Attenuation in trabecular bone: A comparison between numerical simulation and experimental results in human femur. Bossy, E., P. Laugier, F. Peyrin, and F. Padilla. Journal of the Acoustical Society of America 122, no. 4 (2007): 2469–2475.
Résumé: Numerical simulations (finitedifference time domain) are compared to experimental results of ultrasound wave propagation through human trabecular bones. Threedimensional highresolution microcomputed tomography reconstructions served as input geometry for the simulation. The numerical simulation took into account scattering, but not absorption. Simulated and experimental values of the attenuation coefficients (α, dB/cm) and the normalized broadband ultrasound attenuation (nBUA, dB/cm/MHz) were measured and compared on a set of 28 samples. While experimental and simulated nBUA values were highly correlated (R2=0.83), and showed a similar dependence with bone volume fraction, the simulation correctly predicted experimental nBUA values only for low bone volume fraction (BV/TV). Attenuation coefficients were underestimated by the simulation. The absolute difference between experimental and simulated α values increased with both BV/TV and frequency. As a function of frequency, the relative difference between experimental and simulated α values decreased from 60% around 400kHz to 30% around 1.2MHz. Under the assumption that the observed discrepancy expresses the effect of the absorption, our results suggests that nBUA and its dependence on BV/TV can be mostly explained by scattering, and that the relative contribution of scattering to α increases with frequency, becoming predominant (>50 %) over absorption for frequencies above 600kHz.


Transient optoelastography in optically diffusive media. Bossy, E., A. R. Funke, K. Daoudi, A.  C. Boccara, M. Tanter, and M. Fink. Applied Physics Letters 90, no. 17 (2007): 174111.
Résumé: The authors present a camerabased optical detection scheme designed to detect the transient motion created by the acoustic radiation force in soft elastic media. An optically diffusive tissuemimicking phantom was illuminated with coherent laser light, and a high speed camera (2 kHz frame rate) was used to acquire and crosscorrelate consecutive speckle patterns. Timeresolved transient decorrelation of the optical speckle was measured as the result of localized motion induced by the radiation force and the associated propagating shear waves. The proposed technique is sensitive only to the low frequency transient motion induced in the medium by the radiation force. © 2007 American Institute of Physics.
MotsClés: Cameras; Image sensors; Motion estimation; Shear waves; Speckle; Tissue; Optoelastography; Radiation force; Transient decorrelation; Transient motion; Medical imaging


Focusing properties of nearfield time reversal. De Rosny, J., and M. Fink. Physical Review A – Atomic, Molecular, and Optical Physics 76, no. 6 (2007).
Résumé: A timereversal mirror (TRM) is a plane apparatus that generates the time symmetric of a wave produced by an initial source. Here we look for the conditions to obtain subwavelength focusing when the initial source is in the near field of the TRM and the propagating medium is homogeneous and isotropic. Three variants of TRM are studied: TRM made of monopoles, dipoles, or both of them. The analysis is performed in terms of evanescent and propagative waves. We conclude that only the dipoleTRM leads to subwavelength focusing. © 2007 The American Physical Society.
MotsClés: Focusing; Mirrors; Wave propagation; Wavelength; Nearfield time reversal; Propagative waves; Subwavelength focusing; Time symmetric; Time and motion study


MR elastography of breast lesions: Understanding the solid/liquid duality can improve the specificity of contrastenhanced MR mammography. Sinkus, R., K. Siegmann, T. Xydeas, M. Tanter, C. Claussen, and M. Fink. Magnetic Resonance in Medicine 58, no. 6 (2007): 1135–1144.
Résumé: The purpose of this analysis is to explore the potential diagnostic gain provided by the viscoelastic shear properties of breast lesions for the improvement of the specificity of contrast enhanced dynamic MR mammography (MRM). The assessment of viscoelastic properties is done via dynamic MR elastography (MRE) and it is demonstrated that the complex shear modulus of in vivo breast tissue follows within the frequency range of clinical MRE a power law behavior. Taking benefit of this frequency behavior, data are interpreted in the framework of the exact model for wave propagation satisfying the causality principle. This allows to obtain the exponent of the frequency power law from the complex shear modulus at one single frequency which is validated experimentally. Thereby, scan time is drastically reduced. It is observed that malignant tumors obtain larger exponents of the power law than benign tumors indicating a more liquidlike behavior. The combination of the Breast Imaging Reporting and Data System (BIRADS) categorization obtained via MRM with viscoelastic information leads to a substantial rise in specificity. Analysis of 39 malignant and 29 benign lesions shows a significant diagnostic gain with an increase of about 20% in specificity at 100% sensitivity. © 2007 WileyLiss, Inc.
MotsClés: Breast cancer; Frequency power law behavior; MR elastography; MR mammography; Rheology; gadolinium pentetate; adult; aged; article; breast lesion; clinical article; controlled study; elastography; female; human; imaging system; mammography; medical instrumentation; nuclear magnetic resonance; sensitivity and specificity; viscoelasticity; Breast Neoplasms; Contrast Media; Elasticity Imaging Techniques; Female; Gadolinium DTPA; Humans; Image Enhancement; Image Interpretation, ComputerAssisted; Mammography; Middle Aged; Reproducibility of Results; Sensitivity and Specificity


Acoustoelasticity in soft solids: Assessment of the nonlinear shear modulus with the acoustic radiation force. Gennisson, J.  L., M. Rénier, S. Catheline, C. Barrière, J. Bercoff, M. Tanter, and M. Fink. Journal of the Acoustical Society of America 122, no. 6 (2007): 3211–3219.
Résumé: The assessment of viscoelastic properties of soft tissues is enjoying a growing interest in the field of medical imaging as pathologies are often correlated with a local change of stiffness. To date, advanced techniques in that field have been concentrating on the estimation of the second order elastic modulus (μ). In this paper, the nonlinear behavior of quasiincompressible soft solids is investigated using the supersonic shear imaging technique based on the remote generation of polarized plane shear waves in tissues induced by the acoustic radiation force. Applying a theoretical approach of the strain energy in soft solid [Hamilton, J. Acoust. Soc. Am. 116, 4144 (2004)], it is shown that the wellknown acoustoelasticity experiment allowing the recovery of higher order elastic moduli can be greatly simplified. Experimentally, it requires measurements of the local speed of polarized plane shear waves in a statically and uniaxially stressed isotropic medium. These shear wave speed estimates are obtained by imaging the shear wave propagation in soft media with an ultrafast echographic scanner. In this situation, the uniaxial static stress induces anisotropy due to the nonlinear effects and results in a change of shear wave speed. Then the third order elastic modulus (A) is measured in agargelatinbased phantoms and polyvinyl alcohol based phantoms. © 2007 Acoustical Society of America.
MotsClés: Elastic moduli; Elasticity; Medical imaging; Nonlinear analysis; Pathology; Shear waves; Tissue; Acoustic radiation forces; Acoustoelasticity experiments; Shear wave propagation; Soft solids; Acoustic radiators; agar; polyvinyl alcohol; acoustics; anisotropy; article; elasticity; imaging; nonlinear system; phantom; physical chemistry; priority journal; radiation energy; radiodiagnostic equipment and supplies; shear strength; solid; ultrasound; young modulus; Agar; Animals; Anisotropy; Connective Tissue; Elasticity; Gelatin; Humans; Models, Theoretical; Motion; Nonlinear Dynamics; Phantoms, Imaging; Polyvinyl Alcohol; Reproducibility of Results; Shear Strength; Stress, Mechanical; Tensile Strength; Ultrasonics; Viscosity


Optimal adaptive focusing through heterogeneous media with the minimally invasive inverse filter. Vignon, F., J. De Rosny, J.  F. Aubry, and M. Fink. Journal of the Acoustical Society of America 122, no. 5 (2007): 2715–2724.
Résumé: The inverse filter is a technique used to adaptively focus waves through heterogeneous media. It is based on the inversion of the Green's functions matrix between the M transducers of a focusing array and N control points in the focal area. The inverse filter minimizes the pressure deposited around the focal point. However it is highly invasive, requiring the presence of N transducers or hydrophones in the focal area at the control points' locations to measure the Green's functions. This paper presents a way of reaching the inverse filter's focusing quality with a minimally invasive setup: only one transducer (at the desired focal location) is needed. This minimally invasive inverse filter takes advantage of the fact all the information about the propagation medium can be retrieved from the signals backscattered by the medium towards the focusing array, if the propagation medium is lossless. A numerical simulation is performed to test this minimally invasive inverse filter through a scattering, lossless medium. The focusing quality equals the conventional, highly invasive inverse filter's. The average spatial and temporal contrast is increased by up to 10 dB compared to the time reversal focusing. © 2007 Acoustical Society of America.
MotsClés: Acoustic arrays; Acoustic transducers; Acoustic waves; Computer simulation; Green's function; Hydrophones; Green's functions matrixs; Heterogeneous media; Inverse filters; Propagation medium; Adaptive filters; acoustics; article; filter; priority journal; radiation scattering; simulation; spatial discrimination; time perception; transducer


Optimization and characterization of a structured illumination microscope. Chasles, F., B. Dubertret, and A. C. Boceara. Optics Express 15, no. 24 (2007): 16130–16140.
Résumé: Structured illumination microscopy provides a simple and cheap mean to obtain optical sections of a sample. It can be implemented easily on a regular fluorescent microscope and is a scanning free alternative to confocal microscopy. We have analyzed theoretically the performances of the technique in terms of sectioning strength, resolution enhancement along the optical axis, and signal to background as a function of the objective used and the grid's characteristics (pitch and contrast). We show that under optimized conditions, the axial resolution can be improved by a factor of 1.5 in comparison with an epifluorescence microscope, and that optical cuts with a thickness of less than 400nm can be obtained with a 1.4 numerical aperture objective. We modified the original grid instep modulation pattern and used a sinusoidal modulation for the grid displacement. Optical sections are computed by combining four images acquired during one modulation period. This algorithm is very stable even for modulations at high frequencies. The speed of the acquisition is thus only limited by the performance of the detector and the signal/background ratio of the sample. Finally, we compared our technique to commercial setups: a confocal microscope, a Spinning Disk Microscope and a Zeiss Apotome. © 2007 Optical Society of America.
MotsClés: Confocal microscopy; Fluorescence; Modulation; Numerical analysis; Optimization; Scanning; Epifluorescence microscope; Fluorescent microscope; Optical axis; Structured illumination microscopy; Optical microscopy


Theory of the time reversal cavity for electromagnetic fields. Carminati, R., R. Pierrat, J. De Rosny, and M. Fink. Optics Letters 32, no. 21 (2007): 3107–3109.
Résumé: We derive a general expression of the electric dyadic Green function in a timereversal cavity, based on vector diffraction theory in the frequency domain. Our theory gives a rigorous framework to timereversal experiments using electromagnetic waves and suggests a methodology to design structures generating subwavelength focusing after time reversal. © 2007 Optical Society of America.
MotsClés: Diffraction; Electromagnetic waves; Frequency domain analysis; Green's function; Microcavities; Time reversal cavity; Electromagnetic fields


Ultrasonic arrays: New therapeutic developments. Aubry, J.  F., M. Pernot, M. Tanter, G. Montaldo, and M. Fink. Journal de Radiologie 88, no. 11 C2 (2007): 1801–1809.
Résumé: Bursts of focused ultrasound energy a billion times more intense than diagnostic ultrasound have become a noninvasive option for tumor ablation, from prostate cancer to uterine fibroid, during the last decade. Despite this progress, many issues still need to be addressed. First, for brain targeting, the correction of distortions induced by the skull remains today a technological achievement that still needs to be validated clinically. Secondly, the problem of motion artifacts for abdominal treatments becomes today an important research topic. For all these issues, the potential of new ultrasonic therapy devices able to work both in Transmit and Receive modes will be emphasized and clinical results on monkeys and pigs will be presented. © 2007. Éditions Françaises de Radiologie. Édité par Elsevier Masson SAS.
MotsClés: Focused Ultrasound; Motion compensation; Therapy; Time reversal; artifact; echoencephalography; human; in vitro study; in vivo study; medical instrumentation; monkey; non invasive procedure; nonhuman; nuclear magnetic resonance imaging; prostate cancer; review; simulation; skull; swine; three dimensional imaging; ultrasound; ultrasound therapy; uterus myoma; validation study; Abdomen; Animals; Artifacts; Brain; Echoencephalography; Haplorhini; Humans; Models, Animal; Models, Biological; Models, Theoretical; Movement; Swine; Ultrasonic Therapy


Simulation and measurement of the optical excitation of the S1 zero group velocity Lamb wave resonance in plates. Balogun, O., T. W. Murray, and C. Prada. Journal of Applied Physics 102, no. 6 (2007).
Résumé: Recent reports on the thermoelastic generation of Lamb waves in isotropic elastic plates show that a laser source efficiently excites a resonance that occurs at the minimum frequency of the first order symmetric (S1) Lamb mode. The group velocity of the Lamb wave goes to zero at this frequency while the phase velocity remains finite, and the resonance is referred to as the S1 zero group velocity (S1 ZGV) resonance. The S1 ZGV resonance can be employed for the nondestructive evaluation of the elastic properties of plates or plate thickness. A model for the generation of elastic waves in plates using an intensitymodulated continuous wave laser source is developed and used to study the behavior of the S1 ZGV resonance. The effects of the laser source parameters on the generation of the S1 ZGV resonance are explored, and the spatial distribution of the displacement produced at the resonance frequency is determined. The predicted displacement spectrum of Lamb waves generated in micron scale plates is found to compare well with experimental measurements. In addition, experimental measurements demonstrate that the S1 ZGV resonance can be used to map subsurface features in thin (4 μm) membranes at high ultrasonic frequencies (700 MHz). © 2007 American Institute of Physics.
MotsClés: Elastic waves; Group velocity dispersion; Photoexcitation; Plates (structural components); Resonance; Ultrasonics; Isotropic elastic plates; Resonance frequency; Ultrasonic frequencies; Zero group velocity Lamb wave resonance; Surface waves


Nonlinear shear wave interaction in soft solids. Jacob, X., S. Catheline, J.  L. Gennisson, C. Barrière, D. Royer, and M. Fink. Journal of the Acoustical Society of America 122, no. 4 (2007): 1917–1926.
Résumé: This paper describes nonlinear shear wave experiments conducted in soft solids with transient elastography technique. The nonlinear solutions that theoretically account for plane and nonplane shear wave propagation are compared with experimental results. It is observed that the cubic nonlinearity implied in high amplitude transverse waves at f0 =100 Hz results in the generation of odd harmonics 3 f0, 5 f0. In the case of the nonlinear interaction between two transverse waves at frequencies f1 and f2, the resulting harmonics are fi ±2 fj (i,j=1,2). Experimental data are compared to numerical solutions of the modified Burgers equation, allowing an estimation of the nonlinear parameter relative to shear waves. The definition of this combination of elastic moduli (up to fourth order) can be obtained using an energy development adapted to soft solid. In the more complex situation of nonplane shear waves, the quadratic nonlinearity gives rise to more usual harmonics, at sum and difference frequencies, fi ± fj. All components of the field have to be taken into account. © 2007 Acoustical Society of America.
MotsClés: Elastic moduli; Harmonic distortion; Parameter estimation; Burgers equation; Elastography; Nonlinear interaction; Quadratic nonlinearity; Soft solids; Shear waves; acoustics; article; elasticity; elastography; energy; frequency modulation; mathematical analysis; nonlinear system; priority journal; shear rate; solid; theoretical study; young modulus; Acoustics; Anisotropy; Biomechanics; Elasticity; Finite Element Analysis; Humans; Linear Models; Models, Theoretical; Nonlinear Dynamics; Phantoms, Imaging; Rheology; Shear Strength; Sound Spectrography; Tensile Strength; Viscosity


A0 mode interaction with a plate free edge: Theory and experiments at very low frequency by thickness product. Ribay, G., S. Catheline, D. Clorennec, R. K. Ing, and M. Fink. Journal of the Acoustical Society of America 122, no. 2 (2007): 711–714.
Résumé: When a plane acoustic wave reaches a medium with an impedance infinite or null, it experiences a phase shift of zero or π and its amplitude on the edge is maximum or vanishes. The case of a flexion wave (A0 Lamb wave) at a free end is also simple; its amplitude is multiplied by a factor 22 and the phase shift is π 2. The evanescent wave at the origin of these phenomena, perfectly described by the classical flexural plate theory, is identified as the imaginary A1 mode of the exact RayleighLamb theory. The experiences confirm the theoretical predictions. © 2007 Acoustical Society of America.
MotsClés: Acoustic impedance; Phase shift; Rayleigh waves; Surface waves; Evanescent wave; Mode interaction; Plate theory; Thickness product; Acoustic waves; acoustic impedance; amplitude modulation; article; flexural plate theory; lamb wave theory; prediction; priority journal; theory; vibration; waveform; Acoustics; Fourier Analysis; Humans; Models, Theoretical; Sound; Sound Localization; Ultrasonics


Experimental detection and focusing in shallow water by decomposition of the time reversal operator. Prada, C., J. De Rosny, D. Clorennec, J.  G. Minonzio, A. Aubry, M. Fink, L. Berniere, P. Billand, S. Hibral, and T. Folegot. Journal of the Acoustical Society of America 122, no. 2 (2007): 761–768.
Résumé: A rigid 24element sourcereceiver array in the 1015 kHz frequency band, connected to a programmable electronic system, was deployed in the Bay of Brest during spring 2005. In this 10 to 18m deep environment, backscattered data from submerged targets were recorded. Successful detection and focusing experiments in very shallow water using the decomposition of the time reversal operator (DORT method) are shown. The ability of the DORT method to separate the echo of a target from reverberation as well as the echo from two different targets at 250 m is shown. An example of active focusing within the waveguide using the first invariant of the time reversal operator is presented, showing the enhanced focusing capability. Furthermore, the localization of the scatterers in the water column is obtained using a rangedependent acoustic model. © 2007 Acoustical Society of America.
MotsClés: Backscattering; Data acquisition; Frequency bands; Signal receivers; Waveguide components; Acoustic model; Time reversal operator (DORT method); Water column; Water; article; decomposition; echolocation; electronics; frequency modulation; priority journal; receiver operating characteristic; sound detection; sound intensity; water content; Kinetics; Models, Theoretical; Sound; Sound Localization; Time; Water


Giant vesicles containing magnetic nanoparticles and quantum dots: Feasibility and tracking by fiber confocal fluorescence microscopy. Beaune, G., B. Dubertret, O. Clément, C. Vayssettes, V. Cabuil, and C. Ménager. Angewandte Chemie – International Edition 46, no. 28 (2007): 5421–5424.
Résumé: (Figure Presented) Hybrid vesicles: Magnetic nanoparticles (γFe 2O3) and quantum dots (CdSe/ZnS) can be entrapped in stable vesicles by emulsion processes. The hybrid vesicles (HVs) have distinct magnetic and fluorescence properties (see images; scale bars: 10 μm). Fluorescence detection allows magnetic manipulation and tracking of the HVs in vivo by both magnetic resonance and fluorescence imaging. © 2007 WileyVCH Verlag GmbH & Co. KGaA.
MotsClés: Fluorescence; Nanoparticles; Organicinorganic hybrid composites; Quantum dots; Vesicles; Confocal fluorescence microscopy; Fluorescence properties; Organicinorganic hybrid composites; Vesicles; Confocal microscopy; Emulsions; Fluorescence microscopy; Imaging systems; Nanoparticles; Semiconductor quantum dots; Hybrid materials; nanoparticle; quantum dot; animal; article; chemistry; fluorescence microscopy; magnetism; mouse; transmission electron microscopy; ultrastructure; Animals; Magnetics; Mice; Microscopy, Electron, Transmission; Microscopy, Fluorescence; Nanoparticles; Quantum Dots


Polarizationsensitive fullfield optical coherence tomography. Moneron, G., A.  C. Boccara, and A. Dubois. Optics Letters 32, no. 14 (2007): 2058–2060.
Résumé: We present a polarizationsensitive fullfield optical coherence tomography system that can produce highresolution images of the linear retardance and reflectivity properties of biological media. En face images can be delivered at a frame rate of 3.5 Hz by combination of interferometric images acquired by two CCD cameras in an interference microscope illuminated with a tungsten halogen lamp. Isotropic spatial resolution of ∼1.0 μm is achieved. The technique is demonstrated on ex vivo muscle tissues. © 2007 Optical Society of America.
MotsClés: Halogen compounds; Light interference; Light polarization; Optical resolving power; Reflection; Biological media; High resolution images; Linear retardance; Muscle tissues; Optical tomography; animal; anisotropy; article; equipment design; eye refraction; interferometry; light; metabolism; methodology; muscle; optical coherence tomography; optics; oscillometry; pathology; Penaeidae; phase contrast microscopy; tail; Animals; Anisotropy; Equipment Design; Interferometry; Light; Microscopy, Interference; Muscles; Optics; Oscillometry; Penaeidae; Refraction, Ocular; Tail; Tomography, Optical Coherence


Thermal imaging of a vein of the forearm: Analysis and thermal modelling. Boué, C., F. Cassagne, C. Massoud, and D. Fournier. Infrared Physics and Technology 51, no. 1 (2007): 13–20.
Résumé: We analyse the infrared images obtained on a human forearm. In a first part, we present a basic thermal model explaining the temperature at the surface of the skin in the presence of sources such as veins. In a second part, we propose to analyse the infrared images obtained after thermal solicitation. We show how the use of low amplitude, healthsafe, periodical heating or a transient thermal solicitation allows to improve notably the contrast of the images and to extract the radius, depth and the blood flow velocity in a vein. © 2007 Elsevier B.V. All rights reserved.
MotsClés: Blood flow velocity; Depth of a vein; Imaging; Infrared thermography; Skin temperature; Blood; Flow velocity; Mathematical models; Skin; Thermal effects; Blood flow velocity; Periodical heating; Skin temp; Thermal modeling; Thermal solicitation; Infrared imaging


Interaction of a surface wave with a dislocation. Maurel, A., V. Pagneux, F. Barra, and F. Lund. Physical Review B – Condensed Matter and Materials Physics 75, no. 22 (2007).
Résumé: The scattering of a surface wave by a pinned edge dislocation in a semiinfinite, homogeneous, isotropic, threedimensional elastic solid is investigated analytically and numerically. An incident wave excites the dislocation that responds by oscillating as a string endowed with mass, line tension, and damping. The oscillations of the stringlike dislocation generate secondary (“scattered”) elastic waves that are the primary object of interest in this study. The back reaction of the reemitted waves on the dislocation dynamics is neglected, but the wavelength of the radiation is allowed to be large, comparable, or small compared to the length of the dislocation. In view of recent experimental visualizations of these phenomena, we focus particularly on the field behavior at the free surface near the dislocation, and not just on the far field. For the same reason, it is the vertical component of displacement at the free surface that is studied in detail. An efficient numerical procedure for the computation of the appropriate components of the Green's function, using a Filon quadrature for the integration of rapidly oscillating functions, is developed. The numerics is validated with known analytical expressions. The secondary radiation generated by the response of the dislocation to the incident wave is also calculated numerically, and the results are also validated by comparing them with the analytical expressions that can be obtained when the radiation wavelength is very long compared to dislocation length. The interference pattern between incident wave and secondary wave that is generated at the free surface is studied in detail and found to depend strongly not only on wavelength and dislocation geometry (length and orientation) but also on dislocation depth, with the response of the dislocation being a particularly sensitive function of such depth. Results are compared with recent experiments of Shilo and Zolotoyabko [Phys. Rev. Lett. 91, 115506 (2003)] that report visualizations of the surfacewavedislocation interaction using stroboscopic xray imaging. A satisfactory agreement is found. Dislocation velocities of a few percent of the speed of sound and viscosity coefficients of about 105 Pa s are inferred. © 2007 The American Physical Society.


Multiple scattering from assemblies of dislocation walls in three dimensions. Application to propagation in polycrystals. Maurel, A., V. Pagneux, F. Barra, and F. Lund. Journal of the Acoustical Society of America 121, no. 6 (2007): 3418–3431.
Résumé: The attenuation of ultrasound in polycrystalline materials is modeled with grain boundaries considered as arrays of dislocation segments, a model valid for low angle mismatches. The polycrystal is thus studied as a continuous medium containing many dislocation “walls” of finite size randomly placed and oriented. Wave attenuation is blamed on the scattering by such objects, an effect that is studied using a multiple scattering formalism. This scattering also renormalizes the speed of sound, an effect that is also calculated. At low frequencies, meaning wavelengths that are long compared to grain boundary size, then attenuation is found to scale with frequency following a law that is a linear combination of quadratic and quartic terms, in agreement with the results of recent experiments performed in copper [Zhang, J. Acoust. Soc. Am. 116(1), 109116 (2004)]. The prefactor of the quartic term can be obtained with reasonable values for the material under study, without adjustable parameters. The prefactor of the quadratic term can be fit assuming that the drag on the dynamics of the dislocations making up the wall is one to two orders of magnitude smaller than the value usually accepted for isolated dislocations. The quartic contribution is compared with the effect of the changes in the elastic constants from grain to grain that is usually considered as the source of attenuation in polycrystals. A complete model should include this scattering as well. © 2007 Acoustical Society of America.
MotsClés: Dislocations (crystals); Elastic constants; Grain boundaries; Grain size and shape; Multiple scattering; Three dimensional; Wavelength; Dislocation walls; Grain boundary size; Isolated dislocations; Low angle mismatches; Polycrystals; article; crystal; dynamics; materials testing; mathematical analysis; model; priority journal; sound transmission; ultrasound; waveform; Crystallization; Elasticity; Mathematics; Models, Theoretical; Scattering, Radiation; Sound; Viscosity


Optical measurements of the selfdemodulated displacement and its interpretation in terms of radiation pressure. Rénier, M., C. Barrière, and D. Royer. Journal of the Acoustical Society of America 121, no. 6 (2007): 3341–3348.
Résumé: Using a sensitive optical interferometer, the low frequency displacement nonlinearly generated by an ultrasonic tone burst propagating in a liquid is studied. Close to the source, the low frequency displacement contains a quasistatic component, which is affected by diffraction effects farther from the transducer. The experimental setup provides quantitative results, which allow the determination of the nonlinearity parameter of the liquid with a good accuracy. Such measurements are carried out in water and ethanol. Finally, the pressure associated with the low frequency displacement is discussed. Introducing the temporal mean value of the displacement, as already done in lossless solids, the noncumulative part of this second order pressure is associated with the static part of the low frequency displacement. This interpretation leads to extend the definition of the Rayleigh radiation pressure usually introduced for a continuous plane wave radiated in a confined fluid. © 2007 Acoustical Society of America.
MotsClés: Demodulation; Ethanol; Frequency estimation; Rayleigh scattering; Transducers; Ultrasonic waves; Frequency displacement; Nonlinearity parameter; Optical measurements; Plane waves; Rayleigh radiation; Interferometers; alcohol; water; article; liquid; pressure; priority journal; quantitative study; radiation; Acoustics; Computer Simulation; Microscopy, Interference; Pressure; Radiation; Water


Identification of the electroelastic coupling from full multiphysical fields measured at the micrometre scale. Amiot, F., F. Hild, F. Kanoufi, and J. P. Roger. Journal of Physics D: Applied Physics 40, no. 11 (2007): 3314–3325.
Résumé: Metal coated microcantilevers are used as transducers of their electrochemical environment. Using the metallic layer of these cantilevers as a working electrode allows one to modify the electrochemical state of the cantilever surface. Since the mechanical behaviour of micrometre scale objects is significantly surfacedriven, this environment modification induces bending of the cantilever. Using a fullfield interferometric measurement setup to monitor the objects then provides an optical phase map, which is found to originate from both electrochemical and mechanical effects. The scaling of the electrochemicallyinduced phase with respect to the surface charge density is modelled according to GouyChapmanStern theory, whereas the relationship between the mechanical effect and the surface charge density is analysed. An identification technique is described to determine a modelling of the electroelastic coupling and to identify the spatial charge density distribution from fullfield phase measurements. Minimizing the leastsquares gap between the measured phase and a statically admissible phase field, the mechanical effect is found to be chargedriven. The charge density field is also found to be singular on the cantilever edge, and the shear stress versus charge density is found to be nonlinear. © 2007 IOP Publishing Ltd.
MotsClés: Coated materials; Electrochemical electrodes; Interferometry; Metallic films; Shear stress; Surface charge; Electroelastic coupling; GouyChapmanStern theory; Microcantilevers; Optical phase map; Microstructure


Numerical predictions and experiments for optimizing hidden corrosion detection in aircraft structures using Lamb modes. Terrien, N., D. Royer, F. Lepoutre, and A. Déom. Ultrasonics 46, no. 3 (2007): 251–265.
Résumé: To increase the sensitivity of Lamb waves to hidden corrosion in aircraft structures, a preliminary step is to understand the phenomena governing this interaction. A hybrid model combining a finite element approach and a modal decomposition method is used to investigate the interaction of Lamb modes with corrosion pits. The finite element mesh is used to describe the region surrounding the corrosion pits while the modal decomposition method permits to determine the waves reflected and transmitted by the damaged area. Simulations make easier the interpretation of some parts of the measured waveform corresponding to superposition of waves diffracted by the corroded area. Numerical results permit to extract significant information from the transmitted waveform and thus to optimize the signal processing for the detection of corrosion at an early stage. Now, we are able to detect corrosion pits down to 80μm depth distributed randomly on a square centimeter of an aluminum plate. Moreover, thickness variations present on aircraft structures can be discriminated from a slightly corroded area. Finally, using this experimental setup, aircraft structures have been tested. © 2007 Elsevier B.V. All rights reserved.
MotsClés: Corrosion monitoring; Experiments; Finite elements; Lamb waves; Modal decomposition; Modelisation; Aluminum plating; Computer simulation; Corrosion prevention; Finite element method; Signal processing; Surface waves; Aircraft structures; Corrosion monitoring; Corrosion pits; Modal decomposition; Thickness variations; Aircraft


In vivo transcranial brain surgery with an ultrasonic time reversal mirror. Pernot, M., J.  F. Aubry, M. Tanter, A.  L. Boch, F. Marquet, M. Kujas, D. Seilhean, and M. Fink. Journal of Neurosurgery 106, no. 6 (2007): 1061–1066.
Résumé: Object. Highintensity focused ultrasonography is known to induce controlled and selective noninvasive destruction of tissues by focusing ultrasonic beams within organs, like a magnifying glass concentrating enough sunlight to burn a hole in paper. Such a technique should be highly interesting for the treatment of deepseated lesions in the brain. Nevertheless, ultrasonic tissue ablation in the brain has long been hampered by the defocusing effect of the skull bone. Methods. In this in vivo study, the authors used a highpower timereversal mirror specially designed for noninvasive ultrasonic brain treatment to induce thermal lesions through the skulls of 10 sheep. The sheep were divided into three groups and, depending on group, were killed 1, 2, or 3 weeks after treatment. The thermal lesions were confirmed based on findings of posttreatment magnetic resonance imaging and histological examinations. After treatment, the basic neurological functions of the animals were unchanged: the animals recovered from anesthesia without any abnormal delay and did not exhibit signs of paralysis or coma. No major behavioral change was observed. Conclusions. The results provide striking evidence that noninvasive ultrasonographic brain surgery is feasible. Thus the authors offer a novel noninvasive method of performing local brain ablation in animals for behavioral studies. This technique may lead the way to noninvasive and nonionizing treatment of brain tumors and neurological disorders by selectively targeting intracranial lesions. Nevertheless, sheep do not represent a good functional model and extensive work will need to be conducted preferably on monkeys to investigate the effects of this treatment.
MotsClés: Highintensity ultrasonography; Noninvasive surgery; Sheep; Ultrasonography; animal experiment; article; brain surgery; controlled study; device; histology; in vivo study; nonhuman; nuclear magnetic resonance imaging; priority journal; sheep; skull; thermal injury; ultrasonic time reversal mirror; ultrasound; Animals; Behavior, Animal; Brain; Feasibility Studies; Magnetic Resonance Imaging; Neurologic Examination; Neurosurgical Procedures; Sheep; Transducers; Ultrasonics


Symmetry of electron states in semiconductor structures under a magnetic field. Tronc, P., and V. P. Smirnov. Physica Status Solidi (B) Basic Research 244, no. 6 (2007): 2010–2021.
Résumé: We present a grouptheory analysis of the electron states in bulk and lowdimensional semiconductor structures under a uniform magnetic field. The analysis takes into account the gauge transformations under the symmetry operations, It is shown that the symmetry operations commute in dots, rods and tubes whatever is the orientation of the magnetic field whereas they commute in layers only when the field is in the plane. The commutations properties allow using conventional symmetry groups. In bulk materials, the confinement of electrons within rods whose axes are parallel to the field makes it possible to derive approximate wavefunction symmetries from the rod group involving the geometrical symmetry operations common to the field and the crystal but excluding the translations that are not parallel to the field. An approximation of the same kind can also be made for lowdimensional structures. Applications to bulk materials with the wurtzite or zinc blende structure as well as related nanostructures are presented. © 2007 WILEYVCH Verlag GmbH & Co. KGaA.


Direct imaging of a laser mode via midinfrared nearfield microscopy. Moreau, V., M. Bahriz, R. Colombelli, P.  A. Lemoine, Y. De Wilde, L. R. Wilson, and A. B. Krysa. Applied Physics Letters 90, no. 20 (2007).
Résumé: FabryṔrot standing waves inside a midinfrared quantum cascade laser have been imaged using an apertureless scanning nearfield optical microscope. The devices emit at λ≈7.7 μm and they feature airconfinement waveguides, with the optical mode guided at the semiconductorair interface. A consistent portion of the mode leaks evanescently from the device top surface and can be detected in the near field of the device. Imaging of the evanescent wave across a plane parallel to the device surface allows one to directly assess the effective light wavelength inside the laser material, yielding the effective index of refraction. Imaging across a plane perpendicular to the device surface allows one to directly measure the electric field decay length, which is found in excellent agreement with the numerical simulations. © 2007 American Institute of Physics.
MotsClés: Computer simulation; Imaging systems; Interfaces (materials); Optical microscopy; Optical waveguides; Refractive index; Apertureless scanning; Electric field decay length; Optical mode guided; Standing waves; Semiconductor lasers


Second harmonic generation in the near field and far field: A sensitive tool to probe crystalline homogeneity. MahieuWilliame, L., S. Grásillon, M. CuniotPonsard, and C. Boccara. Journal of Applied Physics 101, no. 8 (2007).
Résumé: In order to probe crystalline orientation of Srx Ba1x Nb2 O6 (SBN:x) thin film, we have developed a detection scheme based on a scanning nearfield optical microscope (SNOM). It is used to image simultaneously the fundamental and the second harmonic generation (SHG) of light by the sample under pulsed laser illumination. We demonstrate on SBN thin films that an apertureless SNOM can dramatically improve the resolution and the sensitivity of SNOMSHG. Tip direction and focalization are the two crucial parameters in the SNOMSHG experiments. Moreover, we show the ability of our setup to separate near field from far field contribution to the SHG. This is indeed very helpful in order to measure surfaceSHG coefficients. © 2007 American Institute of Physics.
MotsClés: Crystal orientation; Laser pulses; Near field scanning optical microscopy; Surface properties; Thin films; Crystalline homogeneity; Focalization; Scanning nearfield optical microscope (SNOM); Harmonic generation


Identification of elastic property and loading fields from fullfield displacement measurements. Amiot, F., F. Hild, and J. P. Roger. International Journal of Solids and Structures 44, no. 9 (2007): 2863–2887.
Résumé: A method is introduced to identify simultaneously elastic properties and loading fields from a measured displacement field. Since the mechanical behavior of microelectromechanical systems (MEMS) is governed by surface effects, this type of identification tool is thought to be of major interest. However, increasing the number of parameters to retrieve affects the redundancy necessary for an accurate identification. A finiteelement formulation of a distance between measured and statically admissible (SA) displacement fields is shown to be equivalent to a standard leastsquares distance to kinematically admissible (KA) fields if the used modeling is suitable. Any deviation from this equivalence is then the signature of a modeling error. Balancing the distance to KA and SA displacement fields allows one to retrieve unknown modeling parameters. This method is detailed on heterogeneous EulerBernoulli beams submitted to an unknown loading field and applied to experimental displacement fields of microcantilevers obtained with an electrostatic setup. An elastic property field and a parameterized loading field are then identified, and the quality of the identification is assessed. © 2006 Elsevier Ltd. All rights reserved.
MotsClés: Cantilever; Fullfield measurements; Identification problem; MEMS; Computer simulation; Elastic constants; Finite element method; Identification (control systems); Least squares approximations; Loads (forces); Parameter estimation; Redundancy; Cantilevers; Fullfield measurements; Identification problems; Kinematically admissible (KA) fields; Statically admissible (SA); Microelectromechanical devices


Comment on “multiple scattering: The key to unravel the subwavelength world from the farfield pattern of a scattered wave”. De Rosny, J., and C. Prada. Physical Review E – Statistical, Nonlinear, and Soft Matter Physics 75, no. 4 (2007).
Résumé: Contrary to the main conclusion of Simonetti [Phys. Rev. E 73, 036619 (2006)], we maintain that multiple scattering (MS) is not the “key” for subwavelength detection. Indeed, even with no MS between subwavelength structures, subwavelength detection is still possible. Our statement is numerically confirmed. A simple mathematical argument explains this result. From our point of view, the incorrect conclusion of Simonetti comes from a misinterpretation of the Picard's theorem. © 2007 The American Physical Society.
MotsClés: Numerical methods; Theorem proving; Wavelength; Picard's theorem; Simonetti; Subwavelength structures; Multiple scattering


Analytical method for localizing a fluorescent inclusion in a turbid medium. Laidevant, A., A. Da Silva, M. Berger, J. Boutet, J.  M. Dinten, and A. C. Boccara. Applied Optics 46, no. 11 (2007): 2131–2137.
Résumé: We describe a novel method for localizing a fluorescent inclusion in a homogeneous turbid medium through the use of timeresolved techniques. Based on the calculation of the mean time of the fluorescence curves, the method does not require a priori knowledge of either the fluorescence lifetime or the mean time of the instrument response function since it adopts a differential processing approach. Theoretical expressions were validated and experiments for assessing the accuracy of localization were carried out on liquid optical phantoms with a small fluorescent inclusion. The illumination and detection optical fibers were immersed in the medium to achieve infinite medium geometry as required by the model used. The experimental setup consisted of a timecorrelated singlephoton counting system. Submillimeter accuracy was achieved for the localization of the inclusion. © 2007 Optical Society of America.
MotsClés: Fluorescent inclusion; Response function; Time resolved techniques; Fluorescence; Geometry; Lighting; Optical fibers; Photons; Turbidity; nanoparticle; article; computer assisted diagnosis; evaluation; fluorescence microscopy; image quality; instrumentation; methodology; particle size; photometry; ultrastructure; Image Interpretation, ComputerAssisted; Microscopy, Fluorescence; Nanoparticles; Nephelometry and Turbidimetry; Particle Size; Phantoms, Imaging


Determination of an HCF criterion by thermal measurements under biaxial cyclic loading. Doudard, C., M. Poncelet, S. Calloch, C. Boue, F. Hild, and A. Galtier. International Journal of Fatigue 29, no. 4 (2007): 748–757.
Résumé: A probabilistic twoscale model was recently developed to describe highcycle fatigue (HCF) properties of steels associated with an identification method of the scatter based on thermal measurements. Up to now, this theoretical framework was used for uniaxial load histories. It is proposed to modify the probabilistic twoscale model to account for the effect of a multiaxial and proportional load histories on HCF properties. This modification consists in the introduction of an equivalent activation stress in the process controlling the plasticity kinetics. Thermal measurements are performed under biaxial tensioncompression load histories to identify and validate an HCF criterion. © 2006 Elsevier Ltd. All rights reserved.
MotsClés: Microplasticity; Multiaxial fatigue; Poisson point process; Thermal measurements; Weibull model; Fatigue of materials; Mathematical models; Plasticity; Probabilistic logics; Steel; Weibull distribution; Microplasticity; Multiaxial fatigue; Poisson point process; Thermal measurements; Weibull model; Cyclic loads


Elastography using ultrasound or magnetic resonance: New imaging tools for cancer diagnosis. Tanter, M., J. Bercoff, R. Sinkus, T. Deffieux, J.  L. Gennisson, and M. Fink. Medecine Nucleaire 31, no. 4 SPEC. ISS. (2007): 132–141.
Résumé: Despite recent progress, breast cancer remains today a major public health problem as it represents the main morbidity incidence for woman with 42,000 new cases and 11,600 deaths per year in France. XRay mammography which is the “gold standard” exam for breast screening relies on an excellent sensitivity (nevertheless its quality is varying with respect to breast density). However, its specificity for malignancy diagnosis remains moderate leading to many useless interventions for lesions proven a posteriori to be benign by histology. The other imaging techniques such as echography and magnetic resonance imaging (MRI) also possess their own limits. Echography is strongly operatordependent. Dynamic MRI with injection of contrast agents has a high sensitivity for breast cancer detection (>90%) but suffers from a moderate specificity (50 to 80% according to the type of cancer). In parallel, although it is strongly subjective, the act of palpation remains today a major act in the workflow of breast screening. Since Egyptian ancient ages, the physicians practise the act of palpating body parts in order to determine tissues stiffness and a hardly deformed mass within an organ is often related to the presence of an abnormal lesion. Palpation is not only useful for screening and diagnosis as the surgeon also uses it during interventions to be effectively guided towards the pathological area. Recently, new techniques based on ultrasound or magnetic resonance imaging finally made it possible to map organs elasticity in a quantitative way. These “elastography” techniques could play soon an important role in medical imaging. © 2007 Elsevier Masson SAS. All rights reserved.
MotsClés: Breast; Cancer; Diagnostic; Elastography; Magnetic resonance imaging; Screening; Ultrasound; contrast medium; breast cancer; cancer diagnosis; echography; Egypt; elastography; histology; human; imaging; mammography; morbidity; nuclear magnetic resonance imaging; palpation; physician; screening; sensitivity and specificity; short survey; surgeon; ultrasound


Early chloroplastic alterations analysed by optical coherence tomography during a harpininduced hypersensitive response. Boccara, M., W. Schwartz, E. Guiot, G. Vidal, R. De Paepe, A. Dubois, and A.  C. Boccara. Plant Journal 50, no. 2 (2007): 338–346.
Résumé: The hypersensitive response has been mostly studied by molecular and biochemical methods after sample destruction. The development of imaging techniques allows the monitoring of physiological changes before any signs of cell death. Here, we follow the early steps of a hypersensitivelike response induced by the bacterial elicitor harpin in Nicotiana sp. We describe cytological modifications after inoculation of the harpin protein, using confocal fluorescence microscopy (CFM) and optical coherence tomography (OCT), an interferometricbased microscopy. The changes detected by CFM occurred 5 h after harpin infiltration and corresponded to a redistribution of the chloroplasts from the upper to the inner regions of the palisade mesophyll cells which could be related to a perturbation in the microtubule network. Using OCT, we were able to detect a decrease in chloroplast backscattered signal as early as 30 min after harpin infiltration. A simple physical model, which accounted for the structure and distribution of thylakoid membranes, suggested that this loss of scattering could be associated with a modification in the refractive index of the thylakoid membranes. Our OCT observations were correlated with a decrease in photosynthesis, emphasizing changes in chloroplast structure as one of the earliest hallmarks of plant hypersensitive cell death. © 2007 The Authors Journal compilation 2007 Blackwell Publishing Ltd.
MotsClés: Confocal microscopy; Elicitor; Nicotiana; Nondestructive methods; Photosynthesis; Thylakoid membranes; Elicitor; Nicotiana; Thylakoid membranes; Confocal microscopy; Infiltration; Nondestructive examination; Photosynthesis; Physiology; Plant cell culture; harpin; outer membrane protein; unclassified drug; apoptosis; article; chloroplast; confocal microscopy; cytology; drug effect; fluorescence microscopy; instrumentation; metabolism; methodology; optical coherence tomography; photosynthesis; physiology; tobacco; Apoptosis; Bacterial Outer Membrane Proteins; Chloroplasts; Microscopy, Confocal; Microscopy, Fluorescence; Photosynthesis; Tobacco; Tomography, Optical Coherence; Infiltration; Photosynthesis; Physiology; Plants; Bacteria (microorganisms); Nicotiana; Nicotiana sp.


Compensating for bone interfaces and respiratory motion in highintensity focused ultrasound. Tanter, M., M. Pernot, J.  F. Aubry, G. Montaldo, F. Marquet, and M. Fink. International Journal of Hyperthermia 23, no. 2 (2007): 141–151.
Résumé: Bursts of focused ultrasound energy a thousand times more intense than diagnostic ultrasound have become a noninvasive option for treating cancer, from breast to prostate or uterine fibroid, during the last decade. Despite this progress, many issues still need to be addressed. First, the distortions caused by defocusing obstacles, such as the skull or ribs, on the ultrasonic therapeutic beam are still being investigated. Multielement transducer technology must be used in order to achieve such transcranial or transcostal adaptive focusing. Second, the problem of motion artifacts, a key component in the treatment of abdominal lesions, has been shown significantly to influence the efficacy and treatment time. Though many methods have been proposed for the detection of organ motion, little work has been done to develop a comprehensive solution including motion tracking and feedback correction in real time. This paper is a review of the work achieved by authors in transcranial highintensity focused ultrasound (HIFU), transcostal HIFU and motion compensated HIFU. For these three issues, the optimal solution can be reached using the same technology of multielement transducers devices able to work both in transmit and receive modes.
MotsClés: Adaptive focusing; Brain therapy; Elastography; Monitoring; Motion correction; Time reversal; abdominal disease; animal experiment; animal model; article; artifact; brain tumor; clinical effectiveness; controlled study; diagnostic imaging; feedback system; high intensity focused ultrasound; motion; non invasive procedure; nonhuman; skull; thorax; ultrasound transducer; Animals; Artifacts; Bone and Bones; Brain Neoplasms; Feedback; Humans; Liver Diseases; Motion; Respiration; Ribs; Transducers; Ultrasonic Therapy; Ultrasonography


An improved approximation for the Rayleigh wave equation. Royer, D., and D. Clorennec. Ultrasonics 46, no. 1 (2007): 23–24.
Résumé: We derive a simple expression, which gives an approximate value of the Rayleigh wave velocity in an isotropic solid. This approximation is five times better than that given by Viktorov. The velocity equation can be easily inverted in order to obtain an accurate determination of the elastic constants. This procedure can be worthwhile for elastic microanalysis of bulk materials by scanning acoustic microscopy. © 2006 Elsevier B.V. All rights reserved.
MotsClés: Rayleigh wave velocity; Acoustic microscopes; Microanalysis; Scanning; Velocity measurement; Wave equations; Elastic constants; Elastic microanalysis; Rayleigh wave equations; Rayleigh wave velocity; Scanning acoustic microscopy; Approximation theory; article; radiofrequency radiation; theoretical model; ultrasound; Models, Theoretical; Radio Waves; Ultrasonics


A combined finite element and modal decomposition method to study the interaction of Lamb modes with microdefects. Terrien, N., D. Osmont, D. Royer, F. Lepoutre, and A. Déom. Ultrasonics 46, no. 1 (2007): 74–88.
Résumé: This paper presents a combined finite element and modal decomposition method to study the interaction of Lamb waves with damaged area. The finite element mesh is used to describe the region around the defects. On the contrary to other hybrid models already developed, the interaction between Lamb waves and defects is computed in the temporal domain. Then, the modal decomposition method permits to determine the wave reflected and transmitted by the damaged area. Modal analysis allows also identifying the mode conversions induced by the defects. These numerical results agree with previous finite element results concerning the interaction of Lamb modes with a notch. Experiments, carried out with gauged defects on an aluminum plate, are also compared to numerical predictions to validate the simulation. Compared to classical techniques of simulation, this new method allows us to investigate the interaction of Lamb modes generated at high frequencythickness product with microdefects as corrosion pitting. © 2006 Elsevier B.V. All rights reserved.
MotsClés: Finite element; Interactions; Lamb waves; Microdefects; Modal decomposition; Simulations; Computer simulation; Defects; Modal analysis; Numerical methods; Wave equations; Lamb waves; Microdefects; Modal decomposition; Finite element method; article; computer simulation; evaluation; finite element analysis; radiofrequency radiation; theoretical model; ultrasound; Computer Simulation; Finite Element Analysis; Models, Theoretical; Radio Waves; Ultrasonics


Local and noncontact measurements of bulk acoustic wave velocities in thin isotropic plates and shells using zero group velocity Lamb modes. Clorennec, D., C. Prada, and D. Royer. Journal of Applied Physics 101, no. 3 (2007).
Résumé: An original method for material characterization with acoustic waves is presented. The measurement of the longitudinal and shear wave velocities in thin isotropic plates or shells is performed locally on the same face without any mechanical contact. We exploit the resonance that occurs at the minimum frequency thickness product of the first order symmetric (S1) and of the second order antisymmetric (A2) Lamb modes. At these frequencies the group velocity vanishes, whereas the phase velocity remains finite. Then, the energy, which cannot propagate in the structure, is localized in a zone of diameter half the wavelength. The vibrations are excited in the thermoelastic regime by a laser pulse and detected at the same point by an optical interferometer. For these two Lamb modes we have computed the variations of the frequency thickness product versus Poisson's ratio. The resonance frequency ratio, which is independent of the plate or shell thickness, provides an absolute and local measurement of Poisson's ratio. Provided that the plate thickness is known, each resonance frequency allows us to determine in a single shot the bulk acoustic wave velocities VL and VT. Since it is based on frequency measurements, the method, tested on a large number of materials, is very accurate. © 2007 American Institute of Physics.
MotsClés: Interferometers; Poisson equation; Shear waves; Thin films; Velocity measurement; Antisymmetric Lamb modes; Frequency measurements; Mechanical contacts; Resonance frequency; Acoustic waves


Focusing beyond the diffraction limit with farfield time reversal. Lerosey, G., J. De Rosny, A. Tourin, and M. Fink. Science 315, no. 5815 (2007): 1120–1122.
Résumé: We present an approach for subwavelength focusing of microwaves using both a timereversal mirror placed in the far field and a random distribution of scatterers placed in the near field of the focusing point. The farfield timereversal mirror is used to build the timereversed wave field, which interacts with the random medium to regenerate not only the propagating waves but also the evanescent waves required to refocus below the diffraction limit. Focal spots as small as onethirtieth of a wavelength are described. We present one example of an application to telecommunications, which shows enhancement of the information transmission rate by a factor of 3.
MotsClés: diffraction; microwave radiation; telecommunication; wavelength; acoustics; article; diffraction; lens; lithotripsy; microwave radiation; priority journal; scanning near field optical microscopy; sound transmission; technology; telecommunication; time; ultrasound


Acoustic source localization model using inskull reverberation and time reversal. Catheline, S., M. Fink, N. Quieffin, and R. K. Ing. Applied Physics Letters 90, no. 6 (2007).
Résumé: A processing model of localization based on time reversal of the reverberated sound in a human skull is proposed. The underlying general idea is that bones act as antenna, gathering and conducting information about spatial positioning. Decoding this information is achieved with a time reversal analysis. Tested in a model experiment, the localization works in the azimuthal and sagittal plans, for single or multiple sound sources. Its efficiency is also demonstrated for one sided hearing people. The authors anticipate that this general antennalike concept can be applied to many animals that use sound localization as well as to future design for microphone devices or sonars. © 2007 American Institute of Physics.
MotsClés: Acoustic signal processing; Antennas; Bone; Microphones; Sonar; Acoustic source localization models; Sagittal plans; Spatial positioning; Time reversal analysis; Reverberation


Thermal conductivity of alumina inclusion/glass matrix composite materials: local and macroscopic scales. TessierDoyen, N., X. Grenier, M. Huger, D. S. Smith, D. Fournier, and J. P. Roger. Journal of the European Ceramic Society 27, no. 7 (2007): 2635–2640.
Résumé: The thermal conductivity of a twophase material, based on a glass matrix containing mm sized spherical alumina inclusions, has been studied as a function of the alumina phase volume fraction. The glass matrix and the alumina phase were chosen with almost identical coefficients of thermal expansion to ensure good thermal contact at the interface between the two phases. The thermal conductivity of the alumina phase was determined by local measurements on the inclusions using the mirage technique. For the glass phase and the twophase samples, the thermal conductivity values were evaluated with the laser flash technique and compared to predictions by analytical models. The MaxwellEucken model gives a close agreement to these experimental values for alumina volume fractions up to 55%. In fact, we show that for large mm sized alumina inclusions, Hasselman's correction for the interface thermal resistance is not necessary. © 2006 Elsevier Ltd. All rights reserved.
MotsClés: Composites; Glass; Thermal conductivity; Twophase materials; Alumina; Glass ceramics; Heat resistance; Inclusions; Mathematical models; Maxwell equations; Thermal conductivity; Thermal expansion; Volume fraction; Alumina inclusion/glass matrix composite materials; Laser flash technique; MaxwellEucken model; Twophase material; Composite materials; Alumina; Composite materials; Glass ceramics; Heat resistance; Inclusions; Mathematical models; Maxwell equations; Thermal conductivity; Thermal expansion; Volume fraction


Ultrasonic imaging of highly scattering media from local measurements of the diffusion constant: Separation of coherent and incoherent intensities. Aubry, A., and A. Derode. Physical Review E – Statistical, Nonlinear, and Soft Matter Physics 75, no. 2 (2007).
Résumé: As classical imaging fails with diffusive media, one way to image a multiplescattering medium is to achieve local measurements of the dynamic transport properties of a wave undergoing diffusion. This paper presents a method to obtain local measurements of the diffusion constant D in a multiplescattering medium. The experimental setup consists in an array of programmable transducers placed in front of the multiplescattering medium to be imaged. By achieving Gaussian beamforming both at emission and reception, an array of virtual sources and receivers located in the near field is constructed. The time evolution of the incoherent component of the intensity backscattered on this virtual array is shown to represent directly the growth of the diffusive halo as Dt. A matrix treatment is proposed to separate the incoherent intensity from the coherent backscattering peak. Once the incoherent contribution is isolated, a local measurement of the diffusion constant is possible. The technique is applied to image the longscale variations of D in a randomscattering sample made of two parts with a different concentration of cylindrical scatterers. This experimental result is obtained with ultrasonic waves around 3 MHz. It illustrates the possibility of imaging diffusive media from local measurements of the diffusion constant, based on coherent Gaussian beamforming and a matrix “antisymmetrization,” which creates a virtual antireciprocity. © 2007 The American Physical Society.
MotsClés: Backscattering; Light scattering; Transducers; Transport properties; Ultrasonic waves; Diffusion constants; Multiple scattering medium; Programmable transducers; Scattering media; Ultrasonic imaging


Acoustic impact localization in plates: Properties and stability to temperature variation. Ribay, G., S. Catheline, D. Clorennec, R. K. Ing, N. Quieffin, and M. Fink. IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 54, no. 2 (2007): 378–384.
Résumé: Localizing an impact generated by a simple finger knock on plateshaped solid objects is made possible in an acoustic time reversal experiment. It is shown that the technique works with a single accelerometer. To better understand the phenomenon and to know exactly the nature of the created waves, a twodimensional (2D) elastic simulation is used, showing that in a very good approximation the Ao Lamb mode is the only propagating one. However, it is shown that, within one wavelength distance from the edges, evanescent waves must be taken into account. As a first consequence, the ability to distinguish two neighboring impacts improves when the plate thickness decreases and the frequency increases. As a second consequence, it is expected theoretically that temperature variations lead to a stretching or a contraction of acoustic signatures. The experimental demonstration used a heterodyne interferometer to measure the impulse responses created by a knock on a plate during the cooling. A simple algorithm is shown to perfectly compensate for temperature impacts, which demonstrates the feasibility of the technique for outdoor time reversal interactive experiments. © 2007 IEEE.
MotsClés: Accelerometers; Algorithms; Approximation theory; Computer simulation; Plates (structural components); Acoustic impact localization; Acoustic signatures; Temperature variations; Acoustic distortion; acoustics; article; computer simulation; methodology; radiation dose; radiation scattering; sensitivity and specificity; stimulation; temperature; theoretical model; transducer; vibration; Acoustics; Computer Simulation; Models, Theoretical; Physical Stimulation; Radiation Dosage; Scattering, Radiation; Sensitivity and Specificity; Temperature; Transducers; Vibration


Coherent backscattering and farfield beamforming in acoustics. Aubry, A., A. Derode, P. Roux, and A. Tourin. Journal of the Acoustical Society of America 121, no. 1 (2007): 70–77.
Résumé: Coherent backscattering of waves by a random medium is spectacular evidence of interference effects despite disorder and multiple scattering. It manifests itself as a doubling of the wave intensity reflected exactly in the backward direction. This phenomenon has been observed experimentally in optics, acoustics, or seismology. While optical measurements are realized in farfield conditions with a plane wave illumination and a beamwidth much larger than the wavelength, ultrasonic experiments are carried out with wideband controllable arrays of (nearly) pointlike transducers that directly record the wave field, in amplitude and phase. Therefore it is possible to perform beamforming of the incoming and outgoing wave fields before computing the average backscattered intensity. In this paper, the advantages of plane wave beamforming applied to the study of the coherent backscattering effect are shown. Particularly, the angular resolution, the signaltonoise ratio, as well as the estimation of the enhancement factor can be improved by beamforming. Experimental results are presented with ultrasonic pulses, in the 2.53.5 MHz range, propagating in random collections of scatterers. Since the coherent backscattering effect can be taken advantage of to measure diffusive parameters (transport mean free path, diffusion constant), planewave beamforming can be applied to the characterization of highly scattering media. © 2007 Acoustical Society of America.
MotsClés: Signal interference; Signal to noise ratio; Transducers; Ultrasonics; Beamforming; Coherent backscattering effects; Plane wave beamforming; Acoustic wave backscattering; acoustics; article; beamforming; coherent backscattering; measurement; priority journal; signal noise ratio; transducer

