Multi-input multi-output (MIMO) antennas have garnered significant attention for addressing the demands of high channel capacity, reliable and uninterrupted signal transmission, and high data rates, especially with recent advancements in 5G low Earth orbit (LEO) satellite communications. In addition to these features, automotive applications require antennas with minimal mutual coupling, high gain, multiple resonant frequencies, and compact size for user equipment. To meet these requirements, a 1×2 defected ground structure (DGS)-based fractal MIMO antenna array is proposed, covering various frequencies in the sub-6 GHz bands, including 0.7 GHz, 2.6 GHz, 3.1 GHz, and 3.5 GHz. The proposed antenna provides sufficient channel bandwidths and achieves a gain of 12.9 dBi in the n78 frequency band. The design has been fabricated, and the measured results show good agreement with the simulated ones. Moreover, the proposed antenna design can be integrated into the plastic parts of a car body, offering various automotive applications. It achieves a realistic data rate of approximately 10-12 Mbit/s, as verified through link budget calculations that consider the key parameters of LEO satellite systems.

A reconfigurable patch antenna for X-band applications offers frequency agility and adaptability for systems operating within the 8-12 GHz range. This design allows dynamic tuning of the antenna's operating frequency, making it ideal for radar, satellite communications, and military applications. By incorporating reconfigurable elements, such as switches or tunable materials, the antenna can adjust to varying operational requirements, improving performance and flexibility in compact systems where space and efficiency are crucial. A reconfigurable patch antenna for X-band applications faces several challenges. Incorporating reconfigurable elements, such as switches or tunable materials, can increase the design's complexity and reduce reliability, especially in high-frequency X-band operations. Miniaturization may result in performance trade-offs, potentially affecting the antenna's gain, bandwidth, and radiation efficiency. Additionally, ensuring stable and interference-free operation across the reconfigured frequencies can be difficult. The antenna's power-handling capability may also be limited, which is critical for radar and military applications. Finally, thermal stability and environmental resilience are key concerns, as performance can degrade under varying conditions. Hence, this paper proposes a novel miniature inverted V-slot reconfigurable patch antenna. extended antenna design features a compact radiating patch (10.5 mm x 14 mm) with an inverted `V' slot and corner modifications (chamfering) to enhance performance. Frequency and polarization reconfiguration are achieved through the enable/disable functionality of PIN diodes placed within the inverted `V' slot, allowing dynamic adjustments. The defected ground structure, featuring two vertical slots, further aids in enhancing the antenna's operational capabilities. The antenna operates across multiple frequency bands, specifically 9.84-10.46 GHz, 10.66-11.59 GHz, 11.08-11.98 GHz, and 11.61-12.11 GHz, making it suitable for X-band applications. Additionally, the proposed antenna supports right-hand circular polarization (RHCP), left-hand circular polarization (LHCP), and linear polarization (LP), offering versatile propagation modes. Both practical and simulated results demonstrate good impedance matching across different polarization states. This design is highly suitable for satellite communication and other X-band applications due to its reconfigurable and flexible performance.

This study introduces a compact, dual-band wearable slot antenna with inverted L-shaped partial ground (PG) for Wireless Local Area Networks (WLANs) and X-Band Applications. The proposed antenna design uses a flexible polyamide material of 21×21 mm² dimensions as a dielectric substrate between two metal surfaces. The prime radiator is a rectangular slot antenna patch with several slots etched out, and the ground plane is an inverted L-shaped stub that forms the PG. The insertion of slots in the patch disturbs the surface current path and increases the electrical length to offer miniaturizations. It effectively minimizes the antenna dimensions to resonate at lower frequencies. The dimensions of the PG and its placement on the ground plane attain the dual-band resonance with a good amount of return loss. Different slots are etched on the patch to get the desired frequency bands of operation. The designed antenna has achieved wide impedance bandwidths of 0.55 GHz and 1.04 GHz and peak gains of 6.45 dBi and 6.04 dBi at the 5.15 GHz and 8.13 GHz operating frequencies, respectively. The detuning behavior of the suggested antenna in bending conditions is analyzed. The effect of radiation on the human tissue is calculated in terms of Specific Absorption Rate (SAR), and it is within the standards. The antenna model is fabricated and tested, and a satisfactory agreement between the computed and measured data is achieved. The compactness, flexibility, and radiation pattern make this antenna model suitable for ON/OFF-Body communication in wearable applications.

Magneto-Acousto-Electrical Tomography (MAET), as one of the electrical characterization imaging methods, is used to image the electrical conductivity of biological tissues, which can be used for noninvasive, radiation-free imaging of biological tissues. Currently, most of the studies on MAET are simulations and experimental validations of simple structural models, and there is no sufficient validation of models with complex structures, and most of the results cannot comprehensively invert complex structural models with multi-gradient conductivity distributions. To address this problem, this paper proposes a MAET method for conductivity reconstruction of complex structural models which is applicable to 2D problems and may be extendable to 3D problems. Based on this method, the conductivity distribution of normal and diseased tissues in the simulation model of complex structures was reconstructed, and the consistency between experimental and simulated signals was verified. The results show that the MAET method for conductivity reconstruction of complex structural models proposed in this paper is conducive to improving the image resolution as well as the structural similarity, enhancing the conductivity distribution information of complex structural targets with inhomogeneous shapes and multi-gradient conductivity distributions.

Photonic crystals, often referred to as the ``semiconductors of light,'' have entered a new phase enabling exotic properties once exclusive to topological quantum matter such as topological insulators. While the development of the first three-dimensional (3D) photonic crystal marked the establishment of photonic crystals as an independent field, initial studies in topological photonic crystals focused mainly on one and two dimensions. Though a true photonic crystal counterpart of a 3D strong topological insulator remains elusive, significant progress has been made toward achieving 3D topological photonic crystals. Compared with their lower-dimensional counterparts, 3D topological photonic crystals reveal a richer variety of topological phases and surface manifestation, which enables more degrees of freedom for light manipulation. In this review, concentrating on the novel boundary states unique in 3D systems, we provide a brief survey of the 3D topological photonic crystals and recent advances in this field. We categorize and discuss various topological phases and associated phenomena observed in 3D photonic crystals, including both gapped and gapless phases. Additionally, we delve into some recent developments in this rapidly evolving area, including the realization of 3D topological phases through synthetic dimensions.

A privacy-compliant indoor localization approach utilizing a 3-D near-field (NF) passive radar imaging technique is presented. This technique leverages ubiquitously radiated electromagnetic fields for imaging, with passive tags introduced to enhance the strength of scattering fields, thereby enabling precise localization at the imaging level. The method also supports localization in non-ideal imaging scenarios, such as for limited bandwidth or in highly-reflective environments. Based on their geometrical properties the simple and low-cost passive tags enable intuitive differentiation between individuals or objects. Associated privacy protection mechanisms are discussed, where the frequency-varying properties of the passive tags provide additional flexibility and potential applications under privacy and ethical considerations. Several forms of passive tags are presented, where both simulation and experimental results validate the effectiveness of the proposed passive tag designs.

In this paper, 5G communication system requires high broadband, high efficiency, low distortion and good heat dissipation for RF power amplifier. A GaN RF power amplifier working in broadband is designed. The input and output matching is processed on the Al2O3 ceramic substrate with bond wire, and the tube shell is packaged with CuMoCu copper alloy shell. Because the power loss of the power amplifier will produce a lot of heat, the heat dissipation problem becomes a factor that can not be ignored in the design. Using the finite element thermal simulation analysis method, the maximum temperature of the power amplifier chip under long time operation is 85℃, which meets the heat dissipation demand. Under the continuous wave test conditions, the drain voltage is 30 V; the operating frequency band is 2~6 GHz; the saturation output power is 42 dBm; the power gain is more than 45 dB; and the power added efficiency is 40%. The test results meet the actual demand.

Early detection is critical for effective skin cancer treatment. Micro-/millimeter-wave spectroscopy has emerged as a promising non-invasive and cost-effective detection technique. Tissue models are essential in early numerical studies, which typically represent the first step in detector's feasibility assessment. This paper focuses on quantifying implications of numerical model complexity on computational studies of skin spectroscopy. In our comparative numerical studies, we constructed one finger model that follows anatomical structures, as well as its three simplified versions, subjected to simulated measurements with a slim dielectric probe in the 0.5-50 GHz range. Using the finite-element method (FEM) for simulation, we analyzed mesh count to estimate computational cost and return loss variation to assess model reliability. As a result, we reach recommendations for models that optimize computational resources and can yield meaningful information from the standpoint of skin cancer screening. Simplified models are adequate for lower microwave frequencies (< 10 GHz), but at higher frequencies, models with at least three tissue layers (skin, fat, and ligament) are necessary. Modeling smaller tumors requires greater tissue complexity than larger tumors to achieve comparable reliability. Additionally, squamous cell carcinoma (SCC) scenarios demand higher model complexity than basal cell carcinoma (BCC) and melanoma to achieve similar reliability.

A very compact MIMO antenna for broad-band applications which covers the complete spectrum of X-band applications is represented here. The proposed element in the represented antenna covers a total volume of around 320 mm³. The isolation among radiating elements is improved by placing individual elements orthogonally thereby improving isolation better than 20 dB. This enhanced isolation helps to provide substantial MIMO parameters including ECC, TARC, channel capacity loss, and multiplexing efficiency. The devised antenna is compact (0.066λ × 0.066λ × 0.0024λ mm³) printed over an FR4 substrate which is widely available concerning 6.2 GHz to 11.2 GHz wireless applications. Fabrication of the above-mentioned proposed antenna is done and all the desired calculations are made desirably. Furthermore, the practically measured results conclude that the antenna-measured patterns well correspond to the simulated results.

In order to reduce the coupling between dense antenna arrays in multiple input multiple output (MIMO) systems, this paper proposes a method to reduce the coupling between microstrip antenna arrays by utilizing a defected ground structure (DGS), which consists of ``W''-shaped slits etched in the ground plane. Simulation results show that the structure can achieve -46.6 dB isolation between antenna arrays. To verify the effectiveness of the structure, the microstrip antenna arrays loaded with this DGS are fabricated and measured, and the measured results are consistent with the simulated ones, which verifies the effectiveness of the structure.

We present a self-synchronized dual-color cross-phase-modulation mode-locked (XPM ML) fiber laser with excellent wavelength tunability and signal-to-noise ratio for coherent anti-Stokes Raman scattering (CARS) detection. Cross-phase-modulation gives rise to self-synchronization between the two-color lasers, which enables rapid wavelengths scanning as time delay of the master laser cavity is electrically adjusted. The synchronized cavity without any mode-locking elements helps to improve the mode-locking stability and resistance to environmental interference. The pump (780 nm, 18.5 ps) and Stokes (881.1-899.4 nm, 1.5 ps) pulses obtained by second harmonic generation (SHG) are then sent to a focusing lens for CARS detection for scanning Raman shift of 1470-1701 cm^-1). As an example of analyte, rhodium-bisphosphine complex catalyst samples are detected. This highly stable and fast-tunable two-color XPM synchronized mode-locked laser architecture has the potential for arbitrary waveband extension would greatly improve the possibility of coherent Raman scattering imaging technology from the laboratory to practical applications in e.g. biomedical detection.

A novel compact low-profile Conformal Dielectric Resonator Antenna (CDRA) for wideband applications is proposed. By employing a specially designed dielectric resonator in conjunction with an inverted-trapezoidal patch for feeding, an extensive Impedance Bandwidth (IB) of around 51.5% is realized. The resonant frequencies of 6GHz and 7.5GHz correspond to the observation of the TE21δ mode and the second higher-order TE23δ mode, respectively. Moreover, a realized peak gain of 7.2dBi is attained at 7.4GHz. The proposed DRA offers a wide IB with more than 90% radiation efficiency throughout the bandwidth. Additionally, a good alignment is observed between the measured and simulated results. The proposed DRA is compact and low-profile of 0.1λg, where λg represents the wavelength at the lower cut-off frequency. A CDRA with a conformal feed is an innovative design tailored for wireless communication systems operating within the frequency range from 5.2GHz to 8.8GHz. This antenna configuration is specifically engineered to exhibit conformal properties, enabling it for applications such as the exteriors of vehicles, aircraft, or other non-planar structures.

In this paper, a frog-shaped ultra-wideband (UWB) multiple-input multiple-output (MIMO) antenna is proposed for 5G applications in the n77, n78, n79, and 6 GHz bands with a compact antenna structure of 31×55×1.5 mm³. The designed antenna consists of two frog-shaped monopole antennas and a floor from which part has been removed, and the operating bandwidths range from 3.05 to 13.38 GHz, which meets the design criteria for UWB. The T-shaped floor with two T-shaped slots impedes the flow of coupling currents and improves the isolation of the antenna. This results in an isolation of less than -17 dB over the entire operating bandwidth and less than -20 dB in the 5G band. In addition, the envelope correlation coefficient (ECC) is less than 0.007, the diversity gain (DG) more than 9.96, the total active reflection coefficient (TARC) less than -30 dB, and the channel capacity loss (CCL) less than 0.34 bit/s/Hz. The measured and simulated results agree with each other, demonstrating their potential application in 5G communication systems.

In this study, we introduce a dual-modal fluorescence hyperspectral micro-CT system developed for e.g. bioimaging applications. The system integrates an X-ray computed tomography (CT) module with a custom-designed hyperspectral fluorescence imaging module, achieving high-resolution structural imaging with detailed molecular-level insights. With a spectral resolution of 10 nm across the wavelength range of 450–750 nm, the hyperspectral fluorescence imaging module enables a fine compositional analysis. Using surface-modified nanoparticles, we demonstrate the system's capability to capture fluorescence under both X-ray and UV excitation. Imaging experiments on a mouse model further highlight the system's ability to generate comprehensive Four-dimensional (4D) datasets that integrate spatial, spectral, and structural information. To the best of our knowledge, no such a dual-modal system or the like has even been reported before. This dual-modal approach enhances the visualization and analysis of biological tissues, offering promising applications in e.g. disease diagnosis, surgical guidance, and preclinical research.

In the past decades, with the increasing complexity of topological crystals, artificial electromagnetic (EM) materials, and EM environments, understanding their precise scattering behaviors and characteristis is turning more challenging. Traditional methods for modeling these properties often rely on full-wave simulations or analytical algorithms which are only applicable for regular shapes with plane wave incidences. These methods are inefficient for the design and broadband multiple scattering analysis of general 3D EM structures, as new simulations are required for each different scattering scenario and frequency, while solving a substantial number of unknown variables in each analysis. In this paper, a novel hybrid numerical scattering T-matrix extraction method applicable to scatterers of arbitrary shape and composition is developed in the context of the Foldy-Lax multiple scattering theory (F-L MST). Generalization is also made such that the F-L MST can be applied to multiple scattering problems with arbitrary incident fields. Once the T-matrix elements of individual scatterers are obtained through combining spherical wave expansion with full-wave numerical simulations of surface fields as proposed in the paper, it can be stored and reused, significantly reducing the overall computational complexity. Compared to conventional methods, this approach merely requires matrix inversions of moderate orders in a multiple scattering problem, offering notable efficiency advantages for about an order of magnitude. Meanwhile, the smooth frequency dependence of the T-matrix elements and incident field coefficients suggests the feasibility of interpolating these coefficients for broadband simulations. This proves particularly helpful in the swiftly evolving near-field techniques, and scenarios requiring extensive analysis such as broadband and Monte Carlo analysis. Numerical cases, involving multiple scatterer shapes and arrangements, are explored and compared with COMSOL full-wave simulations. The results validate the accuracy and efficiency of the proposed method, with potential to become a powerful tool for EM simulations and optimization of various wave-functional materials and in many other multiple scattering applications.

Reconfigurability is a crucial capability for electromagnetic devices to achieve high flexibility in accommodating various scenarios. In this study, we present a reconfigurable microwave rasorber with dynamically tunable helicity polarization for the passband wave using a compound unit cell composed of two-bit chiral meta-atoms. Our specific samples demonstrate low reflectivity (< –10 dB) across the entire C-band, while also offering four distinct states (two-bit) for the passband (reflection/transmission) wave in a narrow window around 6.25 GHz, including circular polarization control or complete blockage. We experimentally demonstrated the switching capability for both chirality and intensity of the passing band wave. These results are significant in expanding the application scenarios of rasorbers with more versatile polarization controllability.

Most of the analytical work on general transparent dispersive media to date has been confined to second-order dispersion within the framework of the paraxial approximation. It is the aim in this article to lift this restriction. Specifically, a detailed discussion is provided of modulated (3+1)-dimensional nonparaxial spatiotemporally localized waves in second-order transparent dispersive media. Novel infinite-energy invariant wavepackets and finite-energy almost undistorted solutions are discussed in detail. Illustrative numerical examples of the latter are given for normal dispersion in fused silica and for anomalous dispersion in a Lorentz plasma.

A gap-coupled design of elliptical shape microstrip antennas for wideband circularly polarized response is proposed. The wideband nature of the response is attributed to the gap-coupling between the orthogonal resonant modes on the fed and parasitic elliptical shape patches. With the total substrate thickness of 0.11λ_cAR, the gap-coupled antenna offers the reflection coefficient bandwidth of 784 MHz (55.68%) that includes circularly polarized bandwidth for axial ratio ≤3 dB of 542 MHz (35.82%). The antenna offers a broadside radiation pattern across the bandwidth, with a peak gain larger than 10 dBi. A design methodology to realize a similar gap-coupled antenna in a different frequency range is presented that yields similar wideband results. With the obtained antenna characteristics, proposed designs will find applications in GPS L and GSM 900 frequency bands. An experimental verification for the obtained simulated results is carried out, which provides a close agreement.

Directional and highly-efficient excitation of guided waves is closely related to the on-chip information processing and is of fundamental importance to plasmonics, nanophotonics, and chiral quantum optics. However, during the directional coupling between propagating waves and guided waves, there is a loss of information about the incident polarization state. It remains elusive and challenging to preserve the incident polarization information in the near-field directionality. Here we experimentally demonstrate polarization-maintaining and polarization-dependent near-field directionality at a microwave frequency of 9.5 GHz by exploiting a reflection-free, anisotropic, and gradient metasurface. The s- and p-polarized guided waves are excited only by the s- and p-polarized components of incident waves, respectively, and they propagate predominantly to opposite designated directions. Remarkably, the measured coupling efficiency between propagating waves and guided waves exceeds 85% for arbitrary incident polarization states. Our work thus reveals a promising route to directly and efficiently convert the polarization-encoded photon qubits to polarization-encoded guided waves, a process that is highly sought after in the context of optical network and plasmonic circuitry.

Metasurfaces offer remarkable capabilities for manipulating electromagnetic waves and by incorporating multiplexing techniques can significantly increase the versatility of design possibilities. Here, we designed and experimentally demonstrated a series of dual non-diffractive beam generators for terahertz radiation based on all-dielectric metasurfaces. These generators could produce switchable Bessel beams and abruptly autofocusing beams depending on the spin and frequency of the incident terahertz waves. In addition, by further applying appropriate phase gradients in the design, these non-diffractive beams could be deflected in specified directions. It is also possible to simultaneously generate multiple non-diffractive beams with different properties. The generated non-diffractive beams were measured with near-field scanning terahertz microscopy, and the results agreed well with simulations. We believe that these metasurface-based beam generators hold tremendous potential in terahertz imaging, communications, non-destructive evaluation, and many other applications.