Vol. 109

A compact triple-band antenna of size 20×13×1.6 mm³ for WLAN (2.4/5 GHz) and WiMAX (3.5 GHz) applications and a metamaterial slab for Specific Absorption Rate (SAR) reduction are proposed in this paper. The antenna comprises a rectangular patch with two conjoint square split rings, attached along its top edge, to excite two resonances in the 2.5 GHz and 5.5 GHz range. The antenna is also backed with a slotted ground plane structure to achieve miniaturization. The radiator is subsequently slotted to yield the third tone around 3.5 GHz. Several parameters are tuned independently to achieve the desired bands of resonance around (2.2-2.6) GHz, (3.40-3.60) GHz, and (5.0-6.9) GHz with impedance bandwidths of 17%, 5.5%, and 46%, respectively. To validate the simulated results, the designed antenna is fabricated and measured experimentally. Later, a metamaterial slab composed of a 5×3 array of pentagonal split-rings printed on a 20×13×1.6 mm³ FR-4 substrate is placed above the antenna at a suitable distance to increase the gain as well as to reduce the SAR. Inclusion of this slab improved the maximum radiation efficiency and gain of the proposed antenna from 65% and 2.7 dB to 80% and 3 dB. A cubical tissue model is designed and used for simulation. SAR reduction of 84.5% is inferred with the metamaterial slab. This paper has taken a cubical tissue model for SAR calculation, which can be further enhanced by taking a human phantom model in future.

This paper introduces a low profile wideband Planar Inverted-F antenna (PIFA) for vehicular applications in the 5G systems (below 6 GHz) and Vehicle-to-Everything (V2X) communications. The antenna covers a wide range of bandwidth which operates from 617 MHz to 6 GHz while having an acceptable filtering on the GNSS bands. This design's physical dimensions and electrical performance make it suitable for low profile wireless applications in the automotive field. Measurement data on Ground plane (GND) and on vehicle are presented from a properly cut metal sheet prototype along with simulated results of the model design. Simulation and measurement results are discussed in terms of VSWR, surface current distribution, radiation patterns, antenna efficiency, and linear average gain (LAG).

Electrical impedance tomography (EIT) is a technique for reconstructing the conductivity distribution by injecting currents at the boundary of a subject and measuring the resulting changes in voltage. Many algorithms have been proposed for two-dimensional EIT reconstruction. However, since the human thorax has the characteristic of three-dimensions, EIT is a truly three-dimensional imaging problem. In this paper, we propose a three-dimensional imaging method using tensors for EIT. A tensor EIT model is established by EIT data and the Tucker decomposition is used to obtain the tensor basis. The tensor basis can form a new way to reconstruct image in three-dimensional space. Experiment results revealed that the data structural information of image can be fully used by the tensor method. A comparison of the peak signal to noise ratio (PSNR) shows that the newly proposed method performs better than other methods, i.e. the Dynamic Group Sparse TV algorithm and Tikhonov algorithm. The newly proposed method is closer to the ground truth, thus it can more accurately reflect the state of a lung than two-dimensional EIT. Finally, the EIT experiment is carried out to evaluate the proposed method. The experimental results show that the accuracy of reconstruction based on the new method is efficiently improved.

In this article, a compact super wideband (SWB) monopole antenna with a wide-frequency is designed and analyzed for future handheld gadgets. The designed antenna is made by etching four slots on a round cornered rectangular patch which are connected through a 50-Ω triangular tapered microstrip transmission feedline (TTMTF) for broadband impedance matching. A triangular slot is etched on the semicircular partial ground plane, which helps to shift the lower frequency edge of 1.07 GHz to 1 GHz. The experimental results show that the proposed antenna operates over a wide frequency range of 1-30 GHz with a reflection coefficient of less than -10 dB. The antenna acquires a compact dimension of 25 x 16 x 0.787 mm³. Further, an equivalent circuit method is used to analyze the proposed structure, and its outcome is compared with the simulated and experimental results. The peak gain of the designed antenna is about 5.5 dBi. The proposed antenna has low cross-polarization even at higher frequencies. Finally, the time domain analysis is also carried out to see the distortion between transmitting and receiving modes. The designed antenna can be used for various wireless applications such as NB-IoT, GPS, Wi-BRO, ISM band, IRNSS, WiMAX, X-band, Ku-band, and K-band.

This article discusses the design analysis of a wideband rectenna (Antenna + Rectifier). It empowers low power devices, battery-less power sensors, and many Internet of Things (IoT) devices. The main focus of this work is divided into two parts. First, to develop the power to operate the wideband frequency of operation without system complexity. To obtain rectifier bandwidth sufficiently, L-section impedance matching with dual Schottky diode HSMS270B is proposed. Second, to improve the rectenna efficiency and output DC power. Wideband rectenna harvests the maximum RF power of 30.590 dBm, 1145.51 mW, 10.703 Volts at 3.2 GHz. The harvested power is easily available to power up the low powered sensor such as gas sensor (500-800 mW), pressure sensor (10-15 mW), and temperature sensor (0.5-5 mW). The peak conversion efficiency of the rectenna is 88.58% at 0 dBm, 34.70% at 10 dBm, and 53.52% at 20 dBm under the load resistance of 100 KΩ. The proposed work shows a 20-25% improvement in conversion efficiency with this approach. For efficient RF energy harvesting applications, the proposed rectenna is capable of covering a wideband application from 1.975 to 4.744 GHz with a single radiation patch. This shows that the novel approach of the considered work and the proposed rectenna has the specialty to capture more energy from a wide area at once.

In general, the problem of the excitation (radiation, scattering) of electromagnetic fields by a system of finite-dimensional material objects in arbitrary electrodynamic volumes is formulated. On the basis of the impedance concept, the problem is reduced to solving two-dimensional integral equations for electric surface currents on material objects. A physically correct transition from the obtained integral equations to a system of one-dimensional equations for currents on electrically thin impedance vibrators (monopoles) with electrophysical and geometric parameters that can be irregular along their length is made. As an example, a system of two monopoles with a variable surface impedance located in a rectangular waveguide is considered. The problem was solved by the generalized method of induced electromotive forces (EMF). A distinctive feature of this method is that the current distribution functions found by the asymptotic averaging method are used to solve integral equations for currents. The numerical and experimental results concerning electrodynamic characteristics of the structure under consideration are presented.

The present paper develops an application of the bandpass (BP) negative group delay (NGD) circuit for the design of an independent frequency phase shifter (PS). The design principle of the innovative PS is constituted by an inductor-capacitor-inductor (LCL) T-shape passive cell in cascade with RLC-network series-based BP NGD circuits. The S-matrix analytical model of the LCL-NGD PS is established in function of the circuit elements. Then, the design equations of the PS elements in the function of the expected PS value and center frequency are formulated. The NGD PS topology is validated with a comparison between the calculated and simulated results of phase, transmission coefficient, and reflection coefficients. As expected, a very good correlation between the analytical model and the simulation is confirmed by the obtained results. It is found that the LCL-NGD PS presents an outstandingly flat phase shift of -120°±5° with 1.2 GHz center frequency. The LCL-NGD PS operates with about 18% relative bandwidth. The PS reflection coefficient presents a magnitude flatness around -3±1.5 dB. Moreover, the reflection coefficient is kept better than -15 dB. The sensitivity of the LCL-NGD PS performances over the NGD circuit element ±5% relative variation is studied. It is found how the PS value and center frequencychange with the R, L, and C components of the NGD circuit.

This paper proposes a new integration of compact ultra-wideband (UWB) slotted monopole antenna with a diplexer and rectifier for simultaneous energy harvesting and data communication applications. The antenna is composed of four symmetrical circularly slotted patches, a feed line, and a ground plane. A slotline open loop resonator based diplexer is implemented to separate the required signal from the antenna without extra matching circuit. A microwave rectifier based on the voltage doubler topology is designed for RF energy harvesting. The prototypes of the proposed antenna, diplexer, and rectifier are fabricated, measured, and compared with the simulation results. The measurement results show that the fractional impedance bandwidth of proposed UWB antenna reaches 149.7% (2.1GHz-14.6 GHz); the diplexer minimum insertion losses (|S₂₁|, |S₃₁|) are 1.37 dB and 1.42 dB at passband frequencies; the output isolation (|S₂₃|) is better than 30 dB from 1 GHz to 5 GHz; and the peak RF-DC conversion efficiency of the rectifier is 32.8% at an input power of -5 dBm. The overall performance of the antenna with a diplexer and rectifier is also studied, and it is found that the proposed new configuration is suitable for simultaneous microwave energy harvesting and data communication applications.

Convex lenses can be used in adjuvant with microwave sources to produce appropriate focus spots for breast cancer hyperthermia therapy. A preclinical system was assessed using a horn antenna together with a convex lens. The horn antenna was built to accommodate the lens size so as to minimize wave spillover. Here, a modified hyperthermia system was tested on a hemisphere phantom of scattered fibro glandular breast tissue with cancer stages I & II. The focus spots were at different locations and depths (up to 2.7 cm) under the skin layer. Transmission and reflection coefficients at the air-breast phantom interface were calculated to determine the best operating frequency (2.45 GHz) for efficient power absorption. Based on these computations, an external dielectric matched layer was added onto the skin of the breast phantom to decrease reflection that would occur between water and skin. This arrangement increased wave transmission inside the breast without increasing applicator input feed. The system could heat regions of tumor at various locations independently using only one applicator. The whole system was fabricated, and measurements were taken to validate the simulated and analytical results.

Knowing the state-of-health (SOH) of equipment, device or component is very essential for the secure and dependable operation of a system. Electrolytic capacitors are undoubtedly one of the essential components of power supply modules used in aerial and underwater vehicles, and every equipment requires a conversion of voltage from one level to another. This has encouraged research into the components of the power supply used in such systems of which electrolytic capacitor is of interest in this study. In this paper, we explore a new approach to implementing prognostics and health management (PHM) for electrolytic capacitors and propose a method of estimating the SOH leading to the prediction of the remaining useful life (RUL). This is accomplished by using a bidirectional long short-term memory (BLSTM) network to capture the degradation trends. We demonstrate the power and leverage that this method brings to bear in encoding time-domain dependencies in accurately estimating the SOH bereft of state models as employed in traditional methods. We validate the proposed approach using capacitor data recorded at different electrical over-stress accelerated aging conditions. The proposed method surpasses other existing methods in RUL prediction as indicated by the error and relative accuracy.

In order to shorten design optimization cycle and reduce the influence of low-order harmonic for multi-phase induction motor, two kinds of five-phase motors - using either a star or pentacle-star hybrid winding - are proposed based on the Y160L-4 three-phase induction motor, which keep the structure size of the stator and rotor and rated power constant, redesign the winding, and adjust the match parameters of the stator and rotor slots. Based on the Fourier series expansion method, the time-space harmonic magnetomotive force (MMF) analytic function of pentacle-star winding was given based on star winding MMF. According to the analysis for the MMF table of three kinds of induction motors, pentacle-star winding with 19th-order harmonic has a better performance than star-winding with 9th-order harmonic and three-phase delta winding with 5th-order harmonic. Further analysis suggests that the harmonic torque generated by the harmonic MMF can be used to improve the electromagnetic torque, and the effective torque characteristics of the three forms of induction motors are given. Two kinds of five-phase motors with different winding configurations can be realized based on the three-phase motor, and some simulated and experimental resluts show that the method is feasible, which provids significant value in engineering applications.

A novel wideband beam reconfigurable magneto-electric dipole patch antenna is presented in this paper. The proposed antenna consists of two H-shaped patches, two folded patches, an E-shaped feeding structure, a side-slotted ground, and a large reflective ground. Two H-shaped patches are horizontally placed on both sides of the feed structure, and two folded patches are assembled vertically to the upper ground, which are designed as the magneto-electric dipole structure. Two symmetrically sided slots are etched on the upper ground to reduce the profile, and an E-shaped strip is employed in the feeding structure to broaden the bandwidth. To suppress the backward radiation, a lower ground with large size is designed as a reflector. Four binary switches are symmetrically integrated on the stubs of H-shaped patches. By switching them ON or OFF simultaneously, the current distribution is changed to achieve beam reconfigurability. Finally, a set of antenna prototype with four configurations is fabricated and measured. The measured results show that maximum impedance bandwidth achieves up to 77.8% at 2.7 GHz from 2.0 GHz to 4.1 GHz. At 2.7 GHz, the measured peak gains are 8.4 dBi, 9.3 dBi, 8.1 dBi, and 8.7 dBi, where the beams point to -21˚, 0˚, 21˚, and 34˚, respectively in E-plane.

Theoretical investigation of optical properties of a metallic sphere coated with uniform layer of anisotropic dielectric material is conducted by studying its polarizability, scattering cross section, absorption and extinction cross section. The dispersive characteristics of metal (tungsten/silver/gold) are mathematically modeled through well known Lorentz-Drude model. A detailed analysis of the behaviors of polarizability, scattering cross-section, absorption and extinction cross section is carried out for different specific values of the radius and components of the tensor permittivity. The impact of variation of different parameters on location and magnitude of the surface plasmon resonance is highlighted.

A low-profile dual-band composite structure antenna is proposed for fifth generation mobile communication system (5G), which is named as Antenna on Antenna (AOA). Loaded with an artificial magnetic conductor (AMC) reflector, the proposed AOA element consists of a pair of dual-polarized lower band (LB) dipole antennas working in the 0.7-1.03 GHz band and four upper band (UB) patch antenna arrays working in the 24.25-27 GHz band, which covers LTE and 5G millimeter wave band. In order to reduce the size of base station antenna, the millimeter wave patch antenna arrays are parasitic on the LB dipoles. While the radiator of the LB antenna is utilized as the ground of the millimeter wave patch antenna array, LB and UB antennas share the same dielectric substrate. The profile height of the antenna is reduced by AMC reflector effectively. Meanwhile, the three-element AOA array loaded with AMC reflector is designed to validate the overall performance of base station antenna. The operation bands of the proposed AOA are 0.7-1.03 GHz (S_nn<-14 dB) and 24.25-27 GHz (S_nn<-10 dB) for the LTE and 5G millimeter bands respectively. Antenna prototype was fabricated and measured to verify the design solution. The measured results which are consistent with simulated results show that the AOA has good impedance matching, port isolation, and stable radiation pattern.

A planner geometry triple-band circularly polarized (CP) antenna is proposed for wireless applications. The antenna consists of rectangular strips on the upper surface along with rectangular slots on the ground plane. The 3dB axial-ratio of the antenna is achieved through a reformed ground plane. Through the aid of these features, a small, compact wideband circularly polarized antenna is fabricated with an area of 25×25×1.02 mm³. The -10 dB impedance bandwidth of the proposed antenna is 8.2% (2.4-2.58 GHz), 33% (3.2-3.9 GHz), and 41.1% (5.2-7.8 GHz). While the 3-dB axial ratio bandwidth achieved by the proposed antenna is 89.7% (2.17-5.8 GHz). The designed antenna is suitable for wireless applications such as WiMAX, WLAN, ISM, Bluetooth, and Wi-Fi.

A novel conformal dielectric resonator antenna (DRA) array based on aperture-coupled series-feeding approach is presented for wireless communication. The antenna is composed of eight curved width-gradated DRA elements with a simple feeding structure. The proposed design presents a tapered current amplitude distribution by using DRA element width gradation method, and low side-lobe level (SLL) characteristic can be obtained. Besides, an extra matching line is inserted into the single feeding line to realize better impedance characteristic. To validate the performance of the proposed design, the conformal array is fabricated and measured in an anechoic chamber. The measured impedance bandwidth (|S₁₁|<-10 dB) of the fabricated prototype is from 5.65 GHz to 5.9 GHz. At 5.8 GHz, the antenna offers a measured peak gain of 14.75 dBi and SLL of -19.8 dB. The polarization discriminations of the array on E- and H-planes are greater than 20 dB. The measured results of the fabricated prototype demonstrate that the proposed design has the potential to be applied to wireless communication system with curved surface.

Characterization of some biological materials relies on absorption imaging. In this paper, a highly translucent flat two-layer structure as part of an imaging system called spectrometer is proposed that has a very high numerical aperture (NA) and high quality factor (QF). The structure can be used to identify micro-biological materials with previously known absorption rate, under single-wavelength electromagnetic absorbance imaging. The proposed two-layer structure is composed of a double-near-zero (DNZ) slab coupled to a high-index dielectric slab with a specific thickness. In DNZ materials, both the permittivity and permeability are close to zero. The DNZ slab operates as a flat lens, and the very high-index dielectric slab functions as a high QF monochromator that at the same time increases NA of the lens without affecting translucidity of the two-layer structure. At the end, a transformation optics (TO) based nonlinear lens is introduced that can be replaced as the DNZ layer. The focus of the nonlinear lens can be tuned by tuning its material parameters.

In this paper, a four-port compact active duplexer based on a complimentary split ring resonator (CSRR) and interdigital loaded microstrip coupled lines (CSRR-IL MCL) is presented. Interdigital capacitor is used on the top layer of the proposed structure and CSRR transmission lines are used on the bottom layer of the coupled lines in order to increase the coupling of the proposed circuit and create triple band resonances, respectively. The proposed active duplexer has one input port and three output ports operating in three distinct operation frequencies which are 1.4 GHz, 1.8 GHz, and 3.2 GHz. The active duplexer is designed to target LTE applications which are prevalent among the new technologies and devices. The input signal is split in terms of frequency into the three designed frequencies and is amplified by 13 dB gain of the amplifiers placed at the output ports. The fractional bandwidths of the proposed structure at 1.4 GHz, 1.8 GHz, and 3.2 GHz are 5.2%, 2.8%, and 9.4%, respectively. It is worth mentioning that the size of the proposed active duplexer is 0.29λ₀×0.38λ₀. The design guide of the proposed structure is presented, and it will be shown that the simulation as well as the measurement results of the proposed active duplexer have an acceptable agreement with each other. It should be noted that the VSWR of the proposed structure is less than 1.5 which means that the active duplexer has low return loss, and it is the plus point of it.

In order to solve the problem that the unbalance vibration caused by rotor mass eccentricity of the six-pole radial hybrid magnetic bearing (HMB) seriously affects stability and security of the system, a feed-forward compensation control strategy for rotor unbalance vibration based on fuzzy least-mean-square (LMS) algorithm is proposed. Firstly, the structure, operation principle and mathematical model of the six-pole radial HMB are introduced, and the cause of rotor vibration is analyzed and the dynamic equation of rotor deduced. Secondly, an LMS self-adapting filter is improved by using a fuzzy inference system, and the step size of the LMS algorithm is combined with the fuzzy control theory. By using the Takagi-Sugeno (TS) fuzzy inference machine system to adjust the step size of the algorithm, the filter output can approach the unbalance vibration signal smoothly and quickly, and realize the vibration compensation of the rotor. Finally, the simulations and experiments are carried out to verify that the proposed method can not only effectively suppress the unbalance vibration of the six-pole radial HMB rotor in real time but also have good compensation accuracy. The results show that the vibration compensation effect of fuzzy LMS algorithm is better than that of fixed step size filtering algorithm.

An artificially two-dimensional metamaterial (ATDM) substrate is proposed as an artificial metamaterial high-constitutive parameter substrate for miniaturizing of a circularly-polarized microstrip antenna. In a circularly-polarized antenna, the electric and magnetic field directions are changing, which requires a two-dimensional metamaterial unit cell. The presented ATDM substrate raises the permeability and permittivity of the underneath substrate for a circularly-polarized patch antenna, and it is constructed of periodically arranged split-ring resonator (SRR) circuits implemented in a low permittivity dielectric underneath substrate. The ATDM attains equal permittivity and permeability material (ε_r ≅ μ_r), which neutralizes the destructive effect of the increased permittivity on the bandwidth. In addition, the ATDM structure is implemented in printed circuit board technology. The area of the ATDM antenna at 2.45 GHz is approximately 75% smaller than a usual microstrip antenna. The proposed antenna bandwidth is enhanced compared to the antennas with high-permittivity substrates. The proposed ATDM substrate antenna is fabricated and measured, and comparisons show good agreements between simulated and measured results.