X Radu

Catholic University of Louvain, Walloon Region, Belgium

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Publications (12)0.73 Total impact

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    ABSTRACT: This paper shows, numerically and experimentally, that imaging is realizable with a strongly curved wire medium. In a first part, simulation results obtained for various curvatures are presented and sub-wavelength imaging on a wide bandwidth is demonstrated. It is also shown that the collimation phenomenon remains very effective for structures having a cross-section corresponding to about a hundredth of the wavelength. In a second part, experimental results are shown for transmission of a medical image through a 63° curved wire medium in which the receiving antenna has been inserted.
    Metamaterials. 01/2009;
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    ABSTRACT: This article analyzes the collimation behavior of a wire medium devoted to magnetic resonance imaging. In the first part, the point-spread function of a doubly infinite wire medium is analyzed for the magnetic field with the help of the array scanning method. In the second part, we present two methods to evaluate the field transmission by the wire medium based on the measure of the magnetic field computed with the method of moments. Simulation results obtained with the MoM are shown. This behavior is validated in the third part with experimental results obtained with a magnetic resonance imaging instrument at the University Hospital of Liége with a straight-wires collimator. Both simulation and experimental results confirm the ability of the wire medium to transfer electromagnetic fields in magnetic resonance imaging operational conditions.
    Electromagnetics 01/2008; 28(7):531-543. · 0.73 Impact Factor
  • Proceedings of the Metamaterial 2007 Conference; 10/2007
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    ABSTRACT: This paper presents an analysis and experimental results for a channeling wire medium. In order to validate the behavior of wire media lens, an experiment has been driven in medical context. A straight wires lens designed to work at magnetic resonance imaging frequency (123 MHZ for 3T magnetic field) is designed and tested. Results are very positive, since the lens allows to transmit images without deformation. The influence of the geometry of the lens, and on the image canalization, is studied. For various geometries, the lens is able to transmit images and concentrate fields.
    Antennas and Propagation Society International Symposium, 2007 IEEE; 07/2007
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    Xavier Radu, Christophe Craeye
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    ABSTRACT: A key point to obtain accurate results with macro basis functions (MBF) is the choice of the size basis and the method used to create it. In this paper, a new method to compute rapidly a reliable basis is presented. Comparisons of the current distributions obtained with MBF, using various methods for the creation of the basis, or with full resolution simulations are shown. The proposed method is fast and leads to more accurate results than other methods, especially for large-scale problems with connected unit cells. A physical explanation is provided. Keyword: Method of moment, Macro basis functions, basis creation.
    01/2007;
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    ABSTRACT: In this paper we show how loop wire medium can allow to tune the index of refraction of metamaterial. The principle and a equivalent circuit is presented in a first time. Then in order to show the influence of their geometric parameters on the plasma frequency, simulations of loop wire medium with a program based on method of moment (MoM) are driven. Comparison with classical wire medium show a decrease of the plasma frequency. In a second step, simulations of loop wire medium combined with a negative permeability structure are carried out, to show their influence on the negative index of refraction: extraction of the negative index of refraction shows a decrease in the presence of medium with high inductance.
    Antennas and Propagation, 2006. EuCAP 2006. First European Conference on; 12/2006
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    ABSTRACT: Wire medium has the ability to manipulate the near-field of an electromagnetic source. The objective of the pre-sent paper is to demonstrate numerically and experimentally that a wire medium can be used to enhance the ho-mogeneity of RF field in 7 Tesla magnetic resonance imaging.
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    X Radu, C Craeye
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    ABSTRACT: This paper shows, numerically and experimentally, that imaging is realizable with a curved wire-medium, with curvature up to 90 • . In a first part, simulation results obtained for various curvatures are shown and sub-wavelength imaging on a wide bandwidth is demonstrated. In a second part, transmission of a medical image through a 63 • curved wire-medium is presented.
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    X Radu, C Craeye
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    ABSTRACT: 1) xavier.radu, (2) christophe.craeye, (3) isabelle.huynen @uclouvain.be Abstract An adaptation of the macro basis function method (MBF) for large scale metamaterial analysis is presented. Anal-ysis of large scale finite metamaterials is important to determine truncation and coupling between antennas and material. The modified MBF method exploits the periodic structure of the metamaterial, and use each cell of SRR and its associated wire, as a new kind of basis function. By solving a small-scale metamaterial and extracting its solutions for each unit cell, the method of moment (MoM) system of equations for the large metamaterial can be simplified and its solution accelerated. The proposed algorithm, for which a very simple formulation is proposed, is easy to implement, and is more efficient in computational complexity and memory requirement, than the MoM taken alone. Numerical results are given to check the validity and efficiency of the proposed method. Excellent agreements with brute-force solution are shown and left handed phenomena are observed for a 3 × 8 × 5 cell material.
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    ABSTRACT: This paper analyses the collimation behavior of a wire medium devoted to magnetic resonance imaging. In a first part, the point spread function of a doubly infinite wire medium is analyzed for the magnetic field with the help of the Array Scanning Method. In a second part, we present two methods to evaluate the field transmission by the wire medium, based on the measure of the magnetic field computed with the Method of Moments. Simulation results obtained with the Method of Moments are shown. This behavior is validated, in a third part, with experimental results obtained with Magnetic Resonance Imaging (MRI) instrument at the University Hospital ofLì ege with a straight-wires collimator. Both simulation and experimental results confirm the ability of the wire medium to transfer EM fields in MRI operational conditions.
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    X Radu, X Dardenne, C Craeye
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    ABSTRACT: In a first part, we present an efficient numerical analysis of a wire medium lens using the Array Scanning Method (ASM) and its interest to compute the structure's point spread function. In a second part, we simulate realistic canalization effects with a wire medium lens, and with a magnetic source placed in a dielectric. Both simulation results confirm the capacity of the medium to canalize images even in the presence of dielectric material.
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    ABSTRACT: CONCLUSION Why use wire medium in MRI ? Metamaterials are materials which, in some frequency bands, enable to manipulate the near-field generated by an electromagnetic source. In the present paper, we propose to use this property to create new devices to facilitate the manipulation of RF transmit and receive field in MRI. The metamaterials structure considered here was initially proposed by Belov et al. [1] and is made of an array of parallel copper wires forming a Fabry-Perot resonator. The properties of the structure are investigated both numerically and experimentally. It is shown how it can beused to create a flexible transmit configuration to excite particular regions with good homogeneity Wire medium properties ABSTRACT A WM offers the possibility to collimate and transfer transmit and receive fields from a source to more distant locations. It can support eigenmodes which could be used to obtain various excitation patterns. Applications include endoscopic transmit-receive devices based on the WM principle and the opportunity to create a flexible transmit configuration to excite particular regions with good homogeneity.