Search

Glucose plays a key role in the regulation of the levels of blood sugar, and the body closely monitors it to maintain proper metabolic function. Although glucose is essential for human health, its excessive consumption can lead to negative effects such as obesity and diabetes. As a result, high-sensitive and accurate glucose detection is considered an essential measure in clinical analysis. Surface-enhanced Raman scattering (SERS) is an accurate method for identifying trace substances. In the present study, SERS-active substrates were used for detecting different concentrations of glucose. First, gold nanoparticles (AuNPs) were prepared by employing a chemical reduction method. Afterward, the fluorine-doped tin oxide (FTO) glass substrates were decorated with AuNPs using the electrodeposition method. Then, glucose was deposited as an analyte on SERS substrates. Interestingly, the limit of detection (LOD) of SERS-active FTO-covered glass substrates (SERS-FGS) for the detection of glucose was 10−9 M. Density functional theory (DFT) method was used to simulate and validate the Raman spectra and peak signals obtained experimentally. Moreover, the average relative standard deviation (RSD) was calculated as 3.06% for ten repeated measurements. Furthermore, the enhancement factor for these SERS-based biosensors, for the identification of molecular vibrations of 10−5 M glucose, was obtained to be 1.4310 × 104 experimentally and 1.5397 × 104 numerically. Therefore, the SERS-FGS developed in this study showed promising results for detecting glucose and controlling diseases, such as diabetes and other problems resulting from an abnormality in glucose levels. [ABSTRACT FROM AUTHOR]

Narrow bipolar events (NBEs) are impulsive and powerful intracloud discharges. Recent observations indicate that some NBEs exhibit a slanted orientation rather than strictly vertical. This paper investigates the effect of the slanted NBEs using a newly developed rebounding‐wave model. The modeling results are validated against the full‐wave Finite‐ Difference Time‐Domain method and compared with measurements for both vertical and slanted NBE cases. It is found that the inclination of the NBEs affects both the waveforms and amplitudes of the electrostatic, induction and radiation components of the electric fields at close distances (≤10 km). However, it primarily influences the amplitudes of the fields for distances beyond 50 km, where the radiation component dominates, resulting in changes of ≥30% when the slant angle exceeds 30°. The slanted rebounding‐wave model improves the agreement with respect to a purely vertical channel and can be extended to any discharge geometry at arbitrary observation distances. Plain Language Summary: Narrow Bipolar Events (NBEs) are unique intracloud discharges that occur either individually or as the initiation event for lightning flashes inside thunderstorms. Knowing the physical mechanisms of NBEs will help us to better understand how lightning initiates inside thunderstorms. Recent studies indicated that NBEs could exhibit a slanted orientation rather than being strictly vertical. However, the inclination of NBEs has not been considered in previous transmission line models, leading to uncertainty when evaluating their characteristics based on electromagnetic fields. Here, in the light of recent observations, we analyze the propagation effect of the slanted NBEs by using a newly developed slanted rebounding‐wave model, and we compare the modeling results with observations. This study contributes to a better understanding of the physical mechanism of NBEs and provides a reference for accurately characterizing NBEs based on their electromagnetic fields. Key Points: The propagation effect of slanted Narrow bipolar events (NBEs) at different distance is investigated and compared with the observationsThe inclination of the NBEs could significantly affect the electromagnetic fields in the close distanceThe proposed equations will improve the quality of inferred features of slanted NBEs and can be extended to any discharge shape [ABSTRACT FROM AUTHOR]

This paper proposes a surface plasmon resonance (SPR) biosensor based on the Kretschmann configuration including a bilayer of silver metal (Ag), molybdenum disulfide (MoS2), molybdenum trioxide (MoO3), titanium carbide MXene (Ti3C2Tx), and a BK7 coupling prism. The proposed device is designed as a refractive index sensor for hemoglobin measurement in human blood samples. The finite difference time domain (FDTD) technique has been used to evaluate the performance parameters of the sensor. Silver metal and 2D material thickness is optimized using an angular interrogation technique to minimize reflectance. The proposed biosensor exhibits the maximum sensitivity (S) of 218 deg/RIU, at a sensing medium of 1.32919–1.34919 with Δns = 0.005 RIU. Other parameters a detection accuracy of 0.182 deg−1, a figure of merit of 40.63 RIU−1, and a limit of detection of 4.587 × 10–6 have been obtained. The proposed SPR biosensor effectively increases the strength of the interaction between the incident light and the analyte, resulting in a relatively reduced propagation loss. Therefore, the suggested sensor is a suitable candidate to detect and analyze biomolecules. [ABSTRACT FROM AUTHOR]

The convolutional perfectly matched layer (CPML) is implemented for the low‐dispersion one‐step leapfrog hybrid implicit‐explicit (HIE) finite‐difference time‐domain (FDTD) method. The implementation process of CPML in the low‐dispersion leapfrog HIE‐FDTD method is demonstrated in this work. In addition, a dual‐band multiple‐input multiple‐output (MIMO) antenna was simulated and designed using the proposed scheme, and the dual‐band MIMO antenna was also fabricated and measured. The effectiveness of the proposed scheme was verified by comparing the simulation and experimental results of scattering parameters, relative errors, and radiation patterns. [ABSTRACT FROM AUTHOR]

In this paper, we have proposed a new type of multi-layer solar cell structure based on multi-walled carbon nanotube (MWCNT) photonic crystals grown on a silicon substrate. The structure is constructed by stacking layers of MWCNTs array with different lattice constants from 100 to 800 nm as an active layer. It exhibits a remarkable absorption efficiency, reaching a peak value of 92.61% within a broad absorption spectrum spanning from 100 to 2000 nm. The absorption capacity and range are significantly improved compared to conventional solar cell structures. The effect of the filling factor on the absorption coefficient was examined. Various filling factor values ranging from 4 to 60% were evaluated to optimize the structure, with the most favorable outcome observed at a filling factor of f = 30%. The host medium is silicon, which is fully compatible with Si technology, enabling seamless easy integration with other Si-based technology devices. [ABSTRACT FROM AUTHOR]

In this paper, we develop a finite-difference time-domain (FDTD) model in which the time-evolving electrical conductivity of the air ionization plasma in DC voltage needed-plate setup is represented. Maxwell's equations are solved using the FDTD method, and the associated currents and discharge fields are computed over time and in three-dimensional space. The proposed model for the electrical conductivity is dependent on time, the applied DC voltage, and the gap length. The necessary data for developing the proposed model is obtained experimentally using a standard discharge needle, with its spherical tip measuring approximately 40 μ m in diameter. Once high voltage is applied, a steady state is achieved. The electrical conductivity σ (t) and its associated parameters are then calculated using nonlinear equations proposed to reproduce the experimentally obtained plasma behavior in the full-wave FDTD model. Voltage ranges from 4 kV to 9 kV, and gap distances are between 4 mm and 8 mm. [ABSTRACT FROM AUTHOR]

The plasma sheath can absorb or reflect electromagnetic waves, thus affecting the communication of hypersonic vehicles. The study of attenuation and enhancement of electromagnetic scattering by plasma is of great significance. We propose a novel Z-transform finite-difference time-domain (ZT-FDTD) method to study the interaction between electromagnetic waves and plasmas. The numerical results show that this method has high accuracy and improves the computational efficiency by 9.8 percent, compared to the traditional ZT-FDTD method. We investigated the enhancement and attenuation of electromagnetic scattering by plasma at different plasma frequencies and plasma collision frequencies. The variation in the electric field amplitude in the plasma was studied under different electromagnetic scattering conditions. Through the hybrid plasma model, the changes in electromagnetic scattering and in the electric field amplitude under plasma stealth were further investigated. The position of the maximum electric field amplitude and the variation in the zero-value region of the electric field amplitude correspond to the different effects of plasma on electromagnetic scattering. The research methods and ideas in this study have important reference values and provide a new perspective for studying plasma stealth technology and solving the “blackout” problem.

In remote sensing problems, broadband scattering investigation becomes increasingly important than ever before. The scattering characteristic changes significantly with the variation of range. Thus, the conventional evaluation method becomes invalid in many situations. Meanwhile, an efficient method for the simulation of electromagnetic wave propagation in electrically large remote sensing problem is also an urgently demanding. In order to alleviate such problems, an alternative Crank-Nicolson Direct-Splitting algorithm is proposed in open regions. To infinite extension of the computational domain, convolutional perfectly match layer with higher order formulation is proposed not only to further enhance the absorption at low-frequency band but also to decrease the reflections during the entire time domain simulation. Efficient method is proposed for scattering characteristics evaluation which ranges from near-field to far-field. Radar remote sensing Problems including ground penetrating radar and early warning radar are introduced to demonstrate the effectiveness of the algorithm. Through the results, it can be concluded that the proposed algorithm shows considerable performance in the simulation of remote sensing problems.

High-quality silicon-based lasers are necessary to achieve full integration of photonic and electronic circuits. Monolithic integration of III–Vmicron lasers on silicon by means of the aspect ratio trapping (ART) method is a promising solution. To obtain sufficient optical feedback to excite the laser without introducing complex fabricating processes, we have designed a high-order surface grating on micron lasers which was epitaxially grown by the ART method and can be fabricated by common UV lithography. The performance of the grating was analyzed by the finite-difference time-domain (FDTD) method and eigenmode expansion (EME) solver. After simulation optimization, the etching depth was set to 0.6 μm to obtain proper reflection. The width of the slots and the slot spacing were selected to be 1.12 μm and 5.59 μm, respectively. Finally, we obtained results of 4% reflectance and 82% transmittance at a 1.55 μm wavelength at 24 periods. [ABSTRACT FROM AUTHOR]

The perfectly matched layer (PML) has the ability to terminate the finite‐difference time‐domain (FDTD) lattice successfully. It is crucial to investigate the interaction between electromagnetic waves and the PML. Utilizing the Runge–Kutta method of order 2 accuracy, we derive a novel and efficient complex frequency‐shifted (CFS) PML implementation algorithm, which is named the RK‐PML. To validate the RK‐PML, we provide two numerical examples, which include rectangular waveguide and plasma cube truncated by the PML. By analyzing the time‐domain relative reflection errors, the frequency‐domain reflection coefficients, the computational time, and the memory footprint, the proposed RK‐PML outperforms slightly the convolutional PML (CPML). [ABSTRACT FROM AUTHOR]

We propose a novel micro-nano structure that can realize a photonic nanojet (PNJ) switch by adjusting the temperature, which is composed of a truncated cylinder coated with a thin vanadium dioxide (VO2) film. The influence of temperature on the maximum strength, full width at half maximum (FWHM), working distance, and focal length of the PNJ were studied by finite-difference time-domain (FDTD) method. The results demonstrate that the structure can adjust the open and close state of the PNJ by changing the temperature. A PNJ with varying characteristics can be obtained at both high and low temperatures, and the maximum intensity ratio of the PNJ can reach up to 7.25. This discovery provides a new way of optical manipulation, sensing and detection, microscopy imaging, optoelectronic devices, and other fields. [ABSTRACT FROM AUTHOR]

The original Factorization‐Splitting (FS) algorithm solves large number of coefficients and components in each iteration cycle which significantly affects the computational resources and calculation efficiency. Meanwhile, it can merely solve problems in uniform domains due to the limitation of discretized mesh sizes. In order alleviate these drawbacks, system incorporated factorization‐splitting algorithm is proposed to efficiently solve problems in nonuniform domains. The finite‐difference time‐domain (FDTD) domain is terminated by the higher order perfectly matched layer (PML) formulation which shows advantages in improving the absorbing performance. As the employment of the original domain decomposition method results in the algorithm unstable, an alternative domain decomposition method is proposed which can split the entire nonuniform domain into several sub‐regions. Metamaterial structure is introduced to demonstrate the performance of the proposed algorithms. Through results, the proposed algorithm can decrease memory consumption and simulation duration due to the calculation prevention of repeated components and coefficients. The absorption can be further improved especially in the low‐frequency band due to the enhanced absorption of propagation waves. In addition, the alternative domain decomposition method shows considerable advantages in the simulation of nonuniform domains. [ABSTRACT FROM AUTHOR]

In this paper, the results of studies on sub-micrometer planar structures used for aimed frequency-dependent electromagnetic radiation dissipation are presented. The proposed specific geometry of periodic parts of surface structures should enable the occurrence of phenomena related to selective reflectance and interference. The inner porous structure should lead to the formation of destructive interference of electromagnetic radiation and its dissipation. The investigated structures were irradiated by a Gaussian-type radiation source. The propagation was analyzed using the MEEP software package for electromagnetic simulation via the finite-difference time-domain method. The reflectance spectra were obtained by the Fourier transform of the response to the short pulse. The obtained results showed that the surface structures are mainly responsible for reflected electromagnetic spectrum composition, while the porous parts were responsible for thermal radiation dissipation. [ABSTRACT FROM AUTHOR]

In one-dimensional phononic crystals, as a result of multiple destructive interferences of a mechanical wave, the phononic band gap phenomenon occurs, i.e., the lack of propagation of a wave of a given frequency through the structure due to internal reflections at the layer boundary and destructive interference. In dynamic phononic crystals, the incident monochromatic mechanical wave at the boundary of the media does not propagate according to Fresnel's relations, but is transformed into a wave spectrum, which affects the phononic properties of the examined structures and allows them to be dynamically controlled. The paper analyzes the transmission and influence of the frequency of changes in the properties of the elements of the finite phononic structure described by sinusoidal functions on the propagation of mechanical waves. [ABSTRACT FROM AUTHOR]

Nowadays, miniaturized optical integrated circuits make a great evolution in optical microelectronics technology. In data processing chains, the need for an ultra-fast all-optical encoder is necessary for a large data transfer. In this work, we have proposed an all-optical encoder structure based on nonlinear 2D photonic crystals with Kerr effect exploiting a nonlinear polymer material of high third-order optical susceptibility. In addition, to generate the telecommunication domain wavelength at 1.55 µm, an optimization of the optical-geometry parameters has been realized. Simulations will be performed using plane wave expansion and finite difference time domain methods. The nonlinear effect allows an excellent average contrast ratio of 37.02 db, as the structure requires a very low threshold intensity estimated at 1.5 mW/µm2. The significant power transmitted to the output is equal to 73% and 0.015% of input power equivalent to logic state "1" and logic state "0" respectively. The proposed structure generates a bit rate of 2.23 Tb/s, therefore able to adapt with other ultrafast all-optical circuits. [ABSTRACT FROM AUTHOR]

In this paper, a metal–insulator–metal waveguide is paired with a hexagonal irregular ring resonator to construct a high sensitivity refractive index plasmonic nano-sensor in this work. The sensing properties of the proposed design are studied using a numerical solution in the finite-difference time-domain. The acquired results reveal a linear connection between the material's refractive index (RI) and the wavelength of resonances. Furthermore, the maximum linear sensitivity for the second mode is S = 2417 nm/RIU, with a figure of merit (FOM) of 38, whereas the highest for the first mode is S = 1002 nm/RIU, with a FOM of 28.6. With a sensitivity of 1.02 nm/°C, this sensor is also being examined as a temperature sensor. When ethanol is employed as the measuring liquid, the sensor's operating temperature range is between—114.3 and 78 °C. This device can create a path toward RI by being highly sensitive for the label-free diagnosis of different molecules and providing temperature sensing abilities. It can also be used in microchip processors and has a wide spectrum of biological applications. [ABSTRACT FROM AUTHOR]

In this paper, we develop a finite-difference time-domain (FDTD) model in which the time-evolving electrical conductivity of the air ionization plasma in DC voltage needed-plate setup is represented. Maxwell’s equations are solved using the FDTD method, and the associated currents and discharge fields are computed over time and in three-dimensional space. The proposed model for the electrical conductivity is dependent on time, the applied DC voltage, and the gap length. The necessary data for developing the proposed model is obtained experimentally using a standard discharge needle, with its spherical tip measuring approximately 40 μm in diameter. Once high voltage is applied, a steady state is achieved. The electrical conductivity σ(t) and its associated parameters are then calculated using nonlinear equations proposed to reproduce the experimentally obtained plasma behavior in the full-wave FDTD model. Voltage ranges from 4 kV to 9 kV, and gap distances are between 4 mm and 8 mm.

A high-temperature plasma sheath is generated on the surface of the re-entry vehicle through the conversion of kinetic energy to thermal and chemical energy across a strong shock wave at the hypersonic speed. Such a condition results in the forming of a blackout which significantly affects the communication components. To analyze the re-entry vehicle at the hypersonic speed, an unconditionally stable system incorporated factorization-splitting (SIFS) algorithm is proposed in finite-difference time-domain (FDTD) grids. The proposed algorithm shows advantages in the entire performance by simplifying the update implementation in multi-scale problems. The plasma sheath is analyzed based on the modified auxiliary difference equation (ADE) method according to the integer time step scheme in the unconditionally stable algorithm. Higher order perfectly matched layer (PML) formulation is modified to simulate open region problems. Numerical examples are carried out to demonstrate the performance of the algorithm from the aspects of target characteristics and antenna model. From resultants, it can be concluded that the proposed algorithm shows considerable accuracy, efficiency, and absorption during the simulation. Meanwhile, plasma sheath significantly affects the communication and detection of the re-entry vehicle. [ABSTRACT FROM AUTHOR]

We perform full-wave electromagnetic simulations to investigate the formation of higher-order localized surface plasmons (LSP) in a multilayered Au-Si-Au nanodisk architecture and their evolution with the doping level and thickness of the semiconducting layer. We show that higher-order LSP modes can be efficiently excited and controlled not only by changing the thickness of the intermediate Si layer but also by optically tuning its doping level. We provide a detailed study of the nature and origin of the hybrid modes resulting from the hybridization of nanodisk primitive LSP modes. This approach substantially improves the functionality of the nanodisk stack structure and opens up a new practical pathway for the active control of the optical response of plasmonic-based and semiconducting-based devices. [ABSTRACT FROM AUTHOR]

This paper presents a performance comparison of heterostructure surface plasmon resonance (SPR) biosensors for the application of Novel Coronavirus SARS-CoV-2 diagnosis. The comparison is performed and compared with the existing literature based on the performance parameters in terms of several prisms such as BaF2, BK7, CaF2, CsF, SF6, and SiO2, several adhesion layers such as TiO2, Chromium, plasmonic metals such as Ag, Au, and two-dimensional (2D) transition metal dichalcogenides materials such as BP, Graphene, PtSe2 MoS2, MoSe2, WS2, WSe2. To study the performance of the heterostructure SPR sensor, the transfer matrix method is applied, and to analyses, the electric field intensity near the graphene-sensing layer contact, the finite-difference time-domain approach is utilized. Numerical results show that the heterostructure comprised of CaF2/TiO2/Ag/BP/Graphene/Sensing-layer has the best sensitivity and detection accuracy. The proposed sensor has an angle shift sensitivity of 390°/refractive index unit (RIU). Furthermore, the sensor achieved a detection accuracy of 0.464, a quality factor of 92.86/RIU, a figure of merit of 87.95, and a combined sensitive factor of 85.28. Furthermore, varied concentrations (0–1000 nM) of biomolecule binding interactions between ligands and analytes have been observed for the prospects of diagnosis of the SARS-CoV-2 virus. Results demonstrate that the proposed sensor is well suited for real-time and label-free detection particularly SARS-CoV-2 virus detection. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Central South University is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper provides a time domain method for solving the induced currents (and voltages) of frequency-dependent lossy multiconductor transmission lines (MTLs) model randomly excited by electromagnetic pulse (EMP) plane wave. The model is processed based on the generalized polynomial chaos expansion (gPCE) and improved finite difference time domain (FDTD). The improved FDTD method overcomes the shortcomings of the conventional method that oversimplifies the expression of conductor impedance. In addition, when quantifying the influence of uncertainty on induced values, general formula of the global sensitivity analysis is provided by defining the gPCE basis function sequence to solve the complicated search work. The verification shows that the improved FDTD method alone or combined with gPCE to solve the lossy MTLs model excited by EMP is superior to the conventional methods in solving time and accuracy. Finally, compared with the Monte Carlo method, the effectiveness of the sensitivity method is also verified. [ABSTRACT FROM AUTHOR]

A detailed dosimetry study of electromagnetic absorption and temperature rise under real scenarios is delivered when a mobile phone is used inside an elevator cabin. Numerically accurate human models of a 7th month pregnant woman and a 5-year-old female child are utilized as the exposed subjects. The female child acts as the phone user. The mobile phone is modeled in three talk positions (parallel, tilt, and cheek) operating at 1000 MHz and 1800 MHz. From the obtained numerical results for the specific absorption rate (SAR) and temperature rise induced by the mobile radiofrequency (RF) radiation, it is found that the child's RF exposure is significantly affected by the phone position and less affected by the relevant position of the human models. The exact opposite case applies for the pregnant woman model and its fetus. Almost all numerical investigations are carried out inside a metallic elevator cabin. [ABSTRACT FROM AUTHOR]

High-quality silicon-based lasers are necessary to achieve full integration of photonic and electronic circuits. Monolithic integration of III–Vmicron lasers on silicon by means of the aspect ratio trapping (ART) method is a promising solution. To obtain sufficient optical feedback to excite the laser without introducing complex fabricating processes, we have designed a high-order surface grating on micron lasers which was epitaxially grown by the ART method and can be fabricated by common UV lithography. The performance of the grating was analyzed by the finite-difference time-domain (FDTD) method and eigenmode expansion (EME) solver. After simulation optimization, the etching depth was set to 0.6 μm to obtain proper reflection. The width of the slots and the slot spacing were selected to be 1.12 μm and 5.59 μm, respectively. Finally, we obtained results of 4% reflectance and 82% transmittance at a 1.55 μm wavelength at 24 periods.

Low-pressure discharge causes air ionization resulting in performance degeneration or failure for the satellite sensors in outer space. Here, a one-step Crank-Nicolson Direct-Splitting (CNDS) algorithm is proposed to evaluate the electrical behavior of satellite sensors under the low-pressure discharge circumstance. To be more specific, the CNDS algorithm is proposed in the Lorentz medium, which can accurately analyze the ionized air and generated plasma. Higher order perfectly matched layer (PML) is modified in the Lorentz medium to efficiently terminate the unbounded lattice. It can be concluded that the proposed algorithm shows entire considerable performance in the low-pressure discharge evaluation. The proposed PML formulation behaviors enhanced absorbing performance compared with the existing algorithm. Through the experiments, it can be observed that the low-pressure discharge phenomenon causes performance variation, which shows a significant influence on the satellite sensors. Meanwhile, results show considerable agreement between the simulation and experiment results which indicates the effectiveness of the algorithm. [ABSTRACT FROM AUTHOR]

High-intensity focused ultrasound (HIFU) is a therapy method to treat the tumors in prostate, liver, kidney, pancreas, bone, breast, and uterine fibroids. In the HIFU therapy process, the ultrasound generated in an ultrasonic transducer concentrates on a focal zone. At the zone, the temperature rises locally up to 56°C to provoke the necrosis of human tissue. Therefore, to control the therapy process, it is essential to perceive the main principle of heat generation in human tissue. We study FDTD-LBM (finite difference time domain—lattice Boltzmann method) as a method of predicting the temperature distribution in human tissue during HIFU therapy. The nonlinear Westervelt wave equation is employed for computing the pressure distribution in human tissue during ultrasound propagation, while the Pennes bio-heat transfer equation is used for calculating the temperature distribution in the tissue. Finite difference time domain (FDTD) is applied to solving the nonlinear Westervelt wave equation, and the lattice Boltzmann method can solve the Pennes bio-heat transfer equation. Simulation results have shown that the numerical simulation method proposed has improved the accuracy in analyzing the temperature field in human tissue. [ABSTRACT FROM AUTHOR]

This study proposes, designs, and simulates a unique plasmonic Y-shaped MIM waveguide based 2 × 1 multiplexer (MUX) structure utilising opti-FDTD software. Two plasmonic Y-shaped waveguides are positioned facing one another inside a minimum wafer size of 6 µm × 3.5 µm in the 2 × 1 MUX configurations that is being described. The design parameters are adjusted until the plasmonic multiplexer performs as required under optimal conditions. Extinction ratio and insertion loss are two performance metrics that are calculated for performance analysis of the design, which indicate the potential to be applied in plasmonic integrated circuits. [ABSTRACT FROM AUTHOR]

We fabricated amorphous photonic structures (APSs) with different periods and hole diameters. The GaN-based white light emitting diodes (LEDs) at nominal correlated color temperatures (CCTs) of 5000 and 6000 K were surface mounted by these APSs. The electroluminescence (EL) measurements showed less luminous efficiency (LE) and higher CCT than the ones of the virginal white LEDs. However, the LEs of many APS-mounted white LEDs increased compared to white the LEDs without APSs at the same CCTs. A finite-difference time-domain (FDTD) simulation was carried out on the ASPs surface-mounted white LEDs and bidirectional scattering distribution functions (BSDFs) of different emissions were transferred to a Monte Carlo ray tracing simulation. The simulated LEs and CCTs conformed well to the experimental ones. The effects of the blue emission transmission and phosphor concentration were simulated to predict the absolute LE enhancement methods for white LEDs. At last, the hopeful APSs for high Les' general lighting were discussed. [ABSTRACT FROM AUTHOR]

In this letter, Wait's exponential (EXP) model and international reference ionosphere (IRI) model are combined to study the diurnal variation characteristics of very low frequency (VLF) wave propagation. The EXP model is used below the IRI model to compensate for the subionosphere electron density lack of the IRI. The major EXP parameters are reconstructed from the lower IRI electron density for different times of the day. Being capable of characterizing the subionosphere details, the combined IRIEXP model gets higher accuracy than the pure IRI model for VLF diurnal variation prediction. The measurement result is replicated by using the finite-difference time-domain method to validate the presented model. [ABSTRACT FROM AUTHOR]

We propose a novel micro-nano structure that can realize a photonic nanojet (PNJ) switch by adjusting the temperature, which is composed of a truncated cylinder coated with a thin vanadium dioxide (VO2) film. The influence of temperature on the maximum strength, full width at half maximum (FWHM), working distance, and focal length of the PNJ were studied by finite-difference time-domain (FDTD) method. The results demonstrate that the structure can adjust the open and close state of the PNJ by changing the temperature. A PNJ with varying characteristics can be obtained at both high and low temperatures, and the maximum intensity ratio of the PNJ can reach up to 7.25. This discovery provides a new way of optical manipulation, sensing and detection, microscopy imaging, optoelectronic devices, and other fields.

Determining subsurface properties through ground penetrating radar sounding can be challenging, especially in planetary exploration, where little is known about the terrain and additional observations are limited. Analysis and interpretation of data acquired with the Radar Imager for Mars’ Subsurface Experiment (RIMFAX) could therefore be improved by in-detail comparison with forward modeling. RIMFAX transmits a frequency modulated continuous waveform and utilizes a stretch processing receiver, and we demonstrate how accurate modeling can be achieved through finite-difference time-domain simulations. As the simulation scheme do not allow for direct implementation of such radar system, this study presents the necessary steps in order to replicate the same transmitter and receiver characteristics. In particular, we investigate how the method holds for modeling sounding in a realistic subsurface medium with attenuating and dispersive properties, by comparing the results with analytical estimates. The modeling approach is also assessed through comparison with RIMFAX field test measurements.

Based on a higher‐order concept and one‐step leapfrog formulation, an unconditionally stable leapfrog locally 1D (LOD) perfectly matched layer (PML) is proposed to not only enhance the absorbing performance in terminating an unbounded finite‐difference time‐domain (FDTD) algorithm but also improve the computational efficiency compared with the LOD‐FDTD algorithm. Most precisely, the PML is implemented by the auxiliary differential equations method. By applying the proposed scheme to a 3D electromagnetics simulation, the proposal can utilize the unconditionally stable algorithm, one‐step leapfrog formulation, and higher‐order concept in terms of attenuating low‐frequency propagation waves, enhancing the performance, and improving the computational efficiency. Numerical examples including the magic‐T waveguide model, very large‐scale integration circuits, and the structure of metamaterials are investigated to further demonstrate the efficiency, performance, and unconditional stability. The results help conclude that the proposed scheme can attain better performance and efficiency when the time step far surpasses the Courant–Friedrichs–Lewy limit. Most importantly, by employing the one‐step leapfrog formulation in the LOD algorithm, the memory requirements and simulation duration can be reduced significantly, indicating the improvement of the algorithm compared with the published LOD schemes. [ABSTRACT FROM AUTHOR]

This paper presents an approach for the time domain statistical simulation of field-to-wire coupling model with uncertain wire position in traverse direction. The parameters of governing equations of field-to-wire coupling model about the wire position are expanded to the augmented governing equations by using the generalized polynomial chaos technique with normalized orthogonal basis functions. And the coefficients of the polynomial chaos expansions are solved by combining with the stochastic Galerkin method. However, the solution of augmented governing equations is a complex problem. Therefore, a new finite-difference time-domain (FDTD) algorithm based on the implicit Wendroff difference format is proposed to solve the governing equations, and the general iterative equations are given in this paper. The proposed methods are verified by a field-to-wire coupling model. The effectiveness and advantages of the new FDTD algorithm and the uncertainty analysis method based on generalized polynomial chaos technique are verified, which are achieved by comparing with the conventional leapfrog fashion FDTD algorithm and the Monte Carlo technique, respectively. [ABSTRACT FROM AUTHOR]

In this letter, the unconditionally stable associated hermite (AH) finite-difference time-domain (FDTD) method is extended to analyze three-dimensional (3-D) periodic structure. By combining the 3-D AH FDTD method and split-field technique, a 13-points coefficient matrix equation to eliminate phase shift is obtained with the corrected nonzero elements. To deal with the overflow at the periodic boundaries, the coefficient matrix is updated by the Floquet theory as long as the treatment of the angular points at the periodic boundary. The updating equation of the source term is derived by the total-field/scattered-field formula. The proposed method is verified by calculating the reflection coefficients of the infinite dielectric slab and the Jerusalem Cross FSS structure, respectively. The former shows a higher accuracy compared with the analytical solution with the average relative difference below $-$ 60 dB, and reflects less sensitive to the angle of incidence. And the later represents 7 times efficiency than that of the split-field FDTD method while keeping a sound accuracy. [ABSTRACT FROM AUTHOR]

In this letter, the convolution perfectly matched layer (CPML) is modified and implemented for an efficient 3-D finite-difference time-domain method with weighted Laguerre polynomials (WLP-FDTD). The formulations are derived from the CPML equations for conventional WLP-FDTD. A factorization-splitting scheme is used to achieve the high efficiency. Numerical results are given to verify the absorbing performance and efficiency of the proposed CPML. [ABSTRACT FROM AUTHOR]

Based on the auxiliary differential equation (ADE), a performance-enhanced convolution perfectly matched layer (CPML) for the face-centered cubic finite-difference time-domain (FCC-FDTD) method is developed in this letter. Unlike the traditional FDTD methods on Yee’s grids, for which the CPML technique is relatively straightforward to be implemented, poor performance, and even instability may occur in the FCC-FDTD method. To avoid these problems, the ADE technique is incorporated into the derivation, and the impact of node locations on absorbing boundary constitutive parameters is carefully considered. In addition, the derivation of the time-marching formulations is substantially simplified. The optimal ranges of constitutive parameters are found through a numerical sweep. Two numerical examples, the electromagnetic pulse propagation and absorbed power density of a brain model during mobile communication, are examined to validate the performance. The results suggest that the proposed ADE-CPML for the FCC-FDTD method shows good stability and accuracy. [ABSTRACT FROM AUTHOR]

The solution to finely detailed finite-difference time-domain (FDTD) models is often intractable due to the Courant–Friedrichs–Lewy (CFL) condition. Subgridding offers an attractive solution to this problem. In particular, the Huygens subgridding (HSG) exhibits great performance characteristics. It features high subgridding ratios and relatively small interfacing errors. However, late time instability reduces its utility. This article presents the switched Huygens subgridding (SHSG), a fundamental modification to the HSG that improves its stability. It is shown that the SHSG is at least $143 \times $ more stable than the HSG for a 3-D subgridded half-wave dipole problem and at least $10 \times $ more stable for a 1-D resonant subgridding problem. The SHSG runs $1.9 \times $ faster per iteration (in the dipole experiment) since it does not require a PML in the subgrid to enhance stability. The accuracy of the SHSG is shown to be comparable with the HSG. Also, the fields in all overlapping regions are computed equal to the single space solution at all time steps simplifying the extraction of information in these regions. This new SHSG method is more straightforward to implement and optimize due to the simplicity of its proposed stabilization mechanism. [ABSTRACT FROM AUTHOR]

For an accurate and efficient calculation of fine geometry along a single direction in open regions, a bandpass one‐step hybrid implicit–explicit (HIE) procedure with promoted absorption is implemented in this study. More precisely, the proposed scheme is modified by integrating complex envelope (CE) method, higher order concept, perfectly matched layer (PML) formulation, and one‐step leapfrog HIE procedure. Furthermore, by introducing property variables, efficiency can be improved significantly. In addition, the proposed scheme not only overcomes the Courant–Friedrich–Levy stability condition but also solves the efficiency decrement problem of implicit algorithms. The effectiveness of the proposed algorithm is validated and demonstrated both numerically and experimentally. According to the results, we can conclude that the proposed scheme is advantageous in terms of enhanced accuracy, promoted absorption, improved efficiency for fine geometry along a single direction in bandpass open region problems. [ABSTRACT FROM AUTHOR]

Bee's eye has thousands of integrated optical units called ommatidia. Each ommatidium consists of a light-diffracting facet lens, a crystalline cone, and photoreceptor cells with a wave-guiding rhabdom. The presented work shows the simulation of propagation of light in a biologically inspired microwaveguide based on the structure of the bee's sensory elements in compound eyes. The propagation was analyzed using the Meep software package for electromagnetics simulation via the finite-difference time-domain method. The transmittance spectra were obtained by the Fourier transform of the response to the short pulse. [ABSTRACT FROM AUTHOR]

In this letter, the convolutional implementation of the complex frequency shifted perfectly matched layer (CFS-PML) absorbing boundary condition (ABC) is proposed for the finite-difference time-domain (FDTD) method of solving wave equation. The FDTD solution time-marching formulations of the developed wave-equation convolutional CFS-PML (CPML) ABC are derived. Several numerical experiments are used to verify the capacity of the proposed algorithm. Solution results confirm that the proposed CPML ABC can obtain excellent absorption for both traveling waves and evanescent waves. [ABSTRACT FROM AUTHOR]

A large number of sensors work in the narrow bandpass circumstance. Meanwhile, some of them hold fine details merely along one and two dimensions. In order to efficiently simulate these sensors and devices, the one-step leapfrog hybrid implicit-explicit (HIE) algorithm with the complex envelope (CE) method and absorbing boundary condition is proposed in the narrow bandpass circumstance. To be more precise, absorbing boundary condition is implemented by the higher order convolutional perfectly matched layer (CPML) formulation to further enhance the absorption during the entire simulation. Numerical examples and their experiments are carried out to further illustrate the effectiveness of the proposed algorithm. The results show considerable agreement with the experiment and theory resolution. The relationship between the time step and mesh size can break the Courant–Friedrichs–Levy condition which indicates the physical size/selection mesh size. Such a condition indicates that the proposed algorithm behaviors are considerably accurate due to the rational choice in discretized mesh. It also shows decrement in simulation duration and memory consumption compared with the other algorithms. In addition, absorption performance can be improved by employing the proposed higher order CPML algorithm during the whole simulation. [ABSTRACT FROM AUTHOR]

The traditional finite-difference time-domain (FDTD) method is constrained by the Courant–Friedrich–Levy condition and suffers from the notorious staircase error in electromagnetic simulations. This article proposes a 3-D conformal locally one-dimensional FDTD (CLOD-FDTD) method to address the two issues for modeling perfectly electrical conducting (PEC) objects. By considering the partially filled cells, the proposed CLOD-FDTD method can significantly improve the accuracy compared with the traditional locally one-dimensional FDTD (LOD-FDTD) method and the FDTD method. At the same time, the proposed method preserves unconditional stability, which is analyzed and numerically validated using the von Neumann method. Significant gains in central processing unit time are achieved by using large time steps without sacrificing accuracy. Two numerical examples, including a PEC cylinder and a missile, are used to verify its accuracy and efficiency with different meshes and time steps. It can be found from these examples that the CLOD-FDTD method shows better accuracy and can improve the efficiency compared with those of the traditional FDTD method and the traditional LOD-FDTD method. [ABSTRACT FROM AUTHOR]

In this digital era, all-optical logic gates (OLGs) proved its effectiveness in execution of high-speed computations. A unique construction of an all-optical OR, NOR, and NAND gates based on the notion of power combiner employing metal–insulator-metal (MIM) waveguide in the Y-shape with a minimal imprint of 6.2 µm × 3 µm is presented and the structure is evaluated by finite-difference time-domain (FDTD) technique. The insertion loss (IL) and extinction ratio (ER) for proposed model are 6 dB and 27.76 dB for NAND gate, 2 dB and 20.35 dB for NOR gate and 6 dB and 24.10 dB for OR respectively. The simplified model is used in the construction of complex circuits to achieve greater efficiency, which contributes to the emergence of a new technique for designing plasmonic integrated circuits. [ABSTRACT FROM AUTHOR]

Three different silver nanoprisms (AgNPrs) were combined and used as light-trapping materials in organic solar cells (OSCs). These mixed AgNPrs (M-AgNPrs) increased the photocarrier generation in the OSCs due to the broadband absorption, which was attributed to mutual multiple plasmonic excitations covering the entire visible light region. The M-AgNPrs were incorporated into a poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) hole-transport layer in the OSCs. The UV–vis spectra, atomic force microscope images and current density versus voltage curves of the fabricated devices were recorded at different loading concentrations of the M-AgNPrs. Finite-difference time-domain simulation, impedance spectroscopy, and measurement of incident photon-to-current efficiency of the devices confirmed the effect of the multiple plasmonic excitations. The results suggest that, in an optimum condition, the efficiency of the OSCs loaded with M-AgNPrs was 7.9% higher than the reference OSC.