The Experts below are selected from a list of 240 Experts worldwide ranked by ideXlab platform
J.c. Gallop - One of the best experts on this subject based on the ideXlab platform.
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Spatially resolved measurements of HTS microwave Surface Impedance
IEEE Transactions on Appiled Superconductivity, 1999Co-Authors: L. Hao, J.c. GallopAbstract:We describe further development of a novel technique for the characterization of microwave properties of HTS films which allows the spatial variation of this important physical parameter to be measured. The method employs a dielectric puck system that can be moved over the Surface of a large HTS wafer, sampling the Surface Impedance at a number of discrete frequencies between 5 and 15 GHz. The Surface Impedance can also be rapidly measured as a function of microwave magnetic field strength. Spatial resolution for the prototype system is as small as 1-2 mm. The Surface resistance and the shift in Surface reactance can be measured by using a loop oscillator which can be interrupted by a fast microwave switch. The decay of microwave power in the resonator is then monitored as a function of time to determine the power dependent Surface Impedance parameters. This process is extremely fast and straightforward and the loop oscillator configuration permits only relatively inexpensive components to be used. We describe measurements made at 11.5 GHz of the spatial variation of the non-linear Surface Impedance of a number of HTS films at 77 K.
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Characterization of microwave Surface Impedance of high temperature superconductors
Superconductor Science and Technology, 1991Co-Authors: J.c. Gallop, W J RadcliffeAbstract:This paper describes the various methods used to characterize the microwave Surface Impedance of high temperature superconductors.
Ghulam Murtaza - One of the best experts on this subject based on the ideXlab platform.
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Surface Impedance and skin depth for transverse waves in temperature anisotropic unmagnetized plasma
Physics of Plasmas, 2019Co-Authors: Aman-ur-rehman, Tajammal H. Khokhar, H. A. Shah, Ghulam MurtazaAbstract:The anomalous skin depth has been calculated using the Surface Impedance for the transverse waves in unmagnetized plasma. The effect of temperature anisotropy on the Surface Impedance and the anomalous skin effect have been studied using the kinetic model for an electromagnetic wave normally impinging on a plasma Surface filling the half space z > 0. It is noted that the maximum value of the real part of the Surface Impedance occurs when ω ω pe = π 8 v t | | c T ⊥ T | |. The imaginary part, however, is not affected by the temperature anisotropy parameter significantly. It has been found that in the case of anisotropic plasma, the skin depth varies as ω−1 in the low frequency regime which is different from isotropic plasma where the skin depth varies as ω−1/3. In the low frequency regime, the skin depth first increases with the temperature anisotropy and then starts decreasing with an increase in the temperature anisotropy parameter η. However, in the large frequency regime, the skin depth is inversely proportional to the temperature anisotropy parameter η. These results have been confirmed by numerically plotting the Surface Impedance and the skin depth for a wide range of plasma parameters.The anomalous skin depth has been calculated using the Surface Impedance for the transverse waves in unmagnetized plasma. The effect of temperature anisotropy on the Surface Impedance and the anomalous skin effect have been studied using the kinetic model for an electromagnetic wave normally impinging on a plasma Surface filling the half space z > 0. It is noted that the maximum value of the real part of the Surface Impedance occurs when ω ω pe = π 8 v t | | c T ⊥ T | |. The imaginary part, however, is not affected by the temperature anisotropy parameter significantly. It has been found that in the case of anisotropic plasma, the skin depth varies as ω−1 in the low frequency regime which is different from isotropic plasma where the skin depth varies as ω−1/3. In the low frequency regime, the skin depth first increases with the temperature anisotropy and then starts decreasing with an increase in the temperature anisotropy parameter η. However, in the large frequency regime, the ski...
Nongjian Tao - One of the best experts on this subject based on the ideXlab platform.
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Surface Impedance imaging technique.
Analytical chemistry, 2008Co-Authors: Kyle J. Foley, Xiaonan Shan, Nongjian TaoAbstract:We demonstrate here a Surface Impedance imaging technique based on sensitive dependence of Surface plasmon resonance (SPR) on local Surface charge density. By applying a potential modulation to a sensor Surface, we are able to simultaneously obtain three images: the dc component and the amplitude and phase of the ac component. The dc image measures local molecular binding activity on the Surface, as found in the conventional SPR imaging technique, and the ac images are directly related to the local Impedance of the Surface. Our experimental data can be analyzed quantitatively in terms of the simple free electron gas model for the sensor Surface and the Randles equivalent circuit model for interfacial Impedance.
M. L. O’malley - One of the best experts on this subject based on the ideXlab platform.
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Terahertz Surface Impedance of thin YBa2Cu3O7 superconducting films
Applied Physics Letters, 1991Co-Authors: Martin C. Nuss, Keith W. Goossen, P. M. Mankiewich, M. L. O’malleyAbstract:Using coherent terahertz time‐domain spectroscopy, we measure the Surface Impedance of 500‐A‐thick unpatterned superconducting YBa2Cu3O7 films in the normal and the superconducting state. Both real and imaginary parts of the Surface Impedance are measured simultaneously from the amplitude and phase changes of the terahertz bandwidth pulses transmitted through the superconducting films.
David V. Thiel - One of the best experts on this subject based on the ideXlab platform.
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Transient Surface Impedance measurements using spherics — Source identification and characterisation
2010 International Conference on Electromagnetics in Advanced Applications, 2010Co-Authors: David V. Thiel, Gavin T. MogensenAbstract:Transient recordings of the electric and magnetic fields over the audio-band display significant transient pulses (spherics) which can be used for Surface Impedance measurements providing the lighting strike is distant and predominantly vertical. Horizontal lighting strikes, other atmospheric noise and instrument noise creates incorrect Surface Impedance data. Automated spheric selection can be made by calculating the sliding window correlation coefficient, and observing a period of elevated values followed by a rapid transition to a negative value. Data selected in this manner yield coherent Surface Impedance values.
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conductivity and resistivity tensor rotation for Surface Impedance modeling of an anisotropic half space
Radio Science, 2002Co-Authors: Glenn A. Wilson, David V. ThielAbstract:[1] The electromagnetic Surface Impedance of a half-space with inclined conductivity anisotropy can be derived from the isotropic half-space solution provided the conductivity term used in the expressions is the effective horizontal conductivity. For a TM-mode plane wave incidence, the effective horizontal conductivity must be derived from the tensor rotation of the resistivity tensor and not from the tensor rotation of the conductivity tensor. For a TE-mode incident with the same geometry as the TM-mode, the Surface Impedance is independent upon the inclined anisotropy. This same formulation can then be extended to a multiple layered half-space where each layer has an inclined anisotropy. For an anisotropic half-space with coefficient of anisotropy of 4, with a horizontal conductivity of 0.001 S/m inclined at 45° with respect to the horizontal plane, the magnitude of the Surface Impedance calculated using the resistivity tensor rotation is approximately 53% larger than the magnitude of the Surface Impedance calculated using the conductivity tensor rotation.
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Forward and inverse modelling methods for electromagnetic Surface Impedance
ASEG Extended Abstracts, 2001Co-Authors: David V. Thiel, Daniel Arthur James, Glenn A. WilsonAbstract:Low frequency computer modelling of the Surface Impedance response of subSurface structures is time intensive. Consequently automated three-dimensional inversion remains unrealistic. In this paper, a Genetic Algorithm least squares minimization routine was applied to a one-dimension model and results used to seed two-dimensional Surface Impedance data. The Impedance (IM) method is shown to be an efficient numerical solution engine in the inversion method.
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Eddy current modelling using the Impedance method for Surface Impedance profiling
IEEE Transactions on Magnetics, 1999Co-Authors: Daniel Arthur James, Steven Gregory O'keefe, David V. ThielAbstract:In this paper a new technique for determining Surface Impedance is developed. The technique is derived from an eddy current modelling technique, the Impedance method. Considerable extension and development of the Impedance method has been undertaken, enabling the prediction of Surface Impedance measurements for horizontally stratified media and in the vicinity of vertical dislocations. The method is compared with Surface Impedance theory for horizontally stratified media and with field based results near laterally discontinuous structures.
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Surface Impedance time domain reflectometry for the determination of ice depth
Geophysical Research Letters, 1997Co-Authors: Stephen J. Garner, David V. Thiel, Steven Gregory O'keefeAbstract:The analysis of the Surface Impedance of a horizontally stratified earth is similar to the Impedance of a step-wise discontinuous lossy transmission line. Time Domain Reflectometry (TDR) is commonly used in transmission line assessment to determine the location of faults. There are electrical conditions where TDR can be applied to a two layered subSurface to determine the time of flight of the EM wave and hence the thickness of the top layer. When the upper layer resistivity is sufficiently contrasted over a conductive second layer, then transforming Surface Impedance data measured across a broad band of frequencies into the time domain allows one to determine the time of flight to the subSurface boundary. If the maximum frequency, frequency step size and number of steps are optimised for the two layers a periodicity appears in the Surface Impedance profile. It is demonstrated through computer modelling that a layer of ice on rock or sea water gives a return time of flight equal to the separation time of peaks in the time domain Surface Impedance profile. The technique requires a vertically polarised transmitter which steps up to the high frequency (HF) range. For example an ice layer of 30 to 400 meters thickness requires frequencies up to 5MHz. In this paper, the basic theory for the use of TDR techniques in the interpretation of the Surface Impedance data is explained, and computer modelling results are presented
