The Experts below are selected from a list of 27 Experts worldwide ranked by ideXlab platform
C M Soukoulis - One of the best experts on this subject based on the ideXlab platform.
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reply to comments on resonant and Antiresonant Frequency dependence of the effective parameters of metamaterials
Physical Review E, 2004Co-Authors: T Koschny, Peter Markos, David R Smith, C M SoukoulisAbstract:We argue, in agreement with our previous work, that periodicity of the metamaterial is responsible for Antiresonant behavior of the effective permittivity as well as for the negative sign of the imaginary part of an effective permittivity or permeability. This agrees with the Comment of Efros.
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resonant and Antiresonant Frequency dependence of the effective parameters of metamaterials
Physical Review E, 2003Co-Authors: T Koschny, Peter Markos, David R Smith, C M SoukoulisAbstract:We present a numerical study of the electromagnetic response of the metamaterial elements that are used to construct materials with negative refractive index. For an array of split ring resonators (SRR) we find that the resonant behavior of the effective magnetic permeability is accompanied by an Antiresonant behavior of the effective permittivity. In addition, the imaginary parts of the effective permittivity and permeability are opposite in sign. We also observe an identical resonant versus Antiresonant Frequency dependence of the effective materials parameters for a periodic array of thin metallic wires with cuts placed periodically along the length of the wire, with roles of the permittivity and permeability reversed from the SRR case. We show in a simple manner that the finite unit cell size is responsible for the Antiresonant behavior.
T Koschny - One of the best experts on this subject based on the ideXlab platform.
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reply to comments on resonant and Antiresonant Frequency dependence of the effective parameters of metamaterials
Physical Review E, 2004Co-Authors: T Koschny, Peter Markos, David R Smith, C M SoukoulisAbstract:We argue, in agreement with our previous work, that periodicity of the metamaterial is responsible for Antiresonant behavior of the effective permittivity as well as for the negative sign of the imaginary part of an effective permittivity or permeability. This agrees with the Comment of Efros.
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resonant and Antiresonant Frequency dependence of the effective parameters of metamaterials
Physical Review E, 2003Co-Authors: T Koschny, Peter Markos, David R Smith, C M SoukoulisAbstract:We present a numerical study of the electromagnetic response of the metamaterial elements that are used to construct materials with negative refractive index. For an array of split ring resonators (SRR) we find that the resonant behavior of the effective magnetic permeability is accompanied by an Antiresonant behavior of the effective permittivity. In addition, the imaginary parts of the effective permittivity and permeability are opposite in sign. We also observe an identical resonant versus Antiresonant Frequency dependence of the effective materials parameters for a periodic array of thin metallic wires with cuts placed periodically along the length of the wire, with roles of the permittivity and permeability reversed from the SRR case. We show in a simple manner that the finite unit cell size is responsible for the Antiresonant behavior.
Antonino Morassi - One of the best experts on this subject based on the ideXlab platform.
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identification of two cracks in a rod by minimal resonant and Antiresonant Frequency data
Mechanical Systems and Signal Processing, 2015Co-Authors: L Rubio, J Fernandezsaez, Antonino MorassiAbstract:Abstract In this paper we consider the identification of two cracks of equal severity in a uniform free–free rod under longitudinal vibration. Each crack is simulated by a translational spring connecting the two adjacent segments of the rod and the cracks are considered to be small. We show that the inverse problem can be formulated and solved in terms of three Frequency data only, corresponding to a suitable set of low resonant and Antiresonant frequencies. Closed-form expressions of the damage parameters in terms of the measured Frequency shifts are obtained. The paper improves existing results available in the literature, since the use of Antiresonant frequencies allows us to exclude all the symmetrical crack locations occurring when only natural Frequency are used as data. The analysis also explains why the use of high Frequency data introduces spurious damage locations in the inverse problem solution. Numerical simulations show that if accurate input data are available then damage identification leads to satisfactory results.
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reconstruction method for damage detection in beams based on natural Frequency and Antiresonant Frequency measurements
Journal of Engineering Mechanics-asce, 2010Co-Authors: Michele Dilena, Antonino MorassiAbstract:This paper deals with a dynamic method for damage detection in beams. Under the assumption that the damaged beam is a perturbation of the undamaged one, it is shown that natural Frequency and Antiresonant Frequency shifts induced by structural damage contain information on certain generalized Fourier coefficients of the stiffness variation caused by the degradation. A reconstruction method based on this property is proposed to solve the inverse problem. Cases with pseudoexperimental and experimental data are discussed. The results are in good agreement with the theory, provided that average Frequency and Antiresonant Frequency shifts are bigger than modeling/measurement errors.
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structural health monitoring of rods based on natural Frequency and Antiresonant Frequency measurements
Structural Health Monitoring-an International Journal, 2009Co-Authors: Michele Dilena, Antonino MorassiAbstract:In this paper it is shown that natural Frequency and Antiresonant Frequency shifts induced by a structural damage in an axially vibrating rod contain information on certain generalized Fourier coefficients of the stiffness variation caused by the degradation. This property is used to define a reconstruction procedure based on iterative updating of the undamaged configuration. The results of numerical simulations on rods with localized or diffuse damages are in good agreement with the theory, provided that average Frequency and Antiresonant Frequency shifts due to degradation are bigger than the shifts due to modeling/measurement errors. Experimental results obtained on cracked steel rods showed that, in the inverse problem solution, noise and modeling errors on antiresonances are usually amplified strongly with respect to cases in which natural Frequency data is used.
Peter Markos - One of the best experts on this subject based on the ideXlab platform.
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reply to comments on resonant and Antiresonant Frequency dependence of the effective parameters of metamaterials
Physical Review E, 2004Co-Authors: T Koschny, Peter Markos, David R Smith, C M SoukoulisAbstract:We argue, in agreement with our previous work, that periodicity of the metamaterial is responsible for Antiresonant behavior of the effective permittivity as well as for the negative sign of the imaginary part of an effective permittivity or permeability. This agrees with the Comment of Efros.
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resonant and Antiresonant Frequency dependence of the effective parameters of metamaterials
Physical Review E, 2003Co-Authors: T Koschny, Peter Markos, David R Smith, C M SoukoulisAbstract:We present a numerical study of the electromagnetic response of the metamaterial elements that are used to construct materials with negative refractive index. For an array of split ring resonators (SRR) we find that the resonant behavior of the effective magnetic permeability is accompanied by an Antiresonant behavior of the effective permittivity. In addition, the imaginary parts of the effective permittivity and permeability are opposite in sign. We also observe an identical resonant versus Antiresonant Frequency dependence of the effective materials parameters for a periodic array of thin metallic wires with cuts placed periodically along the length of the wire, with roles of the permittivity and permeability reversed from the SRR case. We show in a simple manner that the finite unit cell size is responsible for the Antiresonant behavior.
S R Best - One of the best experts on this subject based on the ideXlab platform.
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impedance bandwidth and q of antennas
IEEE Transactions on Antennas and Propagation, 2005Co-Authors: Arthur D Yaghjian, S R BestAbstract:To address the need for fundamental universally valid definitions of exact bandwidth and quality factor (Q) of tuned antennas, as well as the need for efficient accurate approximate formulas for computing this bandwidth and Q, exact and approximate expressions are found for the bandwidth and Q of a general single-feed (one-port) lossy or lossless linear antenna tuned to resonance or antiresonance. The approximate expression derived for the exact bandwidth of a tuned antenna differs from previous approximate expressions in that it is inversely proportional to the magnitude |Z'/sub 0/(/spl omega//sub 0/)| of the Frequency derivative of the input impedance and, for not too large a bandwidth, it is nearly equal to the exact bandwidth of the tuned antenna at every Frequency /spl omega//sub 0/, that is, throughout Antiresonant as well as resonant Frequency bands. It is also shown that an appropriately defined exact Q of a tuned lossy or lossless antenna is approximately proportional to |Z'/sub 0/(/spl omega//sub 0/)| and thus this Q is approximately inversely proportional to the bandwidth (for not too large a bandwidth) of a simply tuned antenna at all frequencies. The exact Q of a tuned antenna is defined in terms of average internal energies that emerge naturally from Maxwell's equations applied to the tuned antenna. These internal energies, which are similar but not identical to previously defined quality-factor energies, and the associated Q are proven to increase without bound as the size of an antenna is decreased. Numerical solutions to thin straight-wire and wire-loop lossy and lossless antennas, as well as to a Yagi antenna and a straight-wire antenna embedded in a lossy dispersive dielectric, confirm the accuracy of the approximate expressions and the inverse relationship between the defined bandwidth and the defined Q over Frequency ranges that cover several resonant and Antiresonant Frequency bands.
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impedance bandwidth and q of antennas
IEEE Antennas and Propagation Society International Symposium, 2003Co-Authors: Arthur D Yaghjian, S R BestAbstract:The purpose of this paper is twofold: (1) to derive an approximate expression for the bandwidth of a tuned antenna in terms of its input impedance that holds at every Frequency, i.e., throughout its entire Antiresonant and resonant Frequency ranges; (2) to relate this expression for bandwidth to the antenna quality factor Q. The approximate expression for the bandwidth and its relationship to Q are both more generally applicable and more accurate than previous formulas. The validity and accuracy of the expressions are confirmed by the numerical solutions to straight-wire and wire-loop, lossy and lossless tuned antennas over a wide enough range of frequencies covering several resonant and Antiresonant Frequency bands. We show that the matched VSWR bandwidth is a more fundamental measure of bandwidth than conductance bandwidth because it exists in general for all frequencies at which an antenna is tuned. We also find that the Foster reactance theorem does not hold at all frequencies (whether or not the antenna is lossless). Although the general formula we derive for the bandwidth of an antenna involves the Frequency derivative of resistance as well as the Frequency derivative of reactance, quite remarkably, the half-power matched VSWR bandwidth of a general tuned lossy or lossless antenna is proven to approximately equal to 2/Q for all frequencies if Q/spl gsim/4.