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Understanding the feedback effect through the physics of the diffraction-based sensitivity kernel for a target in shallow water: A small-scale experimental demonstration

Christian Marandet 1 Philippe Roux 2 Patrick La Rizza 3 Barbara Nicolas 4
1 ISTerre - Institut des Sciences de la Terre
2 Ondes et Structures
ISTerre - Institut des Sciences de la Terre
3 Géodynamo
ISTerre - Institut des Sciences de la Terre
4 GIPSA-lab - Grenoble Images Parole Signal Automatique
Abstract : Using the feedback effect, we experimentally detect a wavelength-sized target in a shallow ultrasonic waveguide between two source-receiver transducers on acoustic feedback. The waveguide represents a 1-km-long, 50-m-deep ocean acoustic channel at the 1/1000 scale. The feedback phenomenon, or Larsen effect, occurs when a source and a receiver are connected both acoustically through the propagation medium and electrically through an amplifier in such a way that the received signal is simultaneously and continuously added to the emitted signal. A resonance is obtained when the emitter and the receiver are in phase. This resonance is very sensitive to any change in the medium which makes it a good observable for target detection. In presence of a target in the waveguide, the numerical gain of the feedback effect has to increase in order to compensate the scattering of the acoustic field from the target. In a separate experiment, the scattered field may also be recorded in a transmission configuration from the same couple of emitter/receiver with an impulse as a source signal. A comparison is made between the two different approaches.
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https://hal-insu.archives-ouvertes.fr/insu-00680986
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Submitted on : Tuesday, March 20, 2012 - 3:10:48 PM
Last modification on : Monday, July 19, 2021 - 11:22:02 AM

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Christian Marandet, Philippe Roux, Patrick La Rizza, Barbara Nicolas. Understanding the feedback effect through the physics of the diffraction-based sensitivity kernel for a target in shallow water: A small-scale experimental demonstration. Journal of the Acoustical Society of America, Acoustical Society of America, 2011, 130 (4), p.2410. ⟨10.1121/1.3654662⟩. ⟨insu-00680986⟩

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