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Communication Dans Un Congrès Année : 2013

Performance evaluation of ultra-low frequency underwater acoustic projectors

Résumé

Ultra Low Frequency (ULF) underwater waves can travel great distance and are generally used in sonar or oceanography. To generate these waves, underwater transducers, utilized in the 10-400 Hz frequency range, have radiating surfaces whose dimensions are small with respect to the acoustic wavelength. To radiate a high acoustic power with a monopolar ULF transducer, a large volume velocity is required to counterbalance the low radiation resistance. Large volume displacement is generally difficult to obtain using common transduction mechanisms and under the constraint of getting a compact device. Three transduction technologies are available to realize compact high power ULF transducers: hydroacoustic, electromagnetic and active material-based. In the latter case, piezoelectric ceramics and magnetostrictive rare-earth alloys are often associated to flexural vibration such as found in flextensional transducers. Compared to these materials, piezoelectric single crystals which exhibit lower stiffnesses and produce higher strains together with higher energy densities, are potential active materials for future ULF underwater transducers. When dealing with high power, projectors are often evaluated using two figures of merit relative to their total volume or total mass. However, scaling down transducers from few kHz to ultra-low frequency range leads to projectors exhibiting gigantic size and huge power that cannot be reasonably considered by designers. Thus, to identify and evaluate the effective frequency range of a projector technology, it is necessary to express the acoustic radiated power at resonance frequency for families of projectors using homothetic transformations. In this study, acoustic radiated power is obtained by homothetic transformation and represented versus frequency in a log-log scale. Sets of parallel lines corresponding to the optimized solution for given total mass and projector technology are drawn. These graphs produce a global evaluation of existing ULF sources technologies in terms of acoustic power, resonance frequency, and total mass. They can provide a quick evaluation of potential improvement brought by new projector technologies and new active materials on ULF source performance according to these three criteria. In this work, ULF transducers are analyzed in terms of their working frequencies, acoustic powers and total masses. Thirty-two ULF underwater projectors build over the last 25 years are considered. For single crystal transducers, prototypes working at higher frequencies as well as transducers modelled with finite element method are taken into account. Using these data and classical scaling laws, abacuses displaying acoustic power-frequency curves for given masses are constructed for each technology. They show that single crystals transducers at the cost of high price may provide more compact solutions than current ULF projectors with identical radiated power and frequency.
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Dates et versions

hal-01044818 , version 1 (24-07-2014)

Identifiants

  • HAL Id : hal-01044818 , version 1

Citer

Bertrand Dubus, Pascal Mosbah, Jean-Rémi Hartmann, Jacky Garcin. Performance evaluation of ultra-low frequency underwater acoustic projectors. Acoustics 2013 New Delhi Technologies for a Quieter India, 2013, New Delhi, India. session TEA3 : Underwater Transducers, paper TEA3/05, 1133-1138. ⟨hal-01044818⟩
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