We present an efficient wideband multilevel fast adaptive cross approximation-characteristic basis function method (Wideband MLFACA-CBFM) for wideband electromagnetic scattering problems. In this method, the multilevel fast adaptive cross approximation (MLFACA) of the impedance matrices and the generation of the CBFs are performed only once at the highest frequency within the given band. The resulting decomposition and compression information is reused across the entire band, eliminating the need to repeatedly perform the time-consuming MLFACA decomposition and CBF generation at each analyzed frequency. Moreover, impedance interpolation is employed to efficiently construct the approximate decomposed impedance matrices at the analyzed frequencies. As a result, the proposed method effectively reduces the time required to compute the wideband radar cross section.

Efficient computation of multiangle monostatic radar cross section (RCS) using the method of moments (MoM) is hindered by the need to restart the iterative solution process for each incident angle due to the changing excitation. To mitigate this burden, this letter proposes an autoregressive (AR) model-based method for predicting improved initial guesses to accelerate convergence. The AR model parameters are estimated using the Burg algorithm. Predicting each initial guess incurs only O(N) computational complexity, which is lower than the O(N-2) cost of a single iteration in the iterative solver. Compared with those from the conventional phase-corrected initial guess method, the initial guesses predicted by the proposed method are closer to the converged solution. The proposed method effectively reduces the number of iterations, particularly under stringent convergence criteria. Numerical results demonstrate the effectiveness and efficiency of the proposed method.

A new method that utilizes multibranch Rao-Wilton-Glisson (MB-RWG) functions and the electric and magnetic current combined field integral equations is proposed for analyzing piecewise homogeneous dielectric targets of arbitrary shapes with junctions. The proposed method allows for the independent discretization of the outer surface of the object and the interfaces of different materials within it, thus enabling the generation of quasi-nonconformal meshes. This provides superior flexibility during preprocessing, especially when handling interfaces connected to the junctions. At the junctions, where more than two material regions meet, there are quasi-nonconformal boundaries between the meshes, and these quasi-nonconformal meshes are then connected in the form of MB-RWG functions. Due to the natural, normal continuity of MB-RWG, no continuity requirements or special treatments need to be imposed at these junctions. Numerical experiments are given to demonstrate the feasibility and versatility of the proposed method.

The dual testing scheme using the Buffa-Christiansen (BC) basis function not only maintains the good convergence of the magnetic field integral equation (MFIE) but also improves its accuracy. However, in practical applications, fewer unknowns are desired to reduce the computing resources of the nBC-tested MFIE. In this letter, a novel conforming discretization based on characteristic basis functions (CBFs) is proposed to mitigate the problem of the conventional nBC-tested MFIE. The proposed discretization can acquire a well-conditioned discretization of the identity operator leading to a satisfactory iterative convergence while keeping a conforming testing scheme. The resulting system matrix is smaller than the original system matrix of the conventional nBC-tested MFIE while inheriting satisfactory iterative convergence and accuracy. Numerical results are shown to demonstrate the performance of the proposed method.

In this paper, an efficient synthesis method for near- field multi-focus (NFMF) sparse planar arrays (SPAs) is proposed, utilizing a structured sparsity learning (SSL)-based deep neural network (DNN) model. The model is established by connecting physical equations in tandem with the DNN to map the relation between the desired near-field radiation characteristics and SPA geometry. To enhance the sparsity of the SPA, the SSL method, incorporating a group L1/2 (GL1/2) regularizer seamlessly embedded into the model, is employed to prune redundant nodes that represent unnecessary array elements. By incorporating both the physical equations and SSL method, prior knowledge is provided to improve training efficiency of the model. Through appropriate training, the synthesis of the SPA is achieved, generating an optimal SPA layout along with element excitations. The proposed method allows for precise control of the focal position and sidelobe level (SLL) of the near-field pattern with a minimal number of array elements. The effectiveness of this method is demonstrated by two examples focusing on single- and eight-point near-field targets with low SLL. Results show that the proposed method achieves over 65% savings in the number of array elements and at least a 45% reduction in synthesis time compared with the existing synthesis methods.

In this letter, an efficient synthesis method for near-field multifocus (NFMF) sparse planar arrays (SPAs) is proposed, utilizing a structured sparsity learning (SSL)-based deep neural network (DNN) model. The model is established by connecting physical equations in tandem with the DNN to map the relation between the desired near-field radiation characteristics and SPA geometry. To enhance the sparsity of the SPA, the SSL method, incorporating a group L-1/2 (GL(1/2)) regularizer seamlessly embedded into the model, is employed to prune redundant nodes that represent unnecessary array elements. By incorporating both the physical equations and SSL method, prior knowledge is provided to improve the training efficiency of the model. Through appropriate training, the synthesis of the SPA is achieved, generating an optimal SPA layout along with element excitations. The proposed method allows for precise control of the focal position and sidelobe level (SLL) of the near-field pattern with a minimal number of array elements. The effectiveness of this method is demonstrated by two examples focusing on single- and eight-point near-field targets with low SLL. Results show that the proposed method achieves over 65% savings in the number of array elements and at least a 45% reduction in synthesis time compared with the existing synthesis methods.

Using only the RWG functions, the combined source integral equation (CSIE) with weak form combined source condition can achieve fine accuracy and fast iterative convergence for conductor objects. However, compared with a conventional integral equation in the method of moments (MoM), the conventional CSIE involves more matrices and more complex numerical processing, and these make the CSIE inefficient, especially for multiple excitation problems. In this article, a characteristic basis function (CBF)-based CSIE with initial guess is proposed to mitigate this problem. The CBF is employed to reduce the number of unknowns as well as the storage consumptions and iteration time. In the meantime, an initial guess especially for CBFs is proposed to reduce iterations when solving multiple excitation problems. Numerical results are given to demonstrate the performance of the proposed method.

In this letter, an efficient solution of the wideband partial modification problem involving an original structure with small geometric modifications is proposed. Compared with the conventional partial modification analysis method, the proposed method is more efficient in two aspects: first, the inverse of the impedance matrix of the original structure is solved implicitly in a compressed form. Based on the compressed inverses, all the subsequent modification problems can be quickly solved with the aid of the Sherman-Morrison-Woodbury formula and the partitioned-inverse formula each time the modification takes place. Second, solutions of the original structure at different frequencies are related by the adaptive cross approximation and thus can be quickly solved. Numerical examples are performed to demonstrate the accuracy and efficiency of the proposed method.

Frequency-polarization multiplexing metasurfaces (FPMMSs) capable of generating vortex beams carrying orbital angular momentum (OAM) have facilitated the actualization of high information capacity in optical and microwave communication. However, poor frequency controllability and the deficiency of theoretical methodology for frequency modulation of meta-atom remain challenges for existing FPMMSs with orthogonal linear polarization. In this work, a strategy to customize the operating band of the “I”-shaped meta-atom (ISMA) based on phase analysis of the equivalent circuit is proposed. A frequency modulation factor is introduced to adjust the operating band of the ISMA over a wide range based on the relationships between element geometry parameters, capacitance and inductance values in the equivalent circuit model, and the reflected phase of ISMA-type meta-atom. Then, a dual-band dual-polarized meta-atom is proposed by placing subunits operating at different bands cross-orthogonally, allowing the subunits to modulate the phase independently. A dual-band dual-polarized dual-mode OAM beam generator is designed and constructed as a proof-of-concept to verify the methodology. The measured results are in excellent agreement with the simulations. The proposed methodology for customizing frequencies establishes the groundwork for the implementation of OAM-based FPMMSs for secure and high-capacity communication in 6G massive-MIMO systems.

With the rapid development of 5G communication technology, high-frequency electromagnetic interference (EMI) shielding plays a vital role in the normal operation of electrical and electronic equipment and systems, and has attracted surging interest in 5G mm-wave applications. However, many current EMI shielding materials contain highly conductive materials, resulting in strong secondary reflection and environmental pollution. Here, we propose a green high-performance EMI shielding material for 5G mm-wave based on a metamaterial absorber (MMA). Characteristic mode theory and equivalent circuit are employed to inversely design the unit cell's dimension and structure, as well as the resistive value of the proposed MMA. We reveal that from 22 to 43.5 GHz, the shielding effectiveness of higher than 30 dB, and the standard green index of SER < 3.01 dB and g( s) >= 1 can be realized whether the MMA is flat or even bent. Excellent agreement between the measured and simulated results verified the high performance of the proposed EMI shielding MMA. The transmittance of over 85.84% can be achieved within the 380 similar to 800 nm spectrum. The proposed green EMI shielding material integrates multi-functionalities of low profile, flexibility, polarization-insensitiveness, wide-angle, and optical transparency, and can find potential applications in EMI shielding in complex electromagnetic environments.

In this paper, an odd- and even-mode composite spoof surface plasmon polariton (OEC-SSPP) antenna is proposed. OEC-SSPP's odd and even modes can both be excited in a common channel and operate at different frequency bands through different feeding methods, and the operation bands can be controlled easily by controlling the SIW and SSPP parameters. The simulation results of CST STUDIO SUITE software prove the excellent performance of the proposed OEC-SSPP antenna. It covers the frequency range of 6.8 ~ 8.5 GHz (odd mode) and 10.2 ~ 11.6 GHz (even mode). The radiation efficiency exceeds 80% for both modes. The realized peak gain is 6.2 dBi for the odd-mode SSPP antenna and 7.5 dBi for the even-mode.

As a basic configuration, the concentric cylinder is used widely in a range of microstructures. We stud-ied the near-field radiative heat transfer (NFRHT) in a concentric cylindrical system, based on Green's function formalism and fluctuation-dissipation theory. A general formula was derived in cylindrical coor-dinates to study heat transfer both for far-and near-field, and SiO2 was used as an example to illustrate it. Three relations of heat transfer between concentric cylinders is explored in different configuration. Monochromatic heat transfer can be achieved by adjusting the radius at a specific distance. Additionally, we found that the radiation expressed in terms of polarization is not suitable in the NFRHT of concen-tric cylindrical systems. This work provides a new sight for efficient thermal management in near-field cylindrical conditions. (c) 2023 Elsevier Ltd. All rights reserved.

准确高效的电磁散射仿真方法对设计隐身航空发动机排气系统非常重要.将特征基函数法(CBFM)、多层快速多极子算法(MLFMA)、插值分解(ID)算法和并行技术相结合,对发动机排气系统的单站雷达散射截面(RCS)进行仿真计算.插值分解(ID)可以对单站激励矩阵进行低秩压缩,因此可以减少矩阵方程的求解次数,显著提高了传统CBFM-MLFMA的计算效率.为了验证算法的正确性,对轴对称排气系统模型进行了加工和RCS试验测试.与测试结果相比,仿真结果与其吻合良好,验证了算法的精度.

To verify the concept of the metasurfaced reverberation chamber (MRC) which was proposed. This paper reports on measurements in the reverberation chamber (RC) performance by using a 1-bit random coding metasurfaced stirrer. The measurement results are validated and compared with that from two mechanical stirrers (horizontal stirrer and vertical stirrer). Figures of merit such as quality factor (Q factor), number of samples, standard deviation, angle autocorrelation, average K-factor, total scattering cross section (TSCS) and the enhanced back scattering coefficient (eb) are presented. Results indicate the feasibility of the MRC technique in the operation frequency of the RC. And it is possible to enlarge the test volume of the RC by using the 1-bit random coding metasurface stirrer.

An interpolation method for the reduced matrix in the wideband characteristic mode basis function method (WCMBFM) with the wideband adaptive cross approximation (WACA) algorithm is proposed to efficiently compute the wideband electromagnetic scattering problems. In this method, the characteristic mode basis functions (CMBFs) and the selected dominant basis functions of the far-field block pairs obtained by the ACA decomposition are extracted at the highest frequency within the band of interest. Then, the approximate compression of the reduced matrix at other required frequencies within the band of interest can be efficiently generated by the polynomial interpolation. Compared with the conventional interpolation method for the reduced matrix, the proposed method reduces the dimension of the matrix to be interpolated, which makes the construction of the reduced matrix more efficient. The numerical result of the frequency selective surface (FSS) is investigated to show the advantages of the proposed method.

A multibranch curvilinear Rao–Wilton–Glisson (MB-CRWG) basis function is proposed to solve surface integral equations with nonconformal curvilinear meshes. The derivation of the MB-CRWG basis function is given. The structure of the MB-CRWG basis function can be divided into positive and negative parts. The positive part is one curvilinear triangular patch, and the negative part is composed of several curvilinear triangular patches. The MB-CRWG can conveniently connect two surfaces discretized with curvilinear triangular patches of different sizes. Numerical examples of the electromagnetic scattering from multiscale perfect electrically conducting targets are given to demonstrate the effectiveness of the proposed basis function.

In this communication, a wideband Sherman–Morrison–Woodbury formula-based algorithm (WSMWA) is proposed to efficiently compute the wideband and wide-angle electromagnetic scattering problems. In the proposed algorithm, the standard adaptive cross approximation (ACA) decomposition is only performed at the highest frequency of the frequency band of interest to find the dominant basis functions for each far-block pair. Then, at any frequency within the entire frequency band, the approximate compression of the impedance matrix can be efficiently constructed by using the impedance interpolation method with the dominant basis functions selected at the highest frequency. As a result, the WSMWA avoids performing the standard ACA repeatedly and saves a lot of computational time in comparison with the conventional Sherman–Morrison–Woodbury formula-based algorithm (SMWA) for wideband and wide-angle applications. Numerical results for electromagnetic scattering are given to demonstrate the efficiency and accuracy of the proposed algorithm.

Metasurface is extensively studied for generating multicharacteristic orbital angular momentum (OAM) beams. However, designing a highly integrated and independent polarization-frequency multiplexing metasurface for efficient multiscenario OAM-related applications is still a challenge. Here, a triple-band single-layer shared aperture reflective metasurface for triple-polarization channels independent OAM modulations is proposed. The specific frequency quantitative customization resonance phase and quasi-static geometric phase are utilized to manipulate the dual-band (Ku- and K-band) orthogonal linearly polarized (LP) channel and C&X-band right-handed circularly polarized (RHCP) channel. An isolation ring is introduced for eliminating the strong coupling between the structurally compatible RHCP and orthogonal-LP subunits in a shared aperture meta-atom. It is revealed that the isolation ring not only helps realize efficient multipolarization, multiband, and multimode OAM generation, but also expands the operation bandwidth of the RHCP channel OAM. A proof-of-concept prototype of the designed metasurface is constructed to verify the methodology and the experimental results are in excellent agreement with simulations. The proposed independent OAM modulation scheme for extending the functionality of metasurface offers a novel route to realize multipolarization and multiband OAM beams with high isolation, which may have potential applications in OAM-based multichannel multiplexing communications.

为解决5G毫米波带来的电磁辐射及现有电磁屏蔽材料造成的环境二次污染、高雷达散射截面、光学不透明和难以共形等问题,本文以超材料吸波体为基础,提出了一个满足绿色屏蔽指数gs≥1的低雷达散射截面、光学透明和柔性多性能电磁屏蔽材料.该电磁屏蔽材料属于人工可设计的多层结构,使用透明导电材料氧化铟锡作为周期性谐振单元结构和底层铺地所用材料,透明材料聚对苯二甲酸乙二醇酯和聚氯乙烯作为介质层.仿真和实验结果一致性表明:该屏蔽材料在22～30 GHz频段内可实现未共形与共形角度60°状态>30 dB的绿色有效电磁屏蔽及>5 dB的雷达散射截面(RCS)缩减.理论推导的等效电路、等效参数和场分布论证了吸收屏蔽的原理.该绿色多性能电磁屏蔽材料精确覆盖了毫米波n257、n258和n261频段,可有效解决这些频段带来的电磁干扰问题.

In this paper, an ultra-broadband multi-channel Hermite-Gaussian (HG) beams excitation metasurface has been designed. The proposed polarization conversion meta-atom (PCMA) used to form HG metasurface can reflect cross-polarized waves from linearly polarized waves and co-polarized waves from circularly polarized waves in an extremely wide operating band (2.513 GHz to 10.406 GHz). The x-polarized (x-pol), y-polarized (y-pol), left-handed circularly polarized (LHCP), and right-handed circularly polarized (RHCP) high-order HG modes have emerged based on a single HG metasurface under fundamental Gaussian mode illumination. The proposed structure opens a new avenue for applications of polarization diversity technology in microwave and millimeter wave wireless communication.