The growing demand for natural fibers in dielectric composite production has accelerated research into plant-based materials, particularly those derived from agricultural waste. Hence, this study attempts to evaluate the effect of processing factors and their elemental composition on the permittivity value of pineapple fiber-based dielectric composites. The dielectric composite was prepared following the randomized experimental conditions of two-level factorial analysis, and the permittivity value was measured using a G-band rectangular waveguide. The most significant factors affecting the permittivity value of the dielectric composites and the best condition were determined. The elemental composition of the dielectric composite was analyzed through an energy dispersive X-ray (EDX) analysis. The best conditions were obtained at a 1:10 ratio of pineapple leaves to distilled water, 50 minutes pulping times with a heating effect, and 5 g of pineapple leaf powder. The highest permittivity value of the composite was recorded at 3.31, with the heating effect as the most significant factor. The elemental analysis of the composite with the highest permittivity value presents that carbon was the dominant element in the composite at 78.05%. The obtained permittivity value exhibited by the composites shows that the pineapple leaf fiber-based dielectric composite could be a potential alternative as an antenna substrate.
This article presents the design and implementation of a beam-steering antenna array using a 4x4 Butler matrix feed network (BMN) for 5G applications. The proposed antenna array can achieve a gain of 14 dBi and a steering range of (+16º, -47º, +46.5º, -15.7º) to cover angular range extending from 45º to 135º. To achieve that, a simple, 4x4 Butler matrix etched on a single-layer microstrip structure is designed, optimized, and fabricated. The proposed design incorporates phase shifters, 3-dB couplers, and cross-over couplers. The proposed matrix is employed as a feeding network for 4-element wideband LPDA antenna array. The fabrication results of the feeding matrix and antenna array show very good agreement with the simulated results.
A design method of compact dual-band multi-beam antennas is proposed by integrating a dual-band metasurface lens with a dual-band planar antenna array in this paper. The dual-band multi-beam antenna designed through this method has a compact configuration, low cost, and is easy to integrate with other devices for communication. The dual-band multi-beam function of the antenna by this method has been verified through a double-layer dual-band metasurface lens and a five-element dual-bandplanar antenna array. A dual-band meta-cell with relatively independent performance at 13 GHz and 23.5 GHz is designed to form the metasurface lens. Dual-band magnetoelectric (ME) dipole antenna is used as the feed antenna element. The simulated and tested results indicate that the lens antenna generates five independent beams at both 13 GHz and 23.5 GHz. Considering practical applications, solutions to improve antenna performance and reduce losses have also been proposed.
According to the characteristic mode basis function method (CMBFM) in analyzing electrically large problems, blocking and extending lead to the problem of slow convergence in the iterative solution of a reduced matrix equation, and the characteristic mode basis function method combined with principal component analysis (CMBFM-PCA) is proposed in this study. The characteristic modes (CMs), calculated from each extended block, are subjected to PCA to enhance the orthogonality between them and improve the reduced matrix's condition number to facilitate its quick convergence through an iterative solution. The corresponding numerical calculations demonstrate that significant efficiency and accuracy are achieved by the proposed method.
In this research article, we propose a split ring resonator (SRR) based metasurface absorber based on graphene material. The performance of the graphene-based absorber at terahertz frequencies can be altered by varying the chemical potential of graphene material. Because of its excellent tunability and optical responsiveness at terahertz frequency, graphene-based metamaterials have been widely used in optoelectronic devices, sensors, filters, and many more. The proposed structure contains three layers namely graphene-based patch as a conductive layer, lossy silicon as a dielectric layer, and finally gold as a bottom conductive layer. The proposed unit cell resonates at three different absorption peak frequencies of 2.91 THz, 8.1 THz, and 9.61 THz with operating frequency bands at (2.66 THz to 3.12 THz), (7.71 THz-8.47 THz), and (9.57 THz-9.63 THz), respectively. The purpose of this research is to present a thorough investigation of graphene-based THz metamaterial absorbers, including modeling and verification of the structure through an equivalent circuit approach. It is very much beneficial to understand the conductive phenomenon of graphene material by tuning the Fermi chemical potential and achieve a high percent level of absorption for the corresponding absorption frequency bands.
This paper presents a design of high-performance parallel-connected filters using the Chained filtering function. The filtering functions enable the placement of multiple return loss zeros at the same frequency, resulting in reduced sensitivity to fabrication tolerance and design complexity compared to traditional Chebyshev counterparts. To demonstrate the feasibility of this technique, a new filtering function (FN) based on Chained filtering function is derived, and prototypes of fourth and sixth-degree Chained function filters in a parallel-connected topology are designed and fabricated. The overall size of the filters is 2.5 cm x 4 cm (fourth degree) and 2.5 cm x 5 cm (sixth degree). The measured insertion and return losses are 2.833 dB and 16.150 dB (fourth degree), and 2.674 dB and 18.074 dB (sixth degree). The achievable selectivity of the filters is 78.17 (fourth degree) and 89.68 (sixth degree). This design technique can serve as a useful tool for filter design engineers in terms of implementation.
Optical nano-antenna offers a new scheme for solar energy collection by breaking through the band-gap limitation of semiconductor materials. However, complex structure, low efficiency, and narrow bandwidth remain major issues. To address these problems, we propose a novel helical optical nano-antenna based on the bridge structure. The antenna structure consists of two coplanar Archimedes spiral arms and a base layer. We analyze the influence mechanism of structural factors on its radiation efficiency and polarization characteristics. Our results show that the antenna structure achieves a total radiation efficiency of 83.13% in the wide wavelength range of 400 to 1600 nm, which is significantly higher than that of the previously proposed dipole nano-antenna. For different linearly polarized incident waves, the antenna structure obtains the same order electric field at the spiral gap, which indicates that the antenna structure can fully consider the polarization characteristics of sunlight. It fundamentally solves the problem that the linearly polarized antenna can only receive half of the solar energy, improving the absorption efficiency.
In this paper, we propose a new physical model to accurately estimate the absorption characteristics in Metamaterial Perfect Absorbers (MPAs). The proposed model, relying on the reflection and refraction theory of microwaves, explains the physical mechanism of absorption and how unit-cell constitutive parameters can contribute to control the absorption characteristics. By considering Floquet modes (TE and TM) as two incident cross-polarized waves, analytical expressions have been established to estimate the absorption at normal and oblique incidences from the extracted constitutive parameters of the unit-cell. Analytical predictions are in excellent agreement with numerical results, proving the validity of our model. Furthermore, it can give an idea behind the absorption characteristics of MPA unit-cells without passing through full-wave simulation which usually takes time. Compared to previous works reported in the literature, the proposed method is efficient and does not require time-consuming tests and processing steps. Finally, analytical findings in this work hold for the general shapes of MPA resonators.
A dual-band metasurface antenna is designed consisting of three-layer metal patches and two-layer dielectric substrates. To facilitate the modal analysis of the metasurface, Characteristic Mode Analysis (CMA) is used to analyze the metasurface antenna with 4×4 rectangular patches, and the performance of the antenna is optimized based on the Modal Significance (MS) curves. In order to excite the current of different characteristic modes at certain frequencies, the symmetric resonant arms and cross-shaped impedance matching converters are used in the feeding structure. The measured results are consistent with the simulated values, and the designed antenna can yield the gains of 7.67 dBi at 3.5 GHz and 7.28 dBi at 4.9 GHz, which provides the potential applications in 5G and other wireless communications.
This paper presents a new process for additive manufacturing of purely metallic antennas based on Fused Deposition Modeling (FDM), with a filament composed by a mix between rounded shape copper powders with particle size in the range from 20 to 80 μm embedded in a polymeric matrix, to accomplish the desired antenna shape, followed by a post-processing involving de-binding to remove the base polymer and a further sintering process for obtaining a purely metallic component. This new process is validated by means of a prototype antenna consisting on a modified tri-band cactus monopole that is manufactured and measured demonstrating results in accordance with standard and alternative additive manufacturing techniques reported in literature.
This article focuses on the low-frequency magnetic shielding of double-layer conducting plates with periodic circular apertures. The shielding effectiveness (SE) is measured as the insertion loss of the plates when they are placed between a pair of coaxial loops, one for magnetic field emission and the other for receiving. Our experimental results show that the SE sharply increases with the layer-to-layer spacing increasing from zero to the aperture diameter. For aluminum plates with 1 mm thickness, 20 mm unit cell and 10 mm aperture diameter, the enhancement is approximately 10 dB and 20 dB for 3 mm and 9 mm spacing, respectively. In addition, the effect of the lateral deviation on the SE is evident only if the spacing is smaller than the aperture diameter.
High resolution Synthetic Aperture Radar (SAR) images are affected by speckle noise, which considerably reduces their visibility and complicates the target identification. In this paper, a new Compressive Sensing (CS) method is proposed to reduce the speckle noise effects of complex valued SAR images. The sparsity of the SAR images allows solving the CS problem using Multiple Measurements Vector (MMV) configuration. Therefore, a special weighted norm is constructed to solve the optimization problem, so that the Variance-Based Joint Sparsity (VBJS) model is used to calculate the weights. An efficient Alternating Direction Method of Multipliers (ADMM) is developed to solve the optimization problem. The obtained results using raw complex-valued measurements with ground truth demonstrate the effectiveness of the proposed despeckling method in terms of both image quality and computational cost.
Studies of soil moisture with Global Navigation Satellite System (GNSS) have gained the attention of several researchers. Multipath amplitude, multipath phase, and multipath frequency are multipath observables that are utilized in the study of soil moisture. However, an inter-comparison of the performance of these parameters for soil moisture under different roughness and vegetation conditions is very much required to have a better insight so that more robust inversion algorithm for soil moisture retrieval with multipath observables can be designed. Therefore, this paper analyses the performance of these multipath observables for soil moisture over bare smooth soil, rough surface, and vegetated soil. Two different fields have been investigated to include the location variability. Navigation with Indian constellation (NavIC) multipath signal has been used in this study. Statistical parameters such as correlation coefficient (R), Root Mean Square Error (RMSE), and sensitivity have been determined to study the performance of multipath observable for soil moisture under different surface roughness and vegetation conditions.
An asymmetric coplanar waveguide (CPW) fed wideband circularly polarized monopole antenna with a slot structure is proposed in this article. Phase gradient metasurface (PGM) is placed beneath the monopole to improve the gain. Circular polarization (CP) is achieved over wide bandwidth by combining the monopole and slot modes. The asymmetric CPW-fed monopole antenna provides CP at lower frequencies, and slot mode provides CP at higher frequencies. The asymmetric ground plane in the monopole and asymmetric strips in the slot are combined to produce wide axial ratio bandwidth. The proposed design's detailed construction and operation are discussed with experimental validation. The proposed wideband CP antenna provides an impedance bandwidth of 95.46% and axial ratio bandwidth of 67.61%. The peak gain of 5.2 dBic is obtained at 2.35 GHz with 2 dB variation over operating bandwidth. The obtained radiation patterns provide good broadside radiation with better cross-polarization levels than co-polarization.
The safety of the electromagnetic environment of wireless power transfer (WPT) systems is one of the prerequisites for the application of wireless charging technology for electric vehicles (EVs). The electromagnetic characteristics of a wireless charging EV with a new 7.7 kW WPT system were modeled and analyzed in this paper. Firstly, a complete model of the magnetic coupler was built as a source of electromagnetic radiation, and an external excitation source was added by coupling the resonant coils to the double inductor-capacitor-capacitor (LCC-LCC) topology circuit model. Secondly, the finite element analysis software COMSOL Multiphysics was used to solve for the magneto-quasi-static values to verify the electromagnetic safety of the wireless charging process. Then, two charging scenarios were investigated when the GA and VA aligned and misaligned, involving lateral offset and longitudinal offset cases. Finally, the simulation results were compared and analyzed, showing that the values of electromagnetic fields become higher as the offset distance increases. In worst-case scenarios, the highest magnetic flux density (1.1 μT) is observed in the virtual plane of the test on the left side of the vehicle, which occupies only 17.6% of the limits specified in ICNIRP 1998 (6.25 μT), indicating a good EMF safety performance of the wireless charging system.
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