The Experts below are selected from a list of 270 Experts worldwide ranked by ideXlab platform
Habib Ammari - One of the best experts on this subject based on the ideXlab platform.
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On An Elliptic Equation Arising from Photo-Acoustic Imaging in Inhomogeneous Media
International Mathematics Research Notices, 2015Co-Authors: Habib Ammari, Hongjie Dong, Hyeonbae KangAbstract:We study an elliptic equation with measurable coefficients arising from photo-Acoustic Imaging in inhomogeneous media. We establish Holder continuity of weak solutions and obtain pointwise bounds for Green's functions subject to Dirichlet or Neumann condition.
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Quantitative thermo-Acoustic Imaging: An exact reconstruction formula
Journal of Differential Equations, 2013Co-Authors: Habib Ammari, Josselin Garnier, Wenjia Jing, Loc Hoang NguyenAbstract:This paper aims to mathematically advance the field of quantitative thermo-Acoustic Imaging. Given several electromagnetic data sets, we establish for the first time an analytical formula for reconstructing the absorption coefficient from thermal energy measurements. Since the formula involves derivatives of the given data up to the third order, it is unstable in the sense that small measurement noises may cause large errors. However, in the presence of measurement noise, the obtained formula, together with a noise regularization technique, provides a good initial guess for the true absorption coefficient. We finally correct the errors by deriving a reconstruction formula based on the least square solution of an optimal control problem and prove that this optimization step reduces the errors occurring and enhances the resolution.
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Sharp estimates for the Neumann functions and applications to quantitative photo-Acoustic Imaging in inhomogeneous media ∗
Journal of Differential Equations, 2012Co-Authors: Habib Ammari, Hyeonbae Kang, Seick KimAbstract:We obtain sharp Lp and Holder estimates for the Neumann function of the operator ∇⋅γ∇−ik on a bounded domain. We also obtain quantitative description of its singularity. We then apply these estimates to quantitative photo-Acoustic Imaging in inhomogeneous media. The problem is to reconstruct the optical absorption coefficient of a diametrically small anomaly from the absorbed energy density.
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Mathematical models and reconstruction methods in magneto-Acoustic Imaging
European Journal of Applied Mathematics, 2009Co-Authors: Habib Ammari, Hyeonbae Kang, Yves Capdeboscq, Anastasia KozhemyakAbstract:In this paper, we provide the mathematical basis for three different magneto- Acoustic Imaging approaches (vibration potential tomography, magneto-Acoustic tomog- raphy with magnetic induction, and magneto-Acoustic current Imaging) and propose new algorithms for solving the inverse problem for each of them.
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Quantitative Photo-Acoustic Imaging of Small Absorbers
2009Co-Authors: Habib Ammari, Emmanuel Bossy, Vincent Jugnon, Hyeonbae KangAbstract:In photo-Acoustic Imaging, energy absorption causes thermo-elastic expansion of optical absorbers, which in turn leads to propagation of a pressure wave. Recently, we have developed an efficient method for locating small absorbing regions inside a bounded domain from boundary measurements of the induced pressure wave and reconstructing the absorbed density. However, it is the absorption coefficient, not the absorbed energy, that is a fundamental physiological parameter. In this paper, we propose two methods for reconstructing the normalized optical absorption coefficient of a small absorber from the absorbed density. AMS subject classifications. 31B20, 35B37,35L05
Wei Fan - One of the best experts on this subject based on the ideXlab platform.
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experimental study on underwater Acoustic Imaging of 2 d temperature distribution around hot springs on floor of lake qiezishan china
Experimental Thermal and Fluid Science, 2010Co-Authors: Wei Fan, Ying Chen, Huachen Pan, Yong Cai, Zhujun ZhangAbstract:Abstract An experimental study is performed on Acoustic Imaging of underwater temperature fields in Lake Qiezishan, located at Longling Country, Yunnan Province, China. There are hot springs and craters beneath Lake Qiezishan, which lies at 24°32′33″ north latitude and 98°47′44″ east longitude. Using the Acoustic method, the temperature fields are recovered with the computed tomography of the measured time-of-flight data. Regarding the measuring system, hydrophones are used as transmitters and receivers. The signal correlation analysis is performed to obtain accurate Acoustic wave transit time from the transmitted and received Acoustic signals. Both the transmitter emission start time and the receiver capture start time are also estimated using a novel algorithm based on the time-of-flight measurements at different water temperature. The reconstruction of the 2-D temperature field which is an ill-posed problem, is conducted by total least-squares method. The reconstructed temperature distributions are rather approximations to the actual distributions measured with thermocouples. The preliminary results show that the potential of underwater Acoustic Imaging will be useful for the in situ monitoring of temperature distributions around sea-floor hydrothermal vents.
Jerome Antoni - One of the best experts on this subject based on the ideXlab platform.
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Acoustic Imaging applied to fault detection on a rotating machine bench
Proceedings of Isma, 2016Co-Authors: E Cardenas Cabada, Nacer Hamzaoui, Quentin Leclere, Jerome AntoniAbstract:One of the principal application of Acoustic Imaging techniques is to identify the Acoustic sources over a surface. The purpose of this study is to show the relevance of Acoustic Imaging as a fault detection tool. A rotating machine bench is used to generate experimentally bearings and gears faults configurations. A 45 microphones array with a spiral distribution is used to register the Acoustic radiation. Before applying the Acoustic Imaging technique, several operations are applied to the recorded signals. The signals are firstly angularly resampled thanks to an angle encoder. Secondly, the synchronous average is used on the signals in order to separate the synchronous and random parts with regard to the mechanism periodicity. Beamforming is then applied to both extracted signals in order to visualize the synchronous and the random Acoustic sources. The gears and shaft signals are theoretically synchronous with the mechanism frequency while bearing is not necessarily. The fault signature extracted can be visualized spatially thanks to beamforming.
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Acoustic Imaging applied to fault detection in rotating machine
2015Co-Authors: E Cardenas Cabada, Nacer Hamzaoui, Quentin Leclere, Jerome AntoniAbstract:Fault detection in rotating machines is generally based on vibration signal analysis. However, the sound radiated by a structure and its vibration are closely linked. We can therefore imagine that Acoustic measurements could be useful for diagnostic improvement. In this paper, a fault diagnostic method based on Acoustic Imaging is proposed. Beamforming is used to describe the Acoustic field generated by an operating machine. Usually, the source strength is mapped in order to identify the radiating areas. In this paper, fault detection features are plotted instead. The spectral kurtosis is mapped as a function of space and frequency to separate and localise impulsive sources.
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Cylindrical cyclic Acoustic Imaging with a Bayesian approach for cyclostationary sources reconstruction.
Journal of the Acoustical Society of America, 2013Co-Authors: Sébastien Personne, Jerome Antoni, Jean-daniel ChazotAbstract:Standard Acoustic Imaging techniques, such as beamforming or near Acoustical holography, are now widely used in engineering contexts. However, large arrays of microphones are sometimes required to have a good resolution. Besides new challenges arise, particularly in the field of non stationary sources, which need to be identified and solved. Cyclostationary sound sources, a specific kind of non stationary signals, are characterized by statistical properties evolving periodically in time. In practice, the first-order statistical properties contain some periodic components while the second orders may be random with a periodic flow of energy. The present work tackles the Acoustic Imaging of cyclostationary sources with a scanning microphone, i.e., without any array. Cylindrical surfaces, adapted to standard rotating machines, are considered. The reconstruction difficulty of Acoustic sources from discrete measurements is addressed here thanks to the cyclostationary properties. A cyclic sound field is hence extracted from the discrete measurements. Finally, a Bayesian formulation, gathering both physical and probabilistic information on this inverse problem, is used to back propagate the sound over the radiating surface.
Ning Chu - One of the best experts on this subject based on the ideXlab platform.
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Convolution Models with Shift-invariant kernel based on Matlab-GPU platform for Fast Acoustic Imaging
2014Co-Authors: Ning Chu, Nicolas Gac, José Picheral, Ali Mohammad-djafariAbstract:Acoustic Imaging is an advanced technique for Acoustic source localization and power reconstruc-tion from limited noisy measurements at microphone sensors. This technique not only involves in a forward model of Acoustic propagation from sources to sensors, but also its numerical solution of an ill-posed inverse problem. Nowadays, the Bayesian inference methods in inverse methods have been widely investigated for robust Acoustic Imaging, but most of Bayesian methods are time-consuming, and one of the reasons is that the forward model causes heavy matrix multiplication. In this paper, we focus on the acceleration of the forward model by using a 2D-invariant convo-lution and a separable convolution respectively; For hardware acceleration, the Matlab-Graphics Processing Unit application are discussed. For method validation, we use the simulated and real data from the wind tunnel experiment in automobile industry.
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A hierarchical variational Bayesian approximation approach in Acoustic Imaging
2014Co-Authors: Ning Chu, Nicolas Gac, Ali Mohammad-djafari, José PicheralAbstract:Acoustic Imaging is a powerful technique for Acoustic source localization and power reconstruction from limited noisy measurements at microphone sensors. But it inevitably con-fronts a very ill-posed inverse problem which causes unexpected solution uncertainty. Recently, the Bayesian inference methods using sparse priors have been effectively investigated. In this paper, we propose to use a hierarchical variational Bayesian approximation for robust Acoustic Imaging. And we explore the Student-t priors with heavy tails to enforce source sparsity, and to model non-Gaussian noise respectively. Compared to conventional methods, the proposed approach can achieve the higher spatial resolution and wider dynamic range of source powers for real data from automo-bile wind tunnel.
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A variational Bayesian approximation approach via a sparsity enforcing prior in Acoustic Imaging
2014Co-Authors: Ning Chu, Nicolas Gac, Ali Mohammad-djafari, José PicheralAbstract:Acoustic Imaging is an advanced technique for Acoustic source localization and power reconstruction from limited noisy measurements at microphone sensors. To solve this ill-posed inverse problem, the Bayesian inference methods using proper prior knowledge have been widely investigated. In this paper, we propose to use a hierarchical Variational Bayesian Approximation for the robust Acoustic Imaging. And we explore the Student's-t priors with heavy tails to enforce source sparsity and non-Gaussian noises, so that we can achieve the super spatial resolution and wide dynamic range of source powers. In addition, proposed approach is validated by simulations and real data from wind tunnel in automobile industry.
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2D convolution model using (in)variant kernels for fast Acoustic Imaging
2014Co-Authors: Ning Chu, Nicolas Gac, José Picheral, Ali Mohammad-djafariAbstract:Acoustic Imaging is an advanced technique for Acoustic source localization and power reconstruction using limited measurements at microphone sensors. The Acoustic Imaging methods often involve in two aspects: one is to build up a forward model of Acoustic power propagation which requires tremendous matrix multiplications due to large dimension of the power propagation matrix; the other is to solve an inverse problem which is usually ill-posed and time consuming. In this paper, our main contribution is to propose to use 2D convolution model for fast Acoustic Imaging. We find out that power propagation ma-trix seems to be a quasi-Symmetric Toeplitz Block Toeplitz (STBT) matrix in the far-field condition, so that the (in)variant convolution kernels (sizes and values) can be well derived from this STBT matrix. For method validation, we use simulated and real data from the wind tunnel S2A (France) experiment for Acoustic Imaging on vehicle surface.
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A robust super-resolution approach with sparsity constraint in Acoustic Imaging
Applied Acoustics, 2014Co-Authors: Ning Chu, José Picheral, Ali Mohammad-djafari, Nicolas GacAbstract:Acoustic Imaging is a standard technique for mapping Acoustic source powers and positions from limited observations on microphone sensors, which often causes an ill-conditioned inverse problem. In this article, we firstly improve the forward model of Acoustic power propagation by considering background noises at the sensor array, and the propagation uncertainty caused by wind tunnel effects. We then propose a robust super-resolution approach via sparsity constraint for Acoustic Imaging in strong background noises. The sparsity parameter is adaptively derived from the sparse distribution of source powers. The proposed approach can jointly reconstruct source powers and positions, as well as the background noise power. Our approach is compared with the conventional beamforming, deconvolution and sparse regularization methods by simulated, wind tunnel data and hybrid data respectively. It is feasible to apply the proposed approach for effectively mapping monopole sources in wind tunnel tests.
José Picheral - One of the best experts on this subject based on the ideXlab platform.
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Convolution Models with Shift-invariant kernel based on Matlab-GPU platform for Fast Acoustic Imaging
2014Co-Authors: Ning Chu, Nicolas Gac, José Picheral, Ali Mohammad-djafariAbstract:Acoustic Imaging is an advanced technique for Acoustic source localization and power reconstruc-tion from limited noisy measurements at microphone sensors. This technique not only involves in a forward model of Acoustic propagation from sources to sensors, but also its numerical solution of an ill-posed inverse problem. Nowadays, the Bayesian inference methods in inverse methods have been widely investigated for robust Acoustic Imaging, but most of Bayesian methods are time-consuming, and one of the reasons is that the forward model causes heavy matrix multiplication. In this paper, we focus on the acceleration of the forward model by using a 2D-invariant convo-lution and a separable convolution respectively; For hardware acceleration, the Matlab-Graphics Processing Unit application are discussed. For method validation, we use the simulated and real data from the wind tunnel experiment in automobile industry.
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A hierarchical variational Bayesian approximation approach in Acoustic Imaging
2014Co-Authors: Ning Chu, Nicolas Gac, Ali Mohammad-djafari, José PicheralAbstract:Acoustic Imaging is a powerful technique for Acoustic source localization and power reconstruction from limited noisy measurements at microphone sensors. But it inevitably con-fronts a very ill-posed inverse problem which causes unexpected solution uncertainty. Recently, the Bayesian inference methods using sparse priors have been effectively investigated. In this paper, we propose to use a hierarchical variational Bayesian approximation for robust Acoustic Imaging. And we explore the Student-t priors with heavy tails to enforce source sparsity, and to model non-Gaussian noise respectively. Compared to conventional methods, the proposed approach can achieve the higher spatial resolution and wider dynamic range of source powers for real data from automo-bile wind tunnel.
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A variational Bayesian approximation approach via a sparsity enforcing prior in Acoustic Imaging
2014Co-Authors: Ning Chu, Nicolas Gac, Ali Mohammad-djafari, José PicheralAbstract:Acoustic Imaging is an advanced technique for Acoustic source localization and power reconstruction from limited noisy measurements at microphone sensors. To solve this ill-posed inverse problem, the Bayesian inference methods using proper prior knowledge have been widely investigated. In this paper, we propose to use a hierarchical Variational Bayesian Approximation for the robust Acoustic Imaging. And we explore the Student's-t priors with heavy tails to enforce source sparsity and non-Gaussian noises, so that we can achieve the super spatial resolution and wide dynamic range of source powers. In addition, proposed approach is validated by simulations and real data from wind tunnel in automobile industry.
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2D convolution model using (in)variant kernels for fast Acoustic Imaging
2014Co-Authors: Ning Chu, Nicolas Gac, José Picheral, Ali Mohammad-djafariAbstract:Acoustic Imaging is an advanced technique for Acoustic source localization and power reconstruction using limited measurements at microphone sensors. The Acoustic Imaging methods often involve in two aspects: one is to build up a forward model of Acoustic power propagation which requires tremendous matrix multiplications due to large dimension of the power propagation matrix; the other is to solve an inverse problem which is usually ill-posed and time consuming. In this paper, our main contribution is to propose to use 2D convolution model for fast Acoustic Imaging. We find out that power propagation ma-trix seems to be a quasi-Symmetric Toeplitz Block Toeplitz (STBT) matrix in the far-field condition, so that the (in)variant convolution kernels (sizes and values) can be well derived from this STBT matrix. For method validation, we use simulated and real data from the wind tunnel S2A (France) experiment for Acoustic Imaging on vehicle surface.
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A robust super-resolution approach with sparsity constraint in Acoustic Imaging
Applied Acoustics, 2014Co-Authors: Ning Chu, José Picheral, Ali Mohammad-djafari, Nicolas GacAbstract:Acoustic Imaging is a standard technique for mapping Acoustic source powers and positions from limited observations on microphone sensors, which often causes an ill-conditioned inverse problem. In this article, we firstly improve the forward model of Acoustic power propagation by considering background noises at the sensor array, and the propagation uncertainty caused by wind tunnel effects. We then propose a robust super-resolution approach via sparsity constraint for Acoustic Imaging in strong background noises. The sparsity parameter is adaptively derived from the sparse distribution of source powers. The proposed approach can jointly reconstruct source powers and positions, as well as the background noise power. Our approach is compared with the conventional beamforming, deconvolution and sparse regularization methods by simulated, wind tunnel data and hybrid data respectively. It is feasible to apply the proposed approach for effectively mapping monopole sources in wind tunnel tests.