Conformal Finite-difference Time-domain Research Articles

Efficient Parallel FDTD Method Based on Non-Uniform Conformal Mesh

The finite-difference time-domain (FDTD) method is a versatile electromagnetic simulation technique, widely used for solving various broadband problems. However, when dealing with complex structures and large dimensions, especially when applying perfectly matched layer (PML) absorbing boundaries, tremendous computational burdens will occur. To reduce the computational time and memory, this paper presents a Message Passing Interface (MPI) parallel scheme based on non-uniform conformal FDTD, which is suitable for convolutional perfectly matched layer (CPML) absorbing boundaries, and adopts a domain decomposition approach, dividing the entire computational domain into several subdomains. More importantly, only one magnetic field exchange is required during the iterations, and the electric field update is divided into internal and external parts, facilitating the synchronous communication of magnetic fields between adjacent subdomains and internal electric field updates. Finally, unmanned helicopters, helical antennas, 100-period folded waveguides, and 16 × 16 phased array antennas are designed to verify the accuracy and efficiency of the algorithm. Moreover, we conducted parallel tests on a supercomputing platform, showing its satisfactory reduction in computational time and excellent parallel efficiency.

Angle-Dependent Face-Centered SIBC Model of Metamaterial in Conformal FDTD Methods

Angle-Dependent Face-Centered SIBC Model of Metamaterial in Conformal FDTD Methods

Modeling of indoor network channels with dispersive media based on a modified CFDTD method

AbstractIn order to investigate the electromagnetic (EM) propagation characteristics and further get the channel models for indoor environments, a modified conformal finite‐difference time‐domain (CFDTD) method is introduced in this paper. Specifically, the dispersion characteristics of media are modeled by using the auxiliary differential equation (ADE) technique of the Debye model, and the EM field iterative equation is obtained by weighted‐length of various media in the conformal cells for the curved structure. The proposed method is used to simulate the channels of 2.4 GHz wireless fidelity (Wi‐Fi) network and 5G microcellular network, respectively, for the single‐ and complex multi‐room scenarios. The impulse response, power delay profile and path loss exponent are extracted from the simulation data to analyze the effective ultra‐wideband (UWB) channel characteristics. Compared with the traditional FDTD, the proposed method has the advantage of obtaining a stable and good accuracy solution and reducing the time step without the need to solve high‐order differential equations.

Influence of static strong magnetic field on antenna radiation in hypersonic vehicle

To enhance the radiation performance of the Beidou antenna in the near-space hypersonic vehicle, the static strong magnetic field is used to weaken the electron density in plasma surrounding the antenna. In order to demonstrate the effect of this program, a time-domain multi-physical method is proposed. In the proposed method, what is first analyzed is the reduction of electron concentration in plasma sheath by static strong magnetic field with the spectral element time domain (SETD) method, which has spectral accuracy. Then, the electron density after mitigation is extracted to replace the original electron concentration around the antenna. Hence, the distribution of the manipulated plasma sheath can be obtained. Finally, the radiation characteristics of BeiDou antenna installed in the vehicle are analyzed by the conformal finite difference time domain (CFDTD) method. The simulation results exhibit radiation patterns under different conditions. With the plasma sheath, the radiated electromagnetic waves are greatly attenuated, which will significantly affect the transmission of communication signals. Importantly, the radiation patterns are effectively improved with the external static magnetic field, confirming that it provides an effective tool to mitigate the influence of plasma sheath on the radiation performance of antenna in hypersonic vehicle.

Simulation of Borehole Radar Responses to Rough Fractures Based on 3-D Conformal FDTD

Simulation of Borehole Radar Responses to Rough Fractures Based on 3-D Conformal FDTD

A conformal symplectic multi-resolution time-domain method with ADE-PML

In this paper, the conformal finite-difference time-domain (CFDTD) technique and the concept of effective dielectric constant are applied to symplectic multi-resolution time-domain (SMRTD) algorithm based on Daubechies scaling functions, resulting in a conformal SMRTD (C-SMRTD) method. Moreover, a novel implementation of perfect matched layer with auxiliary differential equation (ADE-PML) is presented for the SMRTD method. Numerical results of the radar cross section (RCS) of a dielectric sphere verify the effectiveness of the C-SMRTD method, which shows good agreement with the results derived by analytical methods. It is also shown that the accuracy of the C-SMRTD method has been significantly improved compared with the MRTD method with step approximation, and the proposed method has an advantage over CFDTD at saving the CPU time and memory. Furthermore, a vault-top tunnel model is established with the proposed method, and the characteristic of the field cross-section distribution of the electromagnetic pulse (EMP) propagation in the tunnel model is also presented and discussed.

Comments on “A New Conformal FDTD for Lossy Thin Panels”

In the article titled “A new conformal FDTD for lossy thin panels” by M. R. Cabello et al. , the appearance of spiky antiresonances in the simulation of the shielding properties of lossy thin-shell spherical cavities by FDTD was categorized as spurious solutions. In this article, we briefly clarify this topic and show that these solutions are not really spurious in the common interpretation of the term. Actually, they correspond to physical solutions appearing due to lack of symmetry, inherent to the staggered colocation nature of field components in FDTD.

The Conformal Finite-Difference Time-Domain Simulation of GPR Wave Propagation in Complex Geoelectric Structures

The finite-difference time-domain (FDTD) method adopts the most popular numerical model simulating ground penetrating radar (GPR) wave propagation in an underground structure. However, a staircase approximation method is usually adopted to simulate the curved boundary of an irregular object in the FDTD and symplectic partitioned Runge-Kutta (SPRK) methods. The approximate processing of rectangular mesh parameters will result in calculation errors and virtual surface waves for irregular targets of an underground structure. In this paper, we examine transverse mode (TM) electromagnetic waves with numerical models of electromagnetic wave propagation in geoelectric structures with conformal finite-difference time-domain (CFDTD) method technology in which the effective dielectric parameters are used to accurately simulate the dielectric surface and to absorb waves at the edges of the grid. The third orders of the transmission boundary are used in this paper. Additionally, three complex geocentric models of inclined layered media, spherical media, and three-layered pavement model with structural damages are set up for simulation calculations, then we carry out the actual radar wave detection in a laboratory as the fourth numerical example. Comparison of simulated reflectance waveform of FDTD, symplectic partitioned Runge-Kutta (SPRK), and CFDTD methods shows that at least 50% of the virtual waves can be reduced by using the proposed algorithm. Wiggle diagrams of FDTD and CFDTD methods show that much of the virtual waves have been reduced, and the radar image is clearer than before. This provides a method for the detection of complex geoelectric and layered structures in actual engineering.

Characterization of an Eight-Element Circular Patch Array for Helical Beam Modes

This paper reports on a new method for characterizing intermodal isolation, power penalty, and reception zone area of helical beam (HB) antennas. As an example, an eight-element circular patch array is fully characterized and its performance is critically assessed. Validation through beam measurements is accompanied with precise electromagnetic modeling using conformal finite-difference time domain computation on a graphics processing unit.

A New Conformal FDTD for Lossy Thin Panels

A novel conformal technique for the finite-difference time-domain (FDTD) method is proposed to deal with curved and arbitrarily oriented lossy thin panels. This is formulated as an extension of the existing conformal relaxed Dey–Mittra (CRDM) method combined with subcell algorithms to handle wave propagation across the panel. Two alternatives are presented for this: the classical impedance network boundary condition (INBC) and a recent subgridding boundary condition (SGBC) developed by the authors. Several test cases are employed to demonstrate the capability of the proposed method to remove errors associated with the usual staircased FDTD method.

A Circularly Polarized Single-Frequency Multimode Helical Beam Antenna

An antenna based on a TM coaxial resonant cavity with radiating annular slots on one face and excited by multiple open-ended TE mode coaxial resonators on the opposite face is shown to simultaneously radiate the corresponding circularly polarized helical beams modes over a single-frequency band with good isolation between modes. S-parameters are calculated for a transmit–receive configuration with the antennas separated by 10 wavelengths. The initial antenna concept was developed interactively using the conformal finite difference time domain method with a Titan-XP GPU.

Hybrid Newmark-conformal FDTD modeling of thin spoof plasmonic metamaterials

The aim of this paper is to present a new efficient and accurate semi-implicit finite-difference time-domain (FDTD) method for modeling thin plasmonic metamaterials supporting spoof surface plasmons. The presented method is formulated by combining Yu–Mittra's conformal FDTD technique for dielectrics, the simplified conformal finite integration technique for perfectly electric conductors (PECs) and the Newmark-Beta method. The resultant scheme is magnetically implicit, has a more relaxed stability condition than that of Yee's FDTD scheme, and allows for accurate modeling of both PEC and dielectric curved surfaces. Energy conservation and stability of the presented scheme is theoretically proved with the energy inequality method. Its formulation can be generalized to a class of magnetically implicit FDTD schemes with weakly conditional and unconditional stability in a unified manner. The presented scheme is used to simulate thin structures supporting spoof surface plasmon polaritons and spoof localized surface plasmons, and also applied to recent plasmonic devices such as planar frequency splitter, ultrathin rainbow trapping device and compact planar metadisk with split-ring resonators. The accuracy and efficiency of the presented scheme are assessed in comparison with the conventional explicit and implicit FDTD methods, and their conformal variants.

Chromium plasmonic polarizer for high intensity light

In this work, we investigate a thin-film polarizer for a high intensity of the electromagnetic (EM) beam based on Cr nano wire arrays. Commonly used thin-film polarizing components are very sensitive for high power of EM waves and can be easily damaged by focused beams. The solution to this problem could be the thin-film polarizer based on metallic subwavelengths structures. This type of optical element has huge resistance comparing to typical thin-film polarizers. However, designing such an optical element for proper wavelength of EM wave and transmissions is not easy task. In this paper we present numerical as well as experimental results for specially designed chromium thin-film polarizer for wavelength 532nm Full Text: PDF ReferencesW. Zhou, K. Li, C. Song, P. Hao, M. Chi, M. Yu and Y. Wu, "Polarization-independent and omnidirectional nearly perfect absorber with ultra-thin 2D subwavelength metal grating in the visible region", Opt. Express 23, 11 (2015). CrossRef W. L. Barnes, A . Dereux, and T. W. Ebbesen, "Surface plasmon subwavelength optics", Nature 424, 824-830 (2003). CrossRef C. Lee, E. Sim, D. Kim, "Blazed wire-grid polarizer for plasmon-enhanced polarization extinction: design and analysis", Opt. Express 25, 7 (2017). CrossRef A. Lehmuskero, Metallic thin film structures and polarization shaping gratings (University of Eastern Finland 2010).Y. Leroux, J. C. Lacroix, C. Fave, V. Stockhausen, N. Felidj, J. Grandm, A. Hohenau, J. R. Krenn, "Active plasmonic devices with anisotropic optical response: a step toward active polarizer", Nano Lett. 5, 9 (2009). CrossRef R. T. Perkins, D. P. Hansen, E. W. Gardner, J. M. Thorne, A. A. Robbins, Broadband wire grid polarizer for the visible spectrum, US 6122103 (2000). DirectLink D. M. Sullivan, Electromagnetic simulation using the FDTD method, New York: IEEE Press Series (2000). CrossRef J. P. Berenger, Perfectly Matched Layer (PML) for Computational Electromagnetics, Morgan & Claypool Publishers (2007). CrossRef Yu, W., and R. Mittra, "A conformal FDTD software package modeling antennas and microstrip circuit components", IEEE Antennas Propagat. Magazine 42, 28 (2000) . CrossRef L. W. Bos, D. W. Lynch, "Optical Properties of Antiferromagnetic Chromium and Dilute Cr-Mn and Cr-Re Alloys", Phys. Rev. Sect. B, 2, 4267 (1970). CrossRef

Real-Time Three-Dimensional Microwave Monitoring of Interstitial Thermal Therapy.

We report a method for real-time three-dimensional monitoring of thermal therapy through the use of noncontact microwave imaging. This method is predicated on using microwaves to image changes in the dielectric properties of tissue with changing temperature. Instead of the precomputed linear Born approximation that was used in prior work to speed up the frame-to-frame inversions, here we use the nonlinear distorted Born iterative method (DBIM) to solve the electric volume integral equation (VIE) to image the temperature change. This is made possible by using a recently developed graphic processing unit accelerated conformal finite difference time domain method to solve the forward problem and update the electric field in the monitored region in each DBIM iteration. Compared to our previous work, this approach provides a far superior approximation of the electric field within the VIE, and thus yields a more accurate reconstruction of tissue temperature change. The proposed method is validated using a realistic numerical model of interstitial thermal therapy for a deep-seated brain lesion. With the new DBIM, we reduced the average estimation error of the mean temperature within the region of interest from 2.5 to 1.0 for the noise-free case, and from 2.9 to 1.7 for the 2% background noise case.

Hybrid Newmark-Conformal FDTD Method for Multiphysics Modeling of Short Spark Gaps With Curved Metallic Surfaces

A new semi-implicit conformal finite-difference time-domain (FDTD) method is proposed for accurately modeling a short spark gap between metallic objects with curved surfaces. This new scheme is formulated on the basis of hybridizing the Newmark-Beta method and the simplified conformal scheme without cell enlargement. No dependency of mesh step in the direction of a spark channel is included in the stability condition of this scheme and its maximum stable time step is unaffected by the existence of effectively small meshes near curved perfectly conducting surfaces. The proposed semi-implicit conformal scheme has the same form as the one in the staircase approximation. This feature makes it simpler to couple with nonlinear spark resistance models. The proposed scheme is applied to two typical spark-gap systems with curved surfaces in air: spheres and a spheroid-ground structure. Its accuracy is demonstrated in comparison with the typical explicit and implicit conformal FDTDs, and also the semi-implicit staircase FDTD. It is also shown that the scheme is stable and second-order convergent even with a larger time step than the Courant-Friedrichs-Lewy stability limit. The proposed method is validated in comparison with the existing experimental data.

A Low-Profile Reflector-Enhanced Drop-Shaped Printed Antenna for Wide-Band Wireless Communications

An improved low-profile printed antipodal drop-shaped dipole antenna for wide-band wireless applications is presented. The proposed radiating structure is integrated with a planar metal reflector useful to enhance antenna gain up to 5.5 dBi and the front-to-back ratio up to 21 dB. The geometry of reflector, feeding line, and dipole arms is optimized in order to achieve a broad operating bandwidth useful to meet the requirements of modern wireless communication protocols. Furthermore, the particular shape of the metal reflector and the adoption of a thin low-permittivity dielectric substrate result in a low distortion of the radiated field and a limited back radiation which makes the antenna suitable for UWB applications as well. These features, together with the low profile and the limited occupation area, make the antenna well adapted to mobile terminals as well as radio base stations. A locally conformal FDTD numerical procedure has been adopted to design and analyse the radiating structure, while a SEM technique has been employed to highlight the field perturbation caused by the antenna reflector as well as to extract the characteristics underlying the transient behaviour of the antenna. The experimental measurements performed on an antenna prototype are found to be in good agreement with the numerical computations.

A Conformal FDTD Method With Accurate Waveport Excitation and S-Parameter Extraction

We demonstrate a conformal finite-difference time domain (CFDTD) technique with accurate waveport excitation and S-parameter extraction. We discuss, under the CFDTD framework, object modeling with effective subcell material, impedance calibration for the conformal modeled coaxial feed, waveport mode calculation with a newly developed conformal 2-D finite-difference frequency domain solver, waveport excitation with a modified total field scattered field method, and a modified S-parameter extraction scheme that is compatible with the CFDTD method. Lastly, we present two specific validation cases intended as relevant precursors to the inverse scattering application: modeling of the reflection coefficient of a tapered patch antenna and modeling of the transmission coefficient in a probe-fed rectangular waveguide.

Research on the effect of cathode plasma expansion on x-band relativistic backward wave oscillator using moving-boundary conformal PIC method

The cathode plasma expansion has been widely investigated and is recognized as impedance collapse in a relativistic backward wave oscillator (RBWO). However, the process of formation and expansion of cathode plasma is very complicated, and the thickness of plasma is only several millimeters, so the simulation of cathode plasma requires high temporal and spatial resolutions. Only the scaled-down diode model and the thin gas layer model are considered in the previous hybrid simulation, and there are few numerical studies on the effect of cathode plasma expansion on the RBWO. In this paper, the moving-boundary conformal particle-in-cell method is proposed; the cathode plasma front is treated in this novel method as the actual cathode surface, and the explosive electron emission boundary moves as the expansion of cathode plasma. Moreover, in order to accurately simulate the electromagnetic field near the cathode surface, the conformal finite-difference time-domain method based on the enlarged cell technique is adopted. The numerical simulation indicates that the diode voltage decreases and the beam current increases as cathode plasma expands; when the cathode plasma velocity is 10 cm/μs, the pulse duration of the generated microwave decreases from 30 ns to 10 ns, the working frequency decreases from 9.83 GHz to 9.64 GHz, and the output power decreases 30% in the course of cathode plasma expansion.

SIBC incorporated in conformal FDTD to efficiently simulate the thin conductive layer of periodic structure

In this study, surface impedance boundary condition (SIBC) incorporated in conformal finite-difference time-domain (CFDTD) to efficiently simulate the thin conductive layer of periodic structure is proposed. The method is based on the vector fitting (VF) technique to approximate the frequency-dependent surface impedance of the thin conductive layer by a series of partial fractions in terms of real or complex conjugate pole-residue pairs. A discrete-time equation of SIBC is then derived and incorporated in CFDTD update equations by Laplace transform and time central difference methods. The proposed method takes the following advantages, (i) the time step is no longer bounded by the fine resolution of the thin layer; (ii) The complicated recursive convolution approach is avoided, and the approximation of the frequency-dependent surface impedance of the thin conductive layer can be easy to handle with the VF method. This method is numerically verified for the time- and frequency-dependent scattering characteristics of several periodic structures behaved under normal and oblique incident waves.

誘電性散乱体粒子の接近がインライン・ホログラフィに及ぼす影響のConformal FDTD(2,4)法による検討

In order to numerically simulate the formation of hologram appearing in the in-line holography method with high precision, improvement for FDTD (2,4) method was proposed. Examination about the effect of improvement showed that proposed improvement remarkably suppress the phase error of electro-magnetic wave to negligible level even in the case where large-scale calculation domain is ordered to treat multiple scattering problems, while the ordinal FDTD (2,4) method causes serious error in such cases. In addition, Conformal FDTD methods is combined with the above-mentioned FDTD (2,4) method with improvement in order to suppress the error associated with step-wise approximation of particle shape. At the next stage, examinations were carried out using the above-mentioned Conformal FDTD (2,4) method, about the influence of closeness between two particles on the location error of reconstructed image in the in-line holography method. Results of numerical simulation showed that reconstructed images of particles are deformed when the distance between two particles is shortened, and error appears in the evaluation of particle location. Location error is decreased with elongation of distance between two particles when they go away in the perpendicular direction to incident beam. On the other hand, contrary tendency partly appears when two particles go away in the parallel direction with incident beam. Additionally, it was considered that difference of plane of polarization.