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.