In this work, we analytically enhanced the channel capacity and bandwidth of an MI waveguide system by using multi-layer coils (MLCs) and spread resonance strategy. In this analysis, we considered the practical constraints like parasitic capacitance, ac resistance, skin and proximity effects and inductance of multi-layer coil. The bandwidth is significantly enhanced up to 6 KHz, and a trade-off is observed between the bandwidth and achievable transmission range. Besides, the influence of coil turns, layers and the impact of spread intensity are analyzed. Furthermore, we introduced a new MLC structure with thin-rectangular cross section which has promising characteristics like higher magnetic flux, low ac resistance, and high inductance. The performance of this coil is compared with that of existing round circular and tubular multi-layer coils. These characteristics are comparatively studied through simulations performed in ANSYS Maxwell R21. Based on the results we infer that the proposed coil is more advantageous than the existing standard MLC for MI communication in terms of cost and system performance.

In order to improve the electromagnetic performance of permanent magnet vernier machines (PMVMs) at a high pole ratio, a novel U-type permanent magnet (U-PM) vernier machine with high-temperature superconductor (HTS) bulks is proposed. HTS bulks are introduced between the stator modulating teeth, and alternating flux bridges and U-PMs are added in the rotor yoke. The structure can reduce the magnetic flux leakage, provide a magnetic circuit for the low pole pair working magnetic field, weaken the magnetic barrier effect, and improve the torque density of the machine. The parameterized model of the proposed machine with 23 pole pairs of the rotor and 4 pole pairs of the stator is established by the finite element software. In addition, some key parameters of the proposed machine are layered by parameter sensitivity analysis, and then the machine is optimized by genetic algorithm. Compared with the conventional machine, the proposed machine increases the average electromagnetic torque by 69%, reduces the torque ripple to 1.7%, increases the power factor to 0.73, and increases the efficiency to 85.3%.

This paper thoroughly studies the realization of the reconfigurable function of RLSA antennas in terms of beamsteering at the frequency of 5.8 GHz. In the first step, the study on the characteristic of small RLSA antennas concludes that maximum beamsquint that can be achieved is around 70˚. In the second step, in order to minimize the size of reconfigurable RLSA antennas, a new technique of cutting a small RLSA into sectors is introduced. The analysis on the quarter cut RLSA and the semi cut RLSA shows that their performances do not deviate too much from the full circle RLSA performance. In the third step, study on the most suitable method of realizing the reconfigurable function of RLSA antennas chooses the method of implementing antenna array as the most suitable method. Based on this method, a structure of reconfigurable RLSA antennas is proposed. In the last step, utilizing the proposed structure and four quarter cut RLSA elements, a novel reconfigurable RLSA antenna in terms of beamsteering is simulated and fabricated. To avoid significant coupling effect between the antenna elements, all elements are separated by 20 mm. The antenna has a directivity of 9.2 dB, an efficiency of 97.95%, a bandwidth about 1.5 GHz, the mainlobe direction (in elevation direction) of 45˚, the beamwidth of 32.5˚, and the sidelobe level -6.3 dB. The beam of the reconfigurable antenna can be steered into four different azimuth directions, which are 0˚, 90˚, 180˚, and 270˚. Furthermore, a similar radiation pattern and reflection coefficient between the measurement and simulation verifies the validity of the study.

We extended the previous 2D method of BBGF-MST (Broadband Green's function-Multiple Scattering Theory) approach to 3D problems in periodic structures. Band Structures and Band Field Solutions are calculated. A feature of BBGF is that the lattice Green's functions are broadband so that the coefficients of the spherical wave expansions are calculated rapidly for many frequencies. These are then used for speedy calculations of the matrix elements of the KKR (Korringa-Kohn-Rostoker) eigenvalue equation. Using BBGF-MST, a low order matrix eigenvalue equation for the bands is derived. For the first two bands, the dimension of the KKR matrix equation is only 4 by 4. With the use of BBGF, the CPU requirement for the BBGF-MST technique is 0.27 secondson a standard laptop for solving the KKR eigenvalue equation. Numerical results of the band diagrams are illustrated. Higher order spherical waves are next used to calculate the normalized band field solutions for the entire cell.

This paper proposes an underdetermined direction of arrival (DOA) estimation for multiple input and multiple output (MIMO) sparse additive white Gaussian noise (AWGN) channels. Accurate DOA estimation helps in better signal analysis and noise cancellation in the channel. A novel multiplicative multi-kernel basis vector-based non-negative sparse Bayesian learning (NNSBL) algorithm is implemented over a predefined grid. Simultaneously stochastic cuckoo search algorithm (CSA) is exploited virtually to improve the DOA approximation for a non-uniform linear array (NULA) geometry by an optimized antenna reconfiguration model. The simulated and experimental results show that the proposed algorithm yields an optimized root mean square error (RMSE) for different optimized wavelengths of the randomly generated signals. The RMSE convergence graphs demonstrate the effectiveness of the new method for different signal-to-noise (SNR) values.

This study investigates several substantial questions arising in the diffraction by circular surfaces with the fractional boundary condition, which is the generalization of Dirichlet and Neumann boundary conditions. The study analyses the electromagnetic E-polarized plane wave diffraction by a slotted circular cylinder with the fractional boundary condition. For the first time, the fractional boundary condition regarding circular geometries is employed in the literature. The resonance characteristics for different boundary conditions, angle of incidence, and aperture sizes are analyzed. The new resonances are observed when the surface is different from the perfect electric or magnetic conducting surface.

This paper presents a novel localization method in multiple-input multiple-output (MIMO) systems based on the implementation of passive repeaters. In addition to their ability to enhance performance in MIMO systems by enriching scattering in line-of-sight MIMO environments, and extending coverage area and accessing blind spots in none line-of-sight MIMO environments, passive repeaters can help in localizing users by taking advantage of their spreading in the communication environments. In the proposed method, the target area is divided into a grid. Each location in this grid has a unique field interference created by repeaters. Because of the unique field interference, each location causes a unique field signature at the base station when a user in that location transmits signals. The field signature corresponding to the center of each grid cell is used as a fingerprint for localizing users in that cell, and for all cells, a bank of matched filters corresponding to all stored fingerprints is constructed. Using only the spatial coherence of the measured fields, there is no need for synchronization between users and the base station. When a signal arrives at the base station, the generated field signature is correlated with the bank of matched filters, and the location is determined based on the maximum correlation value. The numerical analysis is performed to verify the validity of the proposed method, and it is found that by means of passive repeaters, the user location can be determined with no need of calculating additional parameters.

This paper introduces and validates a compact two-dimensional Electromagnetic Bandgap (EBG) structure for the improvement of signal integrity (SI) and power integrity(PI) by suppressing Simultaneous Switching Noise (SSN). SSN bandwidth can be increased by using the proposed T bridge compact planar structure. The proposed structure is simulated using Ansys HFSS Software. Simulated and measured results by Vector Network Analyzer provide 3.13 GHz to 11.40 GHz frequency bandgap with good mitigation of SSN at -30 dB noise suppression reference. It will almost cover S, C, and X bands from electromagnetic frequency spectrum. This will be useful for satellite and terrestrial communication and radar communication applications. The proposed structure analyzes signal integrity issues using eye diagram in MATLAB and power integrity in HFSS with input impedance respectively. The main purpose of this work is to provide a compact structure to improve signal and power integrity by the suppression of power/ground noise. Comparative study is also performed with the proposed structure and reference board with similar dimensions.

This paper presents a proposal for a high birefringμeμnce photonic crystal fiber (C-PCF) with a doped liquid into two first ring holes, which is analyzed by the finite element method. It is demonstrated that the proposed fiber has a birefringence value of about 2.643 × 10^-2 at wavelength λ = 1.55 µm and temperature T = 25˚C. Also, a high chromatic dispersion of -272 ps/nm/km, an effective area of 1.693 µm², and a confinement loss of 0.058 dB/m for the x-polarization method were obtained at the same wavelength and temperature. The temperature influence on the modal properties has also been studied. We will demonstrate through the result that the fiber we propose can be used in both sensing and chromatic dispersion applications such as flattened dispersion fibers.

Breast cancer is, by far, the most diagnosed disease for the death of women worldwide. Researchers are working with an alternative technology to detect the tumours before it reaches the terrible stage because of the numerous limitations in the current imaging approach. This article suggests a promising technique by utilising non-ionizing microwave signal and artificial intelligence especially deep learning algorithms for early detection of breast cancer. This contribution will present a method to detect and classify the tumour category using backscatter signals obtained from antenna simulation in CST microwave studio software. The post-processed scattering parameters are utilized to create image through MATLAB programming environment. The high intensity in the image represents the precise position of tumour. The automatic classification of tumour is achieved by YOLOv5 deep learning model from the created microwave images. A training dataset with fifty image samples are formed by preprocessing and then augmentation is applied to create final dataset with 1000 samples. This approach can identify the location and type of early-stage tumour with size of 5 mm.

This letter presents a wideband polarization reconfigurable antenna based on liquid metal (LM) switches. It consists of single-fed crossed bowtie dipoles, a parasitic element grounded via a metallic post, a dual-cavity-backed reflector and liquid metal switches. The two arms of one dipole are loaded with two symmetrical identical slots, and on top of the slots, two sets of fixed-length movable liquid metal columns filled in polytetrafluoroethylene (PTFE) tubes are attached as switches. The altering between linear polarization (LP) and circular polarization (CP) can be achieved by changing the positions of the liquid metal switches. The dual-cavity structure is applied to obtain unidirectional radiation and enhance the circularly polarized performance. A prototype with overall size of 127 × 127 × 57 mm³ is designed and fabricated. The measured results indicate that the impedance bandwidth (IBM) of the antenna is from 1.06 to 2.46 GHz (79.54%) and the axial ratio bandwidth (ARBW) is from 1.39 to 1.91 GHz (31.52%) for CP state. In addition, the IBW for LP state is from 1.06 to 2.30 GHz (73.81%). Moreover, the peak gains can reach 7.73 dBic in CP state and 9.21 dBi in LP state.

Electromagnetic scattering of a Gaussian beam wave from an array of parallel homogeneous anisotropic circular cylinders is presented. The transmitted fields in the anisotropic cylinders are expressed as an infinite summation of eigen-plane waves with different polar angles. The expression of the Gaussian beam is represented as a product of a well-known scattering of a plane wave and a weighting function. The incident field is expressed in local cylindrical coordinates and the scattered field is the summation of contribution of all cylinders. Using the addition theorem of Hankel function, the expression of the scattered field can be transformed from local coordinates to others. By enforcing the boundary conditions on the surface of each cylinder, an infinite set of equations is obtained which can be written in a matrix form. Scattering cross sections and near fields are analyzed and compared finally.

In this paper, a new space-time adaptive processing (STAP) method based on improved nested arrays and pulses configurations is proposed. Specifically, we first decompose the sensor array into two uniform linear arrays (ULAs) plus a separate sensor, similarly for pulse trains. Then, the original received signals from the physical array and pulse trains are introduced into the virtual domain, where the virtual clutter plus noise covariance matrix (CNCM) estimation is performed. Since the system has more virtual sensors and pulses from the perspective of virtual domain, the degrees of freedom (DOF) capability is effectively enhanced to improve the angle and Doppler resolution of radar. With the spatial-temporal smoothing technique, the STAP filter is designed by reconstructing the CNCM and virtual signal steering vector. Simulation results validate the effectiveness and superiority of the proposed algorithm.

An outer rotor coreless bearingless permanent magnet synchronous generator (ORC-BPMSG) is a multivariable, nonlinear, and strongly coupled system. In order to realize the precise control of the ORC-BPMSG, a decoupling control strategy based on online least squares support vector machine (OLS-SVM) inverse system and internal model controllers is proposed. Firstly, on the basis of introducing its operation principle, the mathematical model is established. Secondly, on the basis of analyzing its reversibility, a real-time inverse system of ORC-BPMSG is obtained by using OLS-SVM, and it is connected in series with the original system to form a pseudo-linear system, which realizes the linearization and decoupling of the ORC-BPMSG. Thirdly, the internal model controller is designed to perform closed-loop control of the pseudo-linear system. Finally, the simulated and experimental results show that the proposed control strategy has better stability and decoupling performance than the decoupling control strategy based on the LS-SVM inverse system and PID (Proportion Integral Derivative).

A compact, gain-enhanced, linearly tapered slot antenna (LTSA) with hook-shaped slots in the ground plane and a combined director, consisting of a metallic strip director and double-sided metamaterial (DS-MTM) loading surrounding it, is proposed for ultra wide band (UWB) applications. Hook-shaped slots are appended in the ground plane for miniaturization, whereas a combination of the metallic strip and DS-MTM loading placed above the LTSA is used for gain enhancement. Performance of the proposed combined director is compared with other commonly used director configurations in the literature, such as single strip director, two strip directors, and two-layers of DS-MTM. It was found that gain enhancement effect of the proposed combined director is the greatest over the UWB band, compared to other director configurations. The fabricated prototype of the proposed antenna operates from 2.83 GHz to 11.31 GHz (119.9%) for a voltage standing wave ratio less than 2 with moderate gain of 3.2-7.5 dBi. The dimensions of the proposed LTSA in terms of the free space wavelength at the lowest frequency (λ₀) are 0.28λ₀ × 0.30λ₀ × 0.0075λ₀ (30 mm × 32 mm × 0.8 mm), which are very compact.

Micro-variation monitoring radar based on the differential interference principle can monitor objects prone to micro deformation. However, it is easily affected by human and environmental factors to cause the radar image to loss coherence in the long-term monitoring work, thus affecting the normal monitoring of radar. Therefore, it is of great significance to study the change detection method of micro-variation monitoring radar images, which can provide reference information and quantitative analysis for monitoring work. In this paper, a method of landslide area identification and detection based on micro-variation radar image is proposed. Based on the radar coherence coefficient image of time series, the difference image is produced by logarithmic ratio cumulation. The difference map is decomposed and denoised by wavelet transform, and then the final difference map is produced by reconstructing the processed wavelet coefficients. Finally, the improved K-means is used to cluster the difference map to get the change detection result image. The actual monitoring data of a mining area is used for variation detection. The results show that the proposed method retains the detailed information of the change area and removes a lot of noise. The difference map is easier to cluster, and the clustering result is more accurate.

A three-dimensional negative index (NI) metamaterial (MTM) is realized at terahertz (THz) frequencies. The structure is comprised of orthogonally oriented cross-bars with arrows on each corner embedded in a dielectric cube. The proposed 3-D MTM is symmetric along all the principal axes and shows a polarization-insensitive, wide-incident-angle negative refractive index regime centered at 0.862 THz with an operational bandwidth of 0.234 THz (27.15{%}). Using staircase approximation, the proposed 3-D NI MTM has been designed into a THz parabolic planoconcave lens (PCL). A PCL made of a NI medium is a counterpart of a positive index planoconvex lens and focuses on the near-field region. The designed PCL shows 3-D focusing functionality for linearly and circularly polarized THz waves at 0.85 THz. The designed PCL has a short focal length and high numerical aperture (NA) with sub-wavelength focusing spot sizes. The computed FWHMs along transversal directions are 0.46λ(x) × 0.49λ(y) for transverse electric (TE) polarized wave, 0.46λ(x) × 0.49λ(y) for left-circularly polarized (LCP) wave and 0.50λ(x) × 0.42λ(y) for right-circularly polarized (RCP) wave, respectively. The corresponding back focal lengths of the realized PCLs are 1.07λ, 1.03λ and 0.98λ and the focal depths are 0.40λ, 0.48λ and 0.41λ for linear, LCP and RCP polarized waves, respectively. A short review of recent progress in manufacturing techniques for the fabrication of the proposed 3-D MTM is further highlighted. Since the proposed 3-D MTM PCL configurations show the far-field focusing of linearly/circularly polarized waves, imaging with high optical power requirements can be met for THz waveband applications.

In this paper, the possibility of synthesizing a linear antenna array for multiple objectives with the thinning approach is demonstrated. The thinning space is constrained to three cases (side, central, and random) parts instead of a fully filled linear array. In the case of the side part, a set of elements located on both edges of the array are removed with the optimized elements close to the center remaining unchanged. As in the case of the central part, only a set of elements close to the center are removed. In the case of a random selection of elements, the cancellation process is carried out randomly within the sides and the center. Since the amplitude weights of the elements located on the edges of the array have a small amplitude excitation, the method of side thinning gives better results than the other two cases. Moreover, in cases of side and random thinning, the last element of each side is excluded from the thinning process to maintain the aperture size. The convex algorithm (CA) is used to perform such thinning optimization. CA optimization efficiently computes a multi-objective function in coordination with the thinned array technique, such as preserving the main beam width in all cases with the reduction of the sidelobe levels, generating one or more nulls, and steering the main beam in a certain direction. The simulation results, in all cases, show that 30%-40% of the array elements can be turned off with achieving a multi-objective radiation pattern.

A multiband fractal monopole antenna has been developed for wireless applications. A triangular monopole antenna is considered for this design to achieve the requirement of WLAN and WiMax. Annular rings are etched out from the basic antenna using the fractal concept. To increase its electrical length, notches are introduced at the edges. The volume of an antenna is 54×57×1.6 mm³. Various changes in the ground plane have been done to get the optimum result. The frequency bands at which the antenna resonates are 3.5 GHz, 5.35 GHz, and 6.1 GHz. These bands are best suitable for the WiMax (3.5 GHz) and wireless local area network (5.35 and 6.1 GHz) applications. The simulated and the experimental results show a good match.

The paper presents a new compact directional antipodal Vivaldi antenna that can be employed in modern imaging applications. To obtain wide-band impedance bandwidth in the proposed antenna, a stair case slot is introduced in both the tapered region along with a triangular ground plane. In addition, by means of introducing a parasitic patch close to the centre of radiators, a more directional radiation characteristic is attained within the operational bandwidth. Based on the simulation results, the antenna designed on FR4 substrate provides a wide impedance bandwidth (S₁₁ < -10 dB) of 6.2 GHz i.e., between (3.8-10 GHz) with a gain between 3.5 to 7.5 dB suitable for variety of imaging applications. The designed single feed antenna is compact, low profile and trimmed to provide a triangular geometry with light weight. To validate the directional radiation performance of the antenna, it is fabricated and integrated with a signal generator and spectrum analyzer to obtain the image of a uniform target object i.e., cylinder using the standard back projection Radon transform algorithm. The proposed setup along with the algorithm are promising for the civil and medical applications on applying to other shapes of objects.