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In this paper, the impact of the three-tier, multi-band heterogeneous networks (Het-Nets) performance, comprising of Terahertz (THz) tier, Sub-Terahertz (Sub-THz) tier, and millimeter wave (mmWave) tier has been modeled using stochastic geometry and analyzed under different network conditions. THz-enabled Het-Nets are expected to provide ultra-wide bandwidth and high data rates for next-generation applications. However, due to the inherent characteristics of the THz band such as high path loss, molecular absorption, and line-of-sight (LOS) blockage, THz communications can only offer limited coverage and may remain underutilized in an indoor environment. The coexistence of multi-band communication is considered the main requirement of future communication networks to improve coverage in indoor and outdoor environments. Moreover, the analytical expressions derived for the tier-wise user association probabilities have been validated using Monte-Carlo simulations and the results are found in agreement. The results obtained through this investigation provide a comprehensive insight into the dependency of user association on network parameters like antenna array size, transmit power, and cell range expansion (CRE) bias. Furthermore, this investigation establishes the significance of network and environmental conditions in particular the impact of CRE bias and antenna array sizes on the utilization of THz tier for serving the indoor user. [ABSTRACT FROM AUTHOR]

This article develops an energy-efficient 3D multi-band I/O interface to meet the demand for high computation and improve battery life for future mobile memory interfaces exploiting 3D integration. The proposed multi-band I/O (MBI) interface utilizes 3D integration, for two radio frequency band transceivers, and a CMOS driver with resistive feedback for the baseband (BB) transceiver. The proposed design implements a band-selective transformer to enable transmitting three bands, baseband and 2 RF bands (10&30 GHz), simultaneously. To enable simultaneous transmission of three bands, a band-selective transformer is utilized that reduces signal interference and minimizes component area and distortion for high-quality transmission and design compactness. A narrowband low-noise amplifier combined with the 30 GHz radio frequency band to improve the signal quality and minimize distortion. Furthermore, a low-dropout voltage regulator (LDO) is utilized to raise the frequency and lower the supply voltage for the I/O interface more especially, the connection between the memory and the CPU. The aggregate bandwidth and energy efficiency are greatly increased by this architecture, raising the aggregate data rate and enhancing energy efficiency. The 3D MBI system was implemented in the 130 nm CMOS process technology. It obtains a higher aggregate data rate of 14.4 Gb/s and an energy efficiency of 2.6 pJ/b compared with prior works. [ABSTRACT FROM AUTHOR]

In this paper, a tunable multiband metamaterial perfect absorber based on a metal-graphene multilayer structure is proposed, and the absorber consists of a metal layer, graphene, and a dielectric layer. We demonstrate that the absorber has 99.51% and 99.96% absorption at 2.78 THz and 6.78 THz, respectively. The surface plasmonic excitonic resonance of graphene at terahertz frequencies, as well as electromagnetic resonance, is used to produce multiple absorption peaks. We studied the physical mechanism of a perfect absorber using the impedance matching idea and electric field distribution. The absorbance of the absorption spectrum can be tuned by adjusting the Fermi energy level, relaxation time, medium thickness, or breadth of the cut graphene rectangle. Due to the geometrical symmetry of the structure, the proposed absorber is polarization-insensitive and has unique optical performance over a wide range of incidence angles. The proposed structure is simple to implement and is appropriate for sensing, imaging, and filtering. [ABSTRACT FROM AUTHOR]

The integration of multi-standard and multi-band wireless communication system will be the development trend of mine communication. The mine wireless repeater is an important part of the mine communication system. However, the antenna suitable for wireless repeaters is a vertical whip antenna, which greatly limits the size of the antenna in the horizontal direction. In this paper, an ultra-narrow size slotted sleeve antenna is proposed for the RF front end of wireless repeaters for underground mining. The antenna design process can be divided into three steps. First, a flag shaped slot is cut in the rectangular sleeve to increase the impedance bandwidth of the antenna. Second, the reverse branch is loaded on the top of the sleeve, which ingeniously increases the resonant path of the antenna. Moreover, a T-shaped slot is etched on the transmission line, which further improves the overall performance of the antenna. The electrical size of the antenna with this unique structural design is only 0.41λ × 0.048λ, which is much smaller than the lateral size of similar antennas. The simulation and measurement results of the proposed antenna are in good agreement, and the working bands include 0.79–0.82 GHz, 1.42–1.47 GHz, 2.39–2.59 GHz, 2.63–2.91 GHz, and 5.10–5.75 GHz. [ABSTRACT FROM AUTHOR]

In this paper, based on bionics, a flexible multi-band antenna is designed to mimic the structure of a spider's web, which supports various communication standards such as 4G, 5G, and GPS. The antenna lays out multiple loop branches in a limited space to achieve wideband operations from 1.31 GHz to 2 GHz (42.4%), from 3.4 GHz to 4 GHz (16.2%), and from 5.1 GHz to 5.78 GHz (12.5%). The antenna selects 40 × 50 × 0.1 mm³ polyimide as the dielectric substrate and trapezoidal coplanar waveguide feed. A simulation and experimental analyses demonstrate that the antenna exhibits consistent performance when subjected to different bending scenarios. The design scheme utilizing a flexible dielectric substrate streamlines the integration process, offering a promising avenue for deployment in smart wireless devices. The results of the consistent tests and simulations demonstrate that the device meets the requisite standards for wireless communication. [ABSTRACT FROM AUTHOR]

This paper presents a novel double-sided structure multi-band antenna that cleverly combines a Koch snowflake structure with a hexagonal fractal structure; the front of the antenna features a right semicircle minus a half-order Koch snowflake structure, while the back of the antenna showcases a left semicircle minus half of a hexagonal fractal snowflake structure, which are combined together to form a complete circle. The antenna can cover common communication bands such as fourth to fifth generation (5G) commercial bands, ISM, WLAN, and Bluetooth. The structure of the radiator portion of the antenna is designed by iteratively scaling a basic arc shape multiple times based on a certain scale factor, and after simulation and comparison, three iterations can achieve the best antenna performance, and the antenna uses a microstrip line transmission to broaden the antenna bandwidth. The antenna covers three effective frequency bands: 2.38–2.90 GHz (20.3%), 3.35–3.85 GHz (14.1%), and 5.06–5.80 GHz (13.5%). The antenna dielectric sheet is made of RF-35 from Taconic, which has the advantages of high strength, complete surface inertness, and a long service life, with a dielectric constant of 3.5 and actual dimensions of 50 mm × 54 mm × 0.76 mm. The antenna is fractal-iterated in small dimensions, and the approximation of the frequency bands is accomplished by comparing the ratios of each iteration with the current vector map. The antenna was simulated by HFSS software (Version 21). and measured in an electromagnetic anechoic chamber, and the test results were consistent with the simulation results. [ABSTRACT FROM AUTHOR]

This article proposes an eye-shape enclosed split ring resonator (ESE-SRR) based metamaterial absorber for multi-band microwave applications with high absorption levels. Four-fold rotational symmetric eye-shaped electrical resonators form the structure of the proposed metamaterial absorber (MMA) to achieve polarisation-insensitive characteristics. Eight near-unity absorption peaks between S, C, X, Ku, and K-band are achieved, where peak absorptions are attained at 3.349 GHz, 5.06 GHz, 6.829 GHz, 9.178 GHz, 14.54 GHz, 17.96 GHz, 18.89 GHz, and 20.4 GHz with absorption levels of 99.8%, 99.7%, 92.9%, 99.1%, 96.4%, 93.3%, 91.3%, and 99.35%, respectively. The electrical dimension of the unit cell is 0.112λmin × 0.112λmin × 0.018λmin, making it a subwavelength compact structure for oblique incident angle stable absorption behaviour. The absorption characteristics are also investigated with metamaterial properties, surface current, and electromagnetic field distributions. The designed MMA is validated by prototype fabrication and measurement, which shows good agreement with simulation results. Finally, the proposed MMA shows an electrically compact structure with eight near-unity absorption peaks and polarisation insensitivity, which makes it an attractive candidate for absorption, sensing, radar cross-section reduction, etc. [ABSTRACT FROM AUTHOR]

In this paper, a three-layer structure multi-band terahertz (THz) metamaterial perfect absorber (MPA) with the patterned layer formed by a frame graphene and a square copper, the silica dielectric layer and the copper metal bottom layer is designed and investigated. There are four absorption peaks when the Fermi energy level of graphene is 0.4 eV and relaxation time of graphene is 0.1 ps. The absorptivity at the frequencies of 2.77 THz, 5.41 THz, 7.48 THz, and 7.75 THz reached 99.99%, 99.09%, 97.13%, and 99.84%, respectively. The first absorption peak (peak I) of this absorber has a wide range of high absorption, and the second, third, and fourth absorption peaks (peaks II, III, and IV) have a high Q-factor. The absorber is polarization-insensitive, and the absorptivity of peaks I and II is still above 90% even when the incidence angle reaches 70°. Through exploring the absorption curve of different structures and electric field distribution and using impedance matching theory, the cause of absorption peak and the actual operation of the absorber parameter fault tolerance and tunability have been studied. It is found that the proposed absorber has many advantages such as low cost, simple structure, ease to manufacture and tunability. These explored generic properties of the proposed absorber emphasize its development potential in application areas, such as the design of sensors, wireless communication, controllable switch operation, modulators, etc. [ABSTRACT FROM AUTHOR]

This study introduces a reflective polarization converter based on metasurface, designed to offer both Linear-to-Linear polarization (LLP) and Linear-to-Circular polarization (LCP). The design comprises two periodically arranged split ring resonators with a slotted stripe that operate in the X, Ku, and K bands. The three discrete frequency bands demonstrate over 90% Polarization Conversion Rate for LLP for oblique incidence waves up to 45°. Additionally, the proposed converter achieves Left-Hand Circular Polarization (LHCP) in two sub-bands and Right-Hand Circular Polarization (RHCP) in two sub-bands for oblique incidence waves up to 45°. The metasurface design introduced in this study exhibits significant potential for satellite applications in 6G networks, owing to its versatile LLP and LCP conversion properties in the X, Ku, and K bands.

This paper presents a novel optimization-based procedure for designing a multi-band branch-line coupler with arbitrary output power division ratios and phase differences that are distinct at each of arbitrarily-allocated design frequencies. The procedure aims to find the optimal parameters of the design that result in the best possible performance while maintaining the deviation from the desired specifications within a predefined tolerance level. This procedure uses the analytical S-parameters of the proposed coupler which are derived using even-odd mode analysis. A tri-band (1.5/2.4/4.2 GHz) and a quad-band (1.5/2.4/3.5/4.2 GHz) microstrip prototypes are developed using the proposed procedure to have band-distinct power division ratios and phase differences. For validation, both prototypes are simulated, fabricated, and measured. At all operating frequencies, the measured deviations from the desired power division ratios and phase differences are within 1 dB and 10$^\circ$, respectively. Also, the measured matching and isolation are $< $ −11 dB at all design frequencies. The achieved measurement results and the agreement between measured results and theoretical expectations demonstrate the applicability of the proposed design procedure in practice. The proposed coupler is a candidate for use in analogue multi-band multi-beam antenna arrays, and the proposed design procedure can be applied in designing other multi-band microwave devices.

This article develops an energy-efficient 3D multi-band I/O interface to meet the demand for high computation and improve battery life for future mobile memory interfaces exploiting 3D integration. The proposed multi-band I/O (MBI) interface utilizes 3D integration, for two radio frequency band transceivers, and a CMOS driver with resistive feedback for the baseband (BB) transceiver. The proposed design implements a band-selective transformer to enable transmitting three bands, baseband and 2 RF bands (10&30 GHz), simultaneously. To enable simultaneous transmission of three bands, a band-selective transformer is utilized that reduces signal interference and minimizes component area and distortion for high-quality transmission and design compactness. A narrowband low-noise amplifier combined with the 30 GHz radio frequency band to improve the signal quality and minimize distortion. Furthermore, a low-dropout voltage regulator (LDO) is utilized to raise the frequency and lower the supply voltage for the I/O interface more especially, the connection between the memory and the CPU. The aggregate bandwidth and energy efficiency are greatly increased by this architecture, raising the aggregate data rate and enhancing energy efficiency. The 3D MBI system was implemented in the 130 nm CMOS process technology. It obtains a higher aggregate data rate of 14.4 Gb/s and an energy efficiency of 2.6 pJ/b compared with prior works.

Planar inverted F antenna (PIFA) is one of the emerging technologies suited for various mobile applications. Though it is capable of covering a wide range of applications in wireless services, these antennas are designed for multi-band frequencies. To enhance its applications in the areas of wireless communication, an antenna is integrated with IoT (Internet of Things) devices. The compact size and low profile of the PIFA antenna is a notable feature, enhancing its suitability for integration into small devices. In this research paper, we proposed a Multi-Band Planar Inverted F-Shaped Antenna (PIFA) specifically designed for general close-range Internet of Things (IoT) applications. The proposed designed antenna produces an average gain of 2.62 dBi with a return loss of – 20 dB and its operating bandwidths are 2.40 – 2.45 GHz, 3.9 – 4.3 GHz, and 5 – 5.2 GHz covering Zigbee, Bluetooth, and Wi-Fi frequency band applications. Its multi-band frequency response is obtained by inserting an L-shaped slots of various lengths on a radiating patch of PIFA antenna, allowing for precise tuning of operation frequencies. In the design of an antenna, the resonance frequencies for each band are controlled by manipulating the lengths of the corresponding slots. In addition to the desired frequency and gain, the paper evaluates key parameters including bandwidth, directivity, and radiation patterns with the help CST simulation environment and ensures accuracy in predicting the antenna's performance parameters. [ABSTRACT FROM AUTHOR]

In 5th generation mobile communication networks, the frequency band of the millimeter band of 30–100 GHz is supported to provide a transmission speed of 20 Gbps or higher. Furthermore, a huge transmission capacity, i.e., up to 1 Tbps, is one of the main requirements for the 6th generation mobile communication networks. In order to meet this requirement, the terahertz band is considered a new service band. Hence, we consider multi-band network environments, serving the sub-6Hz band, mmWave band, and additionally sub-terahertz band. Furthermore, we introduce the transmission point selection criteria with multiple connections for efficient multi-connectivity operation in a multi-band network environment, serving and receiving multiple connections from those bands at the same time. We also propose a point selection algorithm based on the selection criteria, e.g., achievable data rate. The proposed point selection algorithm attains lower computational complexity with a 2-approximation of the optimal solution. Our simulation results, applying the channel environment and beamforming in practical environments defined by 3GPP, show that selecting and serving multiple transmission points regardless of frequency band performs better than services through single-connectivity operation. [ABSTRACT FROM AUTHOR]

Robust edge states and corner states in photonic topological insulators provide effective ways to manipulate the propagation of electromagnetic waves. Bandgaps of the previously reported photonic topological insulators are independent of each other. In this paper, a higher‐order valley photonic insulator composed of arrays of dendritic structure is designed. The band structure shows an overlapped bandgap is observed, and the overlapped bandgap divides the band structure into three bandgaps. The evolution of the overlapped bandgap is investigated by changing the geometric parameters and increasing the fractal to break the C3v symmetry drastically. Besides, it is notable that the band structure of the proposed valley photonic insulator is flat bands. It is demonstrated that undistorted transmission can be observed as a plane electromagnetic wave transmits through the proposed valley photonic insulator. The interface consisting of two valley photonic structures with distinct topological nontrivial phases is constructed. Edge states and corner states with strong energy localization are obtained in multi‐band frequencies. Remarkably, two triangular structures with different Wannier center configurations both have corner states in the same bandgap, which does not obey the valley selectivity. The phenomenon is caused by the weak valley locking property due to the overlapped bandgap. The proposed valley photonic insulators are expected to benefit applications in optical devices such as topological lasers. [ABSTRACT FROM AUTHOR]

Wear debris image processing techniques are increasingly employed in health monitoring and fault diagnosis for mechanical equipment. However, during the acquisition and storage of wear debris images, substantial noise is often introduced, leading to significant errors in the subsequent feature extraction and health status assessment. Moreover, the denoising process frequently encounters algorithmic shortcomings, resulting in blurred boundary information, noise artifacts, and incomplete boundaries, greatly hindering further research on wear debris images. Thus, this paper proposes the wavelet-K-singular value decomposition-edge (W-KSVD-EDGE) algorithm, which initially performs two-dimensional discrete wavelet decomposition on noisy images through a multi-band decomposition module, dividing them into four sub-bands of high and low frequencies to enhance image denoising performance. Simultaneously, a second-order decomposition is performed, followed by reconstruction, which reduces high-frequency noise and lowers the complexity of subsequent image processing operations. Subsequently, the K-singular value decomposition (KSVD) algorithm is applied to denoise each sub-band of the initially reconstructed images. Applying the KSVD algorithm to images of different frequency bands, its complexity is mitigated, and the efficiency of image denoising is increased. Consequently, the boundaries of the reconstructed images are further optimized using an improved Canny algorithm for edge enhancement, incorporating edge detection coefficients, resulting in better boundary information restoration for wear debris images. Finally, by analyzing the wear debris information of oil samples collected by a ferrograph, the W-KSVD-EDGE algorithm is employed for denoising both ordinary and wear debris images. The results are evaluated using both subjective and objective methods. The effectiveness and versatility of the proposed algorithm are thereby demonstrated. [ABSTRACT FROM AUTHOR]

The fourth-generation (4 G) cellular network is currently the dominant mobile technology used worldwide. The analysis of the network behavior can help forecast the traffic and thus improve the network. The characterization of mobile user behavior can be useful in evaluating the emerging concepts. We collected traffic traces on a commercial multi-band 4 G cell to better understand and model the network and user behavior. We evaluate the network utilization, the number of connections, and the uplink and downlink cell achieved throughput. In addition, we analyze and identify statistical models that describe the connection inter-arrival time, connection duration, and connection size. The results show daily and weekly patterns that depend not only on the time of day but also on the frequency band. We find that the frequency band and time of day have a limited impact on user behavior. On the contrary, the connection inter-arrival time strongly depends on the frequency band. [ABSTRACT FROM AUTHOR]

This paper presents a partially-grounded dual-band compact patch antenna with high selectivity for 2.4 GHz and 6.4 GHz wireless communication systems. The design concept is to achieve the 2.4 GHz resonance by using a simple patch, then introducing a U-shaped slot at the patch to grant the 6.4 GHz resonance. In order to minimize the design geometry without effecting the antenna performance, a center square cut-out is inserted into the center of the patch with two other cut-outs etched out from the upper part of the patch. For the selectivity enhancement, the partial ground plane is presented and studied. The proposed antenna reveals good performance and both bands can be independently controlled by tuning and adjusting various parts of the antenna. The proposed antenna is designed on a Rogers RT5880 substrate with thickness of 1.57 mm and overall dimension of 30x30 mm2 using CST-MW package and the simulated results are verified experimentally with very good agreement between the two approaches. The impedance bandwidths are 0.4 GHz and 0.2 GHz at 2.4 GHz and 6.4 GHz, respectively. The gains of the proposed antenna are 1.2 dB and 1.21 dB, respectively with return loss of -37.70 dB and 36.90 dB, respectively. The proposed dual-band compact antenna exhibits omni-directional radiation patterns and achieves a better gain in comparison to monopole antennas. [ABSTRACT FROM AUTHOR]

The increasing need for swift, low-latency, and reliable wireless transmission in the age of 5G has led to rapid advancements in 5G technology. MIMO systems, originally implemented in 4G applications, remain an integral part of 5G networks. The sub-6-GHz frequency band holds promise for 5G applications, such as improved link and reduced transmission losses. This comprehensive review explores advancements in patch antenna (PA) structure for sub-6 GHz 5G smartphone utilization, addressing the challenges posed by space constraints in mobile devices and the need for efficient integration of antennas. The paper discusses the significance of MIMO antennas in modern cellular communication, particularly in the context of 5G technology, which utilizes sub-6 GHz. Reconfigurable antennas (RAs) and Microstrip Patch Antennas (MPAs) are introduced as solutions, highlighting their compact, cost-effective, and flexible nature. The review delves into critical factors such as geometry, substrate selection, and feed design in optimizing patch antenna performance. It also covers the importance of addressing both sub-6 GHz and mm-wave bands within a single antenna system. [ABSTRACT FROM AUTHOR]

This paper presents a novel design method for a tri‐band multiple in multiple out (MIMO) antenna. The antenna consists of four sets of identical antenna pairs arranged on the two side frames. Three resonant modes can be obtained using a microstrip coupling feed structure by employing different branches in antenna unit design. The working frequencies of the modes can be adjusted independently. Moreover, in each pair of antennas, two antenna units were closely arranged and a decoupling grounding branch was employed between the adjacent antennas to ensure good isolation. The tri‐band eight‐element MIMO antenna operates at 3.5, 4.9, and 5.6 GHz and the isolations were better than 14 dB. The proposed antenna had a low profile of 0.06λ0 ${\lambda }_{0}$ and good isolation so it has potential applications in 5G mobile terminals. [ABSTRACT FROM AUTHOR]

In this paper, an ultra-thin logo antenna (LGA) operating in multiple frequency bands for Internet of Vehicles (IoVs) applications was proposed. The designed antenna can cover five frequency bands, 0.86–1.01 GHz (16.0%) for LoRa communication, 1.3–1.36 GHz (4.6%) for GPS, 2.32–2.71 GHz (16.3%) for Bluetooth communication, 3.63–3.89 GHz (6.9%) for 5G communication, and 5.27–5.66 GHz (7.1%) for WLAN, as the simulation indicated. The initial antenna started with a modified coplanar waveguide (CPW)-fed circular disk monopole radiator. To create extra current paths and further excite other modes, the disk was hollowed out into the shape of the car logo of the Chinese smart EV brand XPENG composing four rhombic parasitic patches. Next, four triangular parasitic patches were inserted to improve the impedance matching of the band at 5.6 GHz. Finally, four metallic vias were loaded for adjusting resonant points and the return loss reduction. Designed on a flexible substrate, the antenna can easily bend to a certain degree in complex vehicular communication for IoV. The measured results under horizontal and vertical bending showed the LGA can operate in a bending state while maintaining good performance. The proposed LGA addresses the issue of applying one single multi-band antenna to allow vehicles to communicate over several channels, which relieves the need for a sophisticated antenna network. [ABSTRACT FROM AUTHOR]

Surface soil moisture (SSM) plays an important role in agricultural and environmental systems. With the continuous improvement in the availability of remote sensing data, satellite technology has experienced widespread development in the monitoring of large-scale SSM. Synthetic Aperture Radar (SAR) and optical remote sensing data have been extensively utilized due to their complementary advantages in this field. However, the limited information from single-band SARs or single optical remote sensing data has restricted the accuracy of SSM retrieval, posing challenges for precise SSM monitoring. In contrast, multi-source and multi-band remote sensing data contain richer and more comprehensive surface information. Therefore, a method of combining multi-band SAR data and employing machine learning models for SSM inversion was proposed. C-band Sentinel-1 SAR data, X-band TerraSAR data, and Sentinel-2 optical data were used in this study. Six commonly used feature parameters were extracted from these data. Three machine learning methods suitable for small-sample training, including Genetic Algorithms Back Propagation (GA-BP), support vector regression (SVR), and Random Forest (RF), were employed to construct the SSM inversion models. The differences in SSM retrieval accuracy were compared when two different bands of SAR data were combined with optical data separately and when three types of data were used together. The results show that the best inversion performance was achieved when all three types of remote sensing data were used simultaneously. Additionally, compared to the C-band SAR data, the X-band SAR data exhibited superior performance. Ultimately, the RF model achieved the best accuracy, with a determinable coefficient of 0.9186, a root mean square error of 0.0153 cm3/cm3, and a mean absolute error of 0.0122 cm3/cm3. The results indicate that utilizing multi-band remote sensing data for SSM inversion offers significant advantages, providing a new perspective for the precise monitoring of SSM. [ABSTRACT FROM AUTHOR]

In this paper, we propose an absorber with adjustable single-layer graphene multi-band perfect absorption, which has the advantages of simple structure, polarization insensitivity, tunability, multi-band absorption, and high sensitivity. The device can achieve four perfect absorption peaks at the same time, and the absorption rate of all absorption peaks is above 99%. The absorption effect of the absorber can be efficiently adjusted and controlled by adjusting the geometric parameters of the single-layer graphene array and the thickness of the dielectric layer. In addition, by changing the strength of the applied magnetic field, the Fermi level, and the relaxation rate of graphene, the absorption of the device can be dynamically adjusted, and high absorption can be maintained in the range of 0°–70° wide incidence angle. Finally, considering the potential sensing applications of the device, we measured maximum sensitivity (S) of 3.06 THz/RIU and a maximum figure of merit (FOM) of 54.6 when exposed to different ambient refractive indices, suggesting that the device can be used as a refractive index sensor. These results show that this study provides a new idea for the design of the tunable multi-band perfect metamaterial absorber based on graphene, which has great application value in many fields and provides a new reference for future research. [ABSTRACT FROM AUTHOR]

The analogue of an electromagnetically induced transparency (EIT) spectrum is achieved using a metasurface that consists of an array of cross and L-shaped resonators. The mechanism of the EIT-like phenomenon are analyzed, and the influence of geometrical parameters on the effect is discussed. We achieve a multi-band EIT-like through structure configuration. In particular, polarization-independent EIT is realized. A potential application in sensing is suggested and the sensitivity of 65 GHz RIU−1 is obtained. We also investigate the impact of analyte and substrate on the transmission spectrum. We find that when the analyte thickness is higher than 40 μ m, the EIT spectral shift is less affected by the analyte thickness. The thickness insensitive characteristics are beneficial for reducing errors caused by analyte dose, thereby improving the accuracy of sensing. By introducing a phase change material, vanadium dioxide, we obtain active control of the EIT effect. Our results provide valuable insights into the development of multi-band tunable compact devices based on metasurfaces. [ABSTRACT FROM AUTHOR]

The Baihetan reservoir region is characterized by complex geomorphology, significant altitude differences, and rugged terrain. Geological hazards in such areas are often characterized by high concealment, wide distribution, and difficulty in field investigation. Traditional identification techniques are unable to detect and monitor geological hazards on a large scale with high efficiency and accuracy. In recent decades, interferometric synthetic aperture radar (InSAR) techniques, such as small baseline subset InSAR (SBAS-InSAR), have been widely applied to landslide identification. However, due to factors such as vegetation and the degree of landslide deformation, single-band synthetic aperture radar (SAR) still has certain limitations in detecting landslides. In this study, SBAS-InSAR was conducted based on ALOS-2 and Sentinel-1 ascending-descending images covering the Baihetan reservoir region. Deformation identification results were utilized to conduct a statistical analysis of the SAR detection performance and landslide characteristics, and the effect of vegetation on the detection effectiveness of different SAR bands was discussed. The study revealed that when surface vegetation coverage reaches a high degree, the percentage of areas with coverage greater than 0.6 is greater than 95%, the SAR coherence is mainly affected by vegetation thickness; the comparison of the difference change in the average coherence of the C/L bands among the four vegetation types shows that the ratio of the average coherence of the L-bands to the C-bands increases by a factor of three with the increase in thickness and the transition from crops to shrubs and trees. The results showed that the L-band has better detectability than the C-band in alpine-canyon terrain with vegetation coverage and complex vegetation composition. However, considering the high temporal resolution and accessibility of Sentinel-1 SAR data, it is still the main data choice for wide-area identification of landslides in the reservoir area, while other satellite-borne SAR data with different wavelengths and resolutions, such as ALOS, can be used to assist in the identification and monitoring of landslide hazards with significant magnitude of deformations and dense vegetation coverage. Therefore, the combined utilization of multi-band SAR data has the potential to enhance the dependability of landslide identification and monitoring, resulting in more accurate detection results. [ABSTRACT FROM AUTHOR]

A photonic method for flexible multi-band dual-chirped microwave waveform generation is proposed using a recirculating frequency shifting loop (RFSL). The RFSL can be used as an optical frequency comb (OFC) generator with adjustable frequency spacing and line numbers. By heterodyning the OFC with a lightwave modulated by a baseband linearly chirped waveform in a balanced photodetector, a flexible multi-band dual-chirped microwave waveform can be generated. The frequency spacing and the number of the sub-bands can be easily adjusted by tuning the frequency shift and the bandwidth of the optical filter in the RFSL. The bandwidth and duration of each sub-band signal can also be tuned by adjusting the baseband linearly chirped waveform. A numerical simulation is conducted to verify the proposed generator. A flat four-band dual-chirped waveform with frequency spacing of 3 GHz and six-band dual-chirped waveform with frequency spacing of 4 GHz are generated successfully. Due to the flexible reconfigurability and high performance, the proposal may have great potential in multi-band radar systems. [ABSTRACT FROM AUTHOR]

The study presents an innovative approach to designing a Circular Microstrip Patch Antenna capable of covering a broad range of frequency bands. The physical measurements of the antenna are 34x22 x 1.57 mm³. Rogers RT5880 (Lossy) substrate has been chosen to build the antenna, which has a dielectric constant (εr) of 2.2. The antenna's radiating patch layer and the ground plane layer has been structured from copper, each with a thikness of 0.035 mm. The resonance at five distinct frequencies: 5.2 GHz, 6.628 GHz, 9.098 GHz, 12.036 GHz, and 13.076 GHz is the key element of this antenna. These frequencies cover a broad range of applications including WLAN, C-band, X-band, and Ku-band. Simulations has been applied using the CST Software version 2021 to validate the antenna performance. The adaptability of the antenna design, coupled with its successful validation, makes it suitable for a broad range of wireless applications across different frequency bands. This highlights their effect and applicability across a variety of technological fields. [ABSTRACT FROM AUTHOR]

In this paper, multi-band bandstop filters (BSFs) based on mixed electric and magnetic coupling resonators are proposed. These proposed structures include a multimode resonator based on symmetrical open-circuit branches, including upper- and lower-branch filter circuits. Through this design, the center frequencies of the stopbands can be flexibly and autonomously adjusted. In addition, the filters proposed in this paper have excellent characteristics, such as miniature dimensions and abrupt roll-off skirts. Finally, these tri-band to sext-band bandstop filters were fabricated and the measured results agreed well with the simulated ones. The proposed structures can be applied in the fields of communication, information, and coal automation. [ABSTRACT FROM AUTHOR]

This study examines a single-fed, self-isolated, dual-band, 8-element multiple-input multiple-output (MIMO) antenna system for fifth-generation (5G) and beyond-5G (B5G) handsets. The proposed antenna is designed by an innovative composition of two F-shaped slots backed by a slotted ground plane, enabling a dual-band operation in the sub-6 GHz (4.7 to 4.9 GHz, n79) and millimeter wave (mmWave) (28 to 29 GHz, n257) frequency bands. High isolation of >14.4 dB and >25 dB and a high diversity gain of >9.9 dB were achieved at the respective frequency bands without using additional decoupling techniques, exhibiting an efficiency of approximately 90% with high gains of 4.9 and 7.2 dBi at the n79 and n257 bands, respectively. The antenna demonstrates excellent MIMO performance regarding very low envelope correlation coefficient ( $\lt -7.3$ dB and −7 dB). In addition to the safety evaluations, the performance is verified in a realistic mobile device to ensure practical feasibility. The evaluations showed promising results, demonstrating that the proposed design is a suitable, compact, and highly effective MIMO solution for 5G and B5G handsets.

A novel wideband multiplexer is introduced as a communications equipment solution in order to provide simultaneous operation of satellite and terrestrial services in the dedicated $K$/$Ka$ frequency bands (passbands ranging from 19.5 GHz to 30.5 GHz). Advanced RF filtering techniques are applied in order to accommodate a compact multiplexer design while maintaining low insertion loss and high rejection demands up to 33 GHz. Due to the overall wide bandwidth and the demanding requirements for the assigned three operational bands, different filter types have been employed. Thus, the multiplexer considers the combination of filters with rectangular, evanescent combline, and conductor-loaded resonator types. The multiplexer relies on the direct branching approach, i.e., all filters are connected to a central (star-junction) waveguide branching region. This region exhibits a reduced waveguide size to suppress interference by higher order modes. For a verification of the approach, WR34 waveguide interfaces have been considered at all ports for prototype design, however, the design can be well adapted for integrated equipment solutions with associated direct interfaces. Accurate coincidence of analyzed and measured performance of the prototype demonstrates the validity of the special approach. Moreover, additional simulations are provided as an outline for terminals with specific industry demands.

We propose a novel design of hybrid multi-band wavelength/polarization/mode (de)multiplexer based on 800 nm thick Si$_{3}$N$_{4}$ platform. The 16 channels are enabled by asymmetric rib polarization beam splitters, subwavelength polarization rotators and asymmetric directional couplers, consisting of two operating frequency bands, dual polarization and four transmission modes (2$\times 2\times$4). A broad bandwidth range from 930 nm to 1600 nm is supported simultaneously on a same chip. This chip can achieve low insertion loss and crosstalk in the 100 nm range near the center wavelength (1550 nm and 980 nm). Our results demonstrate that all channels of the (de)multiplexer have an average insertion loss of less than −1.1 dB. In addition, the crosstalk in the same band is less than −20 dB, while less than −15 dB in different frequency bands. This hybrid (de)multiplexer chip has a great potential for application in multi-band large-capacity optical communication systems, especially in integrated multi-band (de)multiplexing systems.

This paper presents a linear-to-circular polarization converter (LCPC) used for multi-band functionality. The LCPC surface features symmetrically printed copper strips on a single-layer substrate and is surrounded by a square substrate integrated waveguide (SIW) cavity arranged periodically in two dimensions. The study successfully utilizes the LCPC surface to achieve a desirable axial ratio (AR) band width (BW) below 3 dB in multiple frequency ranges, specifically: 1) 4.51-4.80 GHz, 2) 6.51-6.80 GHz, 3) 9.01-9.20 GHz, 4) 10.90-12.40 GHz, and 5) 17.05-17.49 GHz. The LCPC induces a change in polarization as the wave propagates through it. In the first ( $f_{31}$ ) and fourth ( $f_{34}$ ) frequency bands, the initially linearly polarized (LP) wave transforms into a left-hand circularly polarized (LHCP) wave. Conversely, in the second ( $f_{32}$ ), third ( $f_{33}$ ), and fifth ( $f_{35}$ ) frequency bands, the wave converts into a right-hand circularly polarized (RHCP) wave. Measurement results indicate that the LCPC provides circularly polarized (CP) wave bandwidths of 12.72%, 4.8%, 2.4%, 11.39%, and 3.15% across frequency ranges of 3.9 - 4.43 GHz, 6.21- 6.52 GHz, 8.9-9.08 GHz, 10.51-11.78 GHz, and 16.85-17.39 GHz, respectively. This characteristic renders the LCPC suitable for utilization in the C (4-8 GHz), X (8-12 GHz), and Ku (12-18 GHz) frequency bands.

In this manuscript, replacing traditional antennas with biodegradable PLA substrates aims to reduce e-waste in today's technologically advanced age. This work achieves its objectives by designing the miniaturized (56 x 56 x 1.6) mm3 hexagonal patch antenna with partial ground (18.2 x 52) mm2 and incorporating complementary split ring resonators (CSRRs) in the HFSS (High-Frequency Structure Simulator). This innovative approach combines unconventional antenna design with metamaterial technology to enhance antenna performance, making it flexible, lightweight, and suitable for multi-band applications. An evaluation of PLA compared to other substrates revealed that PLA is more suitable for its eco-friendliness, and the simulation result is also satisfactory for bandwidth, return loss, VSWR, directivity, efficiency, and other parameters. Additionally, the integration of taffeta fabric as a conductive patch material provided elasticity and enhanced wearability. Using this unique method, the proposed antenna resonates at multiband frequencies of 2.6 GHz, 8.6 GHz, 10.5 GHz, 12.4 GHz, and 15.3 GHz, which gives return losses of -26.84 dB, -22.16 dB, -29.87 dB, -39.43 dB, and -26.35 dB, respectively. In addition to its biocompatibility and achievement of the SAR threshold, the antenna serves as a long-term solution for multi-band wireless applications. This further advances the realm of environmentally friendly wearable technology.

In 5th generation mobile communication networks, the frequency band of the millimeter band of 30–100 GHz is supported to provide a transmission speed of 20 Gbps or higher. Furthermore, a huge transmission capacity, i.e., up to 1 Tbps, is one of the main requirements for the 6th generation mobile communication networks. In order to meet this requirement, the terahertz band is considered a new service band. Hence, we consider multi-band network environments, serving the sub-6Hz band, mmWave band, and additionally sub-terahertz band. Furthermore, we introduce the transmission point selection criteria with multiple connections for efficient multi-connectivity operation in a multi-band network environment, serving and receiving multiple connections from those bands at the same time. We also propose a point selection algorithm based on the selection criteria, e.g., achievable data rate. The proposed point selection algorithm attains lower computational complexity with a 2-approximation of the optimal solution. Our simulation results, applying the channel environment and beamforming in practical environments defined by 3GPP, show that selecting and serving multiple transmission points regardless of frequency band performs better than services through single-connectivity operation.

This article reports the Modified Microstrip Feed Hybrid Rectangular Dielectric Resonator Antenna (RDRA). The proposed structure has a ground plane with a plus-shaped slot on an FR4 substrate with a height of 1.6 mm and dimensions of 38 mm x 35 mm. The proposed Dielectric resonator antenna is made of a material with 10 as its dielectric constant, and the dimensions of the DR are 19 x 20 x 18 mm3. The DR is connected to a modified microstrip feed with an octagonal ring through the plus-shaped slot in the ground. The proposed structure operates in frequencies from 2.60 GHz - 2.74 GHz, 3.12 GHz - 3.37 GHz, and 4.25 GHz - 4.37 GHz. The resonant frequency of the final proposed RDRA is 2.68 GHz, 3.26 GHz, and 4.31 GHz, which covers WLAN, WIMAX and Wireless Avionics Intra-Communications (WAIC) applications, respectively. The entire structure was simulated using the CST microwave studio. The simulated results agree with the measured results and both are presented. The compact size, stable radiation pattern and reasonable gain make this antenna suitable for the proposed applications.

In this study, the electronic band structure and the dynamics of the excited carriers in the formamidinium lead bromide (FAPbBr3) perovskite are investigated by combining the information obtained from steady‐state absorption, photoluminescence, femtosecond transient absorption spectroscopy, photoelectron spectroscopy, and density functional theory calculations. A detailed description of the electronic transitions in the UV–vis energy range has been provided, giving an estimation of the exciton binding energy (40 ± 5 meV), the transition energy from the first valence band (VB1) to the conduction band (CB1) (electronic bandgap at 2.37 ± 0.01 eV) and assigning the broad peak at ≈3.4 eV to the transition from the second innermost valence band (VB2) to CB1. The temporal dynamics of the excited carriers involved in these transitions are investigated using different excitation energies and carrier densities. Different trends are observed in the dynamics of the transient signals associated with the VB1→CB1 (PB1) and VB2→CB1 (PB2) transitions. As the carrier density increased, PB1 exhibited a slowing down of its rise time, while PB2 showed an acceleration attributed to the thermalization of the excited holes in VB2. These valuable findings have the potential to unlock new strategies aimed at maximizing the efficiencies and performance of perovskite‐based solar cell devices. [ABSTRACT FROM AUTHOR]

In this manuscript, an original graphene-based metamaterial perfect absorber (MPA) was suggested and investigated with substituting aluminum with graphene. The proposed structure consists of a gold substrate as a conductive layer, a silicon substrate as a middle insulated layer and the patterned graphene layer as a resonator. The suggested structure, with only one metamaterial layer, has a lot of advantages such as simple implementation, cost-effectiveness, simple design and frequency tunability. The results of the proposed absorber, demonstrate that the absorber can provide absorption close to 100% at the frequencies of 0.56, 0.79, 1.02 and 1.25 THz by 0.9 eV graphene chemical potential (μc). With increasing the thickness of the silicone insulating layer, the absorption peaks number can be increased up to XIII bands. Also, changing the Fermi level can cause an absorption frequency shift. Furthermore, this structure is polarization insensitive and it is tolerating incident angles up to 45°. The recommended absorber is an appropriate candidate for filtering, spectroscopy, imaging and sensing application. [ABSTRACT FROM AUTHOR]

Outphasing power amplifiers (OPAs) can be used in wireless information and power transfer systems due to their excellent conversion efficiency. With the rapid advancement of technology, there is a strong demand for OPAs to achieve wideband and multi-band operations to enhance frequency coverage. This paper provides a comprehensive review of the research progress on the development of broadband and multi-band board-level OPAs. Firstly, the paper introduces the fundamental components of an OPA. Then, the paper delves into a detailed analysis of the load modulation of OPAs. Subsequently, previous works on the circuit topology and design methods for broadband and multi-band OPAs are discussed and compared. The paper highlights various design strategies and their respective advantages and disadvantages. Finally, the paper explores some potential design methods for broadband and multi-band OPAs, discussing emerging technologies and highlighting potential research directions. [ABSTRACT FROM AUTHOR]

Wear debris image processing techniques are increasingly employed in health monitoring and fault diagnosis for mechanical equipment. However, during the acquisition and storage of wear debris images, substantial noise is often introduced, leading to significant errors in the subsequent feature extraction and health status assessment. Moreover, the denoising process frequently encounters algorithmic shortcomings, resulting in blurred boundary information, noise artifacts, and incomplete boundaries, greatly hindering further research on wear debris images. Thus, this paper proposes the wavelet-K-singular value decomposition-edge (W-KSVD-EDGE) algorithm, which initially performs two-dimensional discrete wavelet decomposition on noisy images through a multi-band decomposition module, dividing them into four sub-bands of high and low frequencies to enhance image denoising performance. Simultaneously, a second-order decomposition is performed, followed by reconstruction, which reduces high-frequency noise and lowers the complexity of subsequent image processing operations. Subsequently, the K-singular value decomposition (KSVD) algorithm is applied to denoise each sub-band of the initially reconstructed images. Applying the KSVD algorithm to images of different frequency bands, its complexity is mitigated, and the efficiency of image denoising is increased. Consequently, the boundaries of the reconstructed images are further optimized using an improved Canny algorithm for edge enhancement, incorporating edge detection coefficients, resulting in better boundary information restoration for wear debris images. Finally, by analyzing the wear debris information of oil samples collected by a ferrograph, the W-KSVD-EDGE algorithm is employed for denoising both ordinary and wear debris images. The results are evaluated using both subjective and objective methods. The effectiveness and versatility of the proposed algorithm are thereby demonstrated.

This article presents a ±45° dual‐band dual‐polarized filtering antenna. The filtering antenna element is a dual‐polarized patch antenna that loads a parasitic patch with two rectangle slots to achieve compact multi‐array. Multi‐array consists of three 1×2 subarrays arranged, which are designed for 1.8/2.1 GHz FDD band applications. Very close‐arranged antennas exhibit radiation pattern invariance as well as in‐band radiation property. Radiation patterns are conformal with a compact subarray distance of 45 mm (0.29λ0), which is 56% smaller than that of the array using traditional filtering elements. Moreover, the total width is only 180 mm for three subarray‐composed antenna arrays. The average gain is 8.7 dBi with a low profile of 0.069λ0. The proposed array exhibits the filtering property of the subarrays with a very simple structure. [ABSTRACT FROM AUTHOR]

Quasi‐bound state in the continuum (quasi‐BIC) has drawn increasing attention in terahertz biosensing and filtering owing to an extremely narrow linewidth and ultra‐high quality factor. However, it is usually polarization‐sensitive due to broken structure or incidence symmetry and mainly holds for polarization‐dependent single or dual bands, which sets a limitation on practical applications. Here, this article proposes and experimentally demonstrates terahertz multi‐band polarization‐independent quasi‐BICs in tetramer‐based metasurfaces by using the laser etching method. Employing a tetramer cluster with C4v symmetry as the structural unit, which consists of four L‐type copper particles on a flexible and optically‐transparent substrate, the metasurfaces can support dual‐band or tri‐band polarization‐independent quasi‐BICs after performing collective perturbation, specific displacement, or both to the constituent particles. Furthermore, the metasurfaces are integrated with microfluidic channels to explore their potential application in terahertz biosensing. Experimental results indicate that when the concentration of bovine serum albumin solutions is below 4 mg mL−1, both resonance modes of the dual‐band terahertz microfluidic biosensor exhibit a sensitivity of ≈12 GHz mg−1 mL each, and the detection limits reach 0.17 mg mL−1. This work provides a general and simple strategy to construct metasurfaces supporting multi‐band polarization‐independent quasi‐BICs, which have promising applications in biosensing, filtering, and lasing. [ABSTRACT FROM AUTHOR]