Stacked tunable metasurface achieving sharp frequency filtering with polarization and spectral reconfigurability

With the upgrading of electronic countermeasures, the anti-jamming technology of radar seeker is required in modern war. Based on the background of complex electromagnetic environment, this paper summarizes the working principle of radar seeker anti-jamming technology in time domain, space domain, frequency domain and polarization domain, and prospects the development trend of radar seeker anti-jamming technology in the future.

Controlling the polarization state of electromagnetic waves is an important topic in microwaves due to the enormous application potential in radar technology and mobile communications. Here, we propose a programmable metasurface based on single-pole double-throw switches to realize multifunctional polarization conversions. A structure of the double-sided metallic pattern is adopted in the metasurface, in which a novel double-pole double-throw hub is achieved to guide the energy direction. Such a mechanism successfully induces multiple transmission channels into the metasurface structure for functional design. By controlling the states of the switches with a field programmable gate array, the x- and y-polarizations of the incident waves can be efficiently modulated into linear co- and cross-polarizations of transmitted waves, suggesting a higher degree of freedom on wave manipulations. The proposed metasurface can be developed as a near-field information encoder to transmit binary coding sequence according to the energy distribution. Character transmissions are realized by programming binary ASCII codes on the transmitted fields. Nine supercells on the metasurface can encode 9-bit binary information in one frame of near-field imaging, which can be switched in real time with high speed. We envision that this work will develop digital coding applications to control the polarization information.

Graphene-enabled metasurface with independent amplitude and frequency controls in orthogonal polarization channels

With the exponential grow of personal wireless devices, issues like power consumption, communication security and interference immunity are gaining more and more importance. Body Area Networks (BAN), due to their reduced range, are by nature relatively low power, but as an answer to achieve even a more confined range, Near Field Communications (NFC) and Body Coupled Communications (BCC) have been proposed. While the first is used to link two devices that are physically very close, the BCC concept broadens the communication range to the region around the human body. One of the possible technologies supporting BCC is based upon relatively low frequency capacitive coupling between emitter and receiver. Understanding the connection between the physical layout of an electromagnetic system and its electrical model is important to understand its performance and critical aspects. However, although much information exists about antennas and their radiated energy, very few work has been done on how energy is transferred between the electrodes used in a capacitive communication system. In this paper we propose a simple model for estimating the gain of a capacitive coupling system. This model has been validated by 3D electromagnetic simulations and double checked with practical experiments performed in a controlled environment (faraday cage with only the minimum indispensable instrumentation equipment). The results are similar within an order of magnitude which, for the intended use of the model, proves to be accurate enough.

With the exponential grow of personal wireless devices, issues like power consumption, communication security and interference immunity are gaining more and more importance. Body Area Networks (BAN), due to their reduced range, are by nature relatively low power, but as an answer to achieve even a more confined range, Near Field Communications (NFC) and Body Coupled Communications (BCC) have been proposed. While the first is used to link two devices that are physically very close, the BCC concept broadens the communication range to the region around the human body. One of the possible technologies supporting BCC is based upon relatively low frequency capacitive coupling between emitter and receiver. Understanding the connection between the physical layout of an electromagnetic system and its electrical model is important to understand its performance and critical aspects. However, although much information exists about antennas and their radiated energy, very few work has been done on how energy is transferred between the electrodes used in a capacitive communication system. In this paper we propose a simple model for estimating the gain of a capacitive coupling system. This model has been validated by 3D electromagnetic simulations and double checked with practical experiments performed in a controlled environment (faraday cage with only the minimum indispensable instrumentation equipment). The results are similar within an order of magnitude which, for the intended use of the model, proves to be accurate enough.

This paper addresses the design and modeling of millimeter wave tunable filters using CoPlanar Waveguide (CPW) quarter wavelength stubs and MEMS (Micro-Electro-Mechanical-Systems) switches. In order to design bandstop and bandpass tunable MEMS filters an accurate design methodology based on the transmission line theory is presented. The tunable behavior is achieved using original MEMS switches: Two Cantilever Shunt Switch (TCSS). The overall structures, including TCSS, have been manufactured using dielectric membrane, in order to minimize the insertion losses. The obtained simulation and experimental results confirm the accuracy of the proposed design methodology and indicates very good performances in millimeter wave band.

This paper presents the design and optimization of a dual-band polarization-dependent metasurface capable of dynamically switching transmission and reflection characteristics. The metasurface is composed of three metallic patterns, with the bottom layer governing the reflection and transmission phase for both TE-polarization and TM-polarization states. The middle and top layers are strategically employed to ensure optimal transmission and reflection performance. The results confirm that the metasurface enables the transformation of the transmission band into a complete reflection band, and vice versa, through variations in the incident wave polarization. Remarkable transmission and reflection characteristics are achieved within the frequency ranges of 6.1–6.55 GHz and 8.9–9.3 GHz, respectively. The proposed metasurface offers promising applications in advanced communication systems and radar technology, enabling dynamic manipulation of electromagnetic waves.

A dynamically tunable attenuator is proposed by integrating two graphene sandwich structures (GSSs) into a spoof surface plasmon polaritons (SSPPs) waveguide. The attenuator is formed by locating two GSSs symmetrically on both sides of the SSPP waveguide. Both the surface impedance of GSSs and the attenuation of the attenuator are tunable by changing the bias voltage applied to the graphene sheets. The transmission line theory is employed to model the proposed SSPP waveguide and attenuator. Measurement shows two orders of magnitude attenuation range with bias voltage changing from 0 to 4 V. In addition, the proposed SSPPs attenuator achieves 2.5–7.2 times attenuation/ $\lambda $ of GSS compared with the reference works.

A terahertz amplitude modulator based on graphene on a metallic square ring resonant structure is proposed. By separating the graphene and the metallic structure with a thin organic dielectric layer, both the resonant frequency and the amplitude of the transmission resonant peak are modulated when graphene is electrically tuned by a bias voltage. A maximal amplitude modulation depth of 72% at the frequency of 0.6 THz is achieved for the fabricated Terahertz modulator. An analysis model based on the transmission line theory is built to explore the modulation mechanism. Results of the transmission spectrum and the amplitude modulation indicate a good agreement between the transmission line theoretical predictions and the experimental measurements.

Recommender system is widely used in various fields for dealing with information overload effectively, and collaborative filtering plays a vital role in the system. However, recommender system suffers from its vulnerabilities by malicious attacks significantly, especially, shilling attacks because of the open nature of recommender system and the dependence on data. Therefore, detecting shilling attack has become an important issue to ensure the security of recommender system. Most of the existing methods of detecting shilling attack are based on user ratings, and one limitation is that they are likely to be interfered by obfuscation techniques. Moreover, traditional detection algorithms cannot handle different types of shilling attacks flexibly. In order to solve the problems, we proposed an outlier degree shilling attack detection algorithm by using dynamic feature selection. Considering the differences when users choose items, we combined rating-based indicators with user popularity, and utilized the information entropy to select detection indicators dynamically. Therefore, a variety of shilling attack models can be dealt with flexibility in this way. The experiments show that the proposed algorithm can achieve better detection performance and interference immunity.

Broad-band microwave absorption and magnetic properties of M-type Ba(1−2x)LaxNaxFe10Co0.5TiMn0.5O19 hexagonal ferrite in 18.0–26.5 GHz frequency range

Spatiotemporal manipulation of electromagnetic waves has recently enabled a plethora of exotic optical functionalities, such as non‐reciprocity, dynamic wavefront control, unidirectional transmission, linear frequency conversion, and electromagnetic Doppler cloak. Here, an additional dimension is introduced for advanced manipulation of terahertz waves in the space‐time, and frequency domains through integration of spatially reconfigurable microelectromechanical systems and photoresponsive material into metamaterials. A large and continuous frequency agility is achieved through movable microcantilevers. The ultrafast resonance modulation occurs upon photoexcitation of ion‐irradiated silicon substrate that hosts the microcantilever metamaterial. The fabricated metamaterial switches in 400 ps and provides large spectral tunability of 250 GHz with 100% resonance modulation at each frequency. The integration of perfectly complementing technologies of microelectromechanical systems, femtosecond optical control and ion‐irradiated silicon provides unprecedented concurrent control over space, time, and frequency response of metamaterial for designing frequency‐agile spatiotemporal modulators, active beamforming, and low‐power frequency converters for the next generation terahertz wireless communications.

This systematic review evaluates the integration of advanced radar technologies into unmanned ground vehicles (UGVs), focusing on their role in enhancing autonomy in defense, transportation, and exploration. A comprehensive search across IEEE Xplore, Google Scholar, arXiv, and Scopus identified relevant studies from 2007 to 2024. The studies were screened, and 54 were selected for full analysis based on inclusion criteria. The review details advancements in radar perception, machine learning integration, and sensor fusion while also discussing the challenges of radar deployment in complex environments. The findings reveal both the potential and limitations of radar technology in UGVs, particularly in adverse weather and unstructured terrains. The implications for practice, policy, and future research are outlined.

The programmable metasurface or reconfigurable intelligent surface is one of the emerging technologies for next-generation wireless communications, but the existing programmable metasurfaces still rely on human control to reshape the electromagnetic (EM) environment as desired. Here, we propose an adaptively programmable metasurface (APM), which integrates the capabilities of acquiring wireless environment information and manipulating the EM waves in programmable manners. APM can sense the complex EM field distributions around and dynamically manipulate the EM waves and signals in real time under the guidance of the sensed information, eliminating the need for prior knowledge or external input on the wireless environment. For experimental verification, a 6 × 6 APM prototype is constructed and its dual capabilities of sensing and wave manipulation are validated. Different integrated sensing and communication scenarios with and without the aid of APM are established, and the capability of APM in enhancing the communication quality is demonstrated in complex environments, highlighting its beneficial application potentials in future wireless systems.

The article presents a comprehensive analysis of current trends in the development and a model for evaluating the performance characteristics of wireless networks in cognitive radio systems for special purposes. The study focuses on key directions in the development of these technologies, their advantages and limitations, as well as their potential applications in critical sectors. Particular attention is given to the analysis of contemporary scientific research and developments in the field of cognitive radio, especially for military systems, where communication reliability and security are of paramount importance.The article examines the fundamental principles of cognitive radio, such as dynamic spectrum access, adaptability to changing environments, and intelligent resource management. It analyzes the technologies used in cognitive radio systems for special purposes, including software-defined radio (SDR), cognitive radio networks (CRNs), and communication security technologies.The main development trends identified during the study include the use of artificial intelligence and machine learning to optimize network performance, the evolution of heterogeneous networks to ensure greater flexibility and reliability, and the enhancement of security measures to counter cyberattacks and electronic warfare.A key feature of network-centric military communication systems is the rapid and guaranteed access of users to communication services. This work proposes a model for selecting optimal parameters of a self-organizing cognitive communication network that ensures the required availability for its users. The model enables the selection of optimal coverage and channel resource parameters to achieve the desired accessibility of the cognitive communication network.The article also explores the prospects of practical application of cognitive radio in specialized systems, highlighting its potential to provide reliable and efficient communication in complex and dynamic environments. The findings emphasize the importance of continued research in this area to develop more effective and secure cognitive radio systems.