The Experts below are selected from a list of 93 Experts worldwide ranked by ideXlab platform
R. Mittra - One of the best experts on this subject based on the ideXlab platform.
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Response to comments on "An analysis of a staked dipole probe on a lossy Earth Plane using the finite-difference time-domain method" [and reply]
IEEE Transactions on Geoscience and Remote Sensing, 1999Co-Authors: J.r. Wait, D.v. Thiel, R. MittraAbstract:The paper by D.V. Thiel and R. Mittra, IEEE Trans. Geosci. Remote Sensing, vol.35, p.1357-62 (1997) is commented upon. The present author deals with the basis of the expression for the effective complex area of a horizontal electric dipole (HED) over a layered conductive half-space. The second related item deals with a basic flaw in an estimate of the error when the HED is lifted relative to the air/Earth interface. The present author provides an additional analysis. In both cases the HED is oriented to have a maximum response.
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An analysis of a staked dipole probe on a lossy Earth Plane using the finite-difference time-domain method
IEEE Transactions on Geoscience and Remote Sensing, 1997Co-Authors: D.v. Thiel, R. MittraAbstract:Using the finite-difference time-domain (FDTD) method, an electrically short, staked, grounded horizontal probe is shown to have an open circuit voltage directly related to the horizontal electric field at the Earth's surface providing the surface coupling is subtracted from the output. This result is valid not only for an infinitely deep Earth Plane but also for one which is horizontally layered. The effective length of a staked probe is found to be dependent on the conductivity of the upper layer of the Earth, its depth, the length of the stakes, and also the frequency of measurement. The effect is significant at very low frequency (VLF) for ice, permafrost and dry sand-covered regions.
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Surface impedance modeling using the finite-difference time-domain method
IEEE Transactions on Geoscience and Remote Sensing, 1997Co-Authors: D.v. Thiel, R. MittraAbstract:The finite-difference time-domain (FDTD) technique has been used to model the one-dimensional (1D) surface impedance of a lossy Earth Plane having discontinuities in two and three dimensions. Using a horizontal magnetic field aperture source located five cells from an absorbing boundary and 35 cells above the lossy Earth Plane, the surface impedance was accurately modeled at a distance of /spl lambda//sub 0//5000 from the source using both grazing and normal incidence. The technique was validated by comparison with a number of two-dimensional (2D) analytical models. The surface impedance profile in the vicinity of a vertical conductive water filled shaft that extends from the Earth's surface to a conductive basement is presented. Unlike modeling in the frequency domain, a single FDTD solution yields accurate multi frequency surface impedance data providing a number of standard cell size constraints are met. For common Earth electrical constants, the FDTD approach is limited to frequencies above 500 Hz.
D.v. Thiel - One of the best experts on this subject based on the ideXlab platform.
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Response to comments on "An analysis of a staked dipole probe on a lossy Earth Plane using the finite-difference time-domain method" [and reply]
IEEE Transactions on Geoscience and Remote Sensing, 1999Co-Authors: J.r. Wait, D.v. Thiel, R. MittraAbstract:The paper by D.V. Thiel and R. Mittra, IEEE Trans. Geosci. Remote Sensing, vol.35, p.1357-62 (1997) is commented upon. The present author deals with the basis of the expression for the effective complex area of a horizontal electric dipole (HED) over a layered conductive half-space. The second related item deals with a basic flaw in an estimate of the error when the HED is lifted relative to the air/Earth interface. The present author provides an additional analysis. In both cases the HED is oriented to have a maximum response.
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An analysis of a staked dipole probe on a lossy Earth Plane using the finite-difference time-domain method
IEEE Transactions on Geoscience and Remote Sensing, 1997Co-Authors: D.v. Thiel, R. MittraAbstract:Using the finite-difference time-domain (FDTD) method, an electrically short, staked, grounded horizontal probe is shown to have an open circuit voltage directly related to the horizontal electric field at the Earth's surface providing the surface coupling is subtracted from the output. This result is valid not only for an infinitely deep Earth Plane but also for one which is horizontally layered. The effective length of a staked probe is found to be dependent on the conductivity of the upper layer of the Earth, its depth, the length of the stakes, and also the frequency of measurement. The effect is significant at very low frequency (VLF) for ice, permafrost and dry sand-covered regions.
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Surface impedance modeling using the finite-difference time-domain method
IEEE Transactions on Geoscience and Remote Sensing, 1997Co-Authors: D.v. Thiel, R. MittraAbstract:The finite-difference time-domain (FDTD) technique has been used to model the one-dimensional (1D) surface impedance of a lossy Earth Plane having discontinuities in two and three dimensions. Using a horizontal magnetic field aperture source located five cells from an absorbing boundary and 35 cells above the lossy Earth Plane, the surface impedance was accurately modeled at a distance of /spl lambda//sub 0//5000 from the source using both grazing and normal incidence. The technique was validated by comparison with a number of two-dimensional (2D) analytical models. The surface impedance profile in the vicinity of a vertical conductive water filled shaft that extends from the Earth's surface to a conductive basement is presented. Unlike modeling in the frequency domain, a single FDTD solution yields accurate multi frequency surface impedance data providing a number of standard cell size constraints are met. For common Earth electrical constants, the FDTD approach is limited to frequencies above 500 Hz.
G.g. Cook - One of the best experts on this subject based on the ideXlab platform.
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Screened printed monopole spiral antenna for mobile handsets
IEE Colloquium on Design of Mobile Handset Antennas for Optimal Performance in the Presence of Biological Tissue, 1997Co-Authors: G.g. Cook, S.k. Khamas, Richard EdwardsAbstract:Spiral antenna elements have been shown to have useful wide bandwidth and circular polarisation properties. A 'Curl' antenna design has been proposed in the literature where a single spiral arm parallel to and above a groundPlane is fed through this groundPlane via a single wire feed. Such an arrangement provides screening at the back of the groundPlane, and also obviates the need for a balun since the whole antenna is essentially a monopole fed against an Earth Plane, so that an unbalanced coaxial feed may be used. In this contribution the Curl antenna design has been extended to a spiral arm printed on a grounded dielectric substrate, and fed via a wire through the dielectric. In a practical deployment scenario therefore, such a spiral could be printed on the back of a phone with some suitable intervening dielectric grounded by the transceiver casing, which would provide screening of the user's head from the active element. In order to achieve wide bandwidth and good circular polarisation from this printed spiral, the current distribution along the spiral arm must be essentially that of a travelling wave, and this is dependent on parameters such as substrate permittivity and thickness, and also the spiral function and arm length. (6 pages)
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Screened printed monopole spiral antenna for mobile handsets
IEE Colloquium on Design of Mobile Handset Antennas for Optimal Performance in the Presence of Biological Tissue (Digest No. 1997 022), 1997Co-Authors: G.g. Cook, S.k. Khamas, R.m. EdwardsAbstract:Spiral antenna elements have been shown to have useful wide bandwidth and circular polarisation properties. A 'Curl' antenna design has been proposed in the literature where a single spiral arm parallel to and above a groundPlane is fed through this groundPlane via a single wire feed. Such an arrangement provides screening at the back of the groundPlane, and also obviates the need for a balun since the whole antenna is essentially a monopole fed against an Earth Plane, so that an unbalanced coaxial feed may be used. In this contribution the Curl antenna design has been extended to a spiral arm printed on a grounded dielectric substrate, and fed via a wire through the dielectric. In a practical deployment scenario therefore, such a spiral could be printed on the back of a phone with some suitable intervening dielectric grounded by the transceiver casing, which would provide screening of the user's head from the active element. In order to achieve wide bandwidth and good circular polarisation from this printed spiral, the current distribution along the spiral arm must be essentially that of a travelling wave, and this is dependent on parameters such as substrate permittivity and thickness, and also the spiral function and arm length.
J.r. Wait - One of the best experts on this subject based on the ideXlab platform.
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Scattering From a Buried Insulated Loop Excited By an Incident Electromagnetic Plane Wave
Journal of Electromagnetic Waves and Applications, 2012Co-Authors: Samir F. Mahmoud, J.r. WaitAbstract:Rigorous analysis for the electromagnetic fields scattered by a buried insulated loop in a homogeneous Earth is presented. The loop is excited by a Plane wave incident on the air-Earth Plane interface. The Fourier components of the circulating current in the loop are expressed in terms of internal and external impedances. The latter are given in integral forms that can be evaluated semi-analytically. It is shown that peaks of induced current in the loop occur at a set of frequencies which depend on the permittivity of the Earth's medium. The scattered fields in the air are found to have both co-polar and cross-polar components of comparable magnitudes.
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Response to comments on "An analysis of a staked dipole probe on a lossy Earth Plane using the finite-difference time-domain method" [and reply]
IEEE Transactions on Geoscience and Remote Sensing, 1999Co-Authors: J.r. Wait, D.v. Thiel, R. MittraAbstract:The paper by D.V. Thiel and R. Mittra, IEEE Trans. Geosci. Remote Sensing, vol.35, p.1357-62 (1997) is commented upon. The present author deals with the basis of the expression for the effective complex area of a horizontal electric dipole (HED) over a layered conductive half-space. The second related item deals with a basic flaw in an estimate of the error when the HED is lifted relative to the air/Earth interface. The present author provides an additional analysis. In both cases the HED is oriented to have a maximum response.
R.m. Edwards - One of the best experts on this subject based on the ideXlab platform.
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Screened printed monopole spiral antenna for mobile handsets
IEE Colloquium on Design of Mobile Handset Antennas for Optimal Performance in the Presence of Biological Tissue (Digest No. 1997 022), 1997Co-Authors: G.g. Cook, S.k. Khamas, R.m. EdwardsAbstract:Spiral antenna elements have been shown to have useful wide bandwidth and circular polarisation properties. A 'Curl' antenna design has been proposed in the literature where a single spiral arm parallel to and above a groundPlane is fed through this groundPlane via a single wire feed. Such an arrangement provides screening at the back of the groundPlane, and also obviates the need for a balun since the whole antenna is essentially a monopole fed against an Earth Plane, so that an unbalanced coaxial feed may be used. In this contribution the Curl antenna design has been extended to a spiral arm printed on a grounded dielectric substrate, and fed via a wire through the dielectric. In a practical deployment scenario therefore, such a spiral could be printed on the back of a phone with some suitable intervening dielectric grounded by the transceiver casing, which would provide screening of the user's head from the active element. In order to achieve wide bandwidth and good circular polarisation from this printed spiral, the current distribution along the spiral arm must be essentially that of a travelling wave, and this is dependent on parameters such as substrate permittivity and thickness, and also the spiral function and arm length.
