_nullThe optical characteristics and varied applications of lanthanide-doped NaYF₄ upconversion nanocrystals have received considerable interest in recent years, such as in ratiometric thermometry. This review thoroughly examines the various synthesis processes utilized in producing these nanocrystals and their application in temperature sensing. Synthesis of NaYF₄ upconversion nanocrystals is a complex procedure that requires careful management of dopant concentrations, crystal phase, size, and shape. The distinctive luminescent characteristics of lanthanide ions, which facilitate the transformation of photons with low energy into emissions with higher energy, render NaYF₄ nanocrystals very suitable for ratiometric thermometry applications. We explore the fundamental concepts underlying upconversion luminescence in developing ratio metric temperature sensors. In this discourse, we examine the selection of lanthanide dopants, the mechanics underlying their energy transmission, and the development of customized sensor architectures. This review covers the recent progress and utilization of NaYF₄ upconversion nanocrystals in ratiometric thermometry, including diverse areas such as biological temperature detection, environmental surveillance, and material research. We evaluate the obstacles and potential advancements in this domain, specifically emphasizing approaches to improving temperature sensors' precision, responsiveness, and applicability based on upconversion.

Magnetic coupling resonant wireless power transfer (WPT) technology is widely used in a lot of power equipment because of high efficiency and safety. Magnetic field is a key factor to study the energy transmission mechanism, transmission characteristics of WPT system. At present, the research on the WPT system spatial magnetic field mainly focuses on the theoretical research and finite element simulation, with relatively little experimental research. This paper aims to establish an experimental platform for the WPT system, propose and design a magnetic field measurement system suitable for a WPT system, and conduct experimental research on the WPT system magnetic field with the measurement system. The near field region of the magnetic field is divided, and the experimental magnetic field distribution law is obtained using dimensionless and surface fitting methods. Finally, different models are obtained by surface fitting to characterize the distribution law of the experimental magnetic field. The results indicate that the dimensionless magnetic field intensity follows different forms of exponential distribution in different regions. The models are in good agreement with the actual distribution of the magnetic field, which can effectively reflect the changes in actual magnetic field intensity.

At present, 5G technology is gradually applied in coal mine applications. Under this circumstance, a microstrip patch antenna based on a multi-branch structure is firstly designed which can operate at the allocated 5G NR (2.51-2.68 GHz, 3.40-3.60 GHz and 4.80-4.90 GHz) for coal mine. Nevertheless, this antenna exhibits a large size, even at the lowest operating frequency (0.41λ×0.41λ at 2.51 GHz). To reduce the size of the antenna, the three branches are separately bent into C, S, and L shapes from left to right, and a size of 0.33λ×0.33λ at 2.51 GHz is realized, i.e., 35% size reduction is achieved. To further achieve a compact size, a new structure is designed. In particular, two inverted J-shaped branches and a rectangular branch acting as radiating portion are respectively arranged and optimized to cover the above three frequency bands where the rectangular branch is located between the two inverted J-shaped branches. To enhance the impedance matching characteristic of the antenna, a T-shaped structure is loaded on the other side of the substrate. The resultant size of this antenna is 0.20λ×0.16λ at 2.51 GHz, which is around 81% and 71% smaller than the first and second designed antennas. The measured results of the antennas are in good agreement with the simulated ones. Therefore, the third antenna is a good candidate for coal mine applications due to its relatively small size, low profile and easy integration with equipment.

Characterization of radio frequency electromagnetic field exposure levels is considered crucial for green and sustainable wireless-empowered campuses. To investigate the university campus electromagnetic characteristics, we conducted concurrent environment-oriented and human-centric measurement campaigns with broadband and frequency selective methodologies, respectively. The broadband results are derived after processing samples of 6-minute averages of measured electric and magnetic field values, taken at various university indoor and outdoor spots using broadband survey meter. Comparative analysis of broadband measurements shows that campus outdoor electric field levels in the sub 3 GHz band average around 1.67 V/m are at least twice higher than the ones recorded in indoor environments such as dormitories, labs, and classrooms. Students' exposure pattern in the 88 MHz-6 GHz range is derived after post-processing of more than 340 thousand electric field samples which were taken every 5 seconds at various campus environments using narrowband frequency selective measurement equipment. The comparison of cumulative distribution functions per wireless technology and environment shows that Wi-Fi is the main contributor to students' personal exposure levels in indoor environments and exceeds the 2G-5G mobile communication emitted electric fields in campus outdoor environments. The presented results can be used for exposure-aware heterogeneous network planning and optimization in university campuses or comparable environments.

In this letter, a quad-band high-isolated MIMO microstrip antenna is designed for coal mine communications, which can operate at DCS1800, UMTS, WiMAX, WiFi, and 5G NR simultaneously. Firstly, the qual-band property is realized by designing a quaddent structure. In particular, three L-shaped branches (separately operating at 2.6 GHz, 3.5 GHz, and 4.8 GHz) are successively loaded on a monopole antenna (operating at 1.9 GHz). In the sequel, by symmetrically placing two quaddent structures with spacing of 0.19λ, a MIMO antenna is designed. At this time, the isolation level of the MIMO antenna can be as high as around 8 dB. To improve the performance of the MIMO antenna, an inverted cross-shaped branch is loaded on and two rectangular slots are etched off the ground successively between the two elements. In this way, an isolation level of over 20 dB can be achieved across the whole operating frequency bands. To verify the performance of the designed antenna, a prototype is fabricated and tested, and good agreement between the simulated and measured results indicates that the proposed antenna can completely cover DCS1800, UMTS, WiMAX, WiFi, and 5G NR (1.67~2.28 GHz, 2.39~2.79 GHz, 3.13~3.74 GHz and 4.69~5.34 GHz) for mining.

A comprehensive review of multiband MIMO antennas designed for wireless applications in the 5th and 6th generation (5G and 6G) networks is presented. The demand for higher data rates and improved spectral efficiency in advanced wireless networks continues growing, and multiband MIMO antenna systems have emerged as a promising solution. This review aims to provide an in-depth analysis of the existing literature on multiband MIMO antennas for 5G and 6G wireless applications. The paper's main objectives are: (1) to emphasize the requisite of MIMO antenna for the sub-6 GHz of 5G/6G wireless communication, (2) to explore and evaluate the various design approaches to target 5G/6G frequencies, (3) To demonstrate various techniques to generate multiband, (4) To highlight the challenges and their potential solutions to design multiband MIMO for 5G/6G. (5) To investigate the methods to attain circular polarization (CP) and pattern diversity for better system performance. The review critically analyzes the latest advancements, challenges, and future research directions for multiband MIMO antennas in the context of 5G and 6G wireless networks. This comprehensive review serves as a valuable resource for researchers, engineers, and practitioners seeking a deeper understanding of multiband MIMO antennas and their potential to support the demands of the ever-evolving wireless communication technology.

A novel frequency beam-scanning circularly-polarized leaky-wave antenna with the axial ratio (AR) of less than 3 dB in all the half-power beamwidth ranges based on an H-shaped slow-wave transmission line is proposed for X-band applications. The proposed circularly-polarized leaky-wave antenna is composed of a novel slow-wave transmission line and two rows of elliptical patch structures, leading to wide AR bandwidth, backward-to-forward beam scanning, and stable gain. To verify the proposed antenna, one prototype with a center frequency of 10 GHz is designed and fabricated. Measured results indicate that the main beam scans from -25° to +28° within the operating frequency variation from 8.7 to 11.5 GHz. The 3-dB AR bandwidth and maximum gain are 27.7% and 10.28 dBic, respectively.

This paper presents a wideband dual slant polarized cross dipole antenna used to serve 2G/3G/4G/5G frequency bands. The proposed antenna model consists of two linearly polarized bent cross-dipole antennas, a cross-shaped director, and a metal reflector with walls in an open box manner. Bent dipole arms are etched on PCB to make the element compact. These cross dipoles are fed by hook-shaped wideband baluns. A cross director was placed on top of the cross dipole structure to achieve wideband impedance matching. The linearly polarized dipoles are placed orthogonally to achieve ±45° slant polarization. Two orthogonal polarizations were realized by exciting two input ports separately. A prototype has been fabricated, and measurements are carried out to validate the antenna performance. The measured results show that the antenna is well matched over the wide bandwidth, and the impedance bandwidth is ranging from 617 MHz to 990 MHz for VSWR<2, which is about 48%. The measured isolation between two orthogonal ports of the antenna was observed to be better than 33 dB. The radiation characteristics of the proposed model were stable, and the realized gain is in the range of 8.1±0.5 dBi. The values of the cross-polarization discrimination (XPD) are better than 20 dB at the boresight and 8 dB within ±60° directions. The proposed antenna model has advantages like wide impedance bandwidth, wide pattern bandwidth, stable radiation performance, simple structure, and a small overall size of 350 mm × 350 mm × 100 mm.

The dispersion equation for a rectangular tape helix with four rectangular dielectric support rods has been deduced using precise boundary conditions employing field restricting functions. The dispersion equation is a much simplified conjoint expression obtained for axial and transverse directions derived by solving an infinite set of linear homogeneous simultaneous equations, represented as an infinite order matrix whose determinant is zero. Dispersion characteristics plotted from the simplified dispersion equation consist of the dominant and additional higher-order modes similar to an open rectangular slow wave structure (SWS), but with the existence of β⁰a(k⁰a) roots everywhere without the limitations of the forbidden region boundary. The phase velocity curves obtained for the corresponding mode of the dispersion characteristics exhibit comparable behavior to the free-space rectangular helix SWS, especially in the third ``allowed'' region, which offers a wider beam-wave interaction region with phase speed equivalent to the speed of light at higher operating frequencies. The numerically computed dispersion curves and their corresponding phase velocities were plotted. Similar dimensional variations of the structure with discrete support rods were simulated using three-dimensional simulation software. The dispersion characteristics obtained from the simplified dispersion equation along with the dimensional variation of the dielectric-loaded rectangular tape helix SWS determine the capability and limitations of such minuscule traveling wave tubes(TWTs) as planar TWTs suitable for fabrication using micro-machining techniques.

A distinctive low-profile 2x2 MIMO antenna system for Wi-Fi 7 applications is presented in this paper that is compact, easily manufactured and with excellent performance. Because of its compact size and good RF performance, the design can be placed in hidden locations for various applications such as the automotive field in the front side mirrors or front dashboard, and consumer products in laptops and internet wireless routers. The proposed design can cover the entire tri-bands of Wi-Fi 7 (2400-2495 MHz, 5150-5895 MHz, 5945-7125 MHz) using a loaded low-profile Planar Inverted-F Antenna (PIFA) with distinct dimensions and slots across its geometry. The element design and the MIMO system is simulated and a properly made prototype was fabricated to present the results in terms of reflection coefficients, current distribution, combined radiation patterns, passive isolation, ports efficiencies, and Envelope Correlation Coefficient (ECC). The design shows relatively good RF properties across the entire three bands, hence making it an attractive solution to be used for Wi-Fi 7 technology to satisfy the needs of larger omnidirectional coverage area, wider channel bandwidth, and better transmission rates with low interference.

An ultra-wideband (UWB) MIMO antenna based on dual mode transmission line feeding for wireless communication is proposed in this article. The general method of realizing a UWB MIMO antenna is using different shapes of monopoles acting as a MIMO antenna element, while the ultra-wideband character of the proposed MIMO antenna is mainly obtained by the use of a dual-mode transmission line in the coplanar waveguide (CPW) feeding line, which offers a novel method. The proposed MIMO antenna element is a rose-shaped monopole fed by a CPW feeding line. Compared to the traditional monopole, a rose-shaped monopole can introduce several extra resonant frequencies, and the impedance bandwidth can be improved. Besides, a dual-mode transmission line (DMTL) is introduced by adding specific stubs to the CPW feeding line. Arranging the stubs at the half wavelengths of the desired frequencies, mode transformation can be accomplished, and additional resonant modes can be generated. As a result, the impedance bandwidth can be further broadened. Results show that the fractional impedance bandwidth of the proposed UWB antenna element is 165.5% (2.59 GHz to 26.61 GHz). Then, the UWB antenna is applied to design a 4-element MIMO antenna. By loading four u-typed decoupling structures at the center of the MIMO antenna, the port-to-port isolation of the MIMO antenna can be increased to 20 dB within a wide bandwidth, especially 25.3 dB at the higher band (14-25 GHz). The proposed UWB MIMO antenna is manufactured and tested. Experimental results show that the impedance bandwidth covers 2.40 GHz to 25 GHz (165%). The diversity gain (DG) of the antenna in the operating band is about 10; the envelope correlation coefficient (ECC) is less than 0.002; and the radiation efficiency ranges from 85% to 95% in the whole working band. The design is a preferable candidate for MIMO systems.

A compact branch-line coupler is proposed with capacitance improved capacitor (CIC) using low-temperature co-fired ceramic (LTCC) packaged technology. The proposed CIC is constructed for higher capacitance without any size increment by further separated horizontal finger pads on VIC. The area of the coupler is only 10.3 × 9.4 × 1 mm³, which is equivalent to 0.0041 × 0.0035 × 0.0004λ_g³. The application frequency band covers maritime and aircraft navigation in the very high frequency (VHF)-band. The measured in-band S₁₁, S₂₁, S₃₁ and S₄₁ are better than -15, -4.1, -2.2 and -18 dB from 47 to 67 MHz, respectively. And the measured phase difference between the coupled and through ports is within 90±0.2°, which presents an excellent linear characteristic.

This communication presents the design of a circular monopole ultra-wideband (UWB) reconfigurable antenna with wide notched-band of 1 GHz which ranges from 5 to 6 GHz in UWB. The design involves a circular monopole antenna with embedded three thin slots (two vertical and one horizontal) and one rectangular slot at the top edge. The three p-i-n diodes are inserted in between vertical slots to control the flow of surface current in ON/OFF states. As a result, in all diodes' ON and OFF states, the designed antenna shows switching of its resonance in whole UWB to wide notched band UWB applications. The CST-microwave studio software is used to simulate the structure in time domain. The full modeling of reported reconfigurable antenna that includes reactive effects of the diode is achieved by ADS circuit simulator.

To suppress the torsional vibration caused by the omission of couplings and dampers during flexible power transmission in the permanent magnet (PM) synchronous drive system of pure electric vehicles (EVs), this paper presents a non-singular fast terminal sliding mode control (NFTSMC) torsional vibration suppression strategy based on a sliding mode disturbance observer (SMDO). First, a PM synchronous drive system is simplified as a two-inertia model, and a mathematical model is established. Then, an NFTSMC controller of the load-side speed feedback is designed to suppress torsional vibration. Meanwhile, an SMDO is designed to estimate the load disturbance, and the estimated value is fed back to the controller to perform feedforward compensation. The robustness of the system is improved, and the effect of the load disturbance on the system is reduced. The results of the simulations and experiments show that the presented NFTSMC based on SMDO strategy has a strong torsional vibration suppression effect comparing to PI control and conventional sliding mode control.

This paper aims to design a compact frequency selective surface (FSS) for electromagnetic shielding in the 1.8 GHz band of GSM, ensuring that the stopband width covers the target frequency range in both simulations and actual measurements. The primary focus of this paper is to design a compact FSS with good miniaturization for real-world applications. The proposed FSS structure is a single-layer double-sided structure. The regression models reflecting the mapping relationship between the resonant frequency and the structural parameters are established to guide the design. An equivalent circuit model (ECM) is presented to clearly explain the working mechanism of the FSS. The unit size is only 0.038λ₀, where λ₀ is the wavelength of the resonant frequency in free space. In addition, the proposed FSS provides stable performance under oblique angles of incidence for both TE and TM polarizations. An FSS prototype has been manufactured for verification.

The array covers the L-band and S-band range frequencies used for multifunctional applications and operate between 1.61 GHz and 2.492 GHz. The quad frequency antenna resonates at four frequencies 1.176 GHz, 1.575 GHz, 1.6 GHz, and 2.492 GHz, which cover the L-band and S-band frequencies. The configurations of both antennas are layered patches. Performance measurements of the two antenna arrays have been compared, including side lobe level, return loss, and gain. Both the antennas are fabricated using affordable, easily accessible FR4 Epoxy. By implementing thinning for both array antennas, gain values are observed, and good performances are obtained.

Adaptive beamforming for multiple-input multiple-output (MIMO) radar systems suffers from performance deterioration under the scenarios with multiple random mismatches. This paper explores the theory of tensor algebra and exploits the inherent multidimensional structure of data matrix received by MIMO radar systems. For dealing with the beamforming problem induced by multiple random mismatches including steering vector error, mutual coupling, sensor position error, and coherent local scattering, we develop a robust method based on a third-order tensor in conjunction with a gradient-based optimization process. The proposed method captures the multidimensional structure information embedded in the data matrix received by a MIMO radar and produces appropriate estimates for transmit and receive signal direction vectors required for beamforming. Using a third-order tensor helps to alleviate the effect of the multiple random mismatches in the tensor data domain. The gradient-based optimization process further enhances the capabilities of the third-order tensor in estimating transmit and receive signal direction vectors for adaptive beamforming of a MIMO radar. The main computational complexity of the proposed method is dominated by a trilinear alternating least squares algorithm and the well-known gradient-based algorithm. The proposed method provides better performance than the existing robust methods. Simulation results are presented to confirm the effectiveness of the proposed method.

An elliptical monopole planar antenna for ultra-wideband (UWB) with penta-band-notched characteristics is presented. The frequency band rejection at 3.7 GHz to 4.2 GHz for C-band satellite communication and 5.15 GHz to 5.35 GHz for lower Wireless local area network (WLAN) is achieved by etching two elliptical split ring resonators (ESRRs) in the radiating patch. Dual notches at INSAT (4.5 GHz-4.7 GHz) and upper WLAN band (5.725 GHz-5.825 GHz) are created by special type of metamaterial, i.e., a two via double slot type EBG structure. Then, ITU band (7.95 GHz-8.55 GHz) is suppressed by adding a step impedance resonator (SIR) near the feed line. The proposed antenna is designed over a low cost FR4 material substrate, has a miniaturized size of 0.317λ × 0.317λ × 0.007λ, and possesses the impedance bandwidth from 2.5 GHz to 11 GHz. The band notch behaviour of antenna at specific frequencies is explained by mathematical model and justified with numerically simulated surface current distribution and impedance plot. Constant gain with the peak value of 3 dB is measured for UWB except notch bands. Also, this antenna has application in S(1.97-2.69 GHz), LTE(450 MHz-3.8 GHz), C(3.4-7.025 GHz), X(7.25-8.44 GHz), Ku(10.7-14.5 GHz) bands. The proposed antenna structure is a promising candidate for wireless technology.

Electromagnetic wave scattering (EMWS) is one of the complexities in electromagnetism. Traditionally, three numerical methods are used to solve this problem which are finite element method, finite difference method, and method of moments. Recently, artificial neural networks (ANNs) have gained popularity as tools to solve different problems in a wide variety of disciplines, including electromagnetism. This paper shows that the second ordinary differential equation that represents EMWS from one-dimensional, two-dimensional, and three-dimensional inhomogeneous mediums and deals with complex numbers can be solved using ANN. This is done by reducing the error between the trail solution at the output of the ANN and the second ordinary differential equation that represents the scattered field. The results from solving classical examples using the suggested approach are accurate.

A single-layer reflectarray antenna working at C- and X-bands is designed in this paper. The proposed reflectarray element is mainly composed of three square rings. Four phase delay lines are attached to the outer ring to obtain the phase shift at C-band, and the inner two square rings are utilized to extend the phase range at X-band. The phase shift of the element reaches up to 375° and 560° at 5.9 GHz and 10.4 GHz, respectively. The cross-polarization level of the reflectarray is effectively suppressed by using a mirror symmetric element arrangement. To experimentally validate the proposed design, a center-fed dual-band prototype reflectarray with the size of 180 mm×180 mm is designed, fabricated, and tested. The measured peak gains are 16.5 dBi at 6.2 GHz and 17.1 dBi at 10.3 GHz, respectively. Besides, the measured 1-dB gain bandwidth is 9.15% (5.83-6.37 GHz) at the lower band and 3.27% (10.12-10.46 GHz) at the upper band, respectively. 16Serup, Daniel Edelgaard and Pedersen, Gert Frolund and Zhang, Shuai2340-2345SerupDaniel EdelgaardGert Frolund Pedersen, Shuai ZhangIEEE Transactions on Antennas and Propagation7023402345

Mar.2022journal10.1109/TAP.2021.31111713 Moreover, the cross polarizations at both bands are under -21 dB.