Broadband Radar Cross-Section Reduction Using AMC Technology Iriarte Galarregui, Juan Carlos; Tellechea Pereda, Amagoia; Martinez de Falcon, Jose Luis ...
IEEE transactions on antennas and propagation,
12/2013, Volume:
61, Issue:
12
Journal Article
Peer reviewed
Open access
This paper presents the design, fabrication, and characterization of a planar broadband chessboard structure to reduce the radar cross-section (RCS) of an object. The chessboard -like configuration ...is formed by combining two artificial magnetic conductor (AMC) cells. The bandwidth limitations intrinsic to AMC structures are overcome in this work by properly selecting the phase slope versus frequency of both AMC structures. A 180 ° phase difference has been obtained over more than 40% frequency bandwidth with a RCS reduction larger than 10 dB. The influence of the incidence angle in the working bandwidth has been performed. A good agreement between simulations and measurements is achieved.
Abstract
The sluggish kinetics of Faradaic reactions in bulk electrodes is a significant obstacle to achieve high energy and power density in energy storage devices. Herein, a composite of LiFePO
4
...particles trapped in fast bifunctional conductor rGO&C@Li
3
V
2
(PO
4
)
3
nanosheets is prepared through an in situ competitive redox reaction. The composite exhibits extraordinary rate capability (71 mAh g
−1
at 15 A g
−1
) and remarkable cycling stability (0.03% decay per cycle over 1000 cycles at 10 A g
−1
). Improved extrinsic pseudocapacitive contribution is the origin of fast kinetics, which endows this composite with high energy and power density, since the unique 2D nanosheets and embedded ultrafine LiFePO
4
nanoparticles can shorten the ion and electron diffusion length. Even applied to Li‐ion hybrid capacitors, the obtained devices still achieve high power density of 3.36 kW kg
−1
along with high energy density up to 77.8 Wh kg
−1
. Density functional theory computations also validate that the remarkable rate performance is facilitated by the desirable ionic and electronic conductivity of the composite.
The status of research on the lithium-6 separation method using the lithium-ion separation method by the ionic conductor (LiSMIC) is reported. We describe the advantages of the LiSMIC compared to ...past methods, then give an outline of the method, and the results of single-stage lithium-6 separation experiments. In particular, the latest findings on the effect of the waveform of the applied voltage are presented. Though the square-voltage waveform that gives high isotope separation was shown to lower lithium extraction speed than the continuous voltages, we show that increasing the voltage application time in the square-voltage waveform can make the lithium extraction faster with little effect on the lithium-6 separation. We discuss the scale of the facility required to enrich lithium-6 to 90% based on the data obtained from these experiments and cascade theory. Our analysis reveals that the square-wave voltage gives the minimal facility scale due to the high separation factor despite the slower Li extraction speed. Improving the Li extraction speed can reduce the scale also in the case of other voltages.
•Present a new method to measure the transport AC loss in YBCO coated conductors with artificial transverse crack.•A power law between the AC loss and crack length is found.•The AC loss in the ...vicinity of crack shows no dependence on the frequency, that means it belongs to hysteresis loss.
The purpose of the experiments presented here is to explore the transport alternating current (AC) losses in YBa2Cu3O7−x coated conductor (YBCO CC) that contains a transverse crack. The experimental tests are performed using an improved local calorimetry method with high accuracy. We define a factor called c to describe the ratio between the AC losses of the specimen with and without the crack in terms of unit length. It is found that a power law curve between c and the crack length L coincides perfectly with the experimental results. In addition, we also find that the AC losses in the crack region are hysteretic losses.
The existing standard current-temperature calculations for overhead line (OHL) conductors have been adequate for conventional conductors and their operating temperatures. However, these calculations ...make assumptions and include simplifications about conductor geometry and aero-thermal-dynamics, introducing an error in the High-Temperature Low-Sag conductors operating temperatures. To quantify the error introduced by the shape of strands, the paper employs a Multi-Physics Finite Element Modeling approach that calculates the conjugate heat transfer for trapezoidal stranded OHL conductors. Furthermore, it proposes corrective equations to improve the accuracy of existing methods. The equations incorporate a new Nusselt number correlation for mixed convection and capture the surface area ignored by current calculations. The outer conductor geometry assumptions and the combined natural and forced convective cooling omission in the IEEE and CIGRE methods introduce an error at low (below 0.12 m/s) cross-flow wind speeds suggesting an underestimation of conductor temperature by up to 4%. In medium wind speeds, typically at 0.5 m/s-0.61 m/s, the standard methods overestimate the conductor temperature limiting its current-carrying capability. A 5% uprating for existing OHLs is potentially feasible, particularly for the trapezoidal stranded conductors, when removing the assumptions made in existing methods.
As is frequently seen in sci‐fi movies, future electronics are expected to ultimately be in the form of wearable electronics. To realize wearable electronics, the electric components should be soft, ...flexible, and even stretchable to be human‐friendly. An important step is presented toward realization of wearable electronics by developing a hierarchical multiscale hybrid nanocomposite for highly flexible, stretchable, or transparent conductors. The hybrid nanocomposite combines the enhanced mechanical compliance, electrical conductivity, and optical transparency of small CNTs (d ≈ 1.2 nm) and the enhanced electrical conductivity of relatively bigger Ag nanowire (d ≈ 150 nm) backbone to provide efficient multiscale electron transport path with Ag nanowire current backbone collector and local CNT percolation network. The highly elastic hybrid nanocomposite conductors and highly transparent flexible conductors can be mounted on any non‐planar or soft surfaces to realize human‐friendly electronics interface for future wearable electronics.
Highly stretchable, flexible, or transparent conductors are developed from a hierarchical multiscale nanocomposite to realize wearable electronics. The hybrid nanocomposite shows the enhanced mechanical compliance, electrical conductivity, and optical transparency by providing efficient multiscale electron transport path with a relatively big AgNW (d ≈ 150 nm) current backbone collector and local small CNT (d ≈ 1.2 nm) percolation network.
Sc is used as a dopant to tailor the traditional Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) cathode for protonic ceramic fuel cells (PCFCs). Experiments and first-principles calculations are used in this study ...to explore the influence of Sc-doping on the performance of BSCF cathodes for PCFCs. Sc can only occupy the Co or Fe sites, and doping Sc at the Ba or Sr sites results in the formation of secondary phases. The use of Sc dopant reduces the high thermal expansion of traditional BSCF. More importantly, doping Sc into BSCF reduces the formation of oxygen vacancies while improving hydration and decreasing the proton migration barrier. Doping Sc at the Fe site outperforms doping at the Co site in terms of oxygen vacancy content, hydration capability, and proton migration ability. The new Ba0.5Sr0.5Co0.8Fe0.1Sc0.1O3-δ (Sc doped at Fe site) has a high fuel cell performance of 1666 mW cm−2 at 700 °C and a low polarization resistance of 0.033 Ω cm2. The fuel cell performance is superior to that of most BSCF-based PCFCs reported, indicating the efficacy of using the Sc-doping strategy to tailor BSCF and the importance of selecting the appropriate doping site.
The work presents the investigations of Li1.3Al0.3Ti1.7(PO4)3-xLiF Li-ion conducting ceramics with 0 ≤ x ≤ 0.3 by means of X-ray diffractometry (XRD), 7Li, 19F, 27Al and 31P Magic Angle Spinning ...Nuclear Magnetic Resonance (MAS NMR) spectroscopy, thermogravimetry (TG), scanning electron microscopy (SEM), impedance spectroscopy (IS) and density method. It has been shown that the total ionic conductivity of both as-prepared and ceramic Li1.3Al0.3Ti1.7(PO4)3 is low due to a grain boundary phase exhibiting high electrical resistance. This phase consists mainly of berlinite crystalline phase as well as some amorphous phase containing Al3+ ions. The electrically resistant phases of the grain boundary decompose during sintering with LiF additive. The processes leading to microstructure changes and their effect on the ionic properties of the materials are discussed in the frame of the brick layer model (BLM). The highest total ionic conductivity at room temperature was measured for LATP-0.1LiF ceramic sintered at 800 °C and was equal to σtot = 1.1 × 10−4 S cm−1.
Electric field control of charge carrier density provides a key in situ technology to continuously tune the ground states and map out the phase diagram of correlated electron systems in one device. ...This technique is highly expected to be combined with the modern state-of-the art spectroscopic probes, such as angle-resolved photoemission spectroscopy and scanning tunneling microscopy/spectroscopy (STM/S), to efficiently address these states and the underlying physics. However, it is extremely difficult and not successful so far, mainly because the fabrication process of such devices makes them prohibitive for surface probes. Here, by using a solid Li-ion conductor (SIC) as gate dielectric, we have successfully developed gate-tunable STM/S and visualized the superconductor–insulator transition (SIT) in a thin flake of single crystal (Li, Fe)OHFeSe at the nanoscale. The gate-controlled Li-ion injection first enhances the superconductivity and then drives the flake into an inhomogeneous insulating state, where superconductivity is totally suppressed. This process can be reversed by applying an opposite gate voltage. Importantly, the atomically resolved images allow us to identify the critical role that the injected Li ions play in the tuning process. Our results not only provide clear evidence of the microscopic mechanism of the tunable superconductivity and SIT in the SIC-based (Li, Fe)OHFeSe devices, but also establish SIC-gating STM as a powerful tool for investigating the complicated phase diagram of correlated electron system spectroscopically in a single sample with the field-effect approach.
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