This work proposes a novel probe-fed circular patch antenna which has been fractaled and reconfigured to deliver enhanced performance. The circular ground plane is made defected using Cantor-square fractal geometry which reduces the cross-polarization level by about 12 dB. Further, by appropriate positioning of a PIN diode switch in the ground slot, the fractal Circular Microstrip Patch Antenna (CMPA) is enabled to achieve frequency reconfiguration. A prototype of the proposed antenna is fabricated and tested for the assessment of various parameters. The proposed fractal reconfigurable antenna has a peak gain well above 6 dB, high radiation efficiency, and a maximum bandwidth of about 700 MHz in the X-band (8-12 GHz). The present work aims to focus on the huge potential of fractal reconfigurable antennas in modern dynamic wireless communication systems.

This paper proposes a conformal multiple band four port MIMO antenna for next generation vehicular communications in the extended UWB. The single element consists of a monopole antenna resembling a U-shaped structure with two branches folded and complimentary to each other. It uses coplanar waveguide feeding with a defected ground structure. The antenna is printed on a Kapton Polyamide flexible substrate having a thickness of 0.25 mm. The antenna has dimensions of 0.8λ x 0.8λ x 0.001λ. It resonates at 2.6 GHz, 3.9 GHz and 5.6 GHz which are used in vehicular communications, and can be used in sub-6 GHz 5G applications. It also provides band notches at 2.1 GHz, 3.5 GHz and 4.5 GHz which enables it to mitigate the interferences from any narrow band devices operating in that range. All MIMO parameters are simulated and compared with the measured results, and are found to be in good agreement. The designed antenna can be mounted at any position of the vehicle as it has a conformal structure.

The C-band RDRA with a defective ground structure operated at resonant frequency 6.2 GHz is best suitable for satellite uplink applications. In the C-band, the broad aperture slot and pentagonal-shaped defective ground structure (DGS) offer excellent isolation and great efficiency. The simple prototype of designed pentagonal DGS RDRA is fabricated, tested, and validated. The proposed C-band RDRA has a fractional bandwidth of 12.14%, a return loss of -30 dB, a gain of up to 7.95 dB, and a minimal VSWR at the resonance frequency of 6.2 GHz. It offers a broad beamwidth of 110.87˚ in the E-plane, 43.73˚ in the H-plane, and 91.5% efficiency.

Nanostructure based perovskite solar cell with high performance is the emphasis of study in current work keeping in view the improvement in cell efficiency. In the first part of the study, a plane-layered solar cell is studied by adding a 1D photonic crystal at the bottom of the cell in order to facilitate the photon rotation process. However, in the second part of the study, it is observed that addition of grating enhances the light absorption due to photons trapping. Following that, the light absorption of three different structures is compared. The observations reveal that short-circuit current density (Jsc) is found to be -39.93 mA/cm², which is 87.29% higher than that for a planar structure exhibiting the Jsc value as -21.32 mA/cm². Ultimately, the efficiencies of these perovskite solar cells based on nanostructures are observed to be significant as well. For the proposed solar cell structure, an 87.24% improvement in the power conversion efficiency (PCE) is observed i.e., from 14.03% for the planar structure to 26.27%.

An ultra-wide band (UWB) antenna with C-band and X-band notches for wireless communication is presented. The designed structure is printed on a material of ``Rogers 4350B'' with ε_r = 3.66, tanδ = 0.0037 and a thickness of 0.508 mm. This structure is designed to operate at a UWB range starting from 3.3 GHz up to 10.15 GHz with a stopband range from 6.75 GHz to 8.5 GHz. The rejected bands are the upper C-band (6.75 GHz-8 GHz) and the uplink X-band of the satellite (space to earth) from 7.25 GHz to 7.75 GHz. The overall antenna size is optimized, and its dimensions are 21 × 30 × 0.508 mm³. The antenna gain varies from 2.1 to 4.2 dBi at the passband, and its total radiation efficiency is 96.4%. The suggested structure is designed and simulated using CSTMWS software. Moreover, a prototype of the proposed structure is fabricated and measured. The fabrication process was done using photolithography techniques, and the measurements were done using an R&S vector network analyzer. Good agreement is achieved between the simulated and measured results.

For the sake of decoupling the six-pole radial active magnetic bearing (AMB) with mutual coupling of two degrees of freedom, nonlinear and unstable disturbance, a hybrid active disturbance rejection control strategy based on improved genetic algorithm (HADRC-IGA) is proposed. Firstly, the configuration, magnetic circuit and suspension force model of the six-pole radial AMB are explained and established. Secondly, the HADRC-IGA is designed which is improved on the linear active disturbance rejection control (LADRC). Thirdly, the simulation is carried out, which shows that the capacity of resisting disturbance and the decoupling efficiency of two degrees of freedom of the HADRC-IGA are better than that of conventional LADRC. Finally, the experimental platform is constructed, and the experiments are conducted, which verify the performance of the proposed decoupled control system.

A comprehensive overview of dielectric resonator antenna (DRA) is presented in this paper. Several techniques have been reported in the literature for the performance improvement of DRA. Over the past few decades, circularly polarized (CP) DRAs have been widely explored to mitigate multipath fading and polarization losses in comparison to linearly polarized (LP) antennas. Apart from this, high data transfer rate is required, which needs the development in the field of multi-input-multi-output (MIMO) antenna designs. This includes the increase in the channel capacity without exploiting the limited constraints like signal power and bandwidth. Thus, exploring the concept of MIMO in DRA along with the diversity performance features leads to the development in this field. Furthermore, to mitigate the conduction losses at THz and optical frequencies, high-efficiency DRA proves rationale in extending towards the higher frequency ranges. These scintillating features pave the path for efficient devices integration and on-chip applications at higher frequency ranges where the performance of metallic radiator degrades. Also, the dispersive properties of metal conductivity lead to plasmonic behaviour resulting in the dissipation losses at the optical frequencies. These losses can be substantially mitigated using DRAs. This can be efficiently realized for the future application that requires the manipulation of high-resolution light.

This work proposes and experimentally evaluates a single layer bandpass frequency selective surface (FSS) that resonates at X-band (8-12 GHz). The metal plate of the unit cell has a half-Jerusalem cross slot of size 0.15λ₀, where λ₀ is the wavelength corresponding to 10 GHz centre frequency. The effects of unit cell parameters on filter response are analyzed through parametric analysis. The results reveal that the proposed bandpass FSS exhibits good polarization stability and angular stability at oblique angles up to 45˚. Furthermore, negligible frequency deviations in both TE and TM polarizations have also been achieved using this structure. A prototype of the bandpass FSS was fabricated on an FR4 substrate to validate the proposed design which includes 10×10 elements in a dimension of 45 mm × 45 mm × 1.6 mm. Measurements show that the bandpass FSS has a fractional bandwidth of 40% centered at 10 GHz from 8 GHz to 12 GHz. The unique feature of the proposed filter is its ability to operate in the whole X band (8-12 GHz) by tuning the filter elements.

Microwave imaging of small scatterers is an inverse scattering problem, and recently, the MUSIC algorithm has been proposed to solve this type of problem. The MUSIC algorithm, by assuming that the number of targets is a priori known, can locate the scatterers from the peaks of the well-known pseudospectrum. The noise and multiple scattering create ambiguity to detect the number of targets. Usually, information-based algorithms such as Akaike information criterion (AIC) and minimum description length (MDL) are employed for source number estimation. However, in the cases of low signal-to-noise ratio (SNR) and close targets, the performance of these methods is seriously degraded. In the present work, we propose a two-step approach to enumerate the scatterers in microwave imaging applications for cases where traditional methods fail. Firstly, the MUSIC algorithm is applied to locate all possible targets by assuming the maximum number of targets, and secondly, we can discriminate between the real and unreal targets by using a novel formula that acts as a spatial filter. The efficiency of the proposed method has been examined through various simulation tests using numerical and experimental datasets, and the results verify that the method can accurately specify the location and the number of scatterers in 2D microwave imaging applications.

The systematic design approach of a 42 GHz CW gyrotron has been extensively presented in this paper. Beam-wave interaction of the conventional tapered cylindrical cavity gyrotron is demonstrated using commercially available Particle-In-Cell (PIC) code. Beam absent and beam present cases have been considered to observe the performance of the device. Beam absent case is presented to validate the design in desired mode as well as resonant frequency whereas beam present case is demonstrated to validate and observe the beam-wave interaction behavior of the device in terms of output power. In order to optimize the dimension of interaction structure to achieve desired performance of the device, several parameters were considered. RF output power of the device is estimated with the variation of structure parameters as well as electron beam parameters to achieve better performance in terms of efficiency. Using the designed parameters, beam present analysis offers a saturated output power well above 250 kW. The particles phase space behavior along the interaction length is demonstrated to realize the energy transfer phenomena. The PIC simulation results are found in close agreement with the self-consistent single mode results. The estimated output power and efficiency support the proper design of proposed gyrotron oscillator.

In this paper, a flexible full-duplex antenna is proposed with robust performance and high isolation for 5.8 GHz using foam and PET paper. The patch of the antenna is modified by corner cut and inset feeding, while the defected ground structure is used to improve isolation between transmit and receive ports. Silver nanoparticle ink is used for printing the antenna in an inkjet printer. The fabricated version supports simulated results by showing acceptable performance in desired bandwidth. Bending tests and human body loading experiments are carried out on the fabricated antenna to demonstrate antenna's effectiveness for wearable applications. To the best of authors' knowledge, this is the first flexible full duplex antenna designed, achieving a high isolation level of -50 dB. Moreover, wide bandwidth, improved gain, radiation efficiency, low cost, easy fabrication, and robust performance make it a good option for 5.8 GHz wearable applications.

The rapid development of telecommunication systems has promoted the research of electromagnetic metamaterial absorbers. Based on the equivalent circuit theory, this paper proposes and designs a broadband absorption absorber based on electromagnetic metamaterials, which adopts a sandwich structure with an overall absorber thickness of 3.234 mm. The results show that the absorber has an absorption rate of more than 90% in the X-, Ku-, and K-bands (8.06 GHz-18.46 GHz) for the incident angle varying in the range of 0-50°. The absorption rate is higher than 90% for TE and TM mode electromagnetic waves and electromagnetic waves with polarization angle in the range of 0-50°. The absorber still has good absorption characteristics. The study shows that the absorber has small size, thin thickness, and broad angle broadband absorption characteristics.

A 4-port planar multiple-input multiple-output (MIMO) antenna system design is proposed. The antenna elements are modified meandered wideband antennas which cover frequencies from 674 MHz to 1 GHz, 1.9 GHz to 2.1 GHz, 3.175 GHz to 3.476 GHz, 4.529 GHz to 4.761 GHz and 5.254 to 5.513 GHz for long term evolution (LTE), Internet of Things (IoT), and sub-6 GHz applications and thus can be used for robotic navigation, logistics, healthcare, tracking, transportation etc. Due to very small envelope correlation coefficient (ECC) between the ports (< 0.5), the MIMO configuration can be efficiently implemented which helps in increasing the data rates. It is very compact in size and thus can be used for portable handheld devices. Since there is the problem of current localization due to common ground, the future work aims at minimizing coupling and improving the impedance matching using novel decoupling networks. These MIMO antennas are connected to a common slotted ground plane. Antenna simulation has been done using Computer Simulation Technology (CST) Microwave Studio Suite simulator. A low cost FR-4 substrate with dimensions 65 mm × 90 mm × 1.6 mm has been used for antenna fabrication, and experimental results are obtained using an anechoic chamber and a vector network analyser. ECC and realized gain of the antenna are also obtained experimentally and are almost similar to the simulated results.

In order to improve the practicability and versatility of ultra-wideband (UWB) antennas, a reconfigurable band notch antenna is proposed in this paper. It has a compact size of 18 mm×16 mm×1.6 mm. The reconfigurable band notch function is realized by two small tunable units. The tunable unit makes up of a split ring resonator (SRR), a dielectric substrate, and a varactor diode. The simulation results show that the antenna combines the functions of band notch emergence, removal and movement. The applied reconfigurable method can effectively broaden the continuous movement range of band notch. The measurement proves that the antenna has the band notch reconfigurable function, and the measured results are in good agreement with the simulation ones. The radiation patterns are measured, which are stable and consistent under two modes with and without band notch, showing omnidirectional radiation characteristics. These research results provide reference value for the design of band notch UWB antenna shielding civil narrowband communication band.

Amorphous alloy transformers (AMDT) have become the mainstream of energy-saving and environmentally friendly distribution transformers, but the problem of environmental pollution caused by their noise has become more prominent. The high magnetostriction of amorphous alloy strip and its sensitivity to stress are the main reasons for the vibration of AMDT core. Accurate calculation of the overall core vibration of transformers is the key issues in transformer noise research. This paper studies the vibration of amorphous alloy transformers under operating conditions, and establishes a three-dimensional magnetic-mechanical coupling model considering the magnetostrictive effect of the power transformer core, and the magnetic field distribution and core vibration displacement of the dry-type transformer under no-load conditions are calculated by finite element method. Combined with experiments, the mechanism of vibration generation of amorphous alloy transformer core is studied, and an iron core vibration prediction calculation based on electromagnetic field coupling analysis is proposed. The research results not only have important academic value for exploring the vibration mechanism and noise suppression mechanism of amorphous alloy transformers, but also have important significance for ensuring their efficient operation.

To further improve fault diagnosis performance, a new hybrid feature selection approach combined with whale optimization algorithm and extreme learning machine is presented in this study. Firstly, three filter methods based on different evaluation metrics are employed to select and rank 25 input features derived from gases concentration values, gases ratio and energy-weighted dissolved gas analysis. Then, feature fusion approaches are applied to aggregate feature ranks and form a lower-dimension candidate feature subset. Afterwards, the whale optimization-based extreme learning machine model is implemented to optimize parameters and select optimal feature subsets. The accuracy of the model is used to evaluate the fault diagnosis capability of the concerned feature subsets. Finally, novel subsets are determined as the optimal feature subset to establish a fault diagnosis model. According to the experimental results, the average accuracy of the proposed approach is better than that of other conventional methods, which indicates that the optimal feature subset obtained by the proposed method can significantly promote the fault diagnosis accuracy of the power transformer.

Antennas are essential devices to build everything connected in the era of information. However, the quality of communications would be degraded with the presence of raindrops on the antenna surface. Additional antiwater radomes may generate radiation loss and dispersive impedance mismatch over a broad frequency range, which is not acceptable for next-generation communication systems integrating multiple bands. Here, we report the first experimental demonstration of self-hydrophobic antennas that cover the bands of 1.7 GHz, 3.5 GHz, and 8.5 GHz through a laser-direct-writing treatment. Experimental results show that the return loss, radiation pattern, and efficiency of self-superhydrophobic antennas can be maintained in the mimicked rainy weather. Furthermore, writing hydrophobic nanostructures on both dielectrics and metals is compatible with commercial printed circuitry techniques widely used in industries. Our technique will augment the laser fabrication technology for specialized electromagnetic devices and serve as a powerful and generalized solution for all-weather wireless communication systems.

In the conventional virtual synchronous generator (VSG) dual adaptive inertia and damping control schemes, the inertia J and damping D exhibit different variation patterns in different time intervals and are mutually constrained. To address this problem, an adaptive neural-fuzzy network inference system (ANFIS)-based dual adaptive inertia and damping VSG control technique applied to the direct-drive permanent magnet synchronous wind generator (D-PMSWG) system is proposed in this paper. In ANFIS-VSG, the controller is designed on the basis of the ANFIS control principle, and the input and output data are collected by PID control. The Sugeno-type ANFIS controller model is adopted to train the fuzzy inference system (FIS) online. Moreover, the virtual inertia and damping coefficients can be dynamically adjusted in real time according to the frequency variation without taking the different variations and mutual constraints of inertia J and damping D in different intervals into consideration, so the design difficulty and calculation process can be simplified, and the accuracy of the proposed control algorithm is enhanced through training. Furthermore, when the system is subject to load changes, integrating into the grid from an islanded state, and when the output power sets value steps, the power-frequency characteristics and the anti-interference capability of the three-phase output current of VSG can be improved. Finally, the proposed control strategy is simulated and analyzed based on Matlab/Simulink simulation software, which proves the correctness and effectiveness of the proposed control algorithm.

A novel balanced-to-balanced differential-mode negative group delay (NGD) microwave circuit with excellent common-mode suppression is proposed. The proposed circuit consists of two sections of coupled lines, six transmission lines, and four open-circuited stubs. The coupled lines combined with the open-circuited stubs produce the NGD characteristic, which is connected by the λ/2 transmission lines to form a balanced structure for excellent common-mode suppression. To verify the proposed balanced circuit, a microstrip circuit prototype with a center frequency of f₀ = 1.0 GHz is designed, fabricated, and measured. When the prototype is excited in differential mode, the measured NGD time at f₀ is -3.45 ns with an NGD bandwidth of 16.6 MHz (991.7-1008.3 MHz), insertion loss of less than 2.88 dB, and return loss of more than 11.7 dB. Furthermore, the measured common-mode suppression is greater than 41 dB in the NGD band.

A very economical and compact size wearable antenna operating over Ultra-Wide Band (UWB) spectrum is investigated in the proposed work. The antenna is modelled on a thin FR-4 (0.2 mm) material that makes it flexible and well-suited for wearable appliances. The radiating patch structure is the combination of one square and two elliptical patches rotated at 45˚ and fed with a Coplanar Waveguide (CPW) to achieve a wide impedance bandwidth. The complete radiating structure looks like a flower shape, and it has a partial ground to support the radiation from the antenna over the complete UWB. The flexibility of the proposed structure is investigated by bending it along xz and yz planes using cylindrical shape foam. The peak Specific Absorption Rate (SAR) is demonstrated for 1 g and 10 g of tissues at different chosen frequencies like 3.7, 8.4, and 11.2 GHz using a three-layer phantom model. The presented antenna performance analysis and compact size confirm that it is a good candidate for wearable applications.