2025_programme: Low frequency free-field calibration of underwater transducers in a reverberant laboratory test tank

• Day: June 17, Tuesday
    Location / Time: A. TERPSIHORI at 12:00-12:20
• Last minutes changes: -
• Session: 20. Underwater acoustic calibration, measurement, and standards
  Organiser(s): Stephen Robinson
  Chairperson(s): Stephen Robinson, Will Slater
• Lecture: Low frequency free-field calibration of underwater transducers in a reverberant laboratory test tank
  Paper ID: 2113
  Author(s): Ata Can Corakci, Alper Biber, Talha Saydam, Osman Said Biskin, Serkan Aksoy
  Presenter: Ata Can Corakci
  Abstract: Calibration of acoustic transducers is an important topic in underwater acoustic applications. In practice, a free field calibration method is commonly used since it is well described in the relevant standards. The calibration methods can be classified as a free field comparison method and a free field reciprocity method. In practice, these free field calibration methods can be applied to reverberant laboratory test tanks if free field acoustic conditions are valid at the frequency of interest.\nIn this study, a Two-Equations Two-Unknowns (2E-2U) method is applied for low-frequency calibrations (below 1 kHz) of hydrophones and projectors in a reverberant laboratory test tank. At low frequencies, amplitude and phase measurements for the calibration of hydrophones and projectors in the test tank are difficult to perform since the echo-free time of the laboratory test tank is not large enough due to transducer initial transients and tank wall boundary reflections. To overcome these difficulties, the 2E-2U method is applied to received (windowed) signals obtained during calibration measurements. Thus, calibration measurements become possible at frequencies down to 250 Hz. These measurements in the test tank are performed for a hydrophone and a developed flextensional projector. First, the receiving voltage sensitivities for the hydrophone are calculated and validated by comparison with pressure calibration in a closed chamber. Good agreements are obtained between these two measurement platforms, with a maximum difference of 0,5 dB and an uncertainty of 1,3 dB. Then, the transmitting voltage response (TVR) of the flextensional projector is calculated and compared with the calibration data obtained from the method defined in the relevant standards. Good agreements are also obtained between these two TVR data, with a maximum difference of 1,1 dB and an uncertainty of 1,7 dB.
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• Corresponding author: Mr Ata Can Corakci
  Affiliation: CTBTO
  Country: Austria