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The finite-difference time-domain (FDTD) method is a widely used numerical technique for simulating electromagnetic wave interactions with complex media. Various efficient approaches have been used to analyze complex media, and the surface impedance boundary condition (SIBC) is one of the most powerful techniques in FDTD simulations, allowing efficient electromagnetic modeling of lossy materials. However, conventional SIBC-FDTD formulations face challenges when analyzing lossy dispersive materials because of the assumption of frequency-independent relative permittivity and conductivity in the inverse Laplace transform. To address this, we propose a dispersion-modeling approach for the surface impedance of lossy dispersive materials. Additionally, to reduce grid errors in the FDTD discrete domain, we introduce the surface admittance boundary condition (SABC) for lossy dispersive materials. We investigated the numerical accuracy by deriving the numerical surface impedance and admittance for the proposed surface boundary condition (SBC)-FDTD formulations. In addition, we determined the numerical stability conditions of the SBC-FDTD formulations using the von Neumann method combined with the Routh-Hurwitz criterion. Numerical examples validate both the numerical accuracy and stability of the proposed SBC-FDTD formulations. Our findings enhance the understanding and application of the SBC in FDTD simulations, especially for lossy dispersive materials, and provide insights for future research and electromagnetic modeling in various fields. [ABSTRACT FROM AUTHOR]

The finite-difference time-domain (FDTD) method has been widely used for the electromagnetic analysis of complex dispersive media. The shift-operator (SO)-FDTD or auxiliary differential equation (ADE)-FDTD formulation has been mainly employed for dusty plasma. Each FDTD formulation has its pros and cons. SO-FDTD is accurate but not computationally efficient. ADE-FDTD needs fewer computational resources, but its accuracy is poor. Here, we propose an accurate and efficient FDTD formulation for dusty plasma, based on the bilinear transform (BT). We perform a comprehensive study on the numerical permittivity and the computational efficiency for three FDTD formulations. Numerical examples are employed to illustrate that the proposed BT-FDTD outperforms the previously reported FDTD formulations for dusty plasma. In addition, based on the proposed BT-FDTD simulations, the effect of dust particles on EM wave propagation is investigated in the GHz band and the THz band. [ABSTRACT FROM AUTHOR]

In this communication, an electromagnetic boundary-value problem of modulated transverse corrugations in an infinite conducting circular cylinder is rigorously solved based on the Fourier transform, eigenfunction expansion, and the mode matching method. Radar cross section (RCS) of the modulated transverse corrugations is represented in the series form. Computation is performed to analyze scattering characteristics while varying depth, width, and period of the corrugations and to investigate the excitation of surface waves and concomitant RCS reduction. [ABSTRACT FROM AUTHOR]

Recently, based on a quadratic complex rational function, an attractive finite-difference time-domain algorithm was suggested for dispersive modeling of complex media because it is accurate and easy to implement. To fully utilize the quadratic complex rational function finite-difference time-domain, it is essential to investigate its numerical errors based on an exact mathematical approach. Toward this purpose, the exact expression of the numerical permittivity is first derived. From this numerical permittivity, the numerical dispersion, numerical dissipation, and numerical anisotropy inherent to the quadratic complex rational function finite-difference time-domain are examined. Numerical examples illustrate that the numerical errors of the quadratic complex rational function finite-difference time-domain is almost same as those of the nondispersive finite-difference time-domain. [ABSTRACT FROM AUTHOR]

Abstract: Improvement in the light extraction efficiency (LEE) of GaN-based green light emitting diodes (LEDs) with ZnO nanostructures synthesized by a hydrothermal method is reported. Formation of ZnO nanorods, hemispheres, and cones was controlled by varying the pH of the aqueous synthesis solution. The shape of the ZnO nanostructures integrated onto the LEDs shows a strong relationship with the LEE characteristics of GaN-based green LEDs. The electroluminescence (EL) intensity of LEDs covered by ZnO nanostructures increased compared to conventional LEDs. In terms of LEE, LEDs with surface-textured ZnO hemispheres showed the highest EL intensity, which can be attributed to an increase in the effective critical angle, the escape cone, and multiple scattering. Finite difference time domain (FDTD) simulation was conducted to theoretically confirm the experimental results. [Copyright &y& Elsevier]

Abstract: Improved optical absorption and photocurrent for polythiophene–fullerene bulk heterojunction photovoltaic devices is demonstrated using a unique self-assembled monolayer of Ag nanoparticles formed from a colloidal solution. With the presence of suitable nanoparticle organic capping groups that inhibit its propensity to agglomerate, the particle-to-particle spacing can be tailored. Transmission electron microscopy reveals the self-assembled Ag nanospheres are highly uniform with an average diameter of ∼4nm and controllable particle-to-particle spacing. The localized surface plasmon resonance peak is ∼465nm with a narrow full width at half maximum (95nm). In the spectral range of 350–650nm, where the organic bulk heterojunction photoactive film absorbs, an enhanced optical absorption is observed due to the increased electric field in the photoactive layer by excited localized surface plasmons within the Ag nanospheres. Under the short-circuit condition, the induced photo-current efficiency (IPCE) measurement demonstrates that the maximum IPCE increased to ∼51.6% at 500nm for the experimental devices with the self-assembled layer of Ag nanoparticles, while the IPCE of the reference devices without the plasmon-active Ag nanoparticles is ∼45.7% at 480nm. For the experimental devices under air mass 1.5 global filtered illuminations with incident intensity of 100mW/cm2, the increased short-circuit current density is observed due to the enhancement of the photogeneration of excitons near the plasmon resonance of the Ag nanoparticles. [Copyright &y& Elsevier]

The complex-conjugate pole-residue (CCPR) model has been popularly adopted because CCPR-finite-difference time domain (FDTD) can reduce the memory requirement with the help of complex conjugate property of auxiliary variables. To fully utilize CCPR-FDTD, it is of great necessity to investigate its numerical stability since the FDTD method is conditionally stable. Nonetheless, the numerical stability conditions of CCPR-FDTD have not been studied because its derivation is not straightforward. In this communication, the numerical stability conditions of CCPR-FDTD are systematically derived by combining the von Neumann method with Routh–Hurwitz criterion. It is found that the numerical stability conditions of CCPR-FDTD are the same as those of the modified Lorentz-FDTD with bilinear transform. Moreover, the numerical accuracy of CCPR-FDTD is studied, and numerical examples are employed to validate this work. [ABSTRACT FROM AUTHOR]

Finite-difference time domain (FDTD) has been widely used to analyze electromagnetic wave interaction with dispersive media. It is of great necessity to incorporate a dispersion model into FDTD formulation for electromagnetic wave analysis of dispersive media. Recently, it was reported that the modified Lorentz model can cover Debye, Drude, Lorentz, critical point, and quadratic complex rational function models. In this work, it is illustrated that the modified Lorentz model can also cover the complex-conjugate pole-residue model which is one of the most popular dispersion models. Modified Lorentz-based dispersive FDTD has not been thoroughly studied, especially for numerical aspects. In this work, we investigate auxiliary differential equation (ADE)-FDTD formulations for the modified Lorentz model based on electric flux density (D), current (J), or polarization (P). We perform a comprehensive study on memory requirement, the number of arithmetic operations, numerical stability, and numerical permittivity for the above three ADE-FDTD formulations. In addition, the bilinear transformation (BT) is incorporated into modified Lorentz-based FDTD formulations and it will be shown that the utilization of the BT can lead to better performance in terms of numerical stability and numerical accuracy. Numerical examples are used to demonstrate our work. [ABSTRACT FROM AUTHOR]

Chiral metamaterials comprise a promising platform for advanced optoelectronic and biomedical applications. However, conventional fabrication via lithography is limited by its complexity and high cost. Herein, the lithography‐free fabrication of terahertz chiral metamaterials and their enhancement for sensing the chirality of biocrystal enantiomers is presented. Chiral Au microstrip patterns (CHAMs) in a saw‐tooth shape are fabricated by combining two‐step buckling processes and glancing‐angle deposition. Non‐superimposable geometric chirality is achieved by controlling the tilt angle between the asymmetric and biaxial strain axes and the selective area deposition of the Au layers by using the shadow effect. The manufactured chiral metamaterials show mirror‐shaped terahertz circular dichroism (TCD) signals in the range of 0.2–2.5 THz. Coupling of the induced electric and magnetic dipoles to the chiral‐shaped Au surfaces results in effective optical chirality enhancement. Finite‐difference time‐domain computational simulations reveal the homogeneous distribution of optical chirality with an absolute maximum of 2.24 in the near field. Summing the TCD signals for enantiomeric cystine biocrystals onto the chiral metamaterials shows an ≈7‐fold amplification in magnitude. This enhancement can be attributed to the synergistic effects of superchiral field enhancement and the electromagnetic resonance between the CHAMs and biocrystals. [ABSTRACT FROM AUTHOR]

In this paper, an analytical method for evaluation of via-plate capacitance including finite plate thickness in multilayer structures is proposed. An electrostatic boundary-value problem associated with a via in parallel plates is solved based on the Hankel transform and mode matching method, and thereby a fast-converging series-form expression for the via-plate capacitance is derived. The effect of finite plate thickness is taken into account by adopting the mode matching method instead of imposing an artificial perfect magnetic conductor boundary as in the previous works. We perform some computations to show the behaviors of the capacitance in terms of the via geometry, and they are validated through comparison with a static/quasi-static simulation, full-wave electromagnetic simulation, and the previous analytical solutions of via capacitance. [ABSTRACT FROM AUTHOR]

Mode-matching analysis of a coaxially fed annular slot surrounded by corrugations is conducted in this study. An electromagnetic boundary value problem of a coaxially fed annular slot surrounded with corrugations is rigorously solved based on the Hankel transform, eigenfunction expansion, and mode-matching method. The radiated field is represented in a fast-convergent series that is amenable to numerical analysis. Numerical results are presented to illustrate the radiation behaviors in terms of the geometries of the corrugations and compared with measurement data. [ABSTRACT FROM AUTHOR]

This article proposes the design of a four‐element array antenna for the accurate direction of arrival (DOA) estimation of Global Positioning System (GPS) interference signals. The proposed array antenna has four individual antenna elements, and each element consists of a radiating patch on the upper layer and a feeding loop on the lower layer. The patch and loop are intentionally designed in a circular shape to obtain the symmetric current distributions on the radiators. The feeding loop is directly connected by two output ports of an external hybrid chip coupler, and the radiating patch is then electromagnetically coupled by near‐fields of the feeding loop. This feeding mechanism in the proposed structure allows for a more uniform current and H‐field distribution for phase characteristics of the radiation that are close to the ideal isotropic radiators in the azimuth angle. In addition, the high‐dielectric ceramic substrate is adopted to minimize the physical height of the antenna for the phase characteristics of the radiation close to the ideal isotropic radiators in elevation angles. To validate that the phase characteristics are similar to those of an ideal radiator, the DOA estimation performances are observed using a dual‐axis interferometry. The results demonstrate that the proposed four‐element array antenna with phase difference characteristics similar to those of an ideal radiator is suitable for the accurate DOA estimation of GPS interference signals. [ABSTRACT FROM AUTHOR]

A miniaturized spiral antenna with a broadband balun for a partial discharge (PD) localization system is proposed. The proposed antenna has broadband characteristic from 925 MHz to 1.6 GHz and a unidirectional radiation pattern. The overall dimensions of the fabricated antenna are 80 × 80 × 40 mm3, which is the smallest size among antennas for the PD detection system. The measured −10 dB reflection bandwidth starts at 925 MHz, and the measured directivity of the antenna is about 6 dB in the frequency band. [ABSTRACT FROM AUTHOR]

In this work, we present a dispersive finite-difference time-domain (FDTD) algorithm using a four-pole complex rational function (CRF). For the sake of a better curve fitting of the four-pole CRF dispersion model, we use a particle swarm optimization technique. We also discuss an efficient memory storage strategy using a state-space approach. The numerical aspects of four-pole CRF-FDTD, the numerical accuracy and the numerical stability, are investigated in detail. Numerical examples are used to validate four-pole CRF-FDTD and numerical stability issues are discussed in detail. We also discuss the computational accuracy and the computational efficiency of an arbitrary $N$-pole CRF-FDTD. [ABSTRACT FROM PUBLISHER]

This article presents an accurate finite-difference time domain (FDTD) dispersive modelling suitable for complex dispersive media. A quadratic complex rational function (QCRF) is used to characterise their dispersive relations. To obtain accurate coefficients of QCRF, in this work, we use an analytical approach and a particle swarm optimisation (PSO) simultaneously. In specific, an analytical approach is used to obtain the QCRF matrix-solving equation and PSO is applied to adjust a weighting function of this equation. Numerical examples are used to illustrate the validity of the proposed FDTD dispersion model. [ABSTRACT FROM PUBLISHER]

Recently, based on a quadratic complex rational function, a simple and accurate finite-difference time-domain algorithm was introduced for the study of electromagnetic wave propagation in dispersive media. It is of great necessity to investigate the numerical stability of the quadratic complex rational function–finite-difference time-domain to fully utilize this finite-difference time-domain algorithm. In this work, using the von Neumann method with the Routh–Hurwitz criterion, the numerical stability conditions of the quadratic complex rational function–finite-difference time-domain are investigated. It is shown that the numerical stability conditions of the quadratic complex rational function–finite-difference time-domain are not same as those of the conventional finite-difference time-domain schemes. [ABSTRACT FROM AUTHOR]

Electromagnetic transmission through a slit surrounded by rectangular grooves in a conducting plane is investigated. An electromagnetic boundary-value problem associated with a slit surrounded by rectangular grooves in a conducting plane is rigorously solved based on the Fourier transform, eigenfunction expansion and mode matching method. The transmission coefficient through the slit is represented in a series. Computation is performed to illustrate the effect of the groove geometry on the transmission behaviours. [ABSTRACT FROM AUTHOR]

Enhanced transmission through a circular aperture surrounded by concentric surface corrugations in a conducting plane is investigated. A boundary-value problem of electromagnetic wave scattering from a circular aperture surrounded by concentric surface corrugations is rigorously solved based on the Hankel transform, eigenfunction expansion, and mode-matching method. The transmission coefficient is represented in a fast-convergent series that is amenable to numerical analysis. Computation is performed to illustrate the transmission behaviors in terms of the geometries of the concentric corrugations. The effects of the higher-order modes on the transmission coefficients are also discussed. [ABSTRACT FROM AUTHOR]

Directional emission from a slit surrounded by rectangular grooves on the exit surface in a conducting plane is investigated. An electromagnetic boundary-value problem dealing with a slit surrounded by rectangular grooves on the exit surface in a conducting plane is rigourously solved based on the Fourier transform, eigenfunction expansion, and mode-matching method. The radiation pattern from the slit is represented in a series and computed to illustrate the radiation behaviors in terms of the groove geometry. [ABSTRACT FROM PUBLISHER]

We propose a dispersive finite-difference time domain (FDTD) suitable for the electromagnetic analysis of human tissues. The dispersion relation of biological tissues is characterized by a quadratic complex rational function (QCRF) that leads to an accurate FDTD algorithm in 400 MHz–3 GHz. QCRF coefficients are extracted by applying the complex-curve fitting technique, without initial guess. Numerical examples are used to illustrate the computational accuracy and stability of QCRF-based FDTD. [ABSTRACT FROM PUBLISHER]

This letter examines the capacitance of coplanar waveguides (CPWs) in multilayer dielectric substrates.An electrostatic boundary-value problem of CPWs in multilayer dielectric substrates is solved based on the Fourier transform, mode matching technique, and superposition considering the conductor thickness. A series representation for the capacitance is presented. The capacitance is calculated in terms of the CPW geometry to illustrate its behaviors. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:1886-1889, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26938 [ABSTRACT FROM AUTHOR]