A laminated cubic solar absorber (LCSA) with double metal-dielectric layers is proposed. It plays an extremely crucial character in the utilization of solar energy. In particular, it is necessary to ...realize the efficient absorption and heat conversion of solar energy. Through numerical analysis and calculation, it is concluded that the absorption efficiency of LCSA is greater than 90% from 420 nm to 2112 nm. Moreover, the weighted average absorption of Air Mass 1.5 (AM1.5) in the solar radiation range (280 nm–2500 nm) is greater than 96.32%. To explore the mechanism of this absorber, we analyzed the electromagnetic field distribution of the four peaks, and concluded that the reason for achieving the wide-band absorption is that the depth of the double-layer metal dielectric cube produces surface plasmas with different wavelengths. The incident angle insensitivity and polarization independence of LCSA are realized. The simulation results indicate that the thermal radiation efficiency is more than 90% at 2000 K. Based on the above advantages and the high temperature resistance of tungsten (W) and aluminum oxide (Al2O3), the proposed LCSA can be widely used in photothermal conversion and thermal emitters.
We propose a laminated cubic solar absorber (LCSA) with double metal-dielectric layers. The results show that the absorption efficiency of LCSA is more than 90% at 420–2112 nm. In the solar radiation range (280 nm–2500 nm), the weighted average absorptivity is greater than 96.32%. And the thermal radiation efficiency at 2000 K is above 90%. Based on the excellent absorption properties and high temperature resistance of the materials, the proposed LCSA can be widely used in photothermal conversion and heat emitter. Display omitted
•Our proposed solar absorber has a wide absorption range and an average absorption efficiency of more than 93% over the main solar radiation range (280 nm–3000 nm).•The solar absorber has high stability in solar thermal energy conversion.•The weighted average absorption rate at AM1.5 is more than 96% and the thermal radiation efficiency at 2000 K is more than 90%.•The absorber has polarization Angle independence and incident Angle insensitivity.
We provide results of antenna radiation and total radiation efficiency at millimeter-wave frequencies gathered with a new open-ended waveguide-plate method that is compared to a well-known ...two-antenna method. The new method yields improved uncertainty in antenna efficiency measurements. Both methods are based on use of a reverberation chamber. Measurement results are compared to numerical simulations and good agreement (~3% maximum difference) is achieved. Before performing the efficiency measurements, the chamber configuration was assessed with respect to the Rician K-factor, number of uncorrelated paddle orientations, and coherence bandwidth. We calculated the uncertainty using the NIST microwave uncertainty framework capable of performing parallel sensitivity and Monte Carlo analyses. The framework enables us to capture and propagate the uncertainties in the S-parameter measurements to the final efficiency result. The expanded uncertainty that we achieved for these antenna efficiency measurements is 2.60%.
Ammonia, as an alternative option of conventional hydrocarbon energy source, can achieve carbon free emission. However, the production of NOx is responsible for photochemical pollution and human ...health. In order to reduce NOx emission at the premise of guaranteeing energy conversion efficiency, three micro-combustors with different ring-shaped ribs in a cross-sectional view of 1) rectangular, 2) Ո-shaped and 3) Ս-shaped are proposed and fuelled by NH3. Extensive numerical comparisons are made with 3D models built by structured mesh. The effects of 1) inlet velocity, 2) equivalence ratio, 3) rib shape and 4) key parameters of these ribs are evaluated. In addition, the normalized sensitivity of NO formation and related reaction pathways are analyzed. It is found that the double-rib structure is more conducive to achieving better thermal performance. Besides, HNO is found to contribute the most of NO, while NH and NH2 are beneficial to the consumption of NO. When the dimensionless distance x between the rib and the combustor inlet is 3/9, comparing the condition of Φ being 1.1 and 1.0, NO emission is reduced by 47.0%, while the radiation efficiency is only decreased by 1.76%. This work has proven that a high energy conversion efficiency and a low NO emission can be achieved at the same time by properly optimizing the internal structure of the combustor in fuel-rich condition.
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•Micro-combustor with double ribs are studied in fuel-rich combustion.•NOx emission and thermal performance are evaluated in 7 cases.•Sensitivity of NO formation is analyzed under various equivalence ratios.•High radiation efficiency and low NOx emission can be achieved with proper design.
Both the radiation efficiency and bandwidth of electrically small antennas are dramatically reduced as the size decreases. Fundamental limitations on the bandwidth of small antennas have been ...thoroughly treated in the past. However, upper bounds on radiation efficiency have not been established even though it is also of significant importance. Here, radiation from a thin metallic shell is rigorously analyzed to establish fundamental limits on the radiation efficiency of resonant, electrically small antennas in terms of the size and the metal conductivity. Metallic losses are systematically introduced into the circuit model proposed by Chu, and several resonant antennas with maximum radiation efficiencies are analyzed. Resonant electric and magnetic dipole antennas both have maximum radiation efficiencies near 100% until the size is reduced below a critical value, at which point the efficiency scales as electrical size to the fourth power ((ka)4). It is also shown that a helix antenna that resonantly couples the TM10 mode to the TE10 mode has a maximum radiation efficiency, and is about twice that of a resonant dipole or loop antenna. The closed form expressions reported here provide valuable insight into the design of small antennas with optimal efficiencies.
In this paper a compact annular ring micro strip patch antenna with modified ground plane is proposed for UWB applications. The dimensions of proposed antenna are 30 × 26 × 1.6 mm3 which was designed ...on FR4 substrate with the thickness of 1.6 mm, εr = 4.4 and loss tangent parameter 0.02. To enhance the impedance bandwidth of the antenna ground plane is modifiedby extruding an inverted L shape stub and defected with multiple I shaped slots. The radiator consists of annular ringpatch, two circular stubs and one rectangular stub is included to the patch to improve the bandwidth. To design and simulate the proposed antenna CST Studio Suite 2018 is used. The proposed antenna is found with UWB frequency range of 3.1–10 GHz (S11 < −13 dB). Multiple frequency bands are observed in UWB frequency range 3.18 GHz, 6.75 GHz and8.67 GHz with the reflection coefficients of −49.6 dB, −50.2 dB and −45.7 dB respectively. VSWR is less than 2 for the total UWB frequency range. Proposed antenna is better option for UWB applications specially First and third frequency bands (3.18 GHz and 8.67 GHz) are suitable for Radio location (G59) services and second frequency band (6.75 GHz) is suitable for satellite and TV broadcasting applications. Performance of the proposed antenna is evaluated in terms of size, radiation efficiency and radiation patterns and it is better compared with existed systems.
The wireless power transfer (WPT) efficiency to implanted bioelectronic devices is constrained by several frequency-dependent physical mechanisms. Recent works have developed several mathematical ...formulations to understand these mechanisms and predict the optimal operating conditions. However, the existing approaches rely on simplified body models, which are unable to capture important aspects of WPT. Therefore, this article proposes the efficiency analysis approach in anatomical models that can provide insightful information on achieving the optimum operation conditions. First, this approach is validated with a theoretical spherical wave expansion (SWE) analysis, and the results for a simplified spherical model and a human pectoral model are compared. The results show that although a magnetic receiver outperforms an electric one for near-field operation and both the sources could be equally use in the far-field range, it is in the mid-field that the maximum efficiency is achieved with an optimum frequency between 1 and 5 GHz depending on the implantation depth. The receiver orientation is another factor that affects the efficiency, with a maximum difference between the best and worst case scenarios around five times for the electric source and over 13 times for the magnetic one. This approach is used to analyze the case of a deep-implanted pacemaker wirelessly powered by an on-body transmitter and subjected to stochastic misalignments. We evaluate the efficiency and exposure, and we demonstrate how a buffered transmitter can be tailored to achieve maximum powering efficiency. Finally, design guidelines that lead to optimal implantable WPT systems are established from the results obtained with the proposed approach.
This work describes the designof an SRR-loaded pentagon monopole antenna for super wideband (SWB) applications on Rogers RT/Duroid 5880 dielectric material with dielectric constant of 2.2, and a ...dielectric loss tangent of 0.0009. The pentagon patch radiator is fed with a 50 Ω transmission line placed on the dielectric size of 16 mm × 14 mm × 0.787 mm. In this paper, SRR is etched from the radiating element, and partial ground is added to improve the performance characteristics. The proposed antenna has a bandwidth ratio (BR) of 185.38 and an impedance bandwidth (IBW) of 66.38 GHz at a reflection coefficient of −10 dB. It has a fractional bandwidth (FBW) of 197.85% and a bandwidth dimension ratio (BDR) of 19,786 dB, with a peak gain of 6.2 dB. The proposed antenna covers microwave applications, which cover the following spectrums: L: 1–2 GHz, S: 2–4 GHz, C: 4–8 GHz, X: 8–12 GHz, Ku: 12–18 GHz, K: 18–26.5 GHz, Ka: 26.5–40 GHz, and limited millimetre wave frequencies up to 70 GHz.
Fundamental bounds on antenna gain are found via convex optimization of the current density in a prescribed region. Various constraints are considered, including self-resonance and only partial ...control of the current distribution. Derived formulas are valid for arbitrarily shaped radiators of a given conductivity. All the optimization tasks are reduced to eigenvalue problems, which are solved efficiently. The second part of this paper deals with superdirectivity and its associated minimal costs in efficiency and Q-factor. This paper is accompanied by a series of examples practically demonstrating the relevance of the theoretical framework and entirely spanning a wide range of material parameters and electrical sizes used in antenna technology. The presented results are analyzed from a perspective of effectively radiating modes. In contrast to a common approach utilizing spherical modes, the radiating modes of a given body are directly evaluated and analyzed here. All crucial mathematical steps are reviewed in the appendices, including a series of important subroutines to be considered making it possible to reduce the computational burden associated with the evaluation of electrically large structures and structures of high conductivity.
The present commentary aims to explicate the veracity of the assertions posited by Capek and Jelinek in their article titled "Transducer and Radiation Efficiency Figures of a Multiport Antenna ...Array." According to the authors, it is not feasible to employ the Total Active Reflection Coefficient (TARC) to determine the transducer and radiation efficiency figures they propose, in most instances. Our findings indicate that TARC has already integrated the suggested figures, thereby obviating the need for further computation. The findings of our mathematical inquiry indicate that the assertion made by the authors is erroneous. We demonstrate the matching technique for a highly coupled asymmetric three-element dipole antenna array and show that the TARC for the worst case scenario is smaller than both conjugate and 50Ω matchings.