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[IEEE 2018 International Conference on Microwave and Millimeter Wave Technology (ICMMT) - Chengdu, China (2018.5.7-2018.5.11)] 2018 International Conference on Microwave and Millimeter Wave Technology (ICMMT) - A Graphene-Based Tunable THz Metamaterial Absorber
摘要： A graphene-based tunable THz metamaterial absorber is presented in this paper. The proposed absorber is a periodical structure with the unit cell composed of four square gold patches on single-layered graphene, which are placed on a dielectric spacer supported by a gold bottom layer. Simulation results indicate that the absorption frequency can be tuned by varying the chemical potential of graphene through controlling of the electrostatic gating or the geometry size of the gold patch. By introducing more gold patches with different size into the unit cell, we can obviously extend the absorption bandwidth to achieve a broadband absorber.
关键词： broadband,THz,metamaterial absorber,tunable,graphene
更新于2025-09-04 15:30:14
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Refractory Ultra-Broadband Perfect Absorber from Visible to Near-Infrared
摘要： The spectral range of solar radiation observed on the earth is approximately 295 to 2500 nm. How to widen the absorption band of the plasmonic absorber in this range has become a hot issue in recent years. In this paper, we propose a highly applicable refractory perfect absorber with an elliptical titanium nanodisk array based on a silica–titanium–silica–titanium four-layer structure. Through theoretical design and numerical demonstration, the interaction of surface plasmon resonance with the Fabry–Perot cavity resonance results in high absorption characteristics. Our investigations illustrate that it can achieve ultra-broadband absorption above 90% from a visible 550-nm wavelength to a near-infrared 2200-nm wavelength continuously. In particular, a continuous 712-nm broadband perfect absorption of up to 99% is achieved from wavelengths from 1013 to 1725 nm. The air mass 1.5 solar simulation from a ?nite-difference time domain demonstrates that this absorber can provide an average absorption rate of 93.26% from wavelengths of 295 to 2500 nm, which can absorb solar radiation ef?ciently on the earth. Because of the high melting point of Ti material and the symmetrical structure of this device, this perfect absorber has excellent thermal stability, polarization independence, and large incident-angle insensitivity. Hence, it can be used for solar cells, thermal emitters, and infrared detection with further investigation.
关键词： large incident-angle insensitivity,ultra-broadband,perfect absorber,refractory
更新于2025-09-04 15:30:14
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Current‐Enhanced Broadband THz Emission from Spintronic Devices
摘要： An ultra-broadband terahertz (THz) emitter covering a wide range of frequencies from 0.1 to 10 THz is highly desired for spectroscopy applications. So far, spintronic THz emitters have been proven as one class of efficient THz sources with a broadband spectrum while the performance in the lower THz frequency range (0.1–0.5 THz) limits its applications. In this work, a novel concept of a current-enhanced broad spectrum from spintronic THz emitters combined with semiconductor materials is demonstrated. A 2–3 order enhancement of the THz signals in a lower THz frequency range (0.1–0.5 THz) is observed, in addition to a comparable performance at higher frequencies from this hybrid emitter. With a bias current, there is a photoconduction contribution from semiconductor materials, which can be constructively interfered with the THz signals generated from the magnetic heterostructures driven by the inverse spin Hall effect (ISHE). These findings push forward the utilization of metallic heterostructure-based THz emitters on the ultra-broadband THz emission spectroscopy.
关键词： spintronic devices,broadband spectrum,photoconduction,terahertz emitters
更新于2025-09-04 15:30:14
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An upgraded interferometer-polarimeter system for broadband fluctuation measurements
摘要： Measuring high-frequency fluctuations (above tearing mode frequencies) is important for diagnosing instabilities and transport phenomena. The Madison Symmetric Torus interferometer-polarimeter system has been upgraded to utilize improved planar-diode mixer technology. The new mixers reduce phase noise and allow more sensitive measurements of fluctuations at high frequency. Typical polarimeter rms phase noise values of 0.05°–0.07° are obtained with 400 kHz bandwidth. The low phase noise enables the resolution of fluctuations up to 250 kHz for polarimetry and 600 kHz for interferometry. The importance of probe beam alignment for polarimetry is also verified; previously reported tolerances of ≤0.1 mm displacement for equilibrium and tearing mode measurements minimize contamination due to spatial misalignment to within acceptable levels for chords near the magnetic axis.
关键词： Faraday rotation,interferometer-polarimeter,planar-diode mixer,broadband fluctuation measurements,phase noise
更新于2025-09-04 15:30:14