Secure microwave communication based on electrical-domain chaos masking and deep learning synchronization

Multispectral compatible stealth is crucial for modern detection environments. Despite conflicts among stealth mechanisms, current strategies lack effective compatibility. This study introduces a flexible gradient metamaterial structure inspired by bionic design and machine learning's forward prediction mechanism. This structure achieves spectral decoupling and enhances stealth performance across infrared, radar, and visible light spectra. The multispectral compatible stealth metamaterials (MCSM) comprise a radar infrared compatible stealth layer (RICSL) with high transmittance (78.56%) and a pixelated tunable visible light camouflage pixel layer (VLCPL). By adjusting the hexagonal patches' filling rate on the infrared stealth layer (ISL), a blend of low infrared emissivity (0.2) and high microwave transmission efficiency is achieved. The structure ensures efficient microwave absorption through gradient impedance transition and multiscale loss mechanisms, with absorption efficiency exceeding 90% in the measured wideband range of 6.34 to 24.91 GHz, along with polarization insensitivity and angular stability. The VLCPL can adapt patterns to mimic jungle, ocean, and desert environments. In practical settings, these metamaterial structures demonstrate flexible adaptive features in infrared and visible light stealth effects, paving the way for innovative multispectral compatible stealth technologies.

ABSTRACT Rainfall estimates from commercial microwave links (CMLs) have become valuable complements to conventional rainfall sensors, especially in the Global South, where ground-based radar and rain gauge networks are sparse. Spaceborne instruments aboard low Earth orbiting satellites also offer valuable precipitation data, especially over inaccessible areas. This study is the first to compare CML rainfall estimates with those derived from the radiometer on the Global Precipitation Measurement (GPM) core satellite across countries with different climates (Netherlands, Sri Lanka, Nigeria) using data from the GPM radar as reference. The weaknesses of CML and radiometers are distinct: radiometers tend to underestimate high-intensity events with a relative bias varying between 10 and 50% depending on the country and the threshold used to differentiate between dry conditions and rainfall, while CML estimates often miss low-intensity rainfall, with a probability of detection (POD) varying between 0.1 (Nigeria) and 0.5 (the Netherlands).

Low-temperature Co-Fired Ceramics necessitate low sintering temperatures to enable cofiring with base metals, while dielectric resonator antennas demand temperature-stable dielectric properties; hexagonal perovskite Ba12Zn0.5Zr0.5Nb9O36 (R3̅m) ceramics exhibit excellent microwave dielectric performance but suffer from a high sintering temperature (1475 °C) and undesirably high temperature coefficient of resonant frequency (τf = 26.4 ppm/°C), limiting their practical applications. A synergistic strategy overcomes these critical bottlenecks by integrating BaWO4 (I41/a) for precise τf tuning and BaCu(B4O8) as a sintering aid to enable low-temperature sintering. XRD Rietveld refinement confirms the composites consist exclusively of impurity-free Ba12Zn0.5Zr0.5Nb9O36 and BaWO4 phases, and Raman spectroscopy validates the characteristic vibrational modes of NbO6 octahedra and [WO4]2- groups. The optimal composite at x = 0.89 exhibits exceptional all-around microwave dielectric properties (εr = 19.0, Q × f = 30100 GHz, τf = 3.0 ppm/°C) when sintered at 1000 °C, coupled with excellent chemical compatibility with Cu electrodes during cofiring. The DRA based on this composite delivers a broad 375 MHz bandwidth, 5.13 dBi gain, and 97.17% radiation efficiency at 9.14 GHz, highlighting its great potential for LTCC technology and microwave communication applications.

Microwave wireless power transfer (MWPT) is a promising technology for powering dedicated industrial Internet of Things (IoT) devices, enabling battery-free operation. However, in realistic MWPT deployments, the received RF signals fluctuate drastically due to varying transmission distances and multipath fading. Additionally, the equivalent impedance of sensor nodes varies significantly during duty cycles, shifting between a low-resistance active state and a high-resistance sleep state. Consequently, maintaining high rectification efficiency under these dynamic conditions remains a critical challenge. This paper proposes a high-efficiency rectifier with a wide input power and load range based on the suppression of second and third harmonics. The rectifier adopts a dual-diode parallel configuration. By leveraging the impedance compensation characteristics of two short-circuited stubs with distinct electrical lengths, it simultaneously achieves fundamental-frequency impedance matching and harmonic suppression without the need for an additional matching network. Validated through theoretical derivation, simulation analysis, and physical prototype testing, the proposed 2.45 GHz rectifier realizes high-efficiency rectification over a wide dynamic range. Experimental results demonstrate that the power dynamic range reaches 10 dB when the rectification efficiency exceeds 70%, and extends to 17 dB when the efficiency is above 60%. Furthermore, the rectification efficiency is insensitive to load variations (100–1200 Ω), making it highly suitable for powering wireless sensor nodes with varying operating modes in complex electromagnetic environments.

Abstract We present a non-local quantum system based on a waveguide QED architecture, comprising two spatially separated and largely detuned superconducting transmon qubits. By applying parametric frequency modulation to one of the qubits, we establish a tunable coherent channel between the two far-detuned qubits, thereby forming an Λ-type three-level system. We demonstrate that tuning the modulation amplitude enables the observation of spectral evolution from electromagnetically induced transparency (EIT) to Autler-Townes splitting (ATS). Furthermore, by exploiting the interplay between the non-local waveguide phase and system dissipation, the system achieves significant non-reciprocal microwave transmission and direction-selective photon emission. The scheme operates without external magnetic fields, offering an efficient pathway for realizing on-chip integrated quantum routers and isolators.

Qualitative and quantitative detection of trace alum in quinoa flour via broadband microwave transmission spectroscopy and nonlinear machine learning

High-precision time synchronization among high-dynamic platforms is an important foundation for distributed detection, cooperative sensing, and networked operation of high-speed mobile platforms. In high-dynamic two-way microwave links, rapid variations in propagation geometry, Doppler-related frequency offsets, and link-quality fluctuations can break the approximate symmetry between uplink and downlink propagation. Although geometric and motion compensation can remove the dominant propagation-asymmetry term, residual asymmetric errors caused by propagation modeling errors, compensation mismatch, and link degradation may still remain and couple into clock-offset estimation, thereby reducing synchronization stability and accuracy. To address this problem, this paper proposes a modeling and joint estimation method for residual asymmetric errors in high-dynamic two-way microwave links. The post-compensation residual error is modeled as a recursively estimable dynamic state, and its rate of change is introduced to characterize the short-term evolution of the residual term. Meanwhile, a four-timestamp and frequency-offset joint observation model is constructed, in which frequency-offset information is used as an observation-level auxiliary constraint to enhance local separability among the clock offset, frequency offset, and residual link state. On this basis, a link-state-information-assisted IMM-IEKF is adopted to realize online joint estimation of clock parameters and link residual errors. Under the equivalent stochastic-error simulation setting, the proposed method effectively suppresses post-compensation residual asymmetric errors and achieves sub-nanosecond synchronization accuracy under strong-dynamic and degraded-link conditions.

Abstract This paper presents a novel co-design approach for wireless applications, integrating mm-wave and microwave technologies. The design features two antennas where a slotted waveguide array is fabricated using 3D-printing technology with an AlMg10Si alloy resonating at mm-wave frequency band, while a printed monopole antenna resonating at microwave frequency band shares a common ground plane with the slotted waveguide array. The electrically small printed monopole is realized on an FR4 substrate, is suitable for WLAN bands, and achieves ease of integration with the antenna at the Ka-band owing to the low profile. The co-design approach is particularly advantageous for wireless applications as it enables the seamless integration of different frequency bands, enhancing system versatility and performance. The antenna achieves dual frequency band operation covering the Impedance bandwidth of 15.27% (5.08-5.92) and 14.56% (26.48-30.64) at microwave and Ka-band frequencies, respectively. The innovative use of materials and advanced fabrication techniques also underscores the design's potential for diverse high-performance wireless applications.

van der Waals heterostructures host a wide range of strongly correlated states, but the imaging of quantum phenomena in three-dimensional heterostructures is challenging because multiple layers may contribute to the detected signal. Here we introduce an imaging technique that resolves electronic states on individual atomic planes of a heterostructure, layer by layer, down to milli-Kelvin temperatures. We demonstrate layer-resolved microwave impedance microscopy of quantum Hall states in double-layer graphene, achieved by precisely modulating the vertical transmission of microwaves into the heterostructure. By visualizing charge fluctuations on individual planes, we shed light on the roles of surface disorder and screening on the stability of fractional quantum Hall states, while extracting key properties such as gap sizes and negative compressibility. This approach is also compatible with microscopy with displacement field control, unlocking access to exotic quantum phenomena that can only be realized in multilayer structures and top-gated devices.

Recent developments in electro-optic (EO) frequency-domain equalizers (EOFDEs) have demonstrated significant potential for extending modulation bandwidth. However, conventional EOFDE architectures typically exceed 10 cm in length, hindering compact integration. Here, we present a folded thin-film lithium niobate (TFLN) EOFDE incorporating capacitively loaded traveling-wave electrodes (CL-TWEs) and curved microwave transmission lines. This folded architecture reduces the device footprint by approximately two-thirds. We established a theoretical model to analyze the EO response, accounting for CL-TWEs with various curved electrode geometries. Our analysis reveals that significant microwave losses originate from slot-line mode excitation. These losses are effectively mitigated by implementing narrow signal electrodes and reducing electrode spacing in the bent sections, thereby preventing a steep decline in high-frequency bandwidth. Experimental characterization demonstrates that the fabricated folded EOFDE achieves a low half-wave voltage of 1.35 V and a 3-dB EO bandwidth of 92 GHz.

This article presents an analysis of the current state and future prospects of technologies for generating electricity in space and its wireless transmission to Earth. The physical principles of wireless power transmission (WPT) are examined, including near-field, mid-field, and far-field zones, along with a comparative analysis of microwave and laser transmission methods. Key techno-economic parameters of space-based solar power (SBSP) systems are analyzed. Based on rigorous verification of peer-reviewed sources and independently validated data, the following is established: i) Star Catcher Industries demonstrated in November 2025 power transmission of >1.1 kW with laser-to-photovoltaic conversion efficiency of 40-50% and total transmitted energy of >10 MJ over the campaign [4, 5, 6]; ii) A research group from Queen’s University Belfast, in a peer-reviewed publication in the IEEE Journal on Wireless Power Technologies (DOI: 10.1109/JWPT.2026.3654513), developed and experimentally validated a 112-element retrodirective array with a measured peak power density of 172 W/m² [1]; iii) The RePowerSiC project (EU Horizon Europe, Grant ID: 101160868, budget €4 million) aims to develop SiC converters with efficiency >80% at an intensity of 1 kW/cm² [2]; iiii) According to the techno-economic analysis from the California Institute of Technology published in Joule (Elsevier, impact factor 38.6, DOI: 10.1016/j.joule.2025.101928), the projected LCOE of the system is 9.4 ¢/kWh [3]. Technological barriers are examined, including transmission losses, atmospheric effects, and the need for kilometer-scale ground rectennas. Based on gap analysis, it is established that retrodirective tracking at GEO distances (36,000 km) remains unproven, and atmospheric absorption for lasers has not been quantitatively assessed.

As oil and gas reservoirs progress into the mid-to-late stages of development, produced fluids increasingly exhibit high water-cut and complex flow regimes. Conventional water-cut measurement techniques based on capacitance, conductance, and resistance often face challenges in terms of accuracy, stability, and adaptability. In this study, a novel non-contact broadband microwave system, based on a ridged-horn antenna microwave transmission sensor (RHAMTS), is proposed to achieve highly sensitive full-range (0-100%) water-cut monitoring. The RHAMTS consists of two identical ridged-horn antennas, whose geometries are optimized through analytical design calculations and full-wave finite-element simulations. Numerical simulations are first performed to elucidate the sensing mechanism. Subsequently, static and dynamic experiments are conducted under two representative conditions: emulsified oil-water mixtures and stratified oil-water layers. The results indicate that the broadband spectral signatures of the RHAMTS can effectively characterize water-cut in both emulsified mixtures and stratified oil-water layers. For emulsified mixtures, both amplitude attenuation and phase shift vary systematically with water-cut, and the RHAMTS can still effectively characterize water-cut under saline conditions. For stratified oil-water flow, results from both static and dynamic experiments demonstrate that amplitude attenuation provides more robust features for practical water-cut discrimination. Compared with conventional methods, the proposed RHAMTS offers non-contact operation, rich spectral information, and compatibility with various flow regimes, providing a feasible and efficient approach for water-cut monitoring under complex field conditions.

Research on the modified tri-frequency combination model for determining geopotential using China space station microwave links

Microwave wireless power transfer (MWPT) for space solar power stations (SSPS) requires high-precision beam pointing in order to maintain effective aperture coupling and transmission efficiency under platform motion and disturbances. This paper proposes a dual-link beam pointing estimation framework that integrates guidance-link interferometric angle-of-arrival (AoA) measurements with power-link energy-field reconstruction. The interferometric chain provides high-rate azimuth and elevation observations for dynamic tracking, while the energy-field reconstruction estimates the energy-centroid displacement from the received-aperture power distribution to correct steady-state pointing bias. A Kalman filter (KF) is developed to fuse the asynchronous multi-rate measurements, yielding continuous and robust pointing estimates for closed-loop beam control. Simulation results show that the proposed fusion method achieves azimuth and elevation RMSEs of 0.0069° and 0.006° with interferometric and energy-centroid error levels of approximately 0.05° and 0.02°, respectively, significantly reducing high-frequency fluctuations. In addition, a sensitivity model is established to quantify the impact of angular errors on capture efficiency. The expected efficiency improves from approximately 0.988 and 0.998 for the individual methods to nearly unity for the fusion output. Quantitative accuracy thresholds corresponding to different efficiency requirements are further derived, providing practical guidelines for SSPS MWPT system design.

ABSTRACT Radome composites demand high radar transmissivity paired with stable mechanical properties across varying ambient temperatures. Building upon previous studies on the room‐temperature quasi‐static mechanical recovery of woven lattice sandwich composites (WLSCs), this study extends the investigation to the restoration of mechano‐electromagnetic performance under diverse thermal and loading conditions. An integrated mechano‐electromagnetic repair method is proposed and evaluated. The study comprehensively investigates the temperature‐dependent mechanical behaviors and microwave transmission characteristics of the structures before and after repair. Quantitative results demonstrate exceptional recovery efficacy: the load‐bearing capacity of repaired double‐layer structures reaches 250.2% of the pristine level under bending loads, and the impact resistance is restored to 166.8%. Furthermore, the electromagnetic transmission efficiency is fully recovered to 100.3% on average, with performance in the X‐ and Ku‐bands surpassing pre‐repair levels. The experimental findings conclusively validate that the proposed repair scheme not only effectively restores the mechanical integrity of WLSC panels under varying temperatures and loading modes but also fully recovers the mechano‐electromagnetic functionality of the WLSC radome.

Metallic Kagome magnets have received a great deal of research attention in recent years for their intriguing magnetic properties. Recently, YMn6Sn6(Y166), which belongs to this family of compounds, has been studied to show different magnetic phases including the distorted spiral (DS), transverse conical spiral (TCS), fan-like (FL) and the forced-ferromagnetic (FF) phases respectively. In this work, we employed very high-frequency electron spin resonance (VHF-ESR) spectroscopy to investigate the local microscopic magnetic interactions of Mn ions in Y166. Particularly, the temperature-dependent ESR behavior at variable very-high microwave frequency (ν= 120, 240, and 300 GHz) was studied. The ESR spectral behavior above room temperature (up to 350 K) on Y166 single crystals, where the magnetic field was applied in-plane and out-of-plane orientations of the sample layers was also investigated. A couple of non-trivial magnetic phases at different temperatures and frequencies, including the TCS, FL and FF phases were identified. The DS phase was not identified because our measurements were taken at fields higher than the fields (0-2 T) at which this phase occurs. In addition, angular dependence of the resonance field at room temperature (290 K) forv= 240 GHz follows a (3cos2θ- 1)- like angular dependence which reveals the 'U-shape' (from 0˚ to 180˚) of the resonance field. This behavior indicates the presence of 2D spin correlations in Y166. This work has implications in emerging applications such as high-frequency microwave and terahertz communications and spintronics.

Abstract This paper presents the design of a novel reflective linear-to-circular polarization conversion metasurface (PCM) and its application to a wideband high-gain circularly polarized (CP) antenna. The proposed PCM efficiently converts incident linearly polarized (LP) waves into CP waves within an ultra-wideband range of 11.8-28.6 GHz, thereby laying a solid foundation for the design of the wideband CP antenna. By adding an LP microstrip antenna as the feed source above the PCM, the metasurface leverages its polarization conversion capability to reflect CP waves, simultaneously enhancing the antenna gain, and thus yields a wideband high-gain CP antenna. The designed CP antenna exhibits an impedance bandwidth and a 3-dB axial ratio (AR) bandwidth both spanning from 13.2 to 18.6 GHz, corresponding to a relative bandwidth of 34%. Notably, the 3-dB AR bandwidth perfectly matches the impedance bandwidth. Meanwhile, the antenna maintains a stable high gain exceeding 11 dBi across the entire operating bandwidth. Excellent agreement is achieved between the measured and simulated results, confirming that the proposed antenna simultaneously achieves a wide CP operating bandwidth, full-band 3-dB AR coverage, and high gain. Such characteristics make it highly valuable for potential applications requiring both wideband CP operation and high gain, such as microwave communications, precision radar, and satellite navigation systems.

AI-Enhanced Rainfall Retrieval Using Commercial Microwave Links in 6G-IoT Networks: Advances, Challenges, and Opportunities

Improving rainfall retrieval accuracy using cross-Modal deep learning: Merging wifi with commercial microwave link