We experimentally demonstrate a liquid crystal-integrated metasurface that dynamically controls millimeter wave polarization across six distinct frequency bands. Specifically, incident y-polarization electromagnetic waves are converted into x-polarization, left-handed circular polarization, and right-handed circular polarization upon reflection. In our experiments, we characterized the evolution of the polarization states over different frequency bands. The results indicate that as the bias voltage is tuned from 0 V to 4 V: the cross-polarization conversion peaks exhibit a tuning range spanning 270–287 GHz and 383–412 GHz; the LHCP peaks are tunable within 263–269 GHz and 408–476 GHz; the RHCP peaks demonstrate a tuning range of 296–314 GHz and 374–387 GHz. The cross-polarization conversion ratio exceeds 0.95, and the axial ratio is less than 1.9 dB during the modulation process. In frequency bands with overlapping tuning ranges, the bias voltage allows switching among distinct polarization states, including cross-polarization, LHCP, and RHCP. This work provides novel insights into the development of multifunctional integrated millimeter wave devices. The proposed technology holds promise for applications in encrypted THz communication, wireless power transfer, and sensing systems.

Reconfigurable intelligent surface (RIS) technology is believed to effectively solve the dilemma of terahertz wireless communication in non-line-of-sight scenarios. Notably, the deployment of large-scale RIS arrays at high frequencies brings about significant near-field effects, resulting in extensive near-field areas, which provides the possibility for the application of near-field communication. In this paper, a pixelated liquid crystal programmable metasurface (PLCPM) is proposed to effectively manipulate terahertz waves in the near-field region. Leveraging the tunability of liquid crystal (LC) materials, the proposed PLCPM achieves 1-bit phase coding capability within the 104-110 GHz frequency band. Subsequently, by combining lithography machining with printed circuit board (PCB) manufacturing technology, the pixelated controllability of the PLCPM is realized. The simulation and experimental results demonstrate that the proposed PLCPM can perform multifunctional near-field beam control for terahertz waves, including focusing beams for different distances and positions, near-field orbital angular momentum (OAM) beams for large-capacity communication, and Bessel beams for long-distance propagation. These results verify the effectiveness of the proposed PLCPM in flexibly controlling near-field beams, paving the way for the application of RIS in terahertz near-field communication. (c) 2026 Chinese Laser Press

This paper introduces a novel highly sensitive microwave humidity sensor based on a pair of planar split ring resonators, incorporating the intensive and localized resonance excited by the interdigital electrodes to detect relative humidity variation in the environment via spectroscopy analysis. A 0.25 mm thick replaceable polyimide (PI) film, whose relative permittivity is in close relate with the relative humidity of the environment, was covered on the interdigital electrodes and used as the moisture sensing material of the proposed sensor. Therefore, the resonance frequency of the sensor, which is highly sensitive to the relative permittivity of the PI film, varies with different humidities. The sensor experimentally demonstrated a high sensitivity of 2.02 MHz/%RH within a wide humidity monitoring range of 30-78 % RH, which significantly outperforms the reported microwave humidity sensors. Meanwhile, the sensor exhibits comparable hysteresis performance to commercial sensors during the testing cycles, which holds significant importance for practical applications. The proposed sensor, features a compact size with low cost and high sensitivity, provides a solution for precise humidity variation detecting from a spectrum measurement perspective.

Microwave turntable imaging for industrial non-destructive testing or contraband detection shares similar imaging geometry with circular synthetic aperture radar (CSAR), but differs distinctly in imaging modality and signal processing. First, its ultra-short standoff distance requires continuous-wave (CW) transmission and a bistatic antenna configuration (to suppress transceiver crosstalk), replacing long-range Synthetic Aperture Radar (SAR)’s “stop–go” mode with a fixed-bistatic-angle CW mode. Second, its large field of view and wide antenna beamwidth cause near-field electromagnetic propagation with significant wavefront curvature, making conventional CSAR algorithms (relying on far-field plane-wave approximation) inapplicable—these induce severe phase errors, leading to range migration correction mismatch and image blurring/distortion. To reduce such errors, cut system costs, and improve resolution/computational efficiency, a circular convolution-based range migration algorithm (RMA) is proposed for slant-plane-to-ground-plane transformation in turntable near-field imaging. The system uses a fixed bistatic angle (BA) antenna pair for slant-plane sampling. The algorithm first compensates elevation-dependent phases to map echoes to an equivalent ground plane, then derives a matched filtering kernel via polar-coordinate spherical wave decomposition, circular convolution, and discrete Fourier transform (DFT) properties, and finally reconstructs images through multi-dimensional inverse DFT and STOLT interpolation. Point-target simulations, full-wave FEKO modeling, and laboratory tests confirm high-resolution imaging over a large bistatic angle aperture.

Carbon-based microwave absorption (MA) materials remain constrained by complex synthesis, toxic precursors and narrow absorption bandwidth. Inspired by the decomposition behavior of carbonates, we report a simple and green in situ gas-foaming strategy to fabricate lychee-like nitrogen-doped hollow carbon spheres (NHCS). MnCO3 is employed as an in situ foaming agent, releasing CO2 during carbonization to generate hierarchical porosity without secondary chemical etching. The resulting hollow architectures can optimize impedance matching, intensify interfacial polarization at the wrinkled surfaces, and thus promote multiple electromagnetic scattering within the internal cavities. Consequently, these NHCS exhibit a strong reflection loss of -51.07 dB and an effective absorption bandwidth (EAB) of 5.92 GHz at a low filler loading of 8 wt%. To overcome the intrinsic bandwidth limits of particulate absorbers, a honeycomb structure was further developed, realizing an ultra-wide EAB of 14.83 GHz. This work establishes a green, template-engineering pathway for microstructure design and offers a viable route toward high-performance MA materials.

Abstract Millimeter-wave beam-scanning antennas face a trade-off between beam quality and control complexity. Conventional 1-bit phase-compensation metasurfaces suffer from mirror parasitic beams, while higher-bit solutions enlarge bias networks. Here we present a 1-bit liquid crystal (LC) reflective holographic metasurface that overcomes this limitation. The proposed method derives binary amplitude weights from the interference between a spherical feed wave and the target wave, mapping two LC bias states (0 V and 13 V) to equivalent ON/OFF aperture modulation. A 25 × 25 Ka-band prototype is fabricated and measured, demonstrating continuous two-dimensional beam steering over ±50° with a measured peak gain of 21.5 dB and a pointing error below 1° at 33.5 GHz, while requiring only two bias voltages.

To resolve the contradiction between the susceptibility of amplitude imaging to information leakage and the implementation complexity of phase imaging technology in metasurface imaging, this paper proposes a polarization-independent 1-bit programmable near-field amplitude imaging metasurface based on liquid crystal, and combines the XOR encryption algorithm to enhance information security. Numerical simulations demonstrate that the proposed metasurface possesses outstanding polarization independence and angular insensitivity within the frequency range of 79.7-92.6 GHz. Additionally, successful imaging of the characters "X," "H," "F," "U," and "T" is achieved, with optimal image resolution attained at a distance of 0.75 mm from the metasurface. The XOR algorithm can generate ciphertext images by performing a bitwise operation on the plaintext and the key, and the same key can restore the plaintext. Notably, "HFUT" can be disguised as "ECNU" to enhance concealment. This design balances imaging quality and information security, offering a promising approach for the application of metasurfaces in secure communication.

Traditional liquid-crystal terahertz absorbers have a fundamental limitation: continuous frequency tuning and easy driving cannot be achieved simultaneously, for standard configurations need precise multi-stage analog voltages to bias homogeneous liquid crystal layers. To tackle this issue, this work introduces a 1-bit spatially encoded liquid-crystal terahertz absorber built on a grating-divided framework. Each hybrid-resonance unit cell integrates seven separately addressable grating electrodes, which integrate split-ring resonators and T-shaped metallic arms. Instead of expanding voltage levels, only two fixed voltages are applied to separate spatial areas to quasi-continuously adjust the resonator’s effective permittivity through spatial encoding. Tests show quasi-continuous absorption tuning from 119.9 to 137.4 GHz with a 17.5 GHz high-absorption bandwidth above 90% for coding patterns, a peak relative bandwidth of 5.69%, and reliable performance under incident angles up to 40° With a 12.7% tuning coefficient under simple binary driving, this design provides a viable solution for programmable terahertz electromagnetic regulation.

Terahertz communication technology is envisioned as a promising candidate for the pivotal spectrum technology in future wireless communication networks. However, the limited penetration ability of terahertz waves makes line-of-sight (LoS) transmission indispensable, hindering the extensive application of terahertz communications. In this work, a novel liquid-crystal programmable metasurface (LCPM) is proposed for the first time, which can effectively achieve dual-broadband beam manipulation to improve link stability and extend coverage for terahertz communications in non-line-of-sight (NLoS) scenarios. The LCPM is operated in both the W band that covers 94 GHz and the D band that covers 140 GHz, corresponding to x-polarized and y-polarized wave incidence, respectively. Based on the proposed LCPM, realistic NLoS terahertz communication links are established and showcased. Communication measurements substantiate that the LCPM is capable of realizing extensive dynamic channel regulations and long-distance communications across both bands in various modulation schemes, supporting real-time high-speed video transmission. The experimental results validate the feasibility of employing the LCPM for terahertz wireless communications, paving the way for developing and implementing ubiquitous terahertz communication networks even with LoS blockage.

The integrated control of transmitted and reflected electromagnetic (EM) waves plays a pivotal role in information processing and security. However, due to the complexity of antenna designs, most existing devices are limited to half-space wave manipulation to ensure high-quality transmission characteristics. Achieving dynamic and integrated control of full-space waves remains a significant challenge, especially at the same aperture in high-frequency applications. This paper introduces a novel liquid crystal (LC) transmission-reflection integrated programmable metasurface (LC-TRIPM). Based on the birefringence effect of LC, each meta-atom can be 1bit coded to modulate the phase of both transmitted and reflected EM waves, allowing full-space manipulation in both the near- and far-fields. Dual-layer LC structure is employed to enable the LC-TRIPM to operate in transmission, reflection, and simultaneous transmission-reflection modes at 94 GHz. Both simulation and experimental results demonstrate the reliable capability of the proposed LC-TRIPM in transmission-reflection integrated control. Full-space far-field beam scanning and near-field dynamic focusing can all be realized by using the proposed LC-TRIPM. This work not only offers a new strategy for integrated full-space EM wave control but also contributes to the development of multifunctional intelligent metasurface technology.

Reconfigurable intelligent surface (RIS) have received significant attention in the field of communication and wireless networks, due to their numerous advantages, such as low cost, low energy consumption, miniaturization, programmability, and ease of deployment. This article proposes an RIS based on liquid crystal (LC) for constructing wireless communication systems. Tunable LC embedded between metal microstructures supported by quartz substrates allows for precise control of the reflected wave phase. The experimental results demonstrate that RIS has more than 360 degrees of phase modulation capability and four stable digital coding states at the optimal operating frequency of 100.2 GHz. In addition, the RIS has a 100 degrees beam scanning capability, providing a solid foundation for tracking and targeting during communications. The communication capability of RIS was then demonstrated in the sub-terahertz band by constructing a 16QAM constellation diagram test system and a video realtime transmission system with varying deflection angles. Our work provides excellent solutions for communication and wireless network applications in the millimeter wave and terahertz (THz) frequency bands.

This paper presents a flexible and broadband metamaterial absorber (MA) with a sandwich structure for W-band absorption. The MA uses a thin FR4 material as the dielectric layer and incorporates multiple patches of varying sizes as the top pattern layer. By optimizing the dimensions and arrangement of the metal patches, an average absorption rate exceeding 94% is achieved across the 75–110 GHz frequency range, effectively covering the entire W-band. The MA, with a thickness of only 0.22 mm and a weight less than 600 g/m2, is polarization-insensitive and maintains high absorption for TM waves within an incident angle of 45°. The structure is simple, low-cost, and compatible with PCB fabrication processes. The experimental results align well with the simulations and demonstrate effective absorbing performance in conformal applications, offering a new solution for flexible millimeter-wave absorption.

A reconfigurable transmitarray antenna (RTA) with 2-bit phase resolution is proposed in this paper. The RTA unit is based on a conventional receive-transmit structure. By incorporating phase-shifting structures in both the receiving and transmitting layers and controlling the states of integrated p-i-n diodes, four phase states $\left(0^{\circ}, \mathbf{9 0}^{\circ}, \mathbf{1 8 0}^{\circ}, \mathbf{2 7 0}^{\circ}\right)$ can be achieved. A $\mathbf{1 4} \times \mathbf{1 4}$ element array is designed and simulated, achieving a maximum gain of 21.2 dB at 5.6 GHz with an aperture efficiency of 38.4%. This array antenna exhibits high aperture efficiency, high phase resolution, and the capability for reconfigurable beam steering, making it highly suitable for future communication and radar systems.

A terahertz (THz) phase shifter based on a liquid crystal and a single-layer metasurface with a shared aperture for dual-band antennas is proposed. The device achieves phase shifts exceeding 180° in dual-frequency bands, with simulations indicating 236.8–248.8 GHz and 462–478 GHz ranges while experimental results demonstrate 239.3–249.4 GHz and 464–472.5 GHz operational bandwidths. Maximum phase shifts of 225.8° at 244.5 GHz and 201° at 468.3 GHz were experimentally recorded. The proposed metasurface is designed for use in a dual-band terahertz antenna system with shared aperture and phased array functionality.

The flexible control of electromagnetic (EM) waves across the entire spatial domain is a long-standing aspiration in metasurface research, driven by its potential to enhance signal coverage and channel capacity. However, most existing full-space metasurfaces are restricted to manipulating incidence within one specific half-space, failing to exploit the EM potential across the entire space. This paper introduces a novel bidirectional transmission-reflection-integrated metasurface (BTRIM) for simultaneous and independent control of full-space incident waves. By dynamically adjusting diode states, the BTRIM can switch among simultaneous and independent forward/backward reflection, forward transmission-reflection (TR), and backward TR functions, each with an independent 1-bit phase response. The core innovation lies in integrating transmission and reflection within a single structure, enabling the metasurface to function at the same frequency and polarization within a compact design. Simulations and experimental validation are conducted to demonstrate BTRIM's ability to implement various wave functions and enhance signal intensity for users in both indoor and outdoor environments. The agreement between simulation and experimental results validates the BTRIM's capacity to simultaneously and independently regulate EM waves from all spatial directions, offering new insights into full-space wave manipulation. This breakthrough creates opportunities for applications in EM sensing, channel enhancement, and next-generation communication systems.

This communication presents a reconfigurable polarization converter based on the liquid crystal (LC) terahertz (THz) metasurface. The proposed structure shows unique ability in achieving the conversion from linearly polarized (LP) waves to selective cross-polarized waves or circularly polarized (CP) waves within a wide frequency range. Experimental results demonstrate that, within the frequency region of 318.0-375.6 GHz, the metasurface can achieve the conversion from LP waves to cross-polarized waves without external biasing. However, when a saturated biasing voltage of 8 V is applied, the y-LP waves can be converted to right-handed CP (RHCP) reflection waves. Similar phenomenon is observed for x-LP incidence, as the x-LP waves were converted to left-handed CP (LHCP) wave in reflection. Unlike previously reported single-function metasurface polarization converters, the proposed design offers a new approach for achieving wideband reconfigurable multifunctional polarization conversion with a cost-effective solution, opening up possibilities for its application in the field of THz sensing and communication.

Images, as prevalent carriers of information, are widely applied in daily life and production. With the development of information technology, concerns over information security have risen, leading to the emergence of image encryption techniques. Metasurfaces demonstrate exceptional electromagnetic wave manipulation capabilities, establishing their potential as encryption platforms for image security. In this work, a chiral metasurface that exhibits completely opposite absorption characteristics for circularly polarized waves in its original and mirror-image configurations is experimentally demonstrated. Then, both the multiple interference model and exceptional point are used for theoretical analysis of the chiral metasurface. Finally, the polarized-dependent metasurface encryption image is designed to achieve different terahertz images based on the chiral structures.

Sub-terahertz (THz) wireless technology is recognized for its potential to deliver terabits per second throughput and ultralow latency, reaching the sub-microsecond level. Its extensive spectral resources enable faster and more reliable data transmissions, ultrahigh throughput short-range communication, and innovative applications, including environmental sensing. Liquid crystal is a kind of soft material with controllable self-assembled structures under external stimuli, offering opportunities for programmable and cost-effective controls of sub-THz waves. Unlike the traditional transmissive metasurfaces integrated with soft material that are constrained in control dimensions and diversity, here we propose an addressable transmissive soft matter metasurface with 24 x 24 units and low-voltage driven (<= 3.6 V). The experimental results show that the proposed meta-atom achieves an amplitude modulation depth (MD) of 18.6 dB and a phase tuning range of approximately 181 degrees at 91.7 and 97.4 GHz, respectively. The fabricated single prototype enables various near-field wavefront engineering applications, such as amplitude-only modulation imaging, phase-only dynamic holography, and arbitrary-direction non-diffractive beam generation. Based on the prototype, we further develop a wireless communication system using the non-diffractive beams, achieving low error vector magnitude in information transmission. The proposed metasurface opens a new pathway for near-field wavefront management and signal enhancement in digital holography and sixth-generation (6G) wireless communications.

This letter presents a reconfigurable broadband transmissive-type linear cross-polarization converter (LCPC) based on liquid crystal (LC) metasurfaces. The proposed structure exhibits broadband linear cross-polarization conversion capabilities and asymmetric transmission (AT) effects, with the ability to tune the operational bandwidth by adjusting the applied bias voltage. Experimental results demonstrate that, without external biasing, the structure can achieve linear cross-polarization conversion functionality with polarization conversion ratio >0.97 over the frequency range of 107.8 GHz to 133.6 GHz. Additionally, the AT effect can be realized within the same frequency band. When a saturated bias voltage of 8 V is applied, the operational bandwidth shifts from 101.7 GHz to 129.3 GHz, resulting in a tuning rate of approximately 4.4%. Compared with traditional grating-based three-layer structures, the proposed design, features low cost, simple configuration, and tunable linear cross-polarization conversion and AT effects, providing new possibilities for practical applications that require flexible operation across varying frequency bands in fields such as wireless communication and imaging.

In this paper, an optically transparent ultra-broadband metamaterial-based microwave absorber using indium tin oxide (ITO) deposited on glasses is proposed. The proposed structure integrates two glasses: the upper one is a glass substrate and the lower one is a glass coated with a hybrid metamaterial structure and a grid mesh ground using ITO film. Owing to the multi-resonances of the metamaterial and the impedance matching of the upper glass, the proposed structure obtains an ultra-broadband absorption covering 4.0–17.0 GHz (a relative bandwidth of 123.8%) with over 90% absorptivity. The structure is compact without air gap and the thickness is ∼0.093 times the upper-cutoff wavelength. The physical mechanism is analyzed using equivalent circuit and surface current distributions. Moreover, a grid mesh ground is first proposed to enhance the visible transparency to 74.69% and ensure a low microwave transmission simultaneously. A prototype is fabricated and measured, and the experiments and simulations are in good agreement. The design yields the advantages of ultra-broadband, high light transmittance, and compact, making it suitable for transparent electromagnetic absorption and shielding devices.