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International Symposium of Applied-Computational-Electromagnetics-Society (ACES)

作者： Le, Madison Hadi, Mohammed Elsherbeni, Atef Colorado Sch Mines Elect Engn Dept Golden CO 80401 USA

ISBN: (纸本)9781733509602

Sub-gridding errors for a 2D finite-difference time-domain (FDTD) simulation are compared for both the standard FDTD and Hybrid higher order FDTD cases. Sub-gridding contrast ratios of 1:3, 1:9, 1:15, and 1:27 are considered and analyzed. A correlation is seen between the increase of contrast ratio with the increase of sub-gridding errors for both standard and hybrid cases. However, a trend of errors reduction when using hybrid formulations over standard formulations. is apparent for each contrast ratio.

关键词： finite-difference time-domain method High Order FDTD Numerical Error Analysis Sub-gridding

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Ultra-fast tunable optoelectronic half adder/subtractor based on photonic crystal ring resonators covered by graphene nanoshells

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OPTICAL AND QUANTUM ELECTRONICS 2021年第7期53卷 380-380页

作者： Naghizade, Saleh Saghaei, Hamed Islamic Azad Univ Tabriz Branch Young Researchers & Elite Club Tabriz Iran Islamic Azad Univ Shahrekord Branch Dept Elect Engn Shahrekord Iran

This paper reports a new design of a tunable optoelectronic half adder/subtractor. Two photonic crystal (PhC) ring resonators are used to realize the proposed structure. Several silicon rods surrounded by silica rods covered with graphene nanoshells (GNSs) form every PhC ring resonator. Setting the chemical potential of GNS with an appropriate gate voltage, we can tune the PhC resonant mode as desired. The plane wave expansion technique is used to study the photonic band structure of the fundamental PC microstructure, and the finite-difference time-domain method is employed in the final design for solving Maxwell's equations to analyze the light propagation inside the structure. We systematically study the effects of physical parameters on the transmission reflection and absorption spectra. By optimizing the geometric dimensions, resonant absorption peaks can be excited at the same time for GNSs. Our numerical results also reveal the maximum time response is about 0.8 ps. The 200 mu m(2) area of the proposed half adder/subtractor makes it the building block of every photonic integrated circuit. Also, the design of various fast signal processing systems in optical communication networks is possible due to using tunable GNSs in PhC ring resonators. This study can introduce the use of two-dimensional materials in the design and implementation of logic circuits.

关键词： Photonic crystal microstructure Nonlinear material Optoelectronic half adder subtractor Ring resonator Plane wave expansion method Optical Kerr effect finite-difference time-domain method

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Bayesian inference for plasmonic nanometrology

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Physical Review A 2021年第5期104卷 053501-053501页

作者： Joseph M. Lukens Ali Passian Quantum Information Science Group Oak Ridge National Laboratory Oak Ridge 37831 TN United States

We introduce a Bayesian method for the characterization of plasmonic nanoparticles, which is applicable to both near- and far-field problems. Designed to combine data generated from any photon-plasmon interaction experiment with physically motivated theoretical models, our approach leverages state-of-the-art Markov chain Monte Carlo sampling techniques and returns parameter estimates on nanometric scales. Simulated spectral data sets, describing resonant scattering of photons from ellipsoidal and toroidal nanoparticles, are explored as concrete examples of our approach, with the resulting Bayesian estimates showing excellent agreement with the ground truth, even under conditions of high statistical noise. By incorporating Bayes factors into the method as well, we reveal how model selection can determine which one of competing geometric shapes better explains the observed data. Our comprehensive nanometrology procedure can be tailored to a variety of light-particle interaction models, and its reliance on Bayesian inference furnishes automatic uncertainty quantification. In addition to applicability to a host of plasmonic configurations such as nanoparticle dimers, trimers, and array studies, it is proposed that the presented analysis can be extended to the quantum regime, where nonclassical photon statistics may provide additional insight for inference of scatterer properties.

关键词： Metrology Plasmonics Surface plasmons Nanoparticles Bayesian methods finite-difference time-domain method Light scattering Metropolis algorithm

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Nanoscale photoemission from a focused propagating surface plasmon

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Physical Review B 2021年第15期104卷 155432-155432页

作者： Guiqi Wang Peng Lang Yulu Qin Boyu Ji Xiaowei Song Jingquan Lin School of Science Changchun University of Science and Technology Changchun 130022 People's Republic of China

Propagating surface plasmons (PSPs) provide an important platform for designing various photoelectric devices such as nanometer-confined ultrafast electron sources. Here, we investigate the nanoscale photoemission from a focused PSP hot spot using time-of-flight photoemission electron microscopy. It is found that the induced photoelectrons from the focused PSP exhibit an obvious feature of the above threshold photoemission process, while the photoelectron spectra from a local surface plasmon (LSP) under the same illumination condition exhibit a characteristic of thermally assisted multiphoton photoemission. In addition, results show that the measured photoelectron yield from the focused PSP region is nearly one order of magnitude higher than that from the LSP region, and we found this is contrary to the calculation results that the yield from the LSP is much higher than that from the focused PSP when the local field intensity and plasmon lifetime of the two plasmonic modes are included. The large discrepancy in the photoelectron energy spectra, as well as in the measured and calculated photoelectron intensity between the focused PSP and LSP, can be attributed to the existence of different decay channels between the two plasmonic modes. This paper provides a deep understanding of the photoemission mechanism induced by plasmon effects, and it shows that the focused PSP is promising as a robust nanoscale electron source which can supply energetic and higher flux electron emission.

关键词： Plasmonics Surface plasmons finite-difference time-domain method Photoelectron emission microscopy time & angle resolved photoemission spectroscopy

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Experimental Research on Evaluation of Soil Water Content Using Ground Penetrating Radar and Wavelet Packet-Based Energy Analysis

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REMOTE SENSING 2021年第24期13卷 5047-5047页

作者： Zhang, Sheng Zhang, Liang Ling, Tonghua Fu, Guihai Guo, Youlin Hunan City Univ Sch Civil Engn Yiyang 413000 Peoples R China Hunan City Univ Hunan Engn Res Ctr Struct Safety & Disaster Preve Yiyang 413000 Peoples R China Changsha Univ Sci & Technol Sch Civil Engn Changsha 410114 Peoples R China

Soil water content is one of the most important factors affecting the safety and stability of buildings or structures, especially in roadbeds, slopes, earth dams and foundations. Accurate assessments of soil water content can ensure the quality of construction, reduce construction costs and prevent accidents, among other benefits. In this study, ground penetrating radar (GPR) was used to detect and evaluate changes in soil water content. The GPR signal is usually nonstationary and nonlinear;however, traditional Fourier theory is typically suitable for periodic stationary signals, and cannot reflect the law of the frequency and energy of the GPR signal changing with time. Wavelet transform has good time-frequency localization characteristics, and therefore represents a new method for analyzing and processing GPR signals. According to the time-frequency characteristics of GPR signals, in this paper, a new biorthogonal wavelet basis which was highly matched with the GPR waveform was constructed using the lifting framework of wavelet theory. Subsequently, an evaluation method, namely, the wavelet packet-based energy analysis (WPEA) method, was proposed. The method was utilized to calculate the wavelet packet-based energy indexes (WPEI) of the GPR single-channel signals for clay samples with water contents ranging from 10% to 24%. The research results showed that there was a highly correlated linear relationship between the WPEI and the soil water contents, and the relationship between the two was fitted with a linear fitting function. The feasibility of the method was verified by comparing our results with those obtained using classical wavelet bases to perform the wavelet packet transform. The large-area, continuous scanning measurement method of GPR was shown to be suitable for evaluations of soil water contents in roadbeds, slopes, earth dams, and foundations.

关键词： soil water content ground penetrating radar (GPR) wavelet packet-based energy analysis (WPEA) biorthogonal wavelet basis finite-difference time-domain method

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Calculating Scattering Spectra using time-domain Modeling of time-modulated Systems

Calculating Scattering Spectra using Time-domain Modeling of...

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International Symposium of Applied-Computational-Electromagnetics-Society (ACES)

作者： Mock, Adam Cent Michigan Univ Sch Engn & Technol Mt Pleasant MI 48859 USA

ISBN: (纸本)9781733509602

Obtaining agreement between theoretical predictions that assume single-frequency excitation and finite-difference time-domain (FDTD) simulations that employ broadband excitation in the presence of time-varying materials is challenging due to frequency mixing. A simple solution is proposed to reduce artifacts in FDTD-calculated spectra from the frequency mixing induced by harmonic refractive index modulation applicable to scenarios in which second order and higher harmonics are negligible. Advantages of the proposed method are its simplicity and applicability to arbitrary problems including resonant structures.

关键词： cavity resonators finite-difference time-domain method time-varying circuits

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Loss reduction in sharply bent optical nanofibers by coupling with Au nanoparticles

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OPTICS COMMUNICATIONS 2021年 497卷 127167-127167页

作者： Yang, Yuxin Gong, Jue Gao, Yixiao Guo, Xin Wang, Pan Tong, Limin Zhejiang Univ Coll Opt Sci & Engn State Key Lab Modern Opt Instrumentat Hangzhou 310027 Peoples R China

Bending losses of sharply bent optical nanofibers or nanowires coupling with Au nanoparticles (Au NPs) are investigated using a finite-difference time-domain (FDTD) method. Relying on the ultra-tight optical confinement of the Au NPs, bending losses of the sharply bent optical nanofibers or nanowires can be effectively reduced by attaching Au NPs to the inner edge of the bent nanofibers or nanowires. At 650-nm wavelength, a bending-loss reduction of 4.7 dB/90 degrees is obtained for a 300-nm-diameter SiO2 nanofiber coupling with seven 140-nm-diameter Au NPs when the bending radius is 1.0 mu m. Our results suggest a potential route to realizing sharply-bent optical nanofibers or nanowires with acceptable bending losses for constructing highly compact photonic integrated circuits or devices.

关键词： Optical nanofibers Bending losses Au nanoparticles Localized surface plasmon resonance finite-difference time-domain method

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Nanomagnetic Self-Organizing Logic Gates

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Physical Review Applied 2021年第2期16卷 024055-024055页

作者： Pieter Gypens Bartel Van Waeyenberge Massimiliano Di Ventra Jonathan Leliaert Daniele Pinna Department of Solid State Sciences Ghent University 9000 Ghent Belgium Department of Physics University of California San Diego La Jolla California 92093 USA Peter Grünberg Institute and Institute for Advanced Simulation Forschungszentrum Jülich 52425 Jülich Germany Department of Physics Johannes Gutenberg Universität 55122 Mainz Germany

The end of Moore’s law for CMOS technology has prompted the search for low-power computing alternatives, resulting in promising approaches such as nanomagnetic logic. However, nanomagnetic logic is unable to solve a class of interesting problems efficiently, as it only allows for forward computing, due to the need for clocking and/or thermal annealing. Here, we introduce nanomagnetic self-organizing logic gates that can dynamically satisfy their logical proposition, irrespective of whether the signal is applied to the traditional input or output terminals, thus allowing for reversible computing. We present a design of a self-organizing nand gate, the logically correct states of which are occupied equally in thermodynamical equilibrium, and illustrate its capabilities by implementing reversible Boolean circuitry to solve a two-bit factorization problem via numerical modeling. Our approach offers an alternative path to explore memcomputing, an unconventional computing paradigm the usefulness of which has already been demonstrated by solving a variety of hard combinatorial optimization problems.

关键词： Fluctuations & noise Magnetic interactions Magnetization switching NP-hard problems Self-organized systems finite-difference time-domain method Landau-Lifschitz-Gilbert equation Micromagnetic modeling

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Analytical Investigations on FDTD Numerical Dispersion

Analytical Investigations on FDTD Numerical Dispersion

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IEEE-MTT-S International Conference on Numerical Electromagnetic and Multiphysics Modeling and Optimization (NEMO)

作者： Cheng, Yu Chen, Guangzhi Wang, Xiang-hua Yang, Shunchuan Beihang Univ Sch Elect & Informat Engn Beijing Peoples R China Beihang Univ Res Inst Frontier Sci Beijing Peoples R China Tianjin Univ Technol & Educ Sch Sci Tianjin Peoples R China

ISBN: (纸本)9781728169668

The numerical dispersion is one of the main factors to affect the accuracy of the finite-difference time-domain (FDTD) method. It can be easy to be taken for granted that a smaller time step leads to smaller simulation errors. This paper reveals that smaller time steps do not always make more accurate results in FDTD simulations. We analytically investigated how time steps affect the numerical dispersion of two FDTD methods: the leapfrog FDTD(2,2) method and the FDTD(2,4) method. The investigations in this paper show that in the FDTD(2,2) method, a larger time step limited by the Courant-Friedrichs-Lewy (CFL) condition is more helpful to reduce the numerical dispersion error. However, in the FDTD(2,4) method, as the time step grows, the numerical dispersion error decreases at the beginning and then increases. Several numerical examples are carried out to verify our analysis.

关键词： finite-difference time-domain method high order methods numerical dispersion time step

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time-modulated Coupled-cavity System for Optical Switching

Time-modulated Coupled-cavity System for Optical Switching

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International Symposium of Applied-Computational-Electromagnetics-Society (ACES)

作者： Mock, Adam Cent Michigan Univ Sch Engn & Technol Mt Pleasant MI 48859 USA

ISBN: (纸本)9781733509602

The scattering parameters of a time-modulated two-coupled-cavity system are obtained using coupled mode theory and verified using the finite-difference time-domain method. We find that a suitably tailored time-modulation of the cavities allows for switching the output on and off. The proposed functionality can be used in direct amplitude modulation of an optical carrier from a frequency-modulated RF message.

关键词： cavity resonators finite-difference time-domain method switch time-varying circuits

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