Based on the finite-difference time-domain (FDTD) method, a wide-band solar absorber (WA) is constructed and simulated in this paper. Due to the Fabry-Perot resonance (FPR), the near-field resonance ...mode, the surface plasmon resonance (SPR) and gap resonance in different structure, the WA obtains efficient and wide-band absorption. The absorption efficiency in 373–1967 nm band is >90 %, and in 817–1830 nm band is >98 %, and the average absorption efficiency at air mass 1.5 (AM 1.5) reaches 91.10 % (280–2500 nm). The structure is insensitive to the change of incident angle. The reduced absorption efficiency is 9.23 % when the incident angle increases from 0° to 60°. In addition, the structure can work stably at high temperature, and the thermal radiation efficiency at 1500 K is as high as 85.13 %. Due to the efficient and wide-band absorption and high thermal emission efficiency, the WA can be widely used in solar energy collection and energy radiation.
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•The bandwidth of the absorption efficiency ≥ 90 % is 1594 nm, and of the absorption efficiency ≥ 98 % is 1013 nm.•The average absorption efficiency of the structure at AM 1.5 is 91.10 %.•The thermal radiation efficiency of the structure is 85.13% % at 1500 K.
Wearable Antennas for Human Identification at 2.45 GHz Saadat, Waqar; Raurale, Sumit A.; Conway, Gareth A. ...
IEEE transactions on antennas and propagation,
2022-Jan., 2022-1-00, 20220101, Letnik:
70, Številka:
1
Journal Article
Recenzirano
In this article, antenna sensitivity to the human body was investigated for the purpose of user identification. Through numerical and experimental analysis, the variation of the antenna return loss ...was measured while interacting with multiple human bodies at 2.45 GHz. A new antenna is proposed, which distributes the field within the tissue, enhancing the identification accuracy of the machine learning algorithm. Experiments conducted on six human subjects gave the classification accuracy of approximately 98%. To overcome the reduction in radiation efficiency, a layered stacked-patch design is introduced, which increases the radiation efficiency to 27% for the close-fitting wearable antenna.
In this study, the sound radiation characteristics of the laminated structures reinforced by honeycomb and composed by viscoelastic material was investigated. Temperature- and frequency-dependent ...behaviors of the viscoelastic material were considered in this analysis, those parameters affected the dynamics effective properties of the composite structure. After the dynamic equivalent effective stiffness and the dynamic deformation of the structure are determined according to the homogenous asymptotic method, the sound radiation behaviors of the structures in fields of frequency and temperature are achieved. Consequently, the sound radiation characteristic, such as the sound pressure in far-field and the sound radiation efficiency that influenced by the geometry dimensions of the honeycomb structure was examined. Finally, the study is validated by the degeneration method with a degeneration mathematical model that performed in the published literature.
Radiation efficiency is one of the key parameters for smartphone antennas. However, the actual mechanism governing radiation efficiency remains unclear, and a few works have been published. This work ...is an attempt to extend the theory of characteristic modes (TCMs) to the lossy smartphone antenna for gaining insight into what causes efficiency variation and realizing efficiency improvement. Compared with the classical TCM, the CM analysis (CMA) adopted in this work has the capacity to handle lossy smartphone antenna. By using such an analysis approach, we find, quite interestingly, that suppressing the higher-order modes is an effective optimization strategy to enhance efficiency. Then, an optimized antenna with considerable improvement in efficiency is proposed. Finally, to meet the requirement of practical application, the additional LC circuit and through holes are introduced into this proposed optimized antenna. GSM 900 of 890-960MHz can be covered by this finally proposed antenna, and the measured peak total efficiency is improved from 26% to 43%. Due to the attractive features of small heights (4 mm) and tiny clearances (0.25 mm), the proposed designs are promising for application in a smartphone with a full-view display and thin profile.
Reverberation chambers are becoming a popular alternative testing facility for a wide range of electromagnetic applications. Because of the statistical environment created inside a reverberation ...chamber, they offer a unique test facility. In particular, these chambers are ideally suited for performing radiated power measurements of either an antenna or device under test, and as such, it is possible to determine the efficiency of antennas. There have been several reverberation chamber techniques proposed over the years for measuring the antenna efficiency; however, these techniques require either the use of a reference antenna (i.e., an antenna with a known efficiency) and/or require the assumption that the two antennas used in the test have identical efficiencies. In this paper, we present three different approaches for determining both the radiation and total efficiencies of an unknown antenna that overcome these limitations and assumptions. We present a one-antenna approach, a two-antenna approach, and a three-antenna approach. We present measured data for three different antennas in order to compare these three approaches. We also discuss the uncertainties related to these types of measurements.
A novel kind of leaky-wave antenna (LWA) array with a power-recycling feeding network is proposed for radiation efficiency improvement. The antenna array is constructed by two kinds of ...substrate-integrated waveguide LWAs with different periodic slots. One kind of the LWA is designed to work on the fundamental (m = 0) wave and radiates in the forward direction. The other one is designed to work on the -1th (m = -1) spatial harmonic and radiates in the backward direction. The nonradiated power at the end of one kind of the LWA is directly fed into the other (adjacent) kind of the LWA in reverse direction. Therefore, the reversed feeding can compensate the opposite radiation direction of the two kinds of LWAs, and result in a superposition of radiation. So, both the gain and radiation efficiency of the antenna can be significantly improved, while the array maintains a compact size as those of traditional planar arrays. Simulation results are compared with measurement results to validate the proposed concept of integrating different leaky-wave structures into one array.
A novel feeding method for linear DRA arrays is presented, illuminating the use of the power divider, transitions, and launchers, and keeping uniform excitation to array elements. This results in a ...high-gain DRA array with low losses with a design that is simple, compact and inexpensive. The proposed feeding method is based on exciting standing waves using discrete metallic patches in a simple design procedure. Two arrays with two and four DRA elements are presented as a proof of concept, which provide high gains of 12 and 15dBi, respectively, which are close to the theoretical limit based on array theory. The radiation efficiency for both arrays is about 93%, which is equal to the array element efficiency, confirming that the feeding method does not add losses as in the case of standard methods. To facilitate the fabrication process, the entire array structure is 3D-printed, which significantly decreases the complexity of fabrication and alignment. Compared to state-of-the-art feeding techniques, the proposed method provides higher gain and higher efficiency with a smaller electrical size.
Mg ferrites are essential to stabilize the spinel structure of magnetic-dielectric composites. This study investigates the effect of Ga ions on the magnetic and dielectric properties and low-loss ...characteristics of Mg–Cd composites sintered at low temperature with the addition of 2.5 wt% Bi2O3. The variation in the Ga substitution of Fe at the octahedral site, with x increasing from 0.00 to 0.18 (Mg0.8Cd0.2Fe2-xGaxO4), increases magnetization, which plays the key role in determining the permeability. The real part of the permeability (μ′) of the Ga-substituted ferrites was reported to increase monotonically from 10 H/m to 56 H/m. Meanwhile, the real part of the permittivity (ε′) was optimized by the Ga ions. Consequently, relatively matching impedance factor (Z ≈ 1.34) and wideband characteristic factor (BWR ≈ 2.5 × 10−3) were obtained to achieve miniaturization and high radiation performance of antennas. Additionally, enhanced magnetization (Ms = 22.32 emu/g, Hc = 55.07 Oe) as well as magnetic (tanδμ~10−2) and dielectric tangents (tanδε~10−4-10−3) of low orders of magnitude promise outstanding operating performance in the high-frequency region.
Optical bound states in the continuum (BICs) offer strong interactions with quantum emitters and have been extensively studied for manipulating spontaneous emission, lasing, and polariton ...Bose–Einstein condensation. However, the out-coupling efficiency of quasi-BIC emission, crucial for practical light-emitting devices, has received less attention. Here, we report an adaptable approach for enhancing quasi-BIC emission from a resonant monocrystalline silicon (c-Si) metasurface through lattice and multipolar engineering. We identify dual-BICs originating from electric quadrupoles (EQ) and out-of-plane magnetic dipoles, with EQ quasi-BICs exhibiting concentrated near-fields near the c-Si nanodisks. The enhanced fractional radiative local density of states of EQ quasi-BICs overlaps spatially with the emitters, promoting efficient out-coupling. Furthermore, coupling the EQ quasi-BICs with Rayleigh anomalies enhances directional emission intensity, and we observe inherent opposite topological charges in the multipolarly controlled dual-BICs. These findings provide valuable insights for developing efficient nanophotonic devices based on quasi-BICs.
A micro-scaled printed log periodic dipole array (LPDA) antenna is proposed for terahertz (THz) applications. The proposed low profile graphene conductor based LPDA antenna is designed with ...integrated protudent dipoles to realize super wide bandwidth and high gain characteristics. The suggested THz antenna is designed on a 10 µm thick Rogers RT / Duroid 5880 ™ substrate material of dimension 450 µm × 500 µm. The proposed antenna exhibits 2:1 VSWR operating super wide bandwidth (SWB) of 30050 GHz (0.09–30.14 THz) with a peak gain of 16.02 dBi. The designed antenna shows fractional bandwidth of 199.46% along with a huge bandwidth ratio of 334.88:1. The radiation efficiency balancing from 85% to 98.2% is maintained throughout the whole operating –10 dB SWB (0.09–30.14 THz). Design formulation of the proposed structure, structural parametric analysis, surface current distribution and characteristics parameters are discussed in detail in this paper. The proposed antenna covers the entire frequency band of the terahertz region to support a number of sub-terahertz and terahertz communication applications such as high speed short distance communication, video rate imaging, biomedical imaging, surveillance, mine detection, sensing, and security scanning.
