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Non-linear and diffraction phenomena in sound propagation through inhomogeneous and complex media such as biological tissue and turbulent atmosphere

Objective

Propagation of nonlinear acoustic waves through inhomogeneous medium is important for many applications, including sonic booms in a turbulent atmosphere, explosive waves in a fluctuating ocean, and intense ultrasound and shock waves in biological tissues. In all of these problems, the combined effects of inhomogeneities, diffraction, and nonlinear propagation determine the peak and average characteristics of the acoustic field. Similarly to wave propagation in a continuously inhomogeneous medium, a complex diffraction pattern with multiple foci can form when ultrasound is radiated from sources with regular or random inhomogeneous structure. The main objective of the proposed project is to develop theoretical and numerical models, and experimental tools to study nonlinear propagation of broadband acoustic signals in media with regular or random inhomogeneities. A nonlinear parabolic model with inclusion of both scalar and vortex inhomogeneities, and with arbitrary initial periodic or single shock waveforms will be employed. More rigorous models will be developed for accurate descriptions of the diffraction effects in the acoustic fields generated by ultrasound sources with complex spatial structure. The effects of thermal, vortex, sound speed, and density inhomogeneities, on nonlinear acoustic field pattern will be investigated. Special attention will be given to the distinctive features in transmission of nonlinear signals through regular and random foci or caustics formed either because of the medium inhomogeneities, or due to the initial spatial distribution of acoustic sources. Critical problems of nonlinear acoustic propagation in complex media such as turbulent atmosphere and biological tissue will be studied theoretically and experimentally in air, water, and tissue phantoms. Experimental research will be performed using both existing and developing laboratory facilities established in Lyon for atmospheric measurements, and in Moscow and London for biomedical measurements. The following specific topics related to sonic boom propagation will be addressed: 1/ the effect of scalar and vector inhomogeneities on the amplitude and rise time of the sonic boom after passing through random caustics, 2/ whether the spatial spectrum of the inhomogeneities can be recovered from the waveform of the transmitted acoustic signal. The following specific problems related to novel medical applications of intense ultrasound will be addressed: 1/ effect of tissue inhomogeneities on nonlinear harmonics generation, and the corresponding distortion of the focal region of HIFU and diagnostic transducers, 2/ acoustic holography for characterization of medical probes nonlinear, 3/ synthesis of appropriate velocity distribution at the surface of random sparse 2D phased arrays to optimize spatial pattern of the therapeutic acoustic field, 4/ noninvasive acoustic monitoring of HIFU-induced temperature rise in tissue, 5/ cavitation mechanisms of tissue destruction

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Coordinator

ECOLE CENTRALE DE LYON

Address

Avenue Guy De Collongue, 36
Ecully

France

Administrative Contact

Philippe BLANC-BENON

Participants (3)

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ANDREEV ACOUSTICS INSTITUTE

Russia

IMPERIAL COLLEGE OF SCIENCE, TECHNOLOGY AND MEDICINE

United Kingdom

MOSCOW STATE UNIVERSITY (MGU)

Russia

Project information

Grant agreement ID: INTAS 2005-1000008-7841

  • Start date

    1 October 2006

  • End date

    31 March 2009

Funded under:

IC-INTAS

  • Overall budget:

    € 120 000

  • EU contribution

    € 150 000

Coordinated by:

ECOLE CENTRALE DE LYON

France