Magnetic resonant wireless power transfer (WPT) is an emerging technology that may create new applications for wireless power charging. However, the output voltage and efficiency fluctuations resulting from lateral misalignments are main obstructing factors for promoting this technology. In this paper, a structure of tower-type coils is proposed. The mathematical model of the proposed structure is built based on equivalent circuit method. The expressions of the output voltage and efficiency are then derived by solving the system equivalent equations. In addition, a method of optimizing the mutual inductance between the transmission coil and intermediate coil and the strong-coupling parameters between the intermediate coil and receiving coil is proposed. The mutual inductance between the transmission coil and intermediate coil can be kept nearly constant with lateral misalignments, and the optimum strong-coupling parameter between the intermediate coil and the receiving coil can be obtained by the proposed method. Therefore, the output voltage and efficiency can be kept nearly constant with different lateral misalignments. The WPT system based on tower-type coils via magnetic resonance coupling is designed. Simulated and experimental results validating the proposed method are given.

A novel CPW-fed planar printed monopole antenna with broadband circular polarization (CP) characteristic is presented. The proposed antenna consists of a copper coin-shaped patch (CCSP) and an asymmetrical ground plane. To achieve a broadband CP wave, a vertical stub is added to the CCSP to produce orthogonal surface currents for right-hand circular polarization (RHCP). The design of the CCSP greatly increases the impedance bandwidth (IBW) of 89.2% which can cover the whole CP bandwidth of 71% completely. The measured results show that the proposed antenna has not only a broad 3-dB AR bandwidth (ARBW) of 71% (3900 MHz, 3.1-7 GHz) with respect to the CP center frequency 5.8 GHz, but also a wide 10-dB return loss bandwidth of 89.2% (5040 MHz, 2.16-7.2 GHz) centered at 5.65 GHz.

In this work, a new design of small microstrip antenna with variable band-notched filtering characteristic for super ultra-wideband (UWB) applications including 5G/IoT networks is presented. In the proposed structure by creating steps with optimized appropriate sizes and angles in the lower edges of the quasi-square patch antenna and by a new technique of modifying the ground plane, more efficient radiation patterns and characteristic impedance are achieved. Moreover, the omnidirection allow cross-polarized H-plane radiation patterns are obtained infrequency band of 3-11 GHz. Also, its radiation patterns are improved between 11 and 14.5 GHz and have better performance especially with tuning capacitors between 14.5 and 20 GHz. In addition, its frequency bandwidth with VSWR<2 is from 3 GHz to 50 GHz which covers 5G networks and both ultra-wideband (UWB) and super wideband (SWB) communications. A rectangular slot on the patch is used to create an integrated band-notch filter in the structure to avoid interference with other wireless systems like wireless local area networks (WLANs), and this specification can be activated or deactivated by a PIN diode. In addition, the center frequency of the filter can be tuned by just a varactor diode or a variable capacitor and/or by changing the position of the capacitors in frequency range of about 3.5-6 GHz, which rejects interference of all WLANs and even lower and upper bands of them and nulls in the radiation patterns can be changed especially in upper bands as well. The final structure simulation results are in good agreement with measurement ones.

The aim of this work is to reduce the torque ripple of a low-speed/high-torque Doubly Salient Permanent Magnet (DSPM) generator for wind turbine applications. To do this, a combined design and control-based approaches are set up to improve the overall machine performance. The design-based approach helps to develop a form of small stator/rotor teeth combination, focusing on the shapes and dimensions of the teeth that will minimize torque ripple. On the other hand, in the second approach, a control technique is designed. It employs indirect torque control (Torque Sharing Function: TSF), including a PI-controller with gains adjusted continuously for regulating the reference current. The obtained results show that by combining these two approaches, the ripple rate of the electromagnetic torque for the studied DSPM is reduced to a minimum when the teeth shapes are trapezoidal in both the stator and rotor, and the command approach also allows an improvement in the total torque shape, such that the ripple rate decreases by about 96%.

A compact differential-fed ultra-wideband (UWB) antenna with single band-notched characteristicis proposed in this paper. The antenna consists of a ground plane etched with an octagonal groove and two symmetrical hexagonal radiating patches. Return loss and isolation of the antenna can be effectively reduced by loading a rectangular stub on the ground plane and etching a semi-circular groove on the radiation patch. In order to achieve a controllable single band-notched characteristic, two pairs of quarter-wavelength stubsare introduced into the grounding plane. The antenna has lower cross polarization and stable gains than conventional single feed antennas. The measured impedance bandwidth with S₁₁ ≤ -10 dB is 114% from 3 GHz to 11 GHz, and the notch characteristic is realized in the 7.2-8.4 GHz band.

A substrate-integrated-waveguide (SIW) cavity multiple-input-multiple-output (MIMO) antenna using hybrid boundaries and anti-symmetric U-shaped slots is proposed. Unlike conventional SIW cavities completely shorted by metallic vias, the proposed two cavities possess opened edges. Since shorted and opened cavity edges can be regarded as electrically and magnetically conducting boundaries, respectively, hybrid resonating boundaries are achieved. Excited by coaxial ports, antenna elements can radiate cavity energy through the opened edges. Moreover, antenna isolation can be significantly enhanced by introducing a pair of anti-symmetric U-shaped slots on the top and bottom planes. This design has been validated by experiments. With the overall size of 0.44λ₀ × 0.44λ₀ × 0.04λ₀, the fabricated MIMO antenna exhibits operating frequency of 3.51 GHz, high isolation of 20.18 dB, peak gain of 3.15 dBi, and low envelope correlation coefficient of 0.12, which has potential applications for wireless systems.

The electromagnetic scattering from oil-covered sea surface is investigated by two scale model with the help of Lombardini's oil-covered sea spectrum and the semi-empirical reflection model that takes the oil film into consideration. Firstly, a comparison of the clean and oil-covered sea spectra is made to show the influence of the oil film on the sea surface. Then, the backscattering coefficient from the clean sea computed by the two scale model is compared with the measured data in the reference to validate the accuracy of the two scale model used in this paper. Finally, backscattering features from the oil-covered sea surface are discussed in detail and compared with those from the clean sea. In addition, the influence of the thickness of oil film and fractional filling factor on the backscattering coefficient of oil-covered sea are also studied. The simulated results show that the oil film floating on the sea has remarkable influence on the backscattering coefficient of the sea, compared with those of the backscattering coefficient from the clean sea.

It is challenging to design a high-performance UHF RFID tag antenna on a liquid-filled bottle due to the high conductivity, high permittivity and the variety of liquids. A systematic way how to design a high-performance UHF RFID tag antenna on a liquid-filled bottle is presented. A simple design consisting of a folded dipole and a loop matching structure is first proposed for a tag antenna placed on a water bottle. A co-design approach is adopted to make the water and bottle surface become a part of the tag antenna to eliminate the significant influence of the environment. The measurement results at 915 MHz show that the reading range of the simple design can reach 8 m in the absence of the water bottle and reach 4.2 m when it is placed on a water bottle. The folded dipole on the water bottle is then optimized to improve the gain significantly, and a maximum gain of -5.54 dBi is achieved at 915 MHz. Furthermore, the impedance bandwidth for the tag antenna on the water bottle is greatly improved by increasing the number of loops in the impedance matching structure from one to three, and the -6 dB impedance bandwidth of over 100 MHz (simulation) or 84 MHz (experiment) is achieved. The reading range of 5.6 m is achieved when the tag antenna is placed on a water bottle at 915 MHz.

Modeling how electromagnetic waves scatter from a distribution of rough plates poses many applications. Certain systems may be easy to approximate with planar geometry, but use of numerical field solvers to determine the radiated fields could take a long time for nontrivial structures. We propose a new approach based on the Kirchhoff approximation. This method will consider the case of multiple rough, finite-sized rectangular plates. The solution was used for developing software to determine the scattering of waves off of a distribution of rough plates of arbitrary position and orientation between a transmitter and receiver. The method considers each plate individually, calculating the coherent and incoherent scattered fields. Provided that all plates and the transmitter and receiver are sufficiently spaced, we calculate the total fields by summing the result from each individual plate. For many practical situations, the distance from the plate to the receiver may not be much greater than the size of the plate. We will show that the common far-field approximation of the Green's function is not valid for these cases, and we will have to use a more accurate approximation of Green's function.

In this paper a frequency reconfigurable pixel antenna is implemented using PIN diodes. The overall dimension of the patch antenna is 26.9x24.5 mm, and it is fabricated on an FR4 substrate. The design is investigated by the simulation and measurement of S₁₁ parameters and radiation patterns. With different combinations of PIN diode biasing conditions, the antenna can be set to 2.5 GHz, 3.9 GHz, and 10 GHz. The antenna shows a consistent radiation pattern at all the reconfigured frequency bands. In the accessible frequency range, an average gain of 6 dB and low level of cross polarization are also recorded. A good agreement between the measured and simulated results validates the presented concept of frequency reconfiguration.

In this paper, a single-fed high-gain circularly polarized microstrip antenna is proposed. The circular polarization is obtained by two unequal-length arc-shaped radiation patches, which excites two orthogonal linearly polarized modes with a 90° phase difference. The antenna is excited by coaxial feed. The proposed circularly polarized antenna consists of two arc-shaped radiation patches and a ground plane, which has a simple structure and a higher gain than 10.0 dB. The antenna is fabricated and measured to verify the design. The measured results are in good agreements with the simulated ones. The measured results show that the impendenceb and width (IBW) for S₁₁<-10 dB is 16.7% (3.78-4.47 GHz), and the axial-ratio bandwidth (ARBW) for AR<3 dB is 3.6% (4.09-4.24 GHz). Further, the gain from 4.09 to 4.24 GHz is higher than 10.0 dBi. The antenna radiation pattern performs well over the whole band, and the peak gain can reach 10.67 dBi at 4.11 GHz. It is a good candidate for advanced wireless communication systems.

The scattering problem of time-harmonic electromagnetic plane waves by an impedance and a dielectric ellipsoid is considered. A low-frequency formulation of the direct scattering problem using the Rayleigh approximation is described. Considering far-field data, an inverse electromagnetic scattering problem is formulated and studied. A finite number of measurements of the leading-order term of the electric far-field pattern in the low-frequency approximation leads to specifying the semi-axes of the ellipsoid. The orientation of the ellipsoid is obtained by using the Euler angles. Corresponding results for the sphere, spheroid, needle and disc can be obtained considering them as geometrically degenerate forms of the ellipsoid for suitable values of its geometrical parameters.

In this paper, we present a broadband flexible RFID sensor tag antenna to detect the concentration of aqueous solutions. The proposed RFID tag antenna sensor with a T matching network is based on a printed dipole whose arms are loaded with circular disk patches. The structure is printed on a Kapton polyimide flexible substrate. The sensing mechanism of the RFID tag antenna is based on the change of sensitivity of the RFID tag antenna that occurs with the variation of aqueous solution concentration. The proposed sensor is designed using CST Microwave studio, and its various parameters are optimized in order to have a broadband impedance matching that covers the entire RFID band (860-960 MHz). The experimental setup is small, rapid, contactless, and inexpensive. Results are presented for NaCl and sugar aqueous solutions with concentrations ranging from 0% to 80%.

In order to reduce far-end crosstalk between two differential line pairs of microstrip, this paper proposes a method of reducing far end crosstalk by polarity inversion. In this way, the signal line is placed in the middle of PAD of one capacitor to achieve polarity reversal at the AC coupling capacitor of the differential line. The simulation results show that, in this way, the far end crosstalk can be reduced by 63.6%, and this method of far end crosstalk suppression has an effect on both pairs of differential lines.

A novel technique for designing a dual-band reconfigurable aperture coupled cylindrical dielectric resonator antenna is introduced here. The design is based on loading an aperture coupled cylindrical dielectric resonator antenna with a varactor diode located along the lines of the feed network. Loading the antenna with the varactor shifts the first and second resonant frequencies of the antenna. The resonant frequency can be continuously shifted from 4.75 GHz to 4.96 GHz in the lower band, and the resonant frequency of the higher band is shifted from 6.31 GHz to 6.40 GHz as the varactor diode bias voltage is increased from 1 V to 5 V. The proposed antenna offers a stable broadside radiation pattern at both bands and across the entire tunable frequency range for different bias voltages. The parametric analysis on the slot position is done to control the first and second resonant frequencies of the dual-band antenna. The proposed antenna plays a vital role in C-band (4 GHz-8 GHz) applications.

Through-wall imaging (TWI) is one of the useful applications nowadays in microwave tomography field. Reconstructing image of an object becomes more challenging when it is obscured by walls. In practice, the inclusions of noise worsen the reconstruction results. In this paper, Forward-Backward Time-Stepping (FBTS) in time inversion technique is utilized and integrated with Wall Direct Subtraction (WDS) method to reconstruct unknown object behind walls. The investigation includes two types of walls that are homogeneous and heterogeneous. The object is surrounded by closed walls. With noise added in the setup, Singular Value Decomposition (SVD) and Savitzky-Golay (SG) filtering method are used to eliminate the noise and enhance the reconstructed image of an object. The results show that WDS integrated with FBTS has successfully mitigating wall clutter from both homogeneous and heterogeneous walls, and also improves image reconstruction of a hidden object. Further, by using the proposed noise reduction method, lower MSE values can be achieved.

A wideband microstrip open-slot antenna with dual-frequency dual-sense circular polarization (CP) is presented in this paper. A bent feeding structure and three radiating slots, including a modified cross-shaped, an inverted F-shaped, and an inverted L-shaped slots, are designed to excite two orthogonal electric fields with a quadrature phase difference for a radiating right-hand circularly polarized (RHCP) wave at 2.5 GHz and left-hand circularly polarized (LHCP) wave at 3.3 GHz. To improve the axial-ratio (AR), a bent parasitic element is introduced near the microstrip line. Multiple resonances are merged to achieve a large bandwidth of 2620 MHz (104.8%) from 2.2 GHz to 4.82 GHz. The measured AR bandwidths are 460 MHz (18.4%) at the lower band (2.5 GHz) and 2150 MHz (65.1%) at the upper band (3.3 GHz).

This paper studies a computationally efficient algebraic graph theory engine for simulating time-domain one-dimensional waves in a multi-segment transmission line, such as for reflectometry applications. Efficient simulation of time-domain signals in multi-segment transmission lines is challenging because the number of propagation paths (and therefore the number of operations) increases exponentially with each new interface. We address this challenge through the use of a frequency-domain, algebraic graphical model of wave propagation, which is then converted to the time domain via the Fourier transform. We use this model to achieve an exact, stable, and computationally efficient (O(NQ), where N is the number of segments and Q is the bandwidth) approach for studying one-dimensional wave propagation. Our approach requires the reflection and transmission coefficients for each interface and each segment's complex propagation constant. We compare our simulation results with known analytical solutions.

Various formulations of the inverse equivalent surface-source problem and corresponding solution approaches are discussed and investigated. Starting from the radiation integrals of electric and magnetic surface current densities, the probe-corrected inverse equivalent source formulation is set up together with different forms of side constraints such as the zero-field or Love condition. The linear systems of equations resulting from the discretized forms of these equations are solved by the normal residual (NR) and normal error (NE) systems of equations. As expected and as demonstrated by the solution of a variety of inverse equivalent surface-source problems, related to synthetic as well as realistic antenna near-field measurement data, it is found that the iterative solution of the NE equations allows for a better control of the solution error and leads in general to a slightly faster convergence. Moreover, the results show that the incorporation of the zero-field condition into the solution process is in general not beneficial, which is also supported by the structure of the NE systems of equations. If desired, Love surface current densities, or just fields in general, can more easily be computed in a post-processing step. The accuracy of the obtained near-fields and far-fields depends more on the stopping criterion of the inverse source solver than on the particular choice of the equivalent surface-source representation, where the zero-field condition may influence the stopping criterion in a rather unpredictable way.

This paper presents design analysis of a compact CPW fed Wearable Textile Antenna with Dual Band notched characteristics for UWB applications. The proposed wearable textile antenna is designed on two different dielectric substrates; leather and denim with copper foil as conducting element. The performances of the designed textile antenna are compared on two substrates. Band-notched filtering characteristics are achieved by inserting semicircular split ring resonators on the conducting element. The first notch band is obtained from 2.3 GHz-2.5 GHz for Bluetooth application band, and the second notch band is obtained from 3.3 GHz-3.6 GHz for WiMAX application band. The simulated and measured frequency results show that the antenna has an impedance bandwidth of 1.8-10 GHz and reflection coefficient less than -10 dB, except at the two eliminating bands. The proposed antenna is designed and simulated using Ansys HFSS Electromagnetic Simulator. The prototype of the antenna has been developed on the denim substrate, and its performance is measured and compared with the simulated ones.