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Surface Impedance (surface + impedance)

Distribution by Scientific Domains
Engineering40%

Selected Abstracts

Label-Free Impedance Biosensors: Opportunities and Challenges

ELECTROANALYSIS, Issue 12 2007
Jonathan
Abstract Impedance biosensors are a class of electrical biosensors that show promise for point-of-care and other applications due to low cost, ease of miniaturization, and label-free operation. Unlabeled DNA and protein targets can be detected by monitoring changes in surface impedance when a target molecule binds to an immobilized probe. The affinity capture step leads to challenges shared by all label-free affinity biosensors; these challenges are discussed along with others unique to impedance readout. Various possible mechanisms for impedance change upon target binding are discussed. We critically summarize accomplishments of past label-free impedance biosensors and identify areas for future research. [source]

Analysis of microwave circuits including lumped elements based on the iterative method

INTERNATIONAL JOURNAL OF RF AND MICROWAVE COMPUTER-AIDED ENGINEERING, Issue 4 2003
H. Trabelsi
Abstract The work presented here introduces lumped elements to an iterative method based on the wave concept combined with the two-dimentional fast Fourrier transformation algorithm known as fast modal transformation (FMT). We extend this method to the analysis of microwave-distributed circuits containing passive or active, linear or nonlinear lumped elements which are characterized by their surface impedance as defined in this article. Simulation results of varactor-tuned filter and phase-shifter circuit examples are compared with the measurement results. Good agreement between simulated and experimental results validates the use of the iterative method for the analysis of planar circuits, including lumped elements. © 2003 Wiley Periodicals, Inc. Int J RF and Microwave CAE 13: 269,275, 2003. [source]

Reconstruction of cracks of different types from far-field measurements

MATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 8 2010
Jijun Liu
Abstract In this paper, we deal with the acoustic inverse scattering problem for reconstructing cracks of possibly different types from the far-field map. The scattering problem models the diffraction of waves by thin two-sided cylindrical screens. The cracks are characterized by their shapes, the type of boundary conditions and the boundary coefficients (surface impedance). We give explicit formulas of the indicator function of the probe method, which can be used to reconstruct the shape of the cracks, distinguish their types of boundary conditions, the two faces of each of them and reconstruct the possible material coefficients on them by using the far-field map. To test the validity of these formulas, we present some numerical implementations for a single crack, which show the efficiency of the proposed method for suitably distributed surface impedances. The difficulties for numerically recovering the properties of the crack in the concave side as well as near the tips are presented and some explanations are given. Copyright © 2009 John Wiley & Sons, Ltd. [source]

New low profile cavity-backed Hilbert slot antenna

MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 12 2006
Guido Biffi Gentili
Abstract In this paper, the use of a cavity-backed Hilbert surface as an efficient slot-like narrowband radiating aperture is suggested, to exploit its own unique electromagnetic characteristics in the context of radio frequency identification (RFID) applications. The proposed meta-slot antenna (MSA) consists of a Hilbert surface window (HSW) made of a cascade of space-filling slot inclusions of order three and backed by a very shallow cavity that contributes to its surface impedance and radiation characteristics. A straight longitudinal microstrip line printed on a thin, low permittivity substrate, whose ground plane includes the HSW, feeds the aperture through distributed electromagnetic coupling. As illustrated by simulation results and measurements, the antenna behaves as a magnetic current sheet over a ground plane, with a highly frequency-selective impedance response and unidirectional radiation pattern. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 2577,2581, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21995 [source]

Reconstruction of cracks of different types from far-field measurements

MATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 8 2010
Jijun Liu
Abstract In this paper, we deal with the acoustic inverse scattering problem for reconstructing cracks of possibly different types from the far-field map. The scattering problem models the diffraction of waves by thin two-sided cylindrical screens. The cracks are characterized by their shapes, the type of boundary conditions and the boundary coefficients (surface impedance). We give explicit formulas of the indicator function of the probe method, which can be used to reconstruct the shape of the cracks, distinguish their types of boundary conditions, the two faces of each of them and reconstruct the possible material coefficients on them by using the far-field map. To test the validity of these formulas, we present some numerical implementations for a single crack, which show the efficiency of the proposed method for suitably distributed surface impedances. The difficulties for numerically recovering the properties of the crack in the concave side as well as near the tips are presented and some explanations are given. Copyright © 2009 John Wiley & Sons, Ltd. [source]