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Since the discovery of wireless telegraphy in 1897, wireless communication via electromagnetic (EM) signals has become a standard solution to address increasing demand for information transfer in modern society. With the rapid growth of EM wave manipulation technique, programmable metasurface (PM) has emerged as a new type of wireless transmitter by directly modulating digital information without complex microwave components, thus providing an alternative to simplify the conventional wireless communication system. However, the challenges of improving information security and spectrum utilization still exist. Here, a dual‐band metasurface‐assisted wireless communication scheme is introduced to provide additional physical channels for the enhancement of information security. The information is divided into several parts and transmitted through different physical channels to accomplish information encryption, greatly reducing the possibility of eavesdropping. As the proof of concept, a dual‐channel and high‐security wireless communication system based on a 1‐bit PM is established to simultaneously transmit two different parts of a picture to two receivers. Experiments show that the transmitted picture can be successfully retrieved only if the received signals of different receivers are synthetized as predefined. The proposed scheme provides a new route of employing PM in information encryption and spectrum utilization of wireless communication. A metasurface‐assisted wireless communication prototype system with additional physical channels to enhance the information security is proposed here. The information is divided into several parts and transmitted simultaneously through different frequency‐channels to avoid eavesdropping. The system demo proves that a colour picture can be successfully encrypted and retrieved with high reliability.

Smart windows refer to those which can dynamically modulate the transmitted light by changing their colors. Dual‐band electrochromic materials (ECMs) refer to materials that can change their colors and regulate light transmission in both visible (VIS) and infrared (IR) regions under different voltages. The dual‐band ECMs‐based building windows can thus regulate the indoor temperature to reduce the energy consumption for heating and air‐conditioning systems. Therefore, the wide application of ECMs in building windows will contribute a lot to establishing an energy‐saving society. During the past decades, enormous efforts have been made to improve the performance of dual‐band ECMs. This review presents a summary of the recent progress of dual‐band ECMs, focusing on their modulation mechanism, material design, and performance optimization. Finally, the challenges and outlook of dual‐band ECMs are also discussed. In this review, we focus on the EC smart windows and give a summary of dual‐band electrochromic materials, which are based on inorganics, organics, and their composites, and the comparison of EC performance between these different materials is also presented to demonstrate their excellent properties and provide insights for the next investigation.

To meet the increasing need of high-data-rate and broadband wireless communication systems, the devices and its circuits R&D under Millimeter, Sub-Millimeter, or even Terahertz (THz) frequency bands are attracting more and more attention from not only academic, but also industrial areas. Most of the former research on the THz waveband (0.1–10 THz) antenna design is mainly focused on realizing high directional gain, such as horn antennas, even though the coverage area is very limited when comparing with the current Wi-Fi system. One solution for the horizontally omnidirectional communication antenna is using the structure of multiple split-ring resonators (MSRRs). Aiming at this point, a novel 300 GHz microstrip antenna array based on the dual-surfaced multiple split-ring resonators (DSMSRRs) is proposed in this paper. By employing the two parallel microstrip transmission lines, different MSRRs are fed and connected on two surfaces of the PCB with a centrally symmetric way about them. The feeding port of the whole antenna is in between the centers of the two microstrip lines. Thus, this kind of structure is a so-called DSMSRR. Based on the different size of the MSRRs, different or multiple working wavebands can be achieved on the whole antenna. Firstly, in this paper, the quasi-static model is used to analyze the factors affecting the resonance frequency of MSRRs. Simulation and measured results demonstrate that the resonant frequency of the proposed array antenna is 300 GHz, which meets the design requirements of the expected frequency point and exhibits good radiation characteristics. Then, a dual-band antenna is designed on the above methods, and it is proved by simulation that the working frequency bands of the proposed dual-band antenna with reflection coefficient below −10 dB are 274.1–295.6 GHz and 306.3–313.4 GHz.

The excessive use of digital platforms with rapidly increasing users in the wireless domain enforces communication systems to provide information with high data rates, high reliability and strong transmission connection quality. Wireless systems with single antenna elements are not able to accomplish the desired needs. Therefore, multiple-input multiple-output (MIMO) antennas are getting more attention in modern high-speed communication systems and play an essential part in the current generation of wireless technology. However, along with their ability to significantly increase channel capacity, it is a challenge to achieve an optimal isolation in a compact size for fifth-generation (5G) terminals. Portable devices, automobiles, handheld gadgets, smart phones, wireless sensors, radio frequency identification and other applications use MIMO antenna systems. In this review paper, the fundamentals of MIMO antennas, the performance parameters of MIMO antennas, and different design approaches and methodologies are discussed to realize the three most commonly used MIMO antennas, i.e., ultra-wideband (UWB), dual-band and circularly polarized antennas. The recent MIMO antenna design approaches with UWB, dual band and circularly polarized characteristics are compared in terms of their isolation techniques, gain, efficiency, envelope correlation coefficient (ECC) and channel capacity loss (CCL). This paper is very helpful to design suitable MIMO antennas applicable in UWB systems, satellite communication systems, GSM, Bluetooth, WiMAX, WLAN and many more. The issues with MIMO antenna systems in the indoor environment along with possible solutions to improve their performance are discussed. The paper also focuses on the applications of MIMO characteristics for future sixth-generation (6G) technology.

A compact dual-frequency ( 38 / 60   GHz ) microstrip patch antenna with novel design is proposed for 5G mobile handsets to combine complicated radiation mechanisms for dual-band operation. The proposed antenna is composed of two electromagnetically coupled patches. The first patch is directly fed by a microstrip line and is mainly responsible for radiation in the lower band ( 38   GHz ). The second patch is fed through both capacitive and inductive coupling to the first patch and is mainly responsible for radiation in the upper frequency band ( 60   GHz ). Numerical and experimental results show good performance regarding return loss, bandwidth, radiation patterns, radiation efficiency, and gain. The impedance matching bandwidths achieved in the 38   GHz and 60   GHz bands are about 2   GHz and 3.2   GHz , respectively. The minimum value of the return loss is − 42 dB for the 38   GHz band and − 47 for the 60   GHz band. Radiation patterns are omnidirectional with a balloon-like shape for both bands, which makes the proposed single antenna an excellent candidate for a multiple-input multiple-output (MIMO) system constructed from a number of properly allocated elements for 5G mobile communications with excellent diversity schemes. Numerical comparisons show that the proposed antenna is superior to other published designs.

In this paper, a dual-band metamaterial absorber (MMA) ring with a mirror reflexed C-shape is introduced for X and Ku band sensing applications. The proposed metamaterial consists of two square ring resonators and a mirror reflexed C-shape, which reveals two distinctive absorption bands in the electromagnetic wave spectrum. The mechanism of the two-band absorber particularly demonstrates two resonance frequencies and absorption was analyzed using a quasi-TEM field distribution. The absorption can be tunable by changing the size of the metallic ring in the frequency spectrum. Design and analysis of the proposed meta-absorber was performed using the finite-integration technique (FIT)-based CST microwave studio simulation software. Two specific absorption peaks value of 99.6% and 99.14% are achieved at 13.78 GHz and 15.3 GHz, respectively. The absorption results have been measured and compared with computational results. The proposed dual-band absorber has potential applications in sensing techniques for satellite communication and radar systems.

The rectangular microstrip patch antenna (RMPA) had designed and manufactured to operate in two working areas of the worldwide interoperability for microwave access (WiMAX) communication system. Flame retardant (FR-4) material had used for implementation, and the total antenna size was 57.22 × 1.6 mm 3 . The chemical method was used to implement the RMPA. The proposed antenna is capable of working at frequencies 2.51 GHz and 3.87 GHz experimentally. The results were -21.62 dB of return loss, and 50 MHz of bandwidth for the first frequency. Also, for second frequency was -20.01 dB of return loss, and 80 MHz of bandwidth.

Electrochromic smart windows can actively modulate their reversible transition between transparent and opaque states, adapting to varying climatic conditions and thereby offering a sustainable solution for energy‐efficient buildings. However, the operational range of current electrochromic smart windows is mostly limited to the solar spectrum. Expanding this range into the mid‐infrared spectrum could significantly enhance their energy‐saving capabilities. In this study, a dynamic electrochromic (EC) glass that integrates silver electrodeposition/dissolution with mechanical flipping of the glass panel is designed. This design enables bidirectional dynamic modulation of both the solar spectrum (0.3–2.5 µm) and mid‐infrared spectrum (2.5–20 µm), with solar reflectance varying between 87.9% and 19.9%, and mid‐infrared emissivity varying between 90.6% and 10.8%. Consequently, the EC glass can dynamically switch between radiative cooling and solar heating modes. The simulation results show that the architectural application of this EC glass, with climate‐specific operating modes, can achieve a maximum of over 50% annual heating, ventilation, and air conditioning (HVAC) energy savings, contributing to carbon neutrality and sustainable development. In this study, an electrochromic glass is designed by effectively integrating silver electrodeposition with mechanical flipping of the glass panel, enabling bidirectional dynamic regulation of the solar and mid‐infrared spectra. Its capability to dynamically switch between radiative cooling and solar heating modes offers substantial energy‐saving potential for building applications.

In this paper, a compact planar dual-band multiple-input and multiple-output (MIMO) antenna with high isolation is presented to satisfy the increasing requirements of wireless communication. The proposed antenna array consists of two identical radiating elements which are fed through micro-strip lines. A rectangular micro-strip stub with defected ground plane is employed to achieve a high isolation which is less than −15 dB between the two antenna elements. The size of the entire MIMO antenna is 32 × 32 × 1.59 mm3, which is printed on an FR4 substrate. The proposed MIMO antenna is optimized to operate in 2.36–2.59 GHz and 3.17–3.77 GHz bands, which can cover the fifth-generation (5G) n7 (2.5–2.57 GHz) and the fourth-generation (4G) Long Term Evolution (LTE) band 42 (3.4–3.6 GHz). The proposed MIMO antenna is feasible for the 5G and 4G applications.

In this paper, a dual-band wide-input-range adaptive radio frequency-to-direct current (RF–DC) converter operating in the 0.9 GHz and 2.4 GHz bands is proposed for ambient RF energy harvesting. The proposed dual-band RF–DC converter adopts a dual-band impedance-matching network to harvest RF energy from multiple frequency bands. To solve the problem consisting in the great degradation of the power conversion efficiency (PCE) of a multi-band rectifier according to the RF input power range because the available RF input power range is different according to the frequency band, the proposed dual-band RF rectifier adopts an adaptive configuration that changes the operation mode so that the number of stages is optimized. Since the optimum peak PCE can be obtained according to the RF input power, the PCE can be increased over a wide RF input power range of multiple bands. When dual-band RF input powers of 0.9 GHz and 2.4 GHz were applied, a peak PCE of 67.1% at an input power of −12 dBm and a peak PCE of 62.9% at an input power of −19 dBm were achieved. The input sensitivity to obtain an output voltage of 1 V was −17 dBm, and the RF input power range with a PCE greater than 20% was 21 dB. The proposed design achieved the highest peak PCE and the widest RF input power range compared with previously reported CMOS multi-band rectifiers.