In this paper, a miniaturized triple-band gap multi-via electromagnetic band gap (TBMV-EBG) structure is proposed. Lumped LC modelling method is used for the analysis of the proposed TBMV-EBG structure. Triple band gaps in both x and y-directions are obtained since TBMV-EBG unit cell consists of three resonance parallel LC circuits. Ansys (HFSS) simulation is used in eigen mode to simulate a unit cell of the proposed EBG. There is a strong agreement between simulated and experimental results. Comparing the proposed TBMV-EBG with triple band slotted EBG, triple band CSRR-EBG, fractal EBG, and dual band split EBG, size reductions of 6.52%, 7.53%, 23.21%, and 25.86% are obtained respectively which is validated by simulated and experimental results. Demonstration of the proposed TBMV-EBG structure for ultra-wideband (UWB) application is also presented. Simulation and measurement results prove that by using a single TBMV-EBG cell at the feed line of a UWB monopole antenna triple band-notches can be obtained. Moreover, switching characteristics of the proposed antenna are also demonstrated using single P-I-N diode. Depending on the ON and OFF switching status of P-I-N diode, the UWB antenna provides switching from triple band-notches to dual band-notches, respectively. The proposed switchable monopole UWB antenna as a single unit can be useful in applications wherein switching between multi-bands is desirable without changing the geometry of the structure.

This paper presents a highly innovative approach of amplitude steering without the use of variable gain amplifiers (VGA). This approach involves the use of a Reconfigurable Ratio Power Divider (RRPD), and does not suffer from the instability, poor efficiency, and worsened SNR associated with the use of VGAs. The RRPD, which is reconfigured manually by means of a potentiometer, is used to feed a 2 x 1 antenna array. By varying the power dividing ratio of the RRPD, continuous beam steering is achieved through passive amplitude control. The antenna was designed to operate at 2.4 GHz and had a continuous steering range from 0° to 21° while maintaining a stable return loss around the centre frequency. An expression that relates the reconfigurable ratio to the variable resistance was derived empirically. The prototype amplitude steerable antenna was fabricated and measured to validate the analyses.

In this paper, a novel branch line coupler with improved bandwidth and reduced size is presented. The size reduction is achieved by means of capacitive loading. The capacitive loaded transmission line implemented in the proposed design eliminates the need of open stubs. The mechanism of size reduction and bandwidth enhancement of the coupler is discussed analytically with the help of its equivalent circuit. A prototype is fabricated and tested to validate the concept. The measured fractional bandwidth is 40%, ranging from 2.8 GHz to 4.2 GHz which is suitable for 5G systems. Moreover, the obtained phase imbalance between the output ports is less than ±5° for the entire operating range.

Here we propose an L-shaped slot-type MIMO antenna with pattern and circular polarization diversity for WLAN applications. In order to maintain a low profile, the pattern and polarization diversities have been achieved without using additional supporting structures. Both the antenna elements are located at the corners of the same side of the ground plane. One of the antenna elements produces left hand circularly polarized (CP) waves whereas the other element produces right hand CP waves in (front) +z-direction. The senses of polarizations are opposite in (backward) -z-direction. CP waves have been generated using two orthogonal current modes, excited by locating the slots on the corner of the ground plane. The quadrature phase difference between the modes has been employed using the slot geometry. In other directions, the antenna correlation has been reduced using pattern diversity. The measured results confirm the simulated ones. The measured axial ratio bandwidth (< 3 dB) and the matching bandwidth (< -6 dB) are 380 MHz and 110 MHz, respectively. The envelop correlation coefficient is less than 0.1 in the operating band.

There has been a presented modal approach for analyzing the scattering of plane waves that are incident on penetrable gratings with metallic fins lined over both exterior surfaces of each conducting bar to create flanged apertures, which altogether is covered on both sides by multiple dielectric layers. The new degrees of freedom afforded by the special complex geometry offer ways to improve the capabilities of various applications such as beam deflectors, resolution of spectroscopic gratings, grating couplers, and grating pulse compression/decompression, as shall be demonstrated herein for the latter two. All of these entail higher-order diffraction modes, which are advantageously studied by the aforementioned analytical tool. Outcomes of measurements on a fabricated prototype that agree well with expectations from theory are also presented.

The dynamic performance optimization of magnetic gear devices is essential to their industrialization. In this study, upon considering the magnetic field coupling characteristics of different components of a field modulated magnetic gear with intersecting axes (FMMGIA), we first obtained the magnetic coupling stiffnesses of these components via the finite element method. On this basis, we further established a dynamic model as well as the corresponding differential equations for the magnetic gear. Thereafter, we analyzed the modal characteristics and the influences of the primary design parameters on the modal frequency of the FMMGIA system. The results indicated that the magnetic coupling stiffnesses among the FMMGIA components were significantly lower than the meshing stiffnesses of the mechanical gears. In addition, the magnetic gear system consisted of three orders of torsional modals as well as three orders of horizontal vibration modals, among which the torsional modal frequencies of both the input and output rotors were substantially lower than others. Finally, parameters such as the minimum axial length and the permanent magnet remanence demonstrated considerable have impacts on the modal frequencies of the FMMGIA system.

A compound or an offset inclined slot fed by a rectangular waveguide has been analysed using the image method for the evaluation of internal admittance in the Method of Moments framework. The internal admittance has been evaluated from the 2D infinite planar array equivalent image representation of a slot in a waveguide. The advantages offered by this method include the freedom to work in slot coordinates rather than the waveguide coordinates, the reuse of external admittance for air filled waveguides, and the flexibility in the choice of the mutual admittance evaluation technique. Unlike the conventional mode method, the proposed technique does not run into difficulties while evaluating the fields from longitudinal magnetic current for points in the same transverse plane. The θ-algorithm has been used for the convergence acceleration of the series of mutual admittances in the internal admittance evaluation and has been shown to yield better results than other convergence acceleration algorithms investigated. The results obtained from this method have been shown to agree within 0.5% average with those from other theoretical techniques and within 1% average with measurements. The proposed method is useful in the design of compound slot arrays and can be extended to other configurations where the image representation is possible and for various slot aperture distributions.

A narrowband low temperature co-fired ceramic (LTCC) bandpass filter (BPF) with five cascaded physical length-reduced resonators is proposed. Each resonator is built with cascaded horizontal and vertical microstrip lines to produce slow-wave effect, which reduces the physical length of resonators for miniaturization. The entire size of the proposed BPF is only 15 x 2 x 0.3 mm, and a size reduction of 60% is achieved compared with a traditional implementation. A narrowband fractional bandwidth (FBW) of 4% and an average passband insertion loss of only 2.4 dB are achieved. Comparison and discussion are implemented as well.

This article presents a comprehensive review of modeling,analysis,and development of permanent magnet bearings (PMB) for rotating shafts. The different configurations of PMB are highlighted with relevant approaches to estimate their features. The progress in mathematical approaches adopted and optimization of the static and dynamic bearing characteristics in terms of accuracy are discussed in depth. Further, key developments on instability issues and their realization in combination with other bearings for rotors stability in low and high-speed applications are reviewed. Finally, concluding remarks on key aspects to be followed in the design and development of PMB are presented.

The coil stray capacitance is an essential factor for high-frequency coil application, such as wireless power transfer system. In this paper, in order to calculate the planar coil stray capacitance at Megahertz frequency, the theory model has been built. Based on the basic capacitance calculation equation, the mathematical model has been deduced carefully. Then, the mathematical model has been evaluated by a series of simulation models. In the simulation part, the error of the variables of the theory model has been analyzed carefully and quantitatively. In order to verify the theory and simulation model, the verification experiment has been done. The experimental results are consistent with the simulated ones and the theory model. The experimental and simulated results indicate that the theory model of the coil stray capacitance has a satisfactory accuracy, and the model has application potential in the field of wireless power transfer.

In this paper, we propose a new methodology to design an electromagnetic invisibility anti-cloak, which is based on nonlinear coordinate transformation. Cylindrical and elliptical shapes are presented to show the validation of the proposed methodology. We verify and analyze the above model with nonlinear transformation respectively. Full-wave simulations are given to illustrate the ability of the nonlinear transformation, which is advantageous for reducing the design difficulty of the anti-cloak. And the cloak shielding is broken, and the electromagnetic waves can go through the cloak. It is of particular importance in microwave communication applications.

We provide an explicit geometric generalisation of the antenna current Green's function (ACGF) formalism from the perfect electric conducting (PEC) to generic coupled N-body systems composed of arbitrarily shaped coupled PEC and dielectric objects, with the main emphasis on the mathematical foundations and the rigorous construction of the Green's function using distributional limits. Starting from mainly reciprocity, surface equivalence theorems, and other typical regularity conditions, we carefully construct the current Green's function by employing a combination of methods including Riemannian geometry, distribution theory, and functional analysis. The formalism outlined here for composite domains turns out to be more complicated than the PEC-only formulation due to the former's need to explicitly account for the coupling interaction between the magnetic and electric degrees of freedom. The approach is developed for extremely general systems, and use is made of Riemannian geometry to avoid working with specific or concrete configurations, hence retaining high generality in our final conclusions. While the ACGF tensor's matrix representations depend on the coordinate system on the manifolds supporting the electromagnetic boundary conditions, we focus here on providing coordinate-independent integral expressions for the induced current. With the ACGF it is possible to theoretically treat arbitrary N-body coupled PEC-dielectric configurations as space-frequency linear systems with an exact and rigorous response function being the current Green's function itself. While the derivation is very general, it still leaves open questions regarding whether the ACGF can be constructed for nonreciprocal systems or using volume integral equations.

We derive and verify a new type of low-complexity neural networks using the recently introduced spatial singularity expansion method (S-SEM). The neural network consists of a single layer (Shallow Learning approach to machine learning) but with its activation function replaced by specialized S-SEM radiation mode functions derived by electromagnetic theory. The proposed neural network can be trained by measured near- or far-field data, e.g., RCS, probe-measured fields, array manifold samples, in order to reproduce the unknown source current on the radiating structure. We apply the method to wire structures and show that the various spatial resonances of the radiating current can be very efficiently predicted by the S-SEM-based neural network. Convergence results are compared with Genetic Algorithms and are found to be considerably superior in speed and accuracy.

Prestressed steel strands are critical components of prestressed structures, which determine the bearing capacity of the structures. The prestress loss of steel strands causes the bearing capacity to decline. To monitor the stress of prestressed steel strands, a stress monitoring method based on the magnetoelastic effect was proposed. The influence of the material strain was considered to improve monitoring accuracy. To do the monitoring, a coil-based sensor, using a small excitation current to generate a necessary magnetic field, was employed. The sensor converted the stress into inductance. An experimental system was set up and two batches of specimens were tested. The experimental results showed that the measured inductance was stable and repeatable. There was a nonlinear relationship between the inductance and the stress. Strands of different batches need to be calibrated separately to obtain the inductance-stress equation. Based on the calibration equation and the measured inductance, the stress of strands could be calculated. The difference between the calculated stress and the actual stress was small. Besides, to improve the accuracy and ease of the construction, the self-induction coil of the senor should be one layer and with moderate turns.

This paper presents the work of the LAPLACE Electromagnetism Research Group to build an experimental setup able to measure tiny forces that may appear in microwave cavities, in the context of EMDrive investigations. It is based on a commercial balance in the range of 0.1 mN sensitivity, a contactless feeding for more than 150~W RF power, and self calibrating device process. It requires a double cavity system in mirror configuration and is here experimented with frustum cavities, different from the NASA one [1]. The global setup can make force measurement and calibration in less than two seconds. Investigating two different cavities and various electromagnetic modes for the biggest, no force is reported while the 0.1 mN sensitivity is demonstrated.

Previously, an inverse microwave scattering model based on radiative transfer was developed for the retrieval of sea ice thickness using radar backscatter data. The model, called the Radiative Transfer Inverse Scattering Model (RTISM), is a combination of the Radiative Transfer-Dense Medium Phase and Amplitude Correction Theory (RT-DMPACT) forward model and the Levenberg-Marquardt Algorithm (LMA). In this paper, the LMA in the RTISM is replaced with Simulated Annealing (SA) as the optimizer to allow a wider range of inversion capability. SA is a global optimizer, and its settings make it convenient to switch between different target parameters to be optimized for inversion. In this study, the model will first be tested using different data sets to verify its applicability. Next, the model is used to estimate the sea ice thickness around Ross Island, Antarctica using data from ground truth measurements together with satellite data from Radarsat-1 from the year 2006. In order to further validate the model, the data collected from measurements performed during an experiment to grow an ice sheet within a refrigerated facility at the U.S. Army Cold Regions Research and Engineering Laboratory (CRREL) are used to perform the retrieval of saline ice thickness. Preliminary results show that the new model performs as expected and shows potential. However, there are still limitations to the inverse model, and further improvements in the future need to be considered.

A novel single-layer band-pass frequency selective surface (FSS) is proposed in this letter. The unit cell is composed of a series of rotationally symmetrical fishbone-shaped structures surrounded by a modified octagonal loop. This fishbone-shaped FSS exhibits stable resonant frequency while the incident angle ranges from 0˚ to 60˚ for both TE and TM polarizations, which means that polarization insensitivity and angular stability are well demonstrated on the proposed FSS. A prototype is fabricated and measured in an anechoic chamber, and good agreements are obtained between measured and simulated results.

Electric dipoles are the fundamental components of a planar multi-layered circuit. Present work focuses on the theoretical investigations of radiation field due to a vertical electric dipole in a four-layered region composed of a perfect conductor covered with two dielectrics and the air above. Locating a vertical electric dipole (VED) on or near the air-dielectric boundary, approximate formulas are obtained. The resultant analytical formulas have the merit of offering unique insights about the characteristics of the radiation field including direct waves, reflect waves, lateral waves, and trapped surface waves. The amplitude of the field along the boundary exhibits the dependence of ρ^-1/2, which is an intrinsic characteristic of trapped surface waves, where ρ is the propagation distance. In addition, the radiation field is further examined for propagation distance and propagation characteristics of the interference phenomenon. Furthermore, when the observation angle Θ ≥ 88°, the lateral wave still exists; however, the trapped surface wave is a major component of the total field. The proposed formulas have potential to develop planar four-layered circuit structures.

A new compact ultra-wideband (UWB) bandstop filter with good performance is proposed. The proposed UWB bandstop filter is composed of two pairs of quarter-wavelength resonators, a high impedance main transmission line, a half-wavelength resonator, and an H-shaped multiple-mode ring resonator. The proposed H-shaped multiple-mode ring resonator is introduced to achieve three transmission poles appearing in the lower and upper passbands thus to improve the characteristics of selectivity. The proposed quarter-wavelength resonators and half-wavelength resonator are used to obtain four transmission poles showing up in stopband thus to improve the in-band suppression characteristics. To validate the design concept, a new compact UWB bandstop filter with high selectivity and good suppression is designed and fabricated. UWB stopband, low insertion losses, and good selectivity are achieved as demonstrated in both simulation and experiment.

Lenses can be used to focus and disperse the electric field emitted by the antenna. Sustainable and environmentally friendly lenses were made from lithium molybdenum oxide (LMO) glass composite. Half spherical lenses with a diameter of a 30 mm were fabricated from LMO composite, and the antenna properties were measured with a waveguide feed. The lens enhanced radiation pattern was measured at K_u band, and the improvement in the gain was found to be 2 dB.