As the advanced technology in the Internet of Things (IoT), ultra-high frequency radio frequency identification (UHF RFID) tag has broad application prospects and significant research value. However, the transmission performance of UHF RFID on the metal surface and embedded in metal is severely impaired, bringing new challenges to its application for long-distance reading and writing. On this basis, an embedded metal UHF RFID tag design method is proposed in this paper. A planar inverted F antenna (PIFA) structure is optimized to enhance the anti-metal performance of the tag. The embedded feed design is adopted to achieve preferable impedance matching between antenna and chip. Besides, a series of electromagnetic simulations were investigated to optimize the performance of the tag, which can ultimately achieve the maximum gain of -9.7 dB in the metal groove, with the reduced volume of 19.8 mm×25.8 mm×2 mm by employing the meandering technology and the method of adding metal via holes. Finally, when the self-made tag is embedded in the metal groove, the experimental results demonstrate that the maximum reading distance can reach 1.26 m, indicating that the tag developed in this paper has significant practical value in the case of embedded metal.

A MIMO antenna for smartphones with radiation diversity is presented in this article. The proposed design consists of dual-fed Complementary Split Ring Resonator metamaterial antenna components design, which is located at the edges of an FR-4 substrate. The total dimension is 75 mm x 150 mm x 1.6 mm. 50-ohm dual microstrip feed lines placed orthogonal to each other are used to feed the SRR. Due to this orthogonality, radiation diversity is easily achieved. The proposed structure is operated in dual bands from 3.43 GHz to 3.62 GHz and 4.78 GHz to 5.04 GHz. In both, the band's good impedance bandwidth with a reasonable gain is achieved. The entire structure is simulated using CST EM software. All the simulated results are presented, which clearly show that the proposed structure is a good candidate for the future smartphone massive MIMO application.

A multiband circularly polarized microstrip patch antenna including a Minkowski fractal slot for wireless communication applications in the frequency bands 1.39 GHz, 2.45 GHz (WLAN band), 3.48 GHz (Mobile Wi-Max), 5.8 GHz (U-NII high-band) and 6.29 GHz has been proposed. The proposed antenna consists of two substrates mounted on top of the ground plane. The antenna has been fed with a 50 Ω microstripline which is etched on top of the lower substrate. The second iteration Minkowski fractal slot is etched on the truncated square patch which is on top of the upper substrate. The substrate has a size of 80 mm x 82 mm x 1.6 mm. The measured results show that the proposed antenna could excite for five resonant bands of 1.35 GHz, 2.45 GHz, 3.5 GHz, 5.8 GHz and 6.25 GHz and has reflection coefficients of -15 dB for 1.35 GHz, -16 dB for 2.45 GHz, -22 dB for 3.5 GHz, -23 dB for 5.8 GHz and -13 dB for 6.25 GHz as well as an axial ratio bandwidth of 3.42 GHz-3.47 GHz. The maximum gains of the antenna are 5.92 dBi for 1.39 GHz, 6.15 dBi for 2.45 GHz, 8.36 dBi for 3.48 GHz, 9.64 dBi for 5.8 GHz and 6.69 dBi for 6. 29 GHz. The simulations and optimizations have been carried through Computer Simulation Technology Microwave Studio (CST-MWS) software.

A compact pot-shaped Multiple Input Multiple Output (MIMO) Antenna with Triple notched band characteristics is presented for Ultra Wide Band (UWB) Applications. The comprehensive dimension of the presented antenna is 17×32 mm². The presented antenna has two identical pot-shaped radiators, 7-shaped stubs, T-shaped strips, M and C-shaped slots. Two novel 7-shaped stubs are connected to the antenna ground plane to obtain -22 dB enhanced isolation. The presented antenna works from 2.95 to 12.1 GHz with triple stopped WiMAX, WLAN, and X bands. A novel T-shaped strip is connected to the antenna ground plane to stop the WiMAX band (3.3-4.4) GHz. C and M-shaped slots are etched in the antenna radiators to stop WLAN (5.20-6.12) GHz and X (7.6-8.15) GHz bands respectively. The peak gain of the proposed antenna is from 1.5 to 5 dB with a radiation efficiency of 80-90%. The Envelope Correlation Coefficient (ECC) of the proposed antenna is less than 0.01 with a Diversity Gain greater than 9.99 except for the notched bands.

In this paper, a rectangular eight shaped Electromagnetic Band Gap (EBG) structure at 5.8 GHz Industrial, Scientific and Medical (ISM) band for wearable application is proposed with intent to improve impedance bandwidth of antenna. The unit cell of an EBG structure is formed using eight shape on outer ring with inner square patches. The simulation of the eight shape EBG unit cell is carried out using eigen mode solution of Ansys High Frequency Structure Simulator (HFSS). Simulated results are validated by experimental results. The application of proposed EBG for an inverse E-shape monopole antenna at 5.8 GHz is also demonstrated. Band stop property of EBG structure reduces surface waves, and therefore, the back lobe of a wearable antenna is reduced. The frequency detuning of antenna takes place due to high losses in human body. Suitably designed EBG structure reduces this undesirable effect and also improves front to back ratio. The proposed compact antenna with designed EBG has observed the impedance bandwidth of 5.60 GHz to 6.15 GHz which covers 5.8 GHz ISM band. Evaluation of antenna performance under bending condition and on-body condition is carried out. Effectiveness of EBG array structure for Specific Absorption Rate (SAR) reduction on three layer body model is demonstrated by simulations. Calculated values of SAR for tissue in 1 g and 10 g are both less than the limitations. In conclusion, it is appropriate to use the proposed antenna in wearable applications.

In this paper, the effect of flux modulation pole (FMP) number on the performance of a spoke array fault tolerant permanent magnet vernier rim driven machine (SA-FTPMV-RDM) is studied. Firstly, a hybrid stator is adopted in this machine in which armature teeth and isolation teeth are arranged alternatively, and the winding type is single-layer fractional slot concentrated winding (SL-FSCW). Spoke array magnet is employed in the rotor of the machine to achieve flux focusing effect. Then the parameter scanning method is used to optimize the FMP pitch ratio, isolation tooth width ratio, FMP height, and permanent magnet thickness under different numbers of FMPs. It is concluded that there is an optimal FMP number for 12 slots SA-FTPMV-RDM to maximize the torque. Finally, the electromagnetic performances of the optimized machines with different number of FMP are compared by using the finite element analysis (FEA). The results show that the machine with the optimal number of FMPs has the highest torque density and efficiency, strong fault tolerance, but relatively large torque ripple.

A dual-band wideband circularly polarized (CP) microstrip antenna is proposed for sub-6G application. The antenna consists of an upper L-shaped radiator and two circular strips on the ground. This produces the right-handed circular polarization (RHCP) in the Wi-Fi (2.4-2.48 GHz) and n77 (3.3-4.2 GHz) band with the help of two circular strips at the left and right corners on the lower ground. The antenna occupies a small radiating area of 45×45×1.0 mm³. The measured results show wide -10 dB reflection coefficient bandwidths of 46.4%（1.82-2.92 GHz）and 40.5% (3.15-4.75 GHz). The 3-dB axial ratio bandwidths of the antenna are 25.1% (1.88-2.42 GHz) and 40.6% (3.20-4.83 GHz). The measured peak gains are 4.8 and 7.5 dBi at the lower and higher bands, respectively. Therefore, the proposed antenna in this study is suitable for the dual-band wideband CP antenna as a reference.

Cross polarization (X-pol) effect is the undesired radiation of an antenna which wastes bandwidth (BW) and power of the communication system. Especially in the miniaturized microstrip antenna (MSA) the X-pol level is more. The observed X-pol level of the classical MSA at the direction of maximum radiation (φ =0˚) is -49.72 dB, whereas X-pol level of miniaturized H shaped MSA (MHMSA) is -39.96 dB. This paper presents miniaturized complementary split ring resonators loaded H shaped microstrip antenna (CSRR-MHMSA) and slots and CSRRs loaded MHMSA (S-CSRR-MHMSA) with reduced X-pol level. An array of CSRRs and slots are placed at the ground of the proposed antenna. Due to slots, the antenna is miniaturized and the polarizability of the electric field along the desired direction is increased by CSRRs. The CP-XP (Co-pol X-pol) isolation of CSRR-MHMSA and S-CSRR-MHMSA at φ =0˚ are measured. The measured E plane CP-XP isolation for CSRR-MHMSA and S-CSRR-MHMSA is 29.00 dB and 26.73 dB respectively. The measured CP-XP H plane isolation for CSRR-MHMSA and S-CSRR-MHMSA is 27.00 dB and 24.5 dB, respectively. While bandwidth (BW), gain G and radiation efficiency η are improved.

This work presents high isolation UWB-MIMO antenna with a bandwidth of up to 8.6 GHz based on a Minkowski fractal structure. The proposed antenna is fed by microstrip and be comprises two orthogonal monopole antennas, which delivers a decent isolation effect. Moreover, the ground is designed as two separated blocks with an I-shaped branch for improving the isolation degree between the units. The resultant isolation degree of this antenna is greater than 25 dB. Besides, the electromagnetic interference in the partial frequency band (such as Wi-Max band (3.45-4.45 GHz), WLAN band (5.1-5.8 GHz) and X-band (7.25-7.75 GHz)) is further prevented through etching a split-ring resonator (SRR) and C-slot on the unit. The antenna reflection coefficient of the UWB-MIMO antenna at the notch is 3.5 dB, which indicates that the antenna has a conspicuousness anti-interference effect. Through the above judicious design, the proposed UWB-MIMO antenna possesses a relative bandwidth of 113% (up to 8.6 GHz), and the envelope correlation coefficient between antenna units is less than 0.005, and the antenna radiation efficiency is up to 80%. The results indicate that the proposed MIMO antenna meets UWB applications.

In this paper, a novel design of a small printed Ultra-Wideband (UWB) Multi-Input Multi-Output (MIMO) antenna with a wide impedance bandwidth from 3.05 GHz to 11.65 GHz is introduced. The newly designed UWB MIMO antenna has an isolation enhancement of more than -15 dB between the two elements. This isolation is achieved by inserting a three-line stub on the ground plane between the two radiating elements. In addition, these parallel lines improve the impedance matching and the bandwidth of this structure. Dual band notched characteristics are achieved for the 5G band (3.6 GHz) and the Wi-fi 6E application (6 GHz), by loading the split ring resonator (SRR) on the ground plane at the back of antenna and etching a complementary split ring resonator (CSRR) in both the truncated square patch elements, respectively. The SRR and its complement are metamaterials structures, showing the behavior of an LC resonator circuit. The hybrid technique improves impedance matching, bandwidth, minimizes the mutual coupling in UWB frequency range, and delivers dual-notch characteristics. The simulation and measurement results of the proposed antenna with a good agreement are presented. The proposed structure exhibits high performances in terms of envelope correlation coefficient (ECC), diversity gain (DG), efficiency, total active reflection coefficient (TARC), and channel capacity loss (CCL) except the notched band.

A novel Artificial Neural Network (ANN) based two Substrate integrated waveguide (SIW) bandpass filters comprising Complementary Split Ring Resonators (CSRRs) are proposed in this paper. These CSRRs are modelled on the upper layer of the SIW cavity. A feed forward multilayer perceptron (FF-MLP) neural network is used to optimize the physical dimensions of the proposed filters. To validate the analytical results, physical prototypes of the proposed filters are fabricated, and a measurement is carried out with a Combinational Network Analyzer (Anritsu-MS2037C), and the obtained experimental results agree well with the estimated results using full wave analysis. Within the passband from 8.22 to 8.95 GHz, S₁₂ of the first filter shows better than -0.5 dB insertion loss (IL) and a fractional bandwidth of 8.5%, and within the passband from 8.21 to 8.73 GHz, the second filter shows IL about -0.8 dB and a fractional bandwidth of 6.1%.

In this paper, a novel high-sensitive mid-infrared photonic crystal-based slotted-waveguide coupled-cavity sensor to behave as a refractive index sensing device is proposed at mid-infrared wavelength of 3.9 µm. We determine the sensitivity of our sensor by detecting the shift in the resonance wavelength as a function of the refractive index variations in the region around the cavity. Comparison between mid-infrared photonic crystal-based slotted-waveguide coupled-cavity with mid-infrared photonic crystal-based slotted-waveguide shows a higher sensitivity to refractive index changes. The sensitivity can be improved from 938 nm/per refractive index unit (RIU) to 1161 nm/RIU within the range of n = 1 - 1.05 with an increment of 0.01 RIU in the wavelength range of 3.3651 µm to 4.1198 µm by creating a microcavity within the proposed structure, calculated quality factor (Q-factor) of 1.0821 x 10⁷ giving a sensor figure of merit (FOM) up to 2.917 x 10⁶, and a low detection limit of 3.9 × 10^-6 RIU. Furthermore, an overall sensitivity is calculated to be around S = 1343.2 nm/RIU for the case of higher refractive indices of analytes within the range of n = 1 - 1.2 with an increment of 0.05 RIU. The described work and the achieved results by performing 2D-finite-difference time-domain (2D-FDTD) simulations confirm the capability to realize a commercially viable miniaturized and highly sensitive mid-infrared photonic crystal based slotted-waveguide coupled cavity sensor.

In order to satisfy the requirements of terahertz time-domain spectrum system under specific circumstances, an off-axis focus reflective polarization converter in terahertz band is proposed. By combining the principle of phase compensation and phase gradient metasurface, a reflective array containing units is designed. The phase distribution along the metasurface is calculated through the principle of optical path reversibility. Geometric rotation and resonant frequency modulation constitute the phase variation of the unit, which can be superimposed on each other without interference. Compared with the conventional reflective polarization converter in terahertz band, the proposed one could deflect the normally incident terahertz wave while providing larger energy at the focus. The simulation results show that the proposed polarization converter has good performance in both polarization conversion and electromagnetic focus, which has significant practical application in numerous situations.

A simple and novel polarization-dependent phase gradient metasurface (PGMS) is proposed to synthesize a flat-top radiation pattern by dividing the metasurface (MTS) into multiple regions. Each sub-region generates a beam in a particular direction and multiple beams with different directions form a flat-top pattern in the far-field. A flat-top pattern in a single and 3D plane are realized by dividing the MTS into two and four regions, respectively. The proposed MTS consists of a multi-layered elliptical geometry encircled by a square loop. The elliptical shape of the unitcell offers polarization dependent behavior and produces dual-band characteristics for different incident wave polarizations at 10 and 12 GHz. Two microstrip patch antennas operating at 10 GHz and 12 GHz are placed at the focal point of the MTS. The simulated flat-top beamwidths in a single plane with a 1 dB ripple are 36˚ and 34˚ at 10 and 11.8 GHz respectively. Similarly, in 3D space, the beamwidths are 33˚ and 31˚ at 10 and 11.8 GHz, respectively. Both simulated and measured results are presented for 3D flat-top patterns.

The tremendous proliferation of mobile smartphone handsets and their usage worldwide makes human life comfortable, while the radiation hazards associated with them are alarming, especially among children. There is a necessity to minimize the Electro Magnetic Field (EMF) radiation levels. For the evaluation of Radio Frequency (RF) radiation from the mobile phone, one of the dosimetric parameters used is the Specific Absorption Rate (SAR). The RF radiation can be mitigated by incorporating a barrier or a shield of suitable material in the mobile handset design. In the proposed work, the analysis of SAR evaluation absorbed by the human head is determined with the performance of the shielding material called Shielding Effectiveness (SE) using Transmission Line Method (TLM) mathematically. The proposed shielding materials are composed of flexible and transparent thin films. Flexible and transparent thin shielding materials are advantageous over the other shielding materials in reduced size, less weight, non-corrosiveness, and easy processing. These materials include highly conductive Silver film, Silver Nanowire(AgNW) doped with PDDA (poly(diallyldimethyl-ammonium chloride)) polymer single shields, and a laminated shield comprising AgNW/PDDA with PEDOT:PSS (poly(3,4-ethylenedioxythiophene)poly-styrene sulfonate) polymer as lamination. The SARs of planar multi-layered human head models for different ages are estimated at various mobile frequencies with these shields. Under four-layered head models at 6 GHz, adult and child heads absorb 0.0006 W/Kg and 0.000024 W/Kg of RF radiation using pristine Silver film as a single shield. Using a single shield of Ag nanowire and PDDA, the adult and child heads absorb SARs of 0.00058 W/Kg and 0.000023 W/Kg, respectively. With the laminated shield of AgNW/PDDA and PEDOT:PSS as coating material, the same models are exposed to minimal amounts of 0.00054 W/Kg and 0.000012 W/Kg of SAR. At 6 GHz frequency, under seven-layered head models, an adult and a child's head absorb 0.000047 W/Kg and 0.000002 W/Kg of power, respectively, using Ag film. With AgNW/PDDA shield, the adult and child heads absorb a SAR of 0.000046 W/Kg and 0.0000019 W/Kg, respectively. The SARs of 0.000043 W/Kg and a negligible value of 0.0000018 W/Kg are absorbed by adult and child heads individually with the help of AgNW/PDDA/PEDOT:PSS laminated shield. The results exhibit a significant amount of reduction in Specific Absorption Rate with transparent shielding materials compared to SAR absorbed by the head without any shield. This maximum RF exposure rate reduction from mobile phones with the Ag Nanowire/PDDA/PEDOT:PSS laminated shield is achieved for a seven-layered child head model.

In this paper, a coupled-line based dual-band branch-line coupler with port-extensions is presented. The configuration of the coupler consists of a single coupled-lines section, two transmission lines, and an easy to analyze L-section impedance matching network at all four ports of the coupler. A detailed theoretical analysis is carried out to obtain the closed-form design equations to determine the design parameters of the coupling structure. It is observed that the proposed dual-band coupler can support wide band-ratio and arbitrary power division. To validate the proposed design concept, a prototype working at 0.9 GHz and 1.8 GHz is fabricated on a 60 mil Rogers 4003C substrate exhibiting excellent match between the simulated and measured results.

For the first time, an extended hemispherical integrated lens antenna on a low-cost substrate, FR408HR, is presented. The antenna is designed for industrial and automotive radar sensor applications operating in the 24 GHz ISM band. The proposed antenna has a gain of 15.2 dBi, low sidelobes, and half-power beamwidth of 16 degrees. To reduce the cost, we used low loss materials; Teflon for the lens and low-cost FR408HR as a patch antenna substrate. The size of the reported 24 GHz antenna is small. The diameter of the base of the lens is 38 mm (3 times of free space wavelength), and its height is 43.5 mm (with an extended height of 24.5 mm). Simulated results match well with measurements.

This paper investigates the original circuit theory on stopband (SB) negative group delay (NGD) passive topology. The basic specifications of SB-NGD function are defined by considering the voltage transfer function (VTF) of the passive circuit. An original design method and experimentation tests of SB-NGD circuit are developed. The innovative theoretical analysis is elaborated from both magnitude and GD analytical expression of the VTF model from the resonant LC-series network passive topology. The mathematical existence condition of SB-NGD aspect is analytically explored in function of R, L, and C component parameters. The formulations of the basic equations enabling the calculation of the lumped components of the SB-NGD passive circuit in function of the desired specifications as NGD cut-off frequencies, NGD value and attenuation are established. To confirm the effectiveness of the original SB-NGD circuit theory, a proof-of-concept (POC) of SB-NGD circuit board is designed, simulated, fabricated and experimented. As expected, despite the equivalent series resistor (ESR) effect of the inductor element, the theoretical modelling, simulation and measurement results are in good agreement. The SB-NGD behavior is confirmed with lower and upper cut-off frequencies, 0.7 kHz and 1.35 kHz, respectively. Furthermore, the corresponding NGD minimal values are -33 µs and -11 µs, respectively.

In this paper, a patch antenna (PA) and its self-complementary structure, slot antenna (SA) are proposed and designed for directly matching the impedance of a rectifierat 2.45 GHz resonance frequency. The structures of these antennas comprise three sections, meandered-line, spiral, and a double-folded geometries, which make their geometrical parameters to be varied in easy manner according to design equations. In order to enhance both the desired level of a complex reflection coefficient of antenna at given resonance frequencies and the specified lower and higher frequencies constituting the impedance frequency bands, a new fitness function is presented. This fitness function is applied in designing broadband or multiband antennas having approximately perfect conjugate impedance matching with the impedance of a rectifier suitably used for RF Energy Harvesting (RF EH) application. An optimization design methodology based on two programs operating in synchronous manner, the particle swarm optimization (PSO) implemented in MATLAB simulation tool anda CST MWS Electromagnetic (EM) solver, is applied to the designed PA as an illustrative example. The simulation results reveal that our design methodology is helpful to obtain an optimized PA (OPA) having good impedance matching at the desired resonance frequency along with appropriate band. Measured result of the fabricated prototype is in good agreement with the simulated ones. Moreover, acceptable features such as small size, omnidirectional radiation, and broadband operation satisfy the (2.4-2.5 GHz) WLAN band, which strongly makesthe OPA a good candidate for RF EH applications.

A novel algorithm is developed to realize the optimal synthesis of a sparse nonuniform-amplitude nonuniform-distribution planar array (SNANDPA) in microwave power transmission (MPT) systems. The dual compression factor particle swarm optimization (DCFPSO) algorithm and the subarray partition technique are adopted to realize the optimal synthesis of SNANDPA. The DCFPSO algorithm first optimizes beam collection efficiency (BCE) and side-lobe level outside the receiving region (CSL) of SNANDPA which ensure efficient energy transmission of an MPT system and suppress the influence of electromagnetic wave radiated by antenna array on the environment. The subarray partition technique then simplifies the feed network to minimize the system cost. SNANDPA parameters including transmitting aperture, receiving aperture, BCE, CSL, power pattern, element weight, and element distribution, can be obtained efficiently via the proposed method. Representative numerical cases under the different numbers of subarray and elements conditions are analyzed and compared with those of other two traditional MPT array models. Experimental results show that, when the transmitting aperture is 4.5λ×4.5λ and the square receiving region u₀=v₀=0.2, BCE and CSL are 94.96% and -17.09 dB, respectively, and only 64 elements and 8 amplifiers are required. We conclude that the proposed model can be used to create an efficient and low-cost MPT system.