Contactless electromagnetic (EM) sensing has revolutionized biomedical and healthcare applications, enabling non-invasive, real-time monitoring and diagnosis of physiological conditions. Unlike traditional wearable or invasive sensing solutions leading to patient discomfort, contactless EM sensing provides a seamless and unobtrusive solution for continuous health monitoring. This review categorizes EM sensing into imaging-based and signal-based approaches, emphasizing recent technological advancements. Imagingbased sensing techniques provide high-resolution imaging of human anatomy for analysis and diagnosis, while signal-based methods infer physiological conditions through the variations in EM signals caused by human movements. Particularly, metamaterials have significantly enhanced contactless EM human sensing due to their superior ability to precisely manipulate EM waves. Metamaterialbased imaging, such as Magnetic Resonance Imaging (MRI), improves diagnostic accuracy by enhancing imaging contrast and reducing noise. Meanwhile, metamaterial-based sensing, exemplified by metasurface-enabled multi-person vital-sign detection, offers increased spatial resolution and signal-to-noise ratio, enabling reliable and efficient human health monitoring. Furthermore, the integration of metamaterials with artificial intelligence (AI) has transformed EM human sensing, enhancing its accuracy and adaptability across various environments. By highlighting recent progress and discussing future challenges, this review underscores the importance of further research to unlock the full potential of EM sensing in advancing biomedical and healthcare technologies.

This paper introduces a hexagon-shaped microstrip fractal antenna over ultra-wideband frequencies for medical purposes when it is positioned in close proximity to the human body. A foam substrate of 2 mm thickness is used with copper as conducting material to investigate the on body performance. The proposed antenna of size 50×38×2 mm³ demonstrated broad frequency coverage from 2.05 to 14.75 GHz and achieved a peak gain of 7.07 dB at 2.5 GHz with maximum return loss of -28.06 dB. The addition of stub has resulted in good impedance matching and is ideal for real-time health tracking, body-centric communication. Its compact size, flexibility, and low-profile nature make it well suited for continuous use in medical environments. A detailed SAR evaluation is performed over a three-layer (Skin, fat, and muscle) phantom equivalent to human tissue for 1 and 10 grams. The on-body, 1 mm and 2 mm away context has been carried out and compared to validate SAR less than the safety threshold as prescribed by IEEE.

In this paper, a dual-circularly polarized (DCP), metasurface-loaded broadband antenna is designed to operate across frequencies covering the Sub-6 GHz 5G band for RF energy harvesting (RFEH) applications. The DCP antenna can collect RF energy both left-hand circularly polarized (LHCP) and right-hand circularly polarized (RHCP) waves by the same antenna. In this view, the antenna structure features two crossed metallic strips enclosed within symmetrically loaded metallic rhombic loops. Unequal strip widths in the rhombic loops enhance gain and improve impedance matching. A partial ground plane on the bottom layer fine-tunes the operating frequency, while the metasurface boosts antenna gain. A prototype with optimized dimensions was fabricated, and the results, both experimental and simulated, demonstrated excellent agreement.

In the pursuit of comprehensively assessing the radiation emission characteristics of the balise transmission module (BTM) antenna within diverse train environments, this paper puts forward a novel approach grounded in similarity theory. Herein, the ideal radiation emission field distribution of a single BTM antenna serves as the reference two-dimensional dataset. The radiation emission field distribution specific to a given train environment is adopted as the input data. By calculating the similarity coefficients, the extent of influence exerted by different train settings on the radiation emission traits of BTM antennas can be accurately gauged. In addition, 13 representative train environments have been meticulously measured and evaluated. The results reveal that the mean square error (MSE) of this evaluation method is less than 0.011. This compellingly demonstrates the effectiveness of the method's predictive capabilities. In light of the above-mentioned theoretical postulations and practical exigencies, the proposed method empowers us to effectively evaluate the impact of a particular environment on the radiation characteristics of the BTM antenna even prior to the installation of BTM equipment.

A new approach based on an Inverse Artificial Neural Network (IANN) for Multi-Objective Antenna Design is presented in this paper. The network sets the geometrical variables as the output and uses three antenna performances as inputs. The proposed ANN model is structured into two distinct parts: In the first part, three autonomous branches establish the correlation among S-parameters, gain, specific absorption rate (SAR), and antenna geometric variables. The outputs of these branches are used as inputs in the second part to derive a distinctive solution for these geometric variables. The proposed antenna dimensions are 20x24x1.58 mm³, an ultra- wide-band of 4.1 GHz to 8.7 GHz is achieved in free space and on human tissue which coincides with the 5.8 GHz ISM band. Body temperature and specific absorption rate are simulated using the suggested rectangular patch antenna, The resulting optimized antenna holds promising potential for biomedical applications.

The uncertainty analysis method based on surrogate models is a current research topic in electromagnetic compatibility (EMC) simulation. However, research on its convergence determination remains underdeveloped. Based on the multi-surrogate model integration technique, this paper proposes two convergence determination methods: one based on variance and the other on failure rate. Researchers can select the appropriate convergence determination method based on specific application requirements, ultimately identifying the optimal number of sample points to ensure the accuracy and efficiency in EMC uncertainty analysis.

This paper introduces a microstrip patch antenna operating at the 2.4 GHz ISM (Industrial, Scientific, and Medical) band, specifically suitable for Internet of Things (IoT) applications. The proposed antenna comprises a compact 40×10×1.6 mm³ design using an inverse S-shaped meander line, defected ground, and slotted parasitic patch to achieve enhanced bandwidth and very low return loss, contributing significantly to antenna design for IoT applications. FR-4 material is used as substrate for this antenna. The proposed antenna achieves a measured return loss of -24.67 dB at 2.4 GHz, with a bandwidth of 8.75%. Moreover, it provides a gain of 1.14 dB with an efficiency of 73.35%. Also, the designed antenna is integrated into a home automation system to verify its performance in IoT application, and the results are highly satisfactory.

This research proposes a tagging antenna sensor for permittivity detection of solid materials based on a close quarter approach. The sensor is proposed to operate at a frequency of 2.53 GHz using a single port resonator with a reflection coefficient (S₁₁) ≤ -10 dB. The sample is placed directly in the sensing area of the antenna sensor based on the concentration of the electric field. Permittivity detection is proposed based on the resonant frequency shift of the transmission coefficient (S₂₁) using interrogator antennas separated by a distance of (d) = 100 mm determined using the Fresnel region. Based on the measurement results, the antenna sensor has a high accuracy of 96% while the sensitivity and ΔF are 0.39% and 0.012 GHz respectively. Moreover, the sensitivity of the proposed sensor is still low due the low concentration of the electric field. Therefore, increasing the sensitivity of the antenna sensor can be recommended as further work such as combining the structure of single port resonator with another structure such as interdigital capacitor and artificial magnetic conductor (AMC). Finally, this research makes a significant contribution to the permittivity detection of solid materials with a close quarter approach to support real time and flexible measurements and can be recommended for several applications for the biomedical, pharmaceutical, and material quality control industries.

This paper presents a high-gain right-hand circularly polarized (RHCP) magnetoelectric (ME) dipole antenna (MEDA) with microstrip-line aperture-coupled feeding. By extending one pair of diagonal horizontal metallic plates in the traditional linearly polarized MEDA in opposite directions, the electric dipole current becomes parallel to the magnetic dipole current, achieving circular polarization performance. The antenna is excited using a microstrip-line aperture-coupled feeding structure, and its electrical performance is further enhanced by integrating a box-shaped reflector. The measured results of the antenna prototype show that the impedance bandwidth (|S₁₁| ≤ -10 dB) is 46.8% (2.90-4.67 GHz); the 3 dB axial ratio bandwidth is 26.4% (3.58-4.67 GHz); and the maximum in-band gain reaches 12.9 dBic. A cross-polarization level below -18 dB and a front-to-back ratio exceeding 20 dB highlight the superior performance of the proposed antenna.

This study introduces an approach for applying radar-absorbent material (RAM) coatings on aircraft engines to reduce the monostatic radar cross-section (mono RCS), leveraging near-field diagnostic analysis to guide the process. The primary goal is to improve the mono RCS stealth performance within the engine's intricate cavity structure. The finite-difference time-domain (FDTD) method is employed to accurately compute near-field distributions within the cavity, accounting for the complex interactions of electromagnetic wave propagation and scattering. This analysis method identifies critical hotspots within the engine cavity that significantly impact the RCS. An RAM coating scheme is then designed to target these ``hot spots'', resulting in substantial RCS reduction of the engine. The findings highlight the accuracy and effectiveness of this methodology, offering valuable contributions to the advancement of stealth technologies for next-generation aircraft engines.

In this paper, a novel double-sided flux-switching linear motor is proposed. The motor adopts the structure of primary modularization and secondary segment. It has the advantages of high safety, high thrust density, and low thrust fluctuation. In this paper, the detent force characteristics of the proposed motor are analyzed, and the influence of the end effect on the magnetic congregate effect is discussed, which has reference value for the study of the permanent magnet linear motor with transverse magnetization. Moreover, according to the above analysis, suitable and effective structural optimization and parameter optimization methods are designed for the motor. After the optimization, the proposed motor achieves higher thrust output and significantly lower fluctuation. Finally, a prototype is constructed for validation.

This paper proposes a mode-reconfigurable Doherty power amplifier (DPA). By merely exchanging the transistors' gate bias without altering the corresponding circuits, this power amplifier can achieve two different frequency-band DPA modes, enabling wide bandwidth implementation in DPAs Utilizing a single load modulation network. Simultaneously, PIN switches are utilized to improve the amplifier's bandwidth and drain efficiency during mode switching. To validate this approach, a mode-reconfigurable DPA was designed and fabricated using commercial GaN transistors. A reconfigurable Doherty power amplifier with mode 1 operating in the frequency bands of 2.5-2.9 GHz and 3.3-3.7 GHz, mode 2 operating in the frequency band of 2.8-3.4 GHz, with a drain efficiency ranging from 60.2% to 70.2%, a 6 dB output power reduction resulting in a drain efficiency of 43.5% to 53.7%, a gain between 9.4 and 11.3 dB and a saturated output power between 39.4 and 41.3 dBm. This straightforward architecture offers a promising approach for implementing Doherty power amplifiers in 5G frequency bands.

The minimum operating frequency (MOF) of mode-stirred reverberation chambers is often assessed through statistical analysis using goodness-of-fit (GoF) statistical hypothesis tests such as Anderson-Darling or Kolmogorov-Smirnov. However, in the context of MOF determination, hypothesis tests are typically used with the aim of proving the null hypothesis made on the probability distribution of the electric field in the cavity, as opposed to the initial intent of the tests. A new approach avoiding hypothesis testing is proposed in this work by introducing a criterion based on normalized statistical distances. By normalizing the distances, it has been made possible to limit the influence of the sample size on the assessed minimum frequency, thereby improving the consistency of the results.

We present a detailed analytical and numerical study of cylindrical metasurfaces for enhanced scattering applications. Analytical expressions are derived for the surface impedances of single and double metasurface configurations, respectively, which are required to maximize scattering in the forward direction. A surface impedance model is developed for 1-D arrays of dielectric cylinders that is subsequently used to realize and implement numerically the required surface impedances. Our analytical and full-wave numerical results reveal that cylindrical all-dielectric metasurfaces may exhibit superior forward scattering and balanced higher-order mode excitation in comparison to traditional solid dielectric resonators. Two examples, both with silicon dielectric cylinder, have been chosen to showcase our results, and they were found to exhibit extraordinary directional scattering properties with the respective forward scattering efficiencies being 9 and 19 times that of a single mode resonator. The choice of silicon for the cylinder dielectrics highlights the potential of the proposed configuration in optical communications, although the presented theory applies across the other parts of the electromagnetic spectrum.

In the study of synchronous electromagnetic coil launchers, the influence of armature material on system performance is critical. Existing research lacks combined simulation-experimental investigations on the electrical conductivity of armature materials and in-depth exploration of its impact mechanism on propulsion performance. To analyze the influence of armature material conductivity on propulsion characteristics, a mathematical model of the synchronous electromagnetic coil launcher was established, with theoretical derivations clarifying the mechanical properties and motion equations of the armature during acceleration. Through systematic simulations conducted on the Ansys platform, the effects of different armature material conductivities (6061 aluminum alloy, 7075 aluminum alloy, brass) on propulsion effectiveness were quantified. An experimental platform was subsequently constructed to validate simulation reliability using these three engineering-grade materials. Results demonstrate that increased armature conductivity significantly reduces peak reverse force and enhances exit velocity, while revealing a saturation effect: when conductivity exceeds 6 × 10⁷ S/m, further improvements have diminishing returns on propulsion performance.

This paper proposes a single-fed wideband circularly polarized high-gain dielectric resonator antenna (DRA) for millimeter waves. By cutting out a ring slot in the upper and lower parts of the cylindrical dielectric resonator antenna, higher-order modes are excited, effectively broadening the bandwidth and enhancing the gain. To achieve circular polarization, the DRA is fed by a microstrip line through an asymmetric Z-shaped slot coupling. Measurement results show that the antenna's impedance matching S₁₁ < -10 dB bandwidth is 25.6% (35-45.31 GHz). The usable circular polarization (CP) bandwidth is found to be 8.9% (36.2-39.6 GHz), where the -10 dB input impedance bandwidth and the 3-dB axial ratio bandwidth fall within the same passband, with a maximum in-band gain of 10.67 dBi. The proposed antenna employs a single-fed technique, features a simple fabrication process, exhibits excellent performance, and is suitable for FR2 band applications.

This paper presents a hybrid method that combines the improved sparrow search algorithm (ISSA) and convex programming (CP) to synthesize sparse arrays under multiple design constraints. The proposed method initiates with introducing ISSA, which establishes a sparse array layout while effectively reducing peak sidelobe levels (PSLLs) through optimizing nonuniform element positions. Subsequently, when the position is fixed, the subproblem of minimizing PSLL is transformed into a convex problem with beamwidth constraint, employing CP to determine optimal excitation amplitudes. The PSLL serves as the fitness function in ISSA to simultaneously optimize both element position and excitation amplitude, to achieve PSLL reduction of sparse array. Afterward, some examples of linear and rectangular planar arrays with low sidelobe are simulated and discussed in detail. Numerical experiments show the effectiveness and reliability of ISSA-CP, which can further reduce PSLL while saving array elements. Ultimately, utilizing the numerical simulation results as a foundation, a full-wave simulation is undertaken to verify the practicality of the novel hybrid method.

This paper presents amplitude-only control beamforming approaches within advanced linear antenna systems (ALASs) for sixth generation (6G) technology. The principle of these approaches is training the radiation pattern alongside the weight set derived from two types of the linearly constrained minimum variance (LCMV) optimization problem, which are the single null (SN-LCMV) and broad null (BN-LCMV), using deep learning (DL). Thus, they called SN-DL and BN-DL, respectively. The BN-DL effectively establishes broad null, with the median magnitude at null being −37.44 dB. The computation time is notably reduced, attaining a speed that is 8.26 times faster than the BN-LCMV, 6.95 times faster than the SN-LCMV, and 1.11 times faster than the SN-DL. Over 1000 simulations, the BN-DL demonstrates the highest stability, achieving a peak density value of 10.17%, in comparison to the 3.09% recorded in SN-LCMV, 6.74% in BN-LCMV, and 6.94% in SN-DL, respectively.

In this paper, a novel construction approach of characteristic basis functions (CBFs) is proposed to accelerate the traditional multilevel characteristic basis function method (MLCBFM) for the analysis of electrically large scattering problems. The solution of CBFs in the traditional MLCBFM is extremely complicated and time-consuming due to numerous reduced matrix calculation procedures. Nevertheless, in the proposed method, the CBFs can be solved directly in one step using the new construction approach, which leads to a significant reduction in computation time. Numerical simulation results have demonstrated the effectiveness of the proposed method, which achieves higher computational efficiency without any loss of accuracy than the traditional MLCBFM.

A novel switchable frequency selective rasorber (FSR), featuring dual wideband absorption bands and an ultra-wide passband that can be switched to a reflective band, is proposed in this work. This design incorporates a lossy layer and a three-layer reconfigurable frequency selective surface (FSS). An ultra-wideband transmission can be achieved through the lossy layer by means of circular spiral resonators. The switchable function is utilized by a reconfigurable FSS with PIN diodes. Simulation results confirm the FSR's broad absorption from 1.44 to 2.39 GHz (49.6%) and from 5.45 to 6.64 GHz (19.7%). It also achieves an extensive passband with a 1-dB bandwidth of 47.78% (3.17~5.16 GHz) in the absorption-transmission-absorption (A-T-A) mode, which is the widest transmission band in existing designs. The passband is converted into a reflection band in the absorption-reflection-absorption (A-R-A) mode, showcasing the FSR's switchable characteristics. To validate these simulation outcomes, a prototype measuring 300 x 300 mm is constructed and measured.