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Frequency selective surface (FSS) is critical for electromagnetic (EM) radiation protection due to its high spatial filtering performance, especially for active FSS. Recently, artificial neural network (ANN) has shown great potential in solving EM inverse problems and rapid industrial design. In such an inverse model with ANN, it establishes the relationship between the given inputs of S-parameters and the desired structure parameters or material parameters. However, faced with applications where S-parameters vary in a large frequency range with different curve shapes, such as multi-band microwave devices, equal interval sampling may result in high dimensional inputs and will require more complicated neural network. In this work, we present a Fourier subspace-based deep learning method (FS-BDLM) for FSS inverse design, where the dimension of the input is largely reduced by using Fourier subspace to represent the most salient features of the desired S-parameter performance. Compared with existing deep learning methods, the proposed technique makes inverse neural models more compact and more stable to noise contaminations. The validation of the proposed FS-BDLM is conducted both numerically and experimentally through two dual-passband FSS design examples, where the well-designed FSS is fabricated to validate the technique.

This paper presents a stabilized nodal discontinuous Galerkin pseudospectral time domain (DG-PSTD) algorithm for fully anisotropic electromagnetic waves. This solver permits arbitrary high-order basis functions and adaptive hexahedral elements, thus very efficient for large-scale wave propagation in complex media. Maxwell’s equations are reformulated in a unified hyperbolic form, where a localized anisotropic Riemann solver is derived to serve as a numerical flux to exchange information across adjacent elements in the DG-PSTD scheme. This local analysis method also helps impose the time-domain anisotropic plane wave incidence in the total/scattering field framework. Numerical validations and applications demonstrate the efficiency, accuracy, and capability of this new high-order solver for 3-D large-scale generally anisotropic electromagnetic media.

To improve the performance of a pencil beam electron gun for terahertz traveling wave tubes (TWT), a support vector regression (SVR) method combined with a goal attainment algorithm, which is used to optimize its structural parameters considering the periodic permanent magnetic (PPM) focusing system, is proposed in this article. Moreover, a parameter correction method to reduce the impact of the thermal expansion on the electron gun is proposed. An electron gun for 0.22-THz TWT gun is developed, in which a 30-mA/23.8-kV electron beam emitted by a curved barium-tungsten cathode with a beam loading of 4 A/cm² is achieved with the optimized parameters. To the high current density for THz beam-wave interaction, the area compression ratio of electron beam is used in beam tunnel and reaches 144. The experimental results are very similar to the simulation results, which indicate that the methods would be beneficial to the development of TWT.

In this paper, a large-scale electromagnetic-thermal-mechanical co-simulation solver is implemented for simulating complex radio frequency components by using a high performance computing framework. The proposed solver integrates the frequency-domain electric field simulation, with time-domain thermal and thermal induced stress simulations, via a multiphysics coupling iterative process. In order to speed up the co-simulation, a Krylov subspace method with a domain decomposition method (DDM) preconditioner is used. First, the developed multiphysics solver is verified with the commercial software COMSOL Multiphysics. Then, the parallel performance of our co-simulation solver, with different ghost mesh thicknesses, is tested on a supercomputer. Finally, some multiphysics results of filters and a real-world system-in-package (SiP) are obtained with our proposed solver.

An efficient multiconductor transmission line (MTL) model of a shielded twisted wire pair (TWP) with apertures on its sheath is developed for predicting common mode (CM) and differential mode (DM) currents induced in the shielded TWP cable. Its transfer impedance and admittance with one-line apertures on its sheath are derived in a closed form. Therefore, the MTL equations are formulated and solved to obtain the CM and DM currents induced in the shielded TWP. Moreover, the proposed MTL model is generalized to be applicable for the braided–shielded TWP, in which the transfer impedance and admittance are formulated analytically. Results showed that the induced DM current inside the braided–shielded TWP is suppressed dramatically due to the uniform structure of the cable. The models are validated by comparing their results with those obtained by the commercial software FEKO; good agreements are obtained.

This article presents the construction and analysis of a hybrid numerical method for the discretization of the convection-dominated nonlinear carrier transport process in semiconductor devices. In the construction of the method, the edge streamline upwind (SU) current density model is employed to overcome the nonconvergence brought by the nonlinear property of the current continuity equation, and the mixed finite volume-finite element method (FVFEM) is utilized to effectively extend the edge SU current density model to multidimensional applications. The proposed method is more reliable and flexible than the finite box (FB) method and streamline upwind Petrov–Galerkin (SUPG) method. The performance of several popular SU current density models is compared to find the optimal one. The proposed method is validated by comparing the calculated results with those calculated using commercial software. Based on the streamline upwind-finite volume-finite element method (SU-FVFEM), the finite element method (FEM), and the domain decomposition method (DDM), an in-house parallel computing electrothermal simulator is developed for large-scale semiconductor devices. The performance of the in-house developed parallel simulator is evaluated through simulations of a p-n junction diode and a 3-D bipolar transistor. The results demonstrated that the developed parallel simulator possesses good accuracy, applicability, and scalability.

Unintentional as well as intentional electromagnetic interference can cause interference and performance degradation of microwave circuits or systems. In this article, a modified multiport lumped-network finite-difference time-domain method (FDTD) method based on Y-matrix is proposed, where bilinear transform is used to incorporate the V–I relation of the lumped-network into FDTD iteration. It is further used for simulating transient responses of mesfet -based amplifiers, which are often used in many radar and communication systems. The excitation of such an RF amplifier is assumed to be an intentional electromagnetic interference (IEMI) signal but with different waveforms and magnitudes. Parametric studies are performed to show hybrid effects of waveforms and magnitudes of the IEMI signals on the transient coupled voltages at the output port of such mesfet -based amplifier, with useful information obtained for understanding the interaction process between the intentional electromagnetic interference signals and active components.

A hybrid time-domain numerical method based on the full wave finite-difference time-domain (FDTD) method combined with a modified 1-D FDTD method has been proposed to analyze the electromagnetic interference (EMI) of multiscale transmission line networks in a metallic cabin in this article. This method is implemented through two numerical solvers for full wave and transmission line simulations, respectively, by adopting a set of reasonable physical boundary conditions between external fields and transmission line network. By using Ampere's law, the external fields can be transferred to a voltage source that can be further used as the forcing terms in the telegraph equation of the transmission line network. To overcome the challenge introduced by the multiscale size of the transmission line network, we combine 1-D explicit and implicit FDTD methods together to solve the coaxial cables and interconnects in PCB, respectively. Thus, among different subdomains, the hybrid method can be carried with the same time step without the restriction of the stability condition. Numerical examples show the accuracy as well as efficiency of the proposed method compared with the HSPICE and traditional FDTD method. In addition, the method is used successfully in analyzing the EMI effects of a complex transmission line network inside a cabin illuminated by external electromagnetic wave.

The design of a shared-aperture dual-band differentially fed array antenna with microstrip grid and patches is presented in this letter. The patches as high-frequency elements operating at 38 GHz are inserted into microstrip grid array antenna (MGAA) operating at the low-frequency band of 28 GHz. The impedance bandwidth of MGAA can be enhanced from 3% to 16% at 28 GHz due to the introduced resonance from its coupling with the patches. The measurement shows that the proposed antenna can achieve the impedance bandwidths of 15.65% and 16.7%, isolation of more than 20 dB, and peak gains of 14.7 and 14.5 dBi at dual bands of 28 and 38 GHz, respectively. Therefore, the design scheme will be useful for the dual-band millimeter-wave 5G applications.

In this brief, a millimeter-wave (mm-Wave) wideband frequency quadrupler is demonstrated in a 55-nm CMOS technology. It cascades two injection-locked frequency doublers (ILFD). Each of them consists of an oscillator gain stage realized by an injection-locked oscillator (ILO) and a frequency doubler implemented by a push-push pair. A tail feedback loop is proposed and applied in the second ILFD. It effectively boosts the injection current for the second ILFD. Therefore, both the operating bandwidth and output power (Pout) of the circuit are prominently improved. In addition, transformer-based high-order resonators are used to reduce the phase variation of their impedance around 0° and hence extend the locking range of ILOs. According to the measurement results, a frequency range of 30.8 ~ 40 GHz is achieved. The maximum Pout is up to -7.1 dBm without additional buffers. The circuit also attains a wide 3-dB frequency bandwidth of Pout, which is from 32 to 38.4 GHz. The harmonic rejection ratios of the frequency quadrupler are 16.5 ~ 25.9 dBc at the second-order harmonic and 31 ~ 45 dBc at the fundamental and third-order harmonics over the entire operating bandwidth. The core area occupies only 0.24 mm2.

An efficient analytical model for the transfer impedance and admittance of a noncoaxial/twinax braided–shielded cable with apertures on its sheath is proposed by generalizing the old Vance's and Kley's formulas, and it is derived using the complex analyses with an appropriate conformal mapping. Therefore, such a noncoaxial cable is converted into a coaxial one which can be studied using the traditional multiconductor transmission line method. It is shown that the aperture inductance is related to the position of the inner conductor and the radial position of each aperture on its sheath. In addition, the modal domain analysis is performed to obtain the common-mode (CM) and differential-mode (DM) transfer impedance/admittance of the twinax braided–shielded cable, with CM and DM currents inside the inner conductors examined. The proposed model is validated by comparing the results with that obtained by the method of moments (MoM)-based commercial software FEKO. It is found that the uniform distribution of the apertures on the sheath reduces the induced DM current significantly

A generalized multiconductor transmission line (MTL) model is integrated with the polynomial chaos stochastic Galerkin method (PC-SGM) in order to predict the stochastic response of a nonuniform multitwisted bundle of twisted-wire pairs (MTB-TWP) with random parameters, which is excited by random plane waves. The twist pitches of such nonuniform MTB-TWP are considered to be spatial stochastic functions, where its parametric equations are derived in their general form. Moreover, by taking the geometry deformation of the MTB-TWP cable into account, some of its parameters are represented by random variables, and the incident plane-wave fields can also be changed in some random ways. After that, the PC-SGM is applied to the stochastic telegrapher's equations in order to obtain deterministic ones that can be solved by using the MTL model. Therefore, the effects of the uncertainties of the parameters on the common mode and the differential mode currents are investigated in details, where, in each case, the probability density function is given. The results are validated in comparison with Monte Carlo (MC) method, where a very good agreement is obtained. It is shown that the PC-SGM simulation time is much smaller than that of the MC method as the number of random variables is relatively small.

A liquid crystal (LC)-based three-element microstrip parasitic array with beam switching is presented in this study. To understand the beam switching mechanism, a simple theoretical model of three-element Yagi antenna on the ground is given and analysed. In the proposed microstrip parasitic array, LC permittivities under three elements can be adjusted by bias voltages to control their resonant electrical lengths. In the tuning process, the LC-based antenna array can operate at three modes to obtain three beam switching directions. The measured results show that three beam tilt directions (θ = 59°, −2°, −57°) in the H-plane are achieved.

Electromagnetic-thermal cosimulation of large antenna arrays is performed by using a supercomputing-based parallel domain decomposition method. In this letter, frequency-domain electromagnetic and thermal fields are solved self-consistently and then coupled via Joule heat and temperature-dependent material properties. The developed cosimulation solver is first validated with the commercial software COMSOL Multiphysics. Then, the parallel performance of our in-house developed code is examined in terms of scalability and efficiency. Finally, the temperature distributions over large-scale antenna arrays are obtained by our proposed solver in a highly efficient manner.

Spatial frequency filters, which can manipulate the angular spectrum of the incident electromagnetic waves, are significantly important in optical analog processing. Here, magnetic metamirrors with symmetric split-ring resonators, which are used to achieve short circuit for normally incident wave and impedance matching for obliquely incident wave, are fabricated and investigated. Our proposed metamirrors can be considered as high-stop spatial frequency filters, and their operation mechanisms are further revealed by the coupled-mode theory and equivalent transmission line model. The characteristics of the proposed metamirrors with gain media on top are predicted theoretically, and simulation results show that they can act as high spatial frequency amplifiers. Our design provides an alternative approach to spatial frequency filter design and has promising potential in the device design of optical analog processing.

This paper presents a differential microwave microfluidic sensor based on the microstrip complementary split-ring resonator (MCSRR) structure for liquid characterization. At the resonance, the electric field concentrates along the slot, where the microfluidic channel is located. As the liquid sample is injected, the corresponding reflection coefficient is changed, while the reference response is unaffected. The relative permittivity and loss tangent of the liquid can be extracted from the variations in the resonant frequency and quality factor. A prototype of the proposed sensor is fabricated and measured for functionality validation. The proposed sensor exhibits a high sensitivity of 0.626% on average and is capable of suppressing unwanted environmental influences.

A dual-band differential shifted-feed microstrip grid array antenna (DSF-MGAA) with two parasitic patches is presented in this communication. By moving the feed location, a conventional MGAA (C-MGAA) can be turned into an SF-MGAA for dual-band operation. The high-frequency band of SF-MGAA corresponds to the operation mode of the C-MGAA, and its low-frequency band is similar to that of the patch or meshed patch antenna. A new differential feeding scheme and two parasitic patches are adopted to improve the impedance bandwidth of SF-MGAA. The proposed DSF-MGAA can cover a dual band of 3.7 and 28.5 GHz. The measured −10 dB impedance bandwidths of 3.4% and 4.5%, which correspond to the peak gains of 8.98 and 19.2 dBi, are obtained in the low- and high-frequency bands, respectively. The DSF-MGAA can be a potential candidate for the future dual-band wireless communication.

The resistive random access memory with a graphene electrode (GE) is carefully modeled and simulated by considering its geometrical and physical properties. Since the graphene oxide is generated through the migration of oxygen ions from metal oxide to GE affecting current transport in the memory cell, the model of its electrical conductivity with different oxidation degrees is developed, in which the conductivity is exponentially dependent on the oxidation degree. The simulated ${I}$ – ${V}$ characteristics, which agree well with those of the experiment, are obtained by self-consistently solving the current transport, heat conduction, and oxygen vacancy migration equations. Based on the simulation, oxygen vacancy density, temperature distribution, and resistances of high- and low-resistance states are extracted and compared. A low-temperature increase due to low power consumption indicates its great potential for high-density integration.

The effect of the scattered field on the terminal risers in twisted-wire pairs (TWPs) is investigated in the presence of an electromagnetic plane wave incidence. An equivalent circuit of the common mode (CM), represented by a wire above the ground, is used to obtain the CM current along such TWP connected to a floating terminal together with the approximation of their near field. It is shown that the scattered field radiated by a TWP can be coupled with any floating terminals, and in turn, it has significant effects on the differential mode response at the resonant frequencies of such transmission line system.

Design considerations of vertically stacked horizontal nanosheet (NSH) gate-all-around pMOSFETs are examined at the sub-5-nm technology node using in-house-developed non-equilibrium Green’s function (NEGF) quantum ballistic transport simulator. In the individual Si and Ge NSHs, ON-state current and subthreshold swing are evaluated and analyzed for different crystal orientations and various sheet widths. Performance benchmarking of the stacked FET arrays at the iso-footprint is accomplished to explore the roles of sheet configurations further with stack number and sheet spacing changed. It is found that the benefit of the larger effective channel width provided by the wider NSH is always compromised by degraded gate control, especially in the Ge channel. [111] and [100] are shown to be the best transport orientations for individual Si and Ge NSHs, respectively. However, [100] channel vertically confined along [011] shows greater potential for the applications of wider Si and Ge NSHs in the stacked FET array. The process-induced NSH width variation is studied statistically, and it is shown to cause significant performance fluctuations in the stacked array consisting of wide Si or narrow Ge NSHs.

Numerical simulation of fully coupled electrothermal processes in phase-change memory (PCM) arrays is performed in this article. For realizing the ability in simulating the electrothermal responses of large-scale PCM arrays, an in-house parallel simulator based on domain decomposition method (DDM) and time-domain finite element method (FETD) is developed, with its performance evaluated in terms of accuracy and scalability. Then, thermal crosstalk in the PCM array is investigated using the developed simulator, and a diamond layer is introduced to suppress thermal crosstalk. Furthermore, the scaling effects of PCM arrays on their electrothermal performance are examined. A scheme for multibit PCM design is proposed, and the electrothermal characteristics of proposed 2-bit PCM cells and arrays are studied numerically.

A time-domain discontinuous Galerkin Poggio–Miller–Chang–Harrington–Wu integral equation method, which is based on marching-on-in-degree (MOD) scheme, is proposed to simulate electromagnetic pulse (EMP) responses of arbitrarily shaped dielectric objects, where half Rao–Wilton–Glisson basis functions are chosen as the spatial basis ones. Both electric and magnetic current continuities between adjacent elements are guaranteed by introducing additional interior penalty terms. Therefore, three-dimensional dielectric structures with either conformal or nonconformal meshes can be treated. Meanwhile, the weighted Laguerre polynomials are chosen as the temporal basis functions and implemented for the MOD scheme, and stable EMP responses can be captured. Since our method is based on the surface integral equation with the objects’ surface meshed, the number of unknowns are significantly reduced in comparison with that of the volume integral equation method. Some numerical examples are presented to validate both stability and accuracy of the developed algorithm.

This study proposes a set of tuneable terahertz (THz) frequency selective surfaces (FSSs) based on the metal-graphene structure. By the numerical technique, the transmission characteristics of the proposed FSSs are investigated in detail. In particular, the independent frequency tuneability of the proposed multiband FSS is demonstrated, i.e. the resonant frequency of each band can be tuned independently without affecting other bands. Such flexibility makes the proposed FSSs practical and potential for various THz applications including filters, radomes, polarisers, and sensors.

An improved marching-on-in-degree discontinuous Galerkin method for solving time-domain electric field integral equation is presented in this letter. By adopting half-RWGs as spatial basis functions, both conformal and nonconformal discretization scattering problems can be simulated accurately. A combination of three weighted Laguerre polynomials is utilized as new temporal basis functions to derive final equations, where some accumulation terms are eliminated. Therefore, the time spent on computing accumulation term during the iterative procedure is reduced significantly, with the total solution process accelerated. Some numerical examples are presented to demonstrate both accuracy and efficiency of our method.

The four-port cavity model is presented to study a differential dual-polarised annular-ring patch antenna operating at higher order mode TM12. Acceptable agreements among calculated, simulated, and measured impedances and radiation patterns are obtained. Theoretical analysis shows that the differential port-to-port coupling impedance is zero, and its isolation is theoretically infinite. The differential input impedance is about four times of the single-ended input impedance at the resonant frequency of higher order mode TM12. The differential operation can suppress the adjacent modes TM02 and TM22 near the operating mode TM12 and lead to a more symmetrical E-plane radiation pattern and lower cross polarisation level.

A finite-element method-based parallel computing simulator for multiphysics effects in resistive random access memory (RRAM) array, which is suitable for supercomputer platforms even with thousands of cores, is developed to simulate oxygen vacancy migration, current transport, and thermal conduction. Exponentially fit flux Galerkin method is introduced to improve algorithm convergence when solving the 3-D oxygen vacancy drift-diffusion equation. The accuracy of our algorithm is validated by comparison with commercial software. Scalability of our parallel algorithm is also investigated. The simulation results for the high-density integration RRAM array indicate that the heat generated during the writing process can result in high temperature, and lead to severe reliability problem. Even the RRAM cells without bias voltage applied can be transferred from low-resistance state to high-resistance state unintentionally, and lose their stored information. Increasing the feature size or equivalently decreasing the integration density lowers the power density, hence improves reliability performance. Large electrode thickness with Dirichlet boundary applied on their side surfaces can drain out heat faster and enhance reliability of RRAM array.

Because of the metal density requirement in the advanced CMOS processes, dummy metal fills (DMFs) are unavoidable. The DMFs degrade the performance of the on-chip inductors, especially for the ones in the microwave and millimeter-wave circuits. This paper analyzes the impact of the floating DMFs and proposes a scalable double- $\pi $ inductor model including a tunable dummy metal density factor. The metal density factor can be integrated into the process design kit and determined by the designers to pass the design rule check. The proposed model predicts the decrease in the quality factor $(Q)$ and self-resonance frequency $(f_{\mathrm {sr}})$ with the density of DMFs increasing accurately. Furthermore, a fully automatic model extraction method based on the genetic algorithm is presented, which increases the accuracy of models. Inductors with DMFs of different densities are fabricated in a standard 180-nm CMOS technology. Then, the parameters of the inductors’ models are extracted to verify the idea. The models’ calculation results are compared with the measurement results up to 67 GHz.

An efficient simulation of shielding effectiveness of some metallic cabins or enclosures is performed using an improved Calderon preconditioner-based time-domain integral equation method. During its implementation, Rao–Wilton–Glisson and Buffa–Christiansen functions are used as the spatial basis functions for solving the Calderon preconditioned time-domain electric field integral equation, which generate a set of well-conditioned system matrices irrespective of the mesh density. Moreover, a set of approximate prolate spheroidal wave functions is chosen as the temporal basis functions; therefore, both late-time stability and accuracy are improved significantly for simulating electromagnetic pulse responses in some typical cabins. Numerical results are validated in comparison with those obtained by some commercial software. These results are useful for further evaluating electromagnetic environment effects in some complex systems.

A multiconductor transmission line model is developed to characterize electromagnetic wave coupling with a twisted bundle of twisted wire pairs (TBTWPs) running above a ground plane. A set of parametric equations of each wire in each bundle is derived at first, together with its unit tangent vector defined analytically. Furthermore, its averaged per-unit-length parameters are determined according to the derived analytical equations, and the equivalent voltages for describing field–wire coupling are presented. The proposed model is employed for predicting both common mode and differential mode currents induced at different terminal loads of the TBTWP, where fire-side, end-fire, broad-side, and arbitrary electromagnetic wave incidences are investigated. The numerical results of our model are validated in comparison with that of the commercial software FEKO, with good agreement achieved between them. Furthermore, such TBTWP model can be extended for studying electromagnetic wave coupling with multiple TBTWPs employed in many cable systems.