calibrations by measurement of the sound power in the reverberant field [19], or by using a complex weighted moving average (CWMA) method for deriving the transducer response from the reverberant field in a test tank.…”