The Experts below are selected from a list of 279 Experts worldwide ranked by ideXlab platform
Laxminarayan L. Raja - One of the best experts on this subject based on the ideXlab platform.
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Resonant Power Absorption in helicon plasma sources
Physics of Plasmas, 2006Co-Authors: Guangye Chen, Alexey Arefiev, Roger D. Bengtson, Boris Breizman, Charles A. Lee, Laxminarayan L. RajaAbstract:Helicon discharges produce plasmas with a density gradient across the confining magnetic field. Such plasmas can create a radial potential well for nonaxisymmetric whistlers, allowing radially localized helicon (RLH) waves. This work presents new evidence that RLH waves play a significant role in helicon plasma sources. An experimentally measured plasma density profile in an argon helicon discharge is used to calculate the rf field structure. The calculations are performed using a two–dimensional field solver under the assumption that the density profile is axisymmetric. It is found that RLH waves with an azimuthal wave number m=1 form a standing wave structure in the axial direction and that the frequency of the RLH eigenmode is close to the driving frequency of the rf antenna. The calculated resonant Power Absorption, associated with the RLH eigenmode, accounts for most of the rf Power deposited into the plasma in the experiment.
Suwon Cho - One of the best experts on this subject based on the ideXlab platform.
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The effects of the density profile on the Power Absorption and the equilibrium density in helicon plasmas
Physics of Plasmas, 1997Co-Authors: Suwon Cho, Jong-gu KwakAbstract:Power Absorption profiles are computed using numerical integration for radially non-uniform helicon plasmas with finite axial lengths. As in a uniform plasma, the Trivelpiece–Gould mode dominates the Power Absorption causing the surface deposition of the rf Power. In addition to the surface heating, there is bulk electron heating for non-uniform plasmas, and the portion of this bulk heating increases with the degree of the inhomogeneity. It has been also found that the radial inhomogeneity of the plasma density results in the suppression of the m=−1 mode and reveals the axial resonance condition. Finally, the global Power balance is considered to estimate average equilibrium densities, which are found to be in agreement with experimental values.
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The field and Power Absorption profiles in helicon plasma resonators
Physics of Plasmas, 1996Co-Authors: Suwon ChoAbstract:Analytic expressions are presented for electromagnetic waves excited by Boswell and Nagoya III type antennae [F. F. Chen, J. Vac. Sci. Technol. A 10, 1389 (1992)] in a uniform plasma column, and profiles of the wave field and Power Absorption are calculated. The Trivelpiece‐Gould mode is found to be dominant causing the surface electron heating, while the linear dependence of the plasma density on the magnetic field is obeyed. In addition, the fast helicon wave approximation, with which the electron inertia is neglected, is examined in detail and its validity is discussed.
M. Koepke - One of the best experts on this subject based on the ideXlab platform.
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Electron Power Absorption dynamics in capacitive radio frequency discharges driven by tailored voltage waveforms in CF4
Plasma Sources Science and Technology, 2016Co-Authors: S. Brandt, B. Berger, E. Schüngel, Ihor Korolov, A. Derzsi, Bastien Bruneau, E.v. Johnson, Trevor Lafleur, D. O'connell, M. KoepkeAbstract:The Power Absorption dynamics of electrons and the electrical asymmetry effect in capacitive radio-frequency plasmas operated in CF4 and driven by tailored voltage waveforms are investigated experimentally in combination with kinetic simulations. The driving voltage waveforms are generated as a superposition of multiple consecutive harmonics of the fundamental frequency of 13.56 MHz. Peaks/valleys and sawtooth waveforms are used to study the effects of amplitude and slope asymmetries of the driving voltage waveform on the electron dynamics and the generation of a DC self-bias in an electronegative plasma at different pressures. Compared to electropositive discharges, we observe strongly different effects and unique Power Absorption dynamics. At high pressures and high electronegativities, the discharge is found to operate in the drift-ambipolar (DA) heating mode. A dominant excitation/ionization maximum is observed during sheath collapse at the edge of the sheath which collapses fastest. High negative-ion densities are observed inside this sheath region, while electrons are confined for part of the RF period in a potential well formed by the ambipolar electric field at this sheath edge and the collapsed (floating potential) sheath at the electrode. For specific driving voltage waveforms, the plasma becomes divided spatially into two different halves of strongly different electronegativity. This asymmetry can be reversed electrically by inverting the driving waveform. For sawtooth waveforms, the discharge asymmetry and the sign of the DC self-bias are found to reverse as the pressure is increased, due to a transition of the electron heating mode from the α-mode to the DA-mode. These effects are interpreted with the aid of the simulation results.
Gerardo F. Goya - One of the best experts on this subject based on the ideXlab platform.
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The relevance of Brownian relaxation as Power Absorption mechanism in Magnetic Hyperthermia
Scientific reports, 2019Co-Authors: T. E. Torres, Rodrigo Fernández-pacheco, Enio Lima, M. Pilar Calatayud, Beatriz Sanz, Alfonso Ibarra, Alvaro Mayoral, Clara Marquina, M. Ricardo Ibarra, Gerardo F. GoyaAbstract:The Linear Response Theory (LRT) is a widely accepted framework to analyze the Power Absorption of magnetic nanoparticles for magnetic fluid hyperthermia. Its validity is restricted to low applied fields and/or to highly anisotropic magnetic nanoparticles. Here, we present a systematic experimental analysis and numerical calculations of the specific Power Absorption for highly anisotropic cobalt ferrite (CoFe2O4) magnetic nanoparticles with different average sizes and in different viscous media. The predominance of Brownian relaxation as the origin of the magnetic losses in these particles is established, and the changes of the Specific Power Absorption (SPA) with the viscosity of the carrier liquid are consistent with the LRT approximation. The impact of viscosity on SPA is relevant for the design of MNPs to heat the intracellular medium during in vitro and in vivo experiments. The combined numerical and experimental analyses presented here shed light on the underlying mechanisms that make highly anisotropic MNPs unsuitable for magnetic hyperthermia.
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Brownian rotational relaxation and Power Absorption in magnetite nanoparticles
Journal of Magnetism and Magnetic Materials, 2007Co-Authors: Gerardo F. Goya, Rodrigo Fernández-pacheco, Manuel Arruebo, N. Cassinelli, M. R. IbarraAbstract:Abstract We present a study of the Power Absorption efficiency in several magnetite-based colloids, to asses their potential as magnetic inductive hyperthermia (MIH) agents. Relaxation times τ were measured through the imaginary susceptibility component χ ″ ( T ) , and analyzed within Debye's theory of dipolar fluid. The results indicated Brownian rotational relaxation and allowed to calculate the hydrodynamic radius close to the values obtained from photon correlation. The study of the colloid performances as Power absorbers showed no detectable increase of temperature for dextran-coated Fe3O4 nanoparticles, whereas a second Fe3O4-based dispersion of similar concentration could be heated up to 12 K after 30 min under similar experimental conditions. The different Power Absorption efficiencies are discussed in terms of the magnetic structure of the nanoparticles.
P.d. Einziger - One of the best experts on this subject based on the ideXlab platform.
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Curvature effect for electromagnetic Power Absorption in biological tissues
2006Co-Authors: A. Shtrom, D. F. Soldea, Daniel Razansky, P.d. EinzigerAbstract:Coupled closely to highly absorbing tissues, a source of electromagnetic radiation (e.g., cellular antenna) can be greatly affected by the curvature of the absorbing surface. Based on our previous planar surface approximations, we suggest an effective and relatively simple procedure for obtaining closed-form corrections for the main Power relations involved in the presence of curved-surface absorbing tissues. The derivation is introduced by considering a two-dimensional prototype models of surface and line sources radiating in the presence of a half-space and an infinite circular cylinder. The Power Absorption efficiencies of the cylindrical model are shown to be tightly bounded from below and above by these of the half-space (planar) models.
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Bounds and estimates for Power Absorption in two-dimensional highly lossy configurations
Journal of Applied Physics, 2004Co-Authors: Daniel Razansky, D. F. Soldea, P.d. EinzigerAbstract:Electromagnetic Power Absorption in biological tissues has recently received due scientific and public attention, particularly, in the areas of cellular communication and hyperthermic treatments. While efficient numerical algorithms, such as the finite difference time domain technique and the method of moments, have been developed as to obtain accurate Power distributions in complicated configurations, their physical interpretation and explicit dependence on problem’s parameters are still difficult to achieve. In attempt to gain a clear insight into the electromagnetic Power Absorption mechanism as well as its estimation and relation to the Specific Absorption Rate (SAR), we have recently proposed an infinite-extent current-sheet model. Herein, the model is further extended by incorporating finite-extent sources, i.e., electric and magnetic line-sources, exciting a highly lossy semi-infinite half-space. This modification results in deeper insight and understanding of the crucially important parameters, co...
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Optimization of plane-wave Power Absorption in lossy media
2003 IEEE International Symposium on Electromagnetic Compatibility 2003. EMC '03., 2003Co-Authors: D. F. Soldea, Daniel Razansky, P.d. Einziger, J. MizrahiAbstract:The phenomenon of microwave Power Absorption has recently become of increased scientific and public interest, particularly in the area of cellular communication. Electromagnetic Power Absorption in biological tissues is a well-known phenomenon. Its evaluation requires, in general, a solution of the 3D frequency-dependent wave equation in complex configurations, which may necessitate quite massive analytical and numerical efforts. Herein, we focus on a simplified 1D model corresponding to normal-incidence of plane-waves upon a lossy half-space. Our model establishes a tight estimate on the maximal (optimal) Power Absorption in realistic mobile phone - human head configurations. Furthermore, the Absorption efficiency as well as the source impedance are obtained via an explicit closed-form expressions, leading to an explicit optimal Power Absorption (worst-case/best-case) criteria for highly lossy tissues
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Plane-wave model for electromagnetic Power Absorption in biological tissues
Journal of Applied Physics, 2003Co-Authors: D. F. Soldea, Daniel Razansky, P.d. EinzigerAbstract:The phenomenon of electromagnetic Power Absorption in biological tissues has recently become of increased scientific and public interest, particularly in the areas of cellular communication and hyperthermia systems. Electromagnetic Power Absorption in biological tissues is a well-known phenomenon. Its evaluation requires, in general, a solution of the three-dimensional frequency-dependent wave equation in complex configurations, which may necessitate quite massive analytical and numerical efforts. Herein, we focus on an elementary plane-wave model. The model establishes a tight estimate on the optimal (maximal/minimal) Power Absorption in realistic microwave configurations, in particular, cellular communications safety assessments. Furthermore, the Absorption efficiency as well as the source impedance are obtained via explicit closed-form expressions, leading to an explicit maximal Power Absorption criterion for highly lossy tissues. The results depend continuously and explicitly on the physical parameters of biological tissues as well as on the plane-wave incidence angle and excitation source location. They are shown to be closely related to electromagnetic specific Absorption rate estimations in biological tissues. In view of the well-known analogy between plane waves and rectangular waveguide modes, our results can be applied to optimization schemes of microwave heating and waveguide based therapeutic hyperthermia systems.
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Estimates on electromagnetic Power Absorption in highly-lossy configurations
2004 23rd IEEE Convention of Electrical and Electronics Engineers in Israel, 1Co-Authors: Daniel Razansky, D. F. Soldea, G. Yankilevich, P.d. EinzigerAbstract:Electromagnetic Power Absorption in biological tissues has recently received due scientific and public attention, particularly in the areas of cellular communication and hyperthermic treatments. While efficient numerical algorithms have been developed for obtaining accurate Power distributions in complicated configurations, their physical interpretation and explicit dependence on the problem's parameters are usually quite problematic. In an attempt to gain a clear insight into the electromagnetic Power Absorption mechanism, we propose a set of prototype models corresponding to typical highly-lossy configurations. These models provide an important physical insight as well as estimates and bounds on major parameters involved in realistic configurations.
