Gemma: A Sandia National Laboratories Electromagnetic Code for Heterogeneous Computer Architectures
Abstract not provided.
Publications
UNCERTAINTY QUANTIFICATION IN ELECTROMAGNETIC PROBLEMS OF HIGHLY RESONANT CAVITIES USING DAKOTA
Abstract not provided.
Modeling Penetration through Slots and Improving Shielding Effectiveness in High-Quality Factor Resonant Cavities
Abstract not provided.
Penetration through slots in cylindrical cavities operating at fundamental cavity modes in the presence of electromagnetic absorbers
Progress In Electromagnetics Research M
Placing microwave absorbing materials into a high-quality factor resonant cavity may in general reduce the large interior electromagnetic fields excited under external illumination. In this paper, we aim to combine two analytical models we previously developed: 1) an unmatched formulation for frequencies below the slot resonance to model shielding effectiveness versus frequency; and 2) a perturbation model approach to estimate the quality factor of cavities in the presence of absorbers. The resulting model realizes a toolkit with which design guidelines of the absorber’s properties and location can be optimized over a frequency band. Analytic predictions of shielding effectiveness for three transverse magnetic modes for various locations of the absorber placed on the inside cavity wall show good agreement with both full-wave simulations and experiments, and validate the proposed model. This analysis opens new avenues for specialized ways to mitigate harmful fields within cavities.
Exascale Method of Moments for Linear Electromagnetics with Gemma
Abstract not provided.
A New Integration Approach in Surface Integral Equation Discontinuous Galerkin(IEDG) Method
Abstract not provided.
Multipole-based cable braid electromagnetic penetration model: Magnetic penetration case
Progress In Electromagnetics Research C
The goal of this paper is to present, for the first time, calculations of the magnetic penetration case of a first principles multipole-based cable braid electromagnetic penetration model. As a first test case, a one-dimensional array of perfect electrically conducting wires, for which an analytical solution is known, is investigated: We compare both the self-inductance and the transfer inductance results from our first principles cable braid electromagnetic penetration model to those obtained using the analytical solution. These results are found in good agreement up to a radius to half spacing ratio of about 0.78, demonstrating a robustness needed for many commercial and non-commercial cables. We then analyze a second set of test cases of a square array of wires whose solution is the same as the one-dimensional array result and of a rhomboidal array whose solution can be estimated from Kley’s model. As a final test case, we consider two layers of one-dimensional arrays of wires to investigate porpoising effects analytically. We find good agreement with analytical and Kley’s results for these geometries, verifying our proposed multipole model. Note that only our multipole model accounts for the full dependence on the actual cable geometry which enables us to model more complicated cable geometries.
Intersubband Polaritonics in Dielectric Metasurfaces
Abstract not provided.
Intersubband Polaritonics in Dielectric Metasurfaces
Abstract not provided.
Exascale Method of Moments for Linear Electromagnetics with Gemma
Abstract not provided.
Modeling shielded cables in Xyce based on transmission-line theory
2019 USNC-URSI Radio Science Meeting (Joint with AP-S Symposium), USNC-URSI 2019 - Proceedings
Electromagnetic shields are usually employed to protect cables and other devices; however, these are generally not perfect, and may permit external magnetic and electric fields to penetrate into the interior regions of the cable, inducing unwanted current and voltages. The aim of this paper is to verify a circuit model tool with our previously proposed analytical model [1] for evaluating currents and voltages induced in the inner conductor of braided-shield cables. This circuit model will enable coupling between electromagnetic and circuit simulations.
Modeling shielded cables in Xyce based on transmission-line theory
Abstract not provided.
MODELING OF HIGH-Q CAVITY WITH SURFACE INTEGRAL EQUATION DISCONTINUOUS GALERKIN (IEDG) METHOD
Abstract not provided.
Broadband and Efficient Second-Harmonic Generation from a Hybrid Dielectric Metasurface/Semiconductor Quantum-Well Structure
ACS Photonics
A prominent nonlinear optical phenomenon that is extensively studied using nanostructured materials is second-harmonic generation (SHG) as it has applications in various fields. Achieving efficient SHG from a nanostructure requires a large second-order nonlinear susceptibility of the material system and large electromagnetic fields. For practical applications, the nanostructures should also have low losses, high damage thresholds, large bandwidths, wavelength scalability, dual mode operation in transmission and reflection, monolithic integrability, and ease of fabrication. While various approaches have demonstrated efficient SHG, to the best of our knowledge, none have demonstrated all these desired qualities simultaneously. Here, we present a hybrid approach for realizing efficient SHG in an ultrathin dielectric-semiconductor nonlinear device with all the above-mentioned desired properties. Our approach uses high quality factor leaky mode resonances in dielectric metasurfaces that are coupled to intersubband transitions of semiconductor quantum wells. Using our device, we demonstrate SHG at pump wavelengths ranging from 8.5 to 11 μm, with a maximum second-harmonic nonlinear conversion factor of 1.1 mW/W2 and maximum second-harmonic conversion efficiency of 2.5 × 10-5 at modest pump intensities of 10 kW/cm2. Our results open a new direction for designing low loss, broadband, and efficient ultrathin nonlinear optical devices.
Enhancing absorption bandwidth through vertically oriented metamaterials
Applied Sciences (Switzerland)
Metamaterials research has developed perfect absorbers from microwave to optical frequencies, mainly featuring planar metamaterials, also referred to as metasurfaces. In this study, we investigated vertically oriented metamaterials, which make use of the entire three-dimensional space, as a new avenue to widen the spectral absorption band in the infrared regime between 20 and 40 THz. Vertically oriented metamaterials, such as those simulated in this work, can be experimentally realized through membrane projection lithography, which allows a single unit cell to be decorated with multiple resonators by exploiting the vertical dimension. In particular, we analyzed the cases of a unit cell containing a single vertical split-ring resonator (VSRR), a single planar split-ring resonator (PSRR), and both a VSRR and PSRR to explore intra-cell coupling between resonators. We show that the additional degrees of freedom enabled by placing multiple resonators in a unit cell lead to novel ways of achieving omnidirectional super absorption. Our results provide an innovative approach for controlling and designing engineered nanostructures.
Modeling and experiments of high-quality factor cavity shielding effectiveness
2019 International Applied Computational Electromagnetics Society Symposium in Miami, ACES-Miami 2019
In this paper, we investigate the coupling from external electromagnetic (EM) fields to the interior EM fields of a high-quality factor cylindrical cavity through a small perturbing slot. We illustrate the shielding effectiveness versus frequency, highlighting bounds on the penetrant power through the slot. Because internal fields may become larger than external ones, we then introduce a small amount of microwave absorbing materials decorating the slot to improve shielding effectiveness considerably, as shown by both simulations and experiments. Although the cylindrical cavity is used for demonstration purposes in this paper, the conclusions presented here can be leveraged for use with more complex cavity structures.
Gemma: an ATDM Electromagnetics Code
Abstract not provided.
Brief Gemma Overview
Abstract not provided.
Modeling and Experiments of High-Quality Factor Cavity Shielding Effectiveness
Abstract not provided.
High-mobility transparent conducting oxides for compact epsilon-near-zero silicon photonic phase modulators
Optics InfoBase Conference Papers
We numerically analyze the role of carrier mobility in transparent conducting oxides in epsilon-near-zero phase modulators. High-mobility materials such as cadmium oxide enable compact photonic phase modulators with a modulation figure of merit >29 º/dB.
Modeling of High-Q Cavity with Surface Integral Equation Discontinuous Galerkin (IEDG) Method
Abstract not provided.
Quality factor assessment of finite-size all-dielectric metasurfaces at the magnetic dipole resonance
Nanomaterials and Nanotechnology
Recently there has been a large interest in achieving metasurface resonances with large quality factors. In this article, we examine metasurfaces that comprised a finite number of magnetic dipoles oriented parallel or orthogonal to the plane of the metasurface and determine analytic formulas for their resonances’ quality factors. These conditions are experimentally achievable in finite-size metasurfaces made of dielectric cubic resonators at the magnetic dipole resonance. Our results show that finite metasurfaces made of parallel (to the plane) magnetic dipoles exhibit low quality factor resonances with a quality factor that is independent of the number of resonators. More importantly, finite metasurfaces made of orthogonal (to the plane) magnetic dipoles lead to resonances with large quality factors, which ultimately depend on the number of resonators comprising the metasurface. In particular, by properly modulating the array of dipole moments by having a distribution of resonator polarizabilities, one can potentially increase the quality factor of metasurface resonances even further. These results provide design guidelines to achieve a sought quality factor applicable to any resonator geometry for the development of new devices such as photodetectors, modulators, and sensors.
Viscoelastic optical nonlocality of low-loss epsilon-near-zero nanofilms
Scientific Reports
Optical nonlocalities are elusive and hardly observable in traditional plasmonic materials like noble and alkali metals. Here we report experimental observation of viscoelastic nonlocalities in the infrared optical response of epsilon-near-zero nanofilms made of low-loss doped cadmium-oxide. The nonlocality is detectable thanks to the low damping rate of conduction electrons and the virtual absence of interband transitions at infrared wavelengths. We describe the motion of conduction electrons using a hydrodynamic model for a viscoelastic fluid, and find excellent agreement with experimental results. The electrons' elasticity blue-shifts the infrared plasmonic resonance associated with the main epsilon-near-zero mode, and triggers the onset of higher-order resonances due to the excitation of electron-pressure modes above the bulk plasma frequency. We also provide evidence of the existence of nonlocal damping, i.e., viscosity, in the motion of optically-excited conduction electrons using a combination of spectroscopic ellipsometry data and predictions based on the viscoelastic hydrodynamic model.
Semiconductor Hyperbolic Metamaterials at the Quantum Limit
Scientific Reports
We study semiconductor hyperbolic metamaterials (SHMs) at the quantum limit experimentally using spectroscopic ellipsometry as well as theoretically using a new microscopic theory. The theory is a combination of microscopic density matrix approach for the material response and Green’s function approach for the propagating electric field. Our approach predicts absorptivity of the full multilayer system and for the first time allows the prediction of in-plane and out-of-plane dielectric functions for every individual layer constructing the SHM as well as effective dielectric functions that can be used to describe a homogenized SHM.
A metasurface optical modulator using voltage-controlled population of quantum well states
Applied Physics Letters
The ability to control the light-matter interaction with an external stimulus is a very active area of research since it creates exciting new opportunities for designing optoelectronic devices. Recently, plasmonic metasurfaces have proven to be suitable candidates for achieving a strong light-matter interaction with various types of optical transitions, including intersubband transitions (ISTs) in semiconductor quantum wells (QWs). For voltage modulation of the light-matter interaction, plasmonic metasurfaces coupled to ISTs offer unique advantages since the parameters determining the strength of the interaction can be independently engineered. In this work, we report a proof-of-concept demonstration of a new approach to voltage-tune the coupling between ISTs in QWs and a plasmonic metasurface. In contrast to previous approaches, the IST strength is here modified via control of the electron populations in QWs located in the near field of the metasurface. By turning on and off the ISTs in the semiconductor QWs, we observe a modulation of the optical response of the IST coupled metasurface due to modulation of the coupled light-matter states. Because of the electrostatic design, our device exhibits an extremely low leakage current of ∼6 pA at a maximum operating bias of +1 V and therefore very low power dissipation. Our approach provides a new direction for designing voltage-tunable metasurface-based optical modulators.
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