The field of navigation has been relentlessly evolving to fulfil its long-standing objective of building a highly accurate universal navigation system. However, in highly urban and indoor locations, line-of-sight signals cannot be guaranteed, and conventional terrestrial-based and satellite-based techniques cannot perform optimally. This paper strives to establish navigation via signals of opportunity (NAVSOP) by proposing a Wireless Fidelity (Wi-Fi)-based indoor localization method using the Received Signal Strength Indicator (RSSI) technique. This proposed method employs the fingerprinting along with the K-Nearest Neighbour (KNN) and again KNN with Inverse Distance Weighting (IDW) approach to offer superior position estimation accuracy. In this paper, we have developed a new neighbourhood dataset by expanding target neighbourhood locations by random point generator algorithm, thereby propounding the utility of NAVSOP for indoor environments to enable future navigation applications in real-world civilian and military domains. The results obtained via the novel IDW approach give a reduced uncertainty in position error estimation of 0.68 m as compared to the traditional approaches of fingerprinting with KNN (1.13 m) and trilateration (2.3 m).

Admittance and impedance (Leontovich) matching conditions at the boundary of a good conductor find widespread usage in the formulation and (numerical) solution of electromagnetic problems. Starting with the known relationships at a stationary interface, we derive manifestly covariant admittance and impedance relations in a flat space-time for a conducting body which moves with uniform velocity in free space. Explicit formulas (in the ordinary space, that is) are given for both isotropic and anisotropic conductors. Under the same hypotheses, we also derive, at the conducting interface, the surface density of four-force by means of the normal component of the relevant energy-momentum tensor. The low-velocity limit of the formulas is also presented because it is of particular interest for practical applications. Moreover, since the covariant admittance and impedance relations as well as the matching condition of the energy-momentum tensor require the unitary four-vector perpendicular to a surface in motion, we outline, in the appendices, the derivation of unitary four-vectors tangential to a hyper-line and perpendicular to a hyper-surface in the Lorentz space.

This article presents the first comprehensive retrospect on an innovative and emerging antenna technology termed antennaon-display (AoD) for wireless mobile devices of 5G and beyond 5G (B5G, including 6G). The main backgrounds, benefits, stack-ups, ingredients, performance requirements, and various representative types of AoD are systematically introduced, analyzed, and discussed. Beyond its original role in wireless communication applications, AoD is also highly suitable for radar-based sensing or even for integrated sensing and communication (ISAC) to enable and enrich human-device interactions for more powerful artificial intelligence (AI) devices. Furthermore, the prospect of integrated millimeter-wave and microwave AoD designs is proposed as a promising development trend for AoD. Finally, an on-site demonstration of a smartphone featuring an AoD solution for real-time wireless video transmission at 28.0 GHz is presented.

Improving only the speed-loop controller in a PMSM drive system is insufficient to address limitations in the current loops, such as integral saturation and severe oscillations. To achieve high-performance current control across the speed-current loop structure, this paper proposes an improved non-singular fast terminal sliding mode continuous composite control (INFTSMC) method, integrated with a fast super-twisting sliding mode observer (STSMO). First, a state-space model of the PMSM speed-current loops is established. Then, the speed and current loop controllers are designed using the STSMO within the INFTSMC framework. The fast super-twisting control law is adopted to reduce the number of observer parameters and to mitigate the severe oscillations caused by high gains in conventional sliding mode observers. Finally, the proposed composite control strategy is compared with conventional PI and SMC+SMO controllers through both simulation and RT-LAB experiments. The results demonstrate that the proposed approach significantly enhances the dynamic response performance of the PMSM drive system.

A compact quasi-Yagi antenna with ultra-wideband and high-gain characteristics is proposed. The design incorporates a conical dielectric cover, a horn reflector, and gradient-shaped Yagi elements. The conical dielectric cover and horn reflector work together to enable high-gain performance, while the arcuate gradient dipole provides a bandwidth of 62% (6.9-13.1 GHz). Measured results indicate a peak gain of 17.5 dBi and a maximum sidelobe level (SLL) of -13.5 dBi. Compared to conventional printed Yagi antennas of similar length, this integrated antenna offers wider bandwidth, higher gain, and lower SLL. It is particularly suitable for tunnel communication and radar detection systems.

This paper presents a simple Liquid Crystal Polymer (LCP) substrate material-based frequency and pattern reconfigurable antenna for body-centric communication applications. The designed antenna is circular in shape with multiple spars in the radiating element. PIN diodes are arranged on either side of the lower portion at the concentric circular arc of the feed line for external switching. The upper portion of the radiating structure is connected with inductor and capacitor for proper impedance matching to attain the desired band of frequency. The constructed LCP substrate-based antenna is flexible in nature and conformal to the congregation surface in body area network applications. Frequency reconfigurability with switching between PCS (1.8-1.9 GHz) to WLAN (5.1-5.3 GHz) and ISM band (5.7-5.8 GHz) makes the model more appropriate for wearable applications with low specific absorption rate (SAR) less than 1.6 w/kg, which is in the standards. Additionally, the projected design demonstrates pattern reconfigurability with a 30-degree tilt at different switching conditions.

In this paper, an ultra-wideband monopole antenna for wireless communication is designed and fabricated based on characteristic mode theory. The antenna is mainly composed of a metal main body and a circular metal patch and the antenna dimensions are 35×30×1.6 mm³. In order to enhance its matching performance, a circular groove is made in the center of the circular metal patch, and an outer ring is added to the outside. In order to expand the covered bandwidth and reduce the reflection loss, an isosceles right triangle is cut off from each side of the ground plane. The length of the ground plane and the side length of the ground plane cut angle are optimized. The key modes are determined through the analysis of the characteristic mode theory. The simulation and measurement results show that this antenna covers the frequency band of 3.03-11.75 GHz, with a maximum return loss of -42.26 dB and excellent radiation performance.

A novel broadband ±45˚ dual-polarization antenna is presented. By introducing coupling slots on the loop dipole arms of the antenna, multi-resonance performance occurs so that the impedance bandwidth is greatly widened. An enhanced impedance bandwidth about 92.5% with VSWR < 2 is obtained at two ports, corresponding to the frequency region of 1.61-4.38 GHz. In the frequency range of 1.61-3.8 GHz, a gain of 8.2 ± 2.2 dBi is obtained. For the frequencies beyond 3.8 GHz, the gain drops sharply and goes down to 1.1 dBi at 4 GHz. Within the operating frequencies, a port-to-port isolation > 22.5 dB is achieved. Especially, the proposed antenna has a very simple configuration and is easy to be fabricated. A mechanical prototype of the antenna has been manufactured and measured. The measurement results have good agreement with the simulations. The work principle and detailed descriptions of the antenna are presented in the paper.

Electromagnetic inverse scattering (EIS) problem is challenging due to its properties of strong nonlinearity and ill-posedness, where existing deep learning approaches often lack systematic network refinement and comprehensive analysis of key factors affecting performance. This work introduces CAMO-Net, a U-Net-based framework for EIS that integrates a channel-attention mechanism and systematically optimizes architectural and training factors to address these limitations. By integrating channel attention into skip connections, adopting a multi-scale channel configuration, and fine-tuning key hyperparameters through controlled experiments, CAMO-Net achieves superior accuracy and robustness. Experimental results demonstrate that it reduces the mean relative error (MRE) by 32.5% and the mean squared error (MSE) by 34.1% compared to the baseline U-Net. Our results demonstrate that joint channel attention and multi-factor optimization provide an effective, reproducible pathway for high-precision EIS imaging, offering new insights for robust reconstruction in EIS problems.

This paper introduces the development of an antenna model with a meandering shape in the industrial, scientific, and medical band (i.e., 2.4-2.48 GHz) proposed for biomedical applications. This design is specifically tailored for stimulation applications, where size and form factors are critical. The design of the meandering patch antenna seeks to optimize performance while ensuring compatibility with the unique requirements of stimulation devices. A Rogers RO3010 (loss tangent = 0.0022, relative permittivity = 10.2) is used in the design as a substrate. The miniaturized antenna (2.5 mm × 2 mm × 0.12 mm), featuring a 400 MHz bandwidth, was engineered to mitigate detuning effects caused by electronic interference and biological tissue heterogeneity. The smaller dimensions of this antenna not only facilitate easier integration within device structures but also aim to enhance characteristics such as impedance matching and bandwidth, addressing the challenges posed by the confined space within the human body. The proposed antenna also exhibits a -33 dB gain and a lower specific absorption rate (SAR) of 272 w/kg. These attributes position it as a promising solution for biomedical implantation.

Diffractive optical elements, including holograms and metasurfaces, are widely employed in imaging, display, and information processing systems. To enhance information capacity, various multiplexing techniques such as wavelength, polarization, and spatial multiplexing have been extensively explored. However, the angular optical memory effect induces strong correlations in the diffracted output under varying angles of incidence, thereby fundamentally limiting the use of illumination angle as an independent degree of freedom in multiplexing strategies. Here, we propose and experimentally demonstrate a globally designed angle-multiplexed metasurface hologram enabled by a diffractive neural network (DNN). Angular multiplexing in the DNN is realized by harnessing illumination angle-dependent phase delays across local units, rather than relying on complex local designs with intrinsic angular dispersion. The DNN is trained using the complex electric field distributions and corresponding target images for each incident angle, enabling end-to-end optimization of the entire metasurface phase profile to encode multiple angular channels simultaneously. Besides, phase modulation of circularly polarized transmitted waves is achieved via geometric phase engineering, using a single-layer and fabrication-compatible meta-atom design without relying on multilayer stacking or inter-resonator coupling. Experimental measurements validate the high-fidelity reconstruction of both images at their respective angles, consistent with numerical simulations. Furthermore, robustness studies confirm that the proposed metasurface can tolerate reasonable variations in incident magnitude, angle, and frequency, as well as fabrication-induced phase errors, while preserving imaging fidelity. The proposed metasurface and design strategy offer a scalable platform for high-density information encoding and multiplexed optical systems, with potential applications in augmented reality, secure communication, and multi-view display technologies.

This paper presents a single-fed wideband circularly polarized high-gain dielectric resonator antenna (DRA) for KU-band applications. The proposed antenna consists of a cylindrical dielectric resonator on top, a double-layer metasurface structure in the middle, and a feeding substrate at the bottom. An asymmetric X-shaped slot coupling feed on the substrate enables the circular polarization characteristic. The DRA incorporates a double-layer metasurface to broaden the 3 dB axial ratio bandwidth and enhance gain. Simulation results show that the antenna achieves a -10 dB impedance bandwidth of 24.2% (13.69-17.46 GHz), a 3 dB axial ratio bandwidth of 20.01% (14.05-17.2 GHz), with a peak gain of 9.89 dBi. The designed antenna operates in the KU-band and is suitable for wireless communication applications including satellite communications and global positioning systems.

This paper introduces a novel, compact, frequency-reconfigurable multiple-input multiple-output (MIMO) filtenna that integrates a defected microstrip structure (DMS)-based bandpass filter (BPF) with a wideband circular patch antenna to support dynamic tuning across sub-6 GHz and X-band applications. The antenna operates efficiently as a wideband system while enabling mechanically controlled narrowband filtering through a reconfigurable BPF structure embedded in the feedline. Tunability is achieved using discrete switching mechanisms, allowing frequency selection from 5.9 GHz up to 12 GHz, with a peak gain of 6 dBi and high radiation efficiency. A two-port MIMO configuration with orthogonal element placement and an embedded decoupling structure ensures superior isolation (< –48 dB), extremely low envelope correlation coefficient (ECC < 0.0035), and diversity gain (DG) approaching 9.998 dB. The proposed antenna demonstrates excellent performance metrics with a compact footprint of 80 × 45 mm², making it well-suited for compact wireless applications in environments with limited spectral availability.

Acoustic/Electromagnetic (EM) waves are at the heart of numerous scientific tools and inventive technologies for plentiful state-of-the art applications. This study describes the design and implementation of a portable and effective acoustic/electromagnetic shark shield electronic system. In order to support the shark deterrent technologies, a double-layer printed circuit board (PCB) circuit that includes a signal generator, pulse width modulation, and power amplifier modules has been designed. The 4-ohm, 3-watts loudspeaker was used in the construction of the acoustic shark shield system as a radiation element, while the EM system uses two electrodes and a wire antenna to produce EM wave radiation. The suggested design has then been subjected to a numerical analysis using the Multisim live demonstration circuit simulator. Lastly, a comparison between the experimental and numerical results was made. According to the findings, maximum peak-to-peak pulse amplitude of nearly 100 V and 55 Hz frequency was attained in a zero-meter distance deterrent system. These values are reduced to 53.2 V at approximately 55 Hz in the case of an EM shark system and with an artificial saltwater tank at 2 m distance, while the obtained peak amplitude for the acoustic shark deterrent system achieved peak-to-peak pulse amplitude value of almost 120 V at 55 Hz.

The paper proposes a microwave absorber in the form of half-spheres placed on a base layer as an alternative to the conventional pyramidal shape. The performance of the absorber is investigated, focusing on the influence of the diameter of the half-sphere, permittivity, loss tangent, and angle of the incident waves. The study also evaluates the case when the absorber is backed by a conducting plate that is required for shielded anechoic chambers. Simulation results using the CST Microwave suite indicate that increasing loss tangent enhances absorption while decreasing permittivity reduces reflectivity. The proposed absorber offers low sensitivity of reflection concerning the angle of incidence due to the symmetry of the spherical surface. The results show that the proposed absorber has a comparative performance to the pyramidal absorber of the same total thickness.

In recent years, uncertainty analysis methods have become a research hotspot in the field of Electromagnetic Compatibility (EMC), and non-intrusive uncertainty analysis methods are widely used in the field of EMC due to their advantages such as easy solver generalization and easy programming. The proposal of Bayesian optimization-based uncertainty analysis method further enhances the competitiveness of non-intrusive uncertainty analysis methods in solving complex EMC simulation problems. However, in traditional Bayesian optimization-based uncertainty analysis methods, Latin hypercube sampling strategy is used to construct the initial Gaussian process model, which lacks adaptive adjustment capability, and the quality of the initial Gaussian process model has a significant impact on the efficiency of subsequent calculations and the accuracy of the final results. This defect limits the computational efficiency and accuracy of Bayesian optimization methods in uncertainty analysis applications. In response to this issue, this paper proposes an active sampling strategy based on the Stochastic Reduced Order Model (SROM) method. This strategy improves the fitness function used by the SROM method in clustering to enhance the representativeness of the training set to the sampling space. By using this active sampling strategy instead of Latin hypercube sampling strategy, a higher quality initial Gaussian process model can be constructed, and the accuracy of Bayesian optimization method uncertainty analysis calculation is improved in the example, verifying the effectiveness of the proposed initial sampling point selection improvement strategy.

The transfer matrix method (TMM) with scattering matrices has been a valuable tool, facilitating the rapid characterization of multilayer devices in a very fast, stable, and memory-efficient manner. This paper presents a generalization of TMM with improved scattering matrices capable of simulating devices with full nine-element material tensors for the layers and any combination of signs for the real and imaginary parts of the isotropic external regions. The formulation of the bianisotropic transfer matrix method (BTMM) algorithm is covered in detail, and notes on implementation are provided. Example devices found in literature were used to benchmark the accuracy of the algorithm. The simulation of the bianisotropic device was corroborated with a bianisotropic finite-difference frequency-domain (FDFD) algorithm and a finite-element method (FEM).

This paper presents a dual-band antenna design for X/Ku bands, featuring asymmetrical feed ports, slot-loaded radiating patches, and a reconfigured defect ground structure (DGS) integrated with a back air cavity to achieve 32.11% reduced patch area and directional radiation. By coplanar waveguide (CPW) feeding and vertical interconnect accesses (VIAs) connecting all metal layers, the antenna miniaturizes via extended surface current paths and broadens bandwidth via DGS. Simulation and measurement show operating bands of 8.30-12.29 GHz (38.75% fractional bandwidth) and 12.91-14.21 GHz (9.58%), with measured gains aligning well with simulations. Compared to traditional dual-band designs, this work reduces physical size by over 30% while maintaining high gain, making it suitable for compact satellite communication, radar, and microwave energy systems.

This paper presents the design and performance evaluation of a flexible, multilayer wearable antenna optimized for sub-6 GHz 5G applications at 3.5 GHz. The proposed antenna introduces a fabrication-ready stackable design using textile-compatible materials, including Felt, a 2 mm EVA foam layer, and Shieldit Super. A key innovation lies in the use of low-permittivity EVA foam as an intermediate spacer, which enhances gain and impedance matching without requiring additional structural elements, thus maintaining a compact and mechanically flexible profile. The antenna achieves a peak realized gain of 7.81 dBi and a wide impedance bandwidth of approximately 15.7%, within a total thickness of just 4.34 mm. The design remains robust under bending and close-body scenarios, with specific absorption rate (SAR) analysis confirming compliance with international safety standards. Experimental and simulated results validate the antenna's consistent performance, underscoring its suitability for wearable and Wireless Body Area Network (WBAN) applications in future 5G systems.

To address the convergence inefficiency of the conventional CS-Krylov-block method in solving electromagnetic scattering problems, this paper presents an adaptive Krylov subspace basis function method (AKSBFM) based on spectral energy thresholds. In this method, Krylov subspace basis functions (KSBFs) are first generated within each extended subdomain using localized self-impedance matrices. Singular value decomposition (SVD) is performed on the candidate basis set to evaluate energy contributions, and only the dominant components exceeding a predefined energy threshold are retained. As a result, the number of basis functions per subdomain is automatically adjusted, and a compact, well-conditioned reduced matrix system is constructed. This energy-guided truncation significantly eliminates redundant modes, yielding improved numerical stability and reducing the condition number by up to two orders of magnitude. Numerical experiments demonstrate that, compared with the traditional CS-Krylov-block method, AKSBFM improves computational efficiency while ensuring computational accuracy.