An effective surface plasmon polariton (ESPP) filtering waveguide-fed D-band antenna is proposed for 6G Internet of Things (IoT) applications. Aiming at cross-band interference and link stability in 6G IoT, the design integrates an ESPP filtering structure with a waveguide slot antenna, achieving high selectivity and deep out-of-band suppression while maintaining stable radiation performance. Through ESPP dispersion engineering, the passband (135.9–143.2 GHz) and out-of-band suppression can be independently tuned. Benefiting from ESPPs’ steep asymptotic dispersion and extended modal bandgap, deep out-of-band suppression (>55 dB) and a stable stopband (147–170 GHz) are realized. Notably, the ESPP-based waveguide ensures robust performance against fabrication errors, maintaining frequency consistency between the filtering and radiation responses. The proposed ESPP-based design provides a high-selectivity and fabrication-tolerant solution, effectively mitigating complex interference in ultra-high-speed 6G IoT links and ensuring reliable operation for heterogeneous devices, such as Vehicle-to-Everything (V2X) sensors and smart city terminals.

Magnetic map matching localization has various strategic applications, such as drone reconnaissance, submarine navigation, cruise missile guidance, etc. However, the complexity of matching localization architectures based on magnetic map often fails to meet the fast position update frequency demands for high-speed moving targets. To address this issue, this article proposes a lightweight matching localization architecture, i.e., an adaptive integrated particle filter (AIPF) method based on magnetic map and inertial sensors. The AIPF method includes the prediction phase, correction phase, normalization phase, integration phase, and estimation phase. By pre-establishing a Bayesian probability integral table (BPIT) based on standard normal probability distribution functions and expectation functions, the integration results can be directly queried from the BPIT adaptively, avoiding the time consuming integration operation when matching the potential magnetic fingerprint. The heading and step length can be obtained by dead reckoning based on inertial sensors. Extensive experiments show that when the heading uncertainty is less than 1.2°, or the step length uncertainty is less than 30% of the precision of reference magnetic map, the AIPF method has comparable positioning accuracy while the computational complexity is reduced to one-tenth of that in the compared methods, such as particle filter, the adaptive optimization firefly algorithm, extended Kalman particle filter, etc. Moreover, when the experimental condition is more challenging, the AIPF method demonstrates better robustness than the compared methods. This work provides a new solution for lightweight matching localization algorithms using magnetic maps and inertial sensors, suitable for various applications requiring high position update frequencies or fast target localization and tracking.

Programmable metasurface based on the design philosophy of information metasurfaces have attracted widespread attention in internet of things (IoT) in recent years due to their advantages of low cost and low complexity. However, most existing radiation-type programmable metasurface are either phase-only coding or amplitude-only coding, which limits their functionality and applications. Here, we propose a high-performance 1-bit radiation-type programmable metasurface with amplitude-phase co-modulation. By adjusting two PIN diodes integrated on each meta-atom, the phase and amplitude can be controlled separately. The meta-atom phase can switch between two states with a phase difference of 1800, with the PIN diode states being 01 and 10 (where 1 represents ON and 0 represents OFF), respectively. The amplitude can be switched between two states, reflection, and radiation, with the PIN diode states being 00/11 and 01/10, respectively. In addition, the meta-atom can acquire an initial phase by rotating within the plane. An 8W8 programmable metasurface is given to verify its functionality. Firstly, the initial phase can be used for suppressing grating lobes of the 1-bit radiation-type programmable metasurface. Second, through amplitude-phase co-modulation, the beam amplitude can be controlled dynamically, including the main lobe and the sidelobe. Therefore, the high performance 1-bit radiation-type programmable can serve as a promising candidate for intelligent IoT applications, including smart city, home, factory, and more.

Nowadays, the number of wireless sensor devices is increasing rapidly, posing persistent challenges related to battery replacement and power wiring. This paper presents a simultaneous wireless information and power transmission (SWIPT) scheme based on a frequency diversity metasurface design, which provides a wireless power supply scheme for electrical devices such as sensors. The metasurface is designed with frequency bands commonly found in the environment, and achieves efficient absorption of electromagnetic (EM) energy at 5.8 GHz and radiation of sensor information at 2.45 GHz, making it possible to take full advantage of the energy in the environment and easy to integrate with existing systems. The branches for the dual-square loop are designed based on spatial impedance matching and equivalent circuit, giving the metasurface advantages such as compact layout (unit size of 0.16λ0×0.16λ0×0.012λ0, where λ0 is the wavelength at 2.45 GHz), high isolation (S21< −20 dB within the operating frequency band), and insensitivity to incident angles (efficiency over 80% within 60°). Integrated with rectification circuits and sensors, it efficiently converts EM waves received by the metasurface into direct current (DC) power for sensor operation. The sensors then radiate information through the metasurface, effectively addressing challenges related to sensor device wiring and battery replacement, thereby offering new solutions for the development of next-generation smart cities.

Abstract Near-field technology is increasingly recognized due to its transformative potential in communication systems, establishing it as a critical enabler for sixth-generation (6G) telecommunication development. This paper presents a comprehensive survey of recent advancements in near-field technology research. First, we explore the near-field propagation fundamentals by detailing definitions, transmission characteristics, and performance analysis. Next, we investigate various near-field channel models—deterministic, stochastic, and electromagnetic information theory based models, and review the latest progress in near-field channel testing, highlighting practical performance and limitations. With evolving channel models, traditional mechanisms such as channel estimation, beamtraining, and codebook design require redesign and optimization to align with near-field propagation characteristics. We then introduce innovative beam designs enabled by near-field technologies, focusing on non-diffractive beams (such as Bessel and Airy) and orbital angular momentum (OAM) beams, addressing both hardware architectures and signal processing frameworks, showcasing their revolutionary potential in near-field communication systems. Additionally, we highlight progress in both engineering and standardization, covering the primary 6G spectrum allocation, enabling technologies for near-field propagation, and network deployment strategies. Finally, we conclude by identifying promising future research directions for near-field technology development that could significantly impact system design. This comprehensive review provides a detailed understanding of the current state and potential of near-field technologies.

The wavefront control of spin or orbital angular momentum (OAM) is widely applied in the optical and radio fields. However, most passive metasurfaces provide limited manipulations, such as the spin-locked wavefront, a static OAM combination, or an uncontrollable OAM energy distribution. We propose a reflection-type multi-feed metasurface to independently generate multi-mode OAM beams with dynamically switchable OAM combinations and spin states, while simultaneously, the energy distribution of carrying OAM modes is controllable. Specifically, four elements are proposed to overcome the spin-locked phase limitation by combining propagation and geometric phases. The robustness of these elements is analyzed. By involving the amplitude term and multi-feed technology in the design process, the proposed metasurface can generate OAM beams with a controllable energy distribution over modes and switchable mode combinations. OAM-based radio communication with four independent channels is experimentally demonstrated at 14 GHz by employing a pair of the proposed metasurfaces. The powers of different channels are adjustable by the provided amplitude term, and the maximum crosstalk is −9 dB, proving the effectiveness and practicability of the proposed method.

A comprehensive review of metamaterials and metasurfaces for wireless power transfer (WPT) and wireless energy harvesting (WEH) is presented in this article. According to the features of the electromagnetic field from the source to the receiver, WPT is divided into nonradiative near-field technology and radiative (near and far-field) technologies. Many different and important designs are reviewed and compared. It is shown that metamaterials and metasurfaces can significantly improve the power transfer efficiency and operational distance for WPT systems. They can also improve the energy conversion efficiency of wireless energy harvesters by making the reception less sensitive to incident wave angle and polarization. A rectenna is a critical element for both WPT and WEH. It is shown that metamaterial-based rectennas can achieve a higher RF to dc conversion efficiency. Furthermore, metamaterials can also be used as either parasitic elements or loading components to improve WEH performance in terms of circuit size, beamwidth, and conversion efficiency. Future development directions and opportunities of metamaterials and metasurfaces for WPT and WEH are also proposed in this article.

Computational microwave imaging (CMI) based on the frequency diversity metasurface apertures (FDMAs) is an emerging technology and has attracted wide attention. FDMA based CMI (FDMA-CMI) can be considered as microwave compressive sensing imaging with the frequency diversity pattern of the FDMA being the sensing matrix and solved by sparse signal reconstruction algorithms. However, the imaging quality is affected by the sensing matrix error and off-grid error seriously. In this paper, we propose a novel algorithm for FDMA-CMI, referred to as OGSISBL, by taking both the off-grid error and sensing matrix error into account. Firstly, we establish the measurement model with both the off-grid error and sensing matrix error. Specifically, the off-grid error is represented as a set of parameters to be estimated in the measurement model and the sensing matrix error is represented as the amplitude-phase drift of the transceiver channels of the imaging system due to the principle of the FDMA. Then, under the framework of the sparse Bayesian learning, a robust imaging algorithm OGSISBL is developed via the variational Bayesian expectation maximization (VBEM), which can not only recover the amplitude and position of the return of the scattered, but also simultaneously calibrate the amplitude-phase drift of the transceiver channels and the off-grid error. The performance of the proposed algorithm is evaluated by both the simulation data and the measured data collected by the self-designed experimental FDMA-CMI system, and the results validate the effectiveness and robustness of the proposed method.

Computational microwave imaging with frequency-diverse metasurface (FDM) apertures is an emerging technology. In this article, we establish an experimental FDM microwave imaging system and address the waveform design problem based on the information theory, aiming to enhance the advantages of the FDM imaging. Two waveform design methods based on the different criteria are proposed for the FDM imaging system. The first waveform is designed by maximizing the mutual information between the object and the measured data with the constant transmitted energy, and the second one is designed by minimizing the transmitted energy while the mutual information is not less than a threshold. The performance of the proposed waveform design methods is evaluated by the data gathered by the self-established experimental FDM imaging system. The results show that the proposed waveform design methods are capable of improving the imaging quality or the imaging efficiency of the FDM imaging system.

In this paper, a novel polarization-reconfigurable converter (PRC) is proposed based on a multilayer frequency-selective surface (MFSS). First, the MFSS is designed using the square patches and the grid lines array to determine the operational frequency and bandwidth, and then the corners of the square patches are truncated to produce the phase difference of 90° between the two orthogonal linear components for circular polarization performance. To analyze and synthesize the PRC array, the operational mechanism is described in detail. The relation of the polarization states as a function of the rotating angle of the PRC array is summarized from the principle of operation. Therefore, the results show that the linear polarization (LP) from an incident wave can be reconfigured to LP, right- and left-hand circular polarizations by rotating the free-standing converter screen. The cell periods along x- and y-directions are the same, and their total height is 6 mm. The fractional bandwidth of axial ratio (AR) less than 3 dB is more than 15% with respect to the center operating frequency of 10 GHz at normal incidence. Simultaneously, the AR characteristics of different incidence angles for oblique incidence with TE and TM polarizations show that the proposed PRC has good polarization and angle stabilities. Moreover, the general design procedure and method is presented. Finally, a circularly shaped PRC array using the proposed PRC element based on the MFSS design is fabricated and measured. The agreement between the simulated and measured results is excellent.