scholarly journals Higher-Order Mode Electromagnetic Analysis of a Material Sample between Two Flanged Coaxial Probes for Broadband Modelling of Dielectric Measurement Setups

2019 ◽  
Vol 2019 ◽  
pp. 1-17 ◽  
Author(s):  
Raúl V. Haro-Báez ◽  
Juan Córcoles ◽  
Jorge A. Ruiz-Cruz ◽  
José R. Montejo-Garai ◽  
Jesús M. Rebollar
Keyword(s):  
Numerical Study ◽  
Higher Order ◽  
Dielectric Measurement ◽  
Analysis Method ◽  
Higher Order Modes ◽  
Wall Boundary Conditions ◽  
Wide Range ◽  
Coaxial Probes ◽  
Material Sample

The characterization of the dielectric properties of a material requires a measurement technique and its associated analysis method. In this work, the configuration involving two coaxial probes with a material for dielectric measurement between them is analyzed with a mode-matching approach. To that effect, two models with different complexity and particularities are proposed. It will be shown how convergence is sped up for accurate results by using a proper choice of higher-order modes along with a combination of perfect electric wall and perfect magnetic wall boundary conditions. It will also be shown how the frequency response is affected by the flange mounting size, which can be, rigorously and efficiently, taken into account with the same type of approach. This numerical study is validated through a wide range of simulations with reference values from another method, showing how the proposed approaches can be used for the broadband characterization of this well-known, but with a recent renewed interest from the research community, dielectric measurement setup.

Numerical Characterization of Hot Gas Ingestion Through Turbine Rim Seals

2016 ◽  
Author(s):  
Riccardo Da Soghe ◽  
Cosimo Bianchini ◽  
Carl M. Sangan ◽  
James A. Scobie ◽  
Gary D. Lock
Keyword(s):  
Flow Rate ◽  
Numerical Study ◽  
Axial Flow ◽  
Radial Clearance ◽  
Buffering Effect ◽  
Hot Gas ◽  
Numerical Predictions ◽  
Wide Range ◽  
Thermal Buffering

This paper deals with a numerical study aimed at the characterization of hot gas ingestion through turbine rim seals. The numerical campaign focused on an experimental facility which models ingress through the rim seal into the upstream wheel-space of an axial-turbine stage. Single-clearance arrangements were considered in the form of axial- and radial-seal gap configurations. With the radial-seal clearance configuration, CFD steady-state solutions were able to predict the system sealing effectiveness over a wide range of coolant mass flow rates reasonably well. The greater insight of flow field provided by the computations illustrates the thermal buffering effect when ingress occurs: for a given sealing flow rate, the effectiveness on the rotor was significantly higher than that on the stator due to the axial flow of hot gases from stator to rotor caused by pumping effects. The predicted effectiveness on the rotor was compared with a theoretical model for the thermal buffering effect showing good agreement. When the axial-seal clearance arrangement is considered, the agreement between CFD and experiments worsens; the variation of sealing effectiveness with coolant flow rate calculated by means of the simulations display a distinct kink. It was found that the “kink phenomenon” can be ascribed to an over-estimation of the egress spoiling effects due to turbulence modelling limitations. Despite some weaknesses in the numerical predictions, the paper shows that CFD can be used to characterize the sealing performance of axial- and radial-clearance turbine rim seals.

Numerical Characterization of Hot-Gas Ingestion Through Turbine Rim Seals

2016 ◽  
Vol 139 (3) ◽  
Author(s):  
Riccardo Da Soghe ◽  
Cosimo Bianchini ◽  
Carl M. Sangan ◽  
James A. Scobie ◽  
Gary D. Lock
Keyword(s):  
Flow Rate ◽  
Numerical Study ◽  
Axial Flow ◽  
Radial Clearance ◽  
Buffering Effect ◽  
Hot Gas ◽  
Numerical Predictions ◽  
Wide Range ◽  
Thermal Buffering

This paper deals with a numerical study aimed at the characterization of hot-gas ingestion through turbine rim seals. The numerical campaign focused on an experimental facility which models ingress through the rim seal into the upstream wheel-space of an axial-turbine stage. Single-clearance arrangements were considered in the form of axial- and radial-seal gap configurations. With the radial-seal clearance configuration, computational fluid dynamics (CFD) steady-state solutions were able to predict the system sealing effectiveness over a wide range of coolant mass flow rates reasonably well. The greater insight of flow field provided by the computations illustrates the thermal buffering effect when ingress occurs: For a given sealing flow rate, the effectiveness on the rotor was significantly higher than that on the stator due to the axial flow of hot gases from stator to rotor caused by pumping effects. The predicted effectiveness on the rotor was compared with a theoretical model for the thermal buffering effect showing good agreement. When the axial-seal clearance arrangement is considered, the agreement between CFD and experiments worsens; the variation of sealing effectiveness with coolant flow rate calculated by means of the simulations displays a distinct kink. It was found that the “kink phenomenon” can be ascribed to an overestimation of the egress spoiling effects due to turbulence modeling limitations. Despite some weaknesses in the numerical predictions, the paper shows that CFD can be used to characterize the sealing performance of axial- and radial-clearance turbine rim seals.

Numerical study of submicroparticle acoustophoresis using higher-order modes in a rectangular microchannel

2018 ◽  
Vol 415 ◽  
pp. 169-183 ◽  
Author(s):  
Jorick van 't Oever ◽  
Jennifer Herek ◽  
Frieder Mugele ◽  
Dirk van den Ende ◽  
Herman L. Offerhaus
Keyword(s):  
Numerical Study ◽  
Higher Order ◽  
Rectangular Microchannel ◽  
Higher Order Modes

scholarly journals Исследование аномальной генерации вертикально-излучающих лазеров спектрального диапазона 850 nm с двойной оксидной токовой апертурой при большой величине спектральной расстройки

2020 ◽  
Vol 128 (8) ◽  
pp. 1151
Author(s):  
С.А. Блохин ◽  
М.А. Бобров ◽  
Н.А. Малеев ◽  
А.Г. Кузьменков ◽  
В.М. Устинов
Keyword(s):  
Quantum Wells ◽  
Anomalous Behavior ◽  
Higher Order ◽  
Cavity Surface ◽  
Carrier Injection ◽  
Transverse Modes ◽  
Higher Order Modes ◽  
Wide Range ◽  
Vertical Cavity Surface ◽  
Emitting Lasers

The static characteristics of 850 nm-range vertical-cavity surface-emitting lasers (VCSEL) based on strained InGaAs/AlGaAs quantum wells were studied in the wide range of oxide current aperture sizes and the origins of their anomalous behavior at large gain-to-cavity detuning was analyzed. The higher-order modes localized at the periphery of the oxide current aperture can appear in the studied VCSELs due to the lateral carrier spreading in the quantum wells and the specific profile of the oxide aperture (leading to the formation of a two-stage effective waveguide). Inhomogeneous carrier injection over the current aperture area in wide-aperture lasers leads anomalous start of lasing via high-order transverse modes, and the subsequent transition to the classical lasing via low-order modes with an increase in the current is due to a change of the gain-to-cavity detuning with an increase in the internal laser temperature. Anomalous lasing via higher-order modes in the case of narrow-aperture VCSELs becomes possible due to the increase in diffraction losses at the edge of the oxide current aperture for the fundamental mode, while the subsequent switching to the two-mode lasing is due to not only a decrease in the gain-to-cavity detuning, but also the thermal lens effect.

Bending effect characterization of individual higher-order modes in few-mode fibers

2017 ◽  
Vol 42 (17) ◽  
pp. 3343 ◽  
Author(s):  
Yao Xu ◽  
Guobin Ren ◽  
Youchao Jiang ◽  
Yixiao Gao ◽  
Haisu Li ◽  
...  
Keyword(s):  
Higher Order ◽  
Bending Effect ◽  
Higher Order Modes

Correction of coupled higher-order modes in the S-parameter characterization of wideband cavity beam position monitors

2021 ◽  
Vol 92 (1) ◽  
pp. 014705
Author(s):  
Liu Yang ◽  
Xiaozhong He ◽  
Ruo Tang ◽  
Quanhong Long ◽  
Linwen Zhang
Keyword(s):  
Higher Order ◽  
Beam Position ◽  
Higher Order Modes ◽  
S Parameter ◽  
Beam Position Monitors

Numerical study of anomalous TE-polarized light scattering by metallic nanowires using realistic data

2014 ◽  
Vol 23 (01) ◽  
pp. 1450005 ◽  
Author(s):  
G. Wesley Putra Data ◽  
Alexander A. Iskandar ◽  
May-On Tjia
Keyword(s):  
Light Scattering ◽  
Numerical Study ◽  
Polarized Light ◽  
Spectral Width ◽  
Higher Order ◽  
Gold Nanowires ◽  
Higher Order Modes ◽  
Resonance Curves ◽  
Refractive Index Data ◽  
Realistic Data

We report the result of a numerical study of surface plasmon induced anomalous behaviors in TE light scattering by single silver and gold nanowires of radius a. Going beyond the restricted case of nondissipative and nondispersive scatterers often reported previously, the current numerical calculation is performed directly on the basis of Mie's general formula, adopting the refractive index data of Johnson and Christy. Our result does not show the appearance of well resolved and multipole resonances in Q sca plotted against q(= 2πa/λ), for certain wire radii. It does show however, the growing contributions of the higher order modes as a increases. A series of closely-placed but well separated resonance curves nevertheless show up for varying wire radii within the range of small q, exhibiting systematic changes indicative of the size effects on the scattered waves. The further deduced Q sca (λ) spectra display the distinct resonance curves for different wire radii showing peculiar mix of monotonous and nonmonotonous variations of the resonance peak and spectral width with increasing a, as a result of complicated competitions among the growing contributions of the higher order modes. Finally, while the silver and gold scatterers appear to exhibit qualitatively similar behaviors, they differ largely in details due to the significantly different indices of refraction and dispersive properties.

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