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Acoustic perfect absorbers via spiral metasurfaces with embedded apertures
摘要： In this work, we analytically and experimentally present perfect acoustic absorbers via spiral metasurfaces composed of coiled channels and embedded apertures. Perfect absorption (reaching 0.999 in experiments) is realized with an ultra-thin thickness down to (cid:2)1/100th of the operating wavelength. Owing to the superior impedance manipulation provided by the embedded apertures, perfect absorption with tunable frequencies is demonstrated. Our results would contribute to paving a way towards designing thin and light absorbers for the low frequency absorption challenge.
关键词： embedded apertures,spiral metasurfaces,impedance manipulation,acoustic perfect absorbers,low frequency absorption
更新于2025-09-09 09:28:46
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Ultra-Narrowband Metamaterial Absorbers for High Spectral Resolution Infrared Spectroscopy
摘要： Metamaterial perfect absorbers (MPAs) are artificial materials composed of an array of subwavelength structures that manipulate electromagnetic waves to achieve extraordinary light absorption properties. Driven by the advent of the Internet of Things, MPAs are employed in microelectromechanical systems for the development of efficient and miniaturized IR detectors, imagers, and spectrometers, thanks to their lithographically tunable peak absorption, spectral selectivity, and ultrathin thickness. MPAs characterized by high absorptance in narrow spectral bands are particularly desirable for the implementation of high-resolution IR spectroscopic sensors. Yet, no accurate analytical model is currently available to guide the design of an MPA with ultra-narrow absorption bandwidth, while meeting all the stringent requirements for spectroscopic sensors. Here, a circuit model capable of accurately predicting spectral responses of metal–insulator–metal (MIM) IR absorbers is reported. The model is experimentally validated in the mid-wavelength IR spectral range and exploited for the first demonstration of an MIM IR absorber that exhibits performance approaching the predicted physical limits: full-width at half-maximum ≈3% and near-unity absorption (η > 99.7%) at 5.83 μm wavelength, while independent of incident angle and polarization of the impinging IR radiation. These unprecedented absorption properties are key enablers for the development of miniaturized, low-cost, and high-resolution spectrometers.
关键词： spectroscopy,microelectromechanical system,plasmonics,infrared absorbers,metamaterials
更新于2025-09-09 09:28:46
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Metamaterials and metasurfaces for designing metadevices: Perfect absorbers and microstrip patch antennas
摘要： In the past twenty years, electromagnetic metamaterials represented by left-handed metamaterials (LHMs) have attracted considerable attention due to the unique properties such as negative refraction, perfect lens, and electromagnetic cloaks. In this paper, we present a comprehensive review of our group’s work on metamaterials and metasurfaces. We present several types of LHMs and chiral metamaterials. As a two-dimensional equivalent of bulk three-dimensional metamaterials, metasurfaces have led to a myriad of devices due to the advantages of lower profile, lower losses, and simpler to fabricate than bulk three-dimensional metamaterials. We demonstrate the novel microwave metadevices based on metamaterials and metasurfaces: perfect absorbers and microwave patch antennas, including novel transmission line antennas, high gain resonant cavity antennas, wide scanning phased array antennas, and circularly polarized antennas.
关键词： microstrip patch antennas,metasurfaces,chiral metamaterials,perfect absorbers,left-handed metamaterials
更新于2025-09-09 09:28:46
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Metamaterials - Devices and Applications || Active and Tunable Metamaterials
摘要： In this chapter, we will first present the research progress on the active and tunable metamaterials based on different realization methods, such as varactor diodes, liquid crystals, superconductivity, and structural-shifting structures. Then we focus on the achievements in our research group for the tunable metamaterials by using the ferrite as the substrate of metamaterials. We will present the designs and theories of single-, dual-, and triple-band tunable metamaterials based on the ferrite and the design of metamaterial absorbers based on the ferrite. It will indicate that the proposed tunable metamaterials have many advantages compared with other active and tunable metamaterials.
关键词： tunable metamaterials and absorbers,ferrite
更新于2025-09-09 09:28:46
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Ultra-wideband and Polarization-Insensitive Perfect Absorber Using Multilayer Metamaterials, Lumped Resistors, and Strong Coupling Effects
摘要： We theoretically and experimentally proposed a new structure of ultra-wideband and thin perfect metamaterial absorber loaded with lumped resistances. The thin absorber was composed of four dielectric layers, the metallic double split ring resonators (MDSRR) microstructures and a set of lumped resistors. The mechanism of the ultra-wideband absorption was analyzed and parametric study was also carried out to achieve ultra-wideband operation. The features of ultra-wideband, polarization-insensitivity, and angle-immune absorption were systematically characterized by the angular absorption spectrum, the near electric-field, the surface current distributions and dielectric and ohmic losses. Numerical results show that the proposed metamaterial absorber achieved perfect absorption with absorptivity larger than 80% at the normal incidences within 4.52~25.42 GHz (an absolute bandwidth of 20.9GHz), corresponding to a fractional bandwidth of 139.6%. For verification, a thin metamaterial absorber was implemented using the common printed circuit board method and then measured in a microwave anechoic chamber. Numerical and experimental results agreed well with each other and verified the desired polarization-insensitive ultra-wideband perfect absorption.
关键词： Ultra-wideband,Polarization,Metamaterial absorbers,Subwavelength structures
更新于2025-09-09 09:28:46
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DESIGN OF NONUNIFORM METALLIC ANECHOIC CHAMBER FOR RADIATION PATTERN MEASUREMENT
摘要： Antenna pattern measurement is an essential step in antenna quali?cation which should be done in anechoic chambers. The common method for construction of the anechoic chamber is to cover all inside walls by the electromagnetic absorbers. In this paper, a new method is presented to design a fully metallic chamber by controlling the electromagnetic wave propagation inside the chamber and guiding them to a piece of absorber. Therefore, a desirable quiet zone is formed inside the chamber while a great reduction of absorber usage is achieved. The proposed chamber is analyzed using ray tracing method, and its performance is evaluated by simulation which shows the practicality of the proposed chamber.
关键词： anechoic chamber,ray tracing method,antenna pattern measurement,electromagnetic absorbers,quiet zone
更新于2025-09-09 09:28:46
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Thermal and electrical wavelength tuning of Bragg reflection with ultraviolet light absorbers in polymer-stabilized cholesteric liquid crystals
摘要： Autonomous stimulus-responsive polymer-stabilized cholesteric liquid crystals (PSCLCs) are promising materials for various applications. In this work, a PSCLC cell whose wavelength of selective reflection changes autonomously according to the temperature or can be controlled by applying an electric field was fabricated by using ultraviolet (UV) light absorbers. The UV light absorbers in the PSCLC cell are used not only for preventing the degradation of the substrate but also for stabilizing the polymeric network by converting the harmful UV radiation into harmless heat. To achieve the optimum conditions, different types of UV light absorbers were examined at various concentrations and UV light intensities. The results revealed that the benzophenone-type UV absorbers provide an extensive blue-shift tuning of the Bragg reflection in the PSCLC. By determining the molar extinction coefficient (e) values, which provide a measure of UV light absorption at a given wavelength, at three important wavelengths—the maximum absorption wavelength (lmax) of the UV absorbers, lmax of the photoinitiator (345 nm), and the UV lamp wavelength (365 nm)—the UV light intensity gradient throughout the cell was defined. Reduction of the e value indicates a sharp drop in the UV light intensity within a PSCLC cell. This phenomenon leads to the diffusion of reactive mesogens towards the UV lamp side of the cell to achieve a tight pitch gradient and extensive blue-shift tuning of the selective reflection.
关键词： thermal tuning,blue-shift tuning,electrical tuning,UV light absorbers,polymer-stabilized cholesteric liquid crystals
更新于2025-09-09 09:28:46
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AIP Conference Proceedings [Author(s) SolarPACES 2017: International Conference on Concentrating Solar Power and Chemical Energy Systems - Santiago, Chile (26–29 September 2017)] - Diffractive gratings to improve TiAlN based spectrally selective solar absorbers
摘要： Based on an optimized TiAlN multilayer structure achieving high absorption and low thermal emission at temperatures above 500°C for CSP receivers, the authors demonstrate that - sub-wavelength period gratings associated with the multilayer can further increase the absorption and thus the efficiency of the CSP system. The C-method (Chandezon Method) is used to theoretically optimize the grating profiles. An experimental demonstration of the combination of lithographic grating fabrication and absorptive layer deposition using Inconel 625 as substrates is also presented. Experimental results show that the microtexturing increases the absorption from 91% to 95% while the emissivity at 550°C is kept at an acceptable level, increasing from 32% to 38%, representing an enhancement of almost 3% of the photothermal efficiency in comparison to non-structured coatings. Textured absorbers were annealed in air at 500°C and demonstrated high thermal stability of their optical properties during more than 336h. Textured absorber would also be greatly efficient for CSP plants working at lower temperature (250-300°C), such as linear Fresnel CSP for process heat production, since optical properties and thermal stability will be excellent at these temperatures.
关键词： diffractive gratings,TiAlN,photothermal efficiency,CSP receivers,spectrally selective solar absorbers
更新于2025-09-04 15:30:14
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[Institution of Engineering and Technology 12th European Conference on Antennas and Propagation (EuCAP 2018) - London, UK (9-13 April 2018)] 12th European Conference on Antennas and Propagation (EuCAP 2018) - Concept of an Asymmetric Metasurface Absorber
摘要： In this talk we show how to break the angular symmetry of electromagnetic response of thin absorbers. Based on our recent results on multichannel metasurfaces, we propose a new concept of asymmetric absorbers in which the absorption coefficient for waves impinging from a given oblique angle is extraordinarily different from that for waves incident from the oppositely tilted direction. The proposed asymmetric structure realizes controllable reflectance (from 0 to 0.99) for waves incident from one direction, exhibiting total absorption when the sign of the incidence angle is reversed. We provide a theoretical analysis for the asymmetric absorber as well as a numerical verification.
关键词： surface impedances,asymmetric,Floquet harmonics,absorbers,multichannel metasurfaces
更新于2025-09-04 15:30:14
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ANALYSIS OF POWER FLOW BY POYNTING VECTORS FOR ELECTROMAGNETIC WAVE ABSORBERS USING FREQUENCY SELECTIVE SURFACES
摘要： The power ?ow for electromagnetic wave absorbers consisting of pattern conductor layers acting as frequency selective surfaces, absorption layers, and short circuit layers was investigated by Poynting vectors. A method was developed to evaluate the ?ow of electromagnetic wave power by an electromagnetic wave absorber upon irradiation with electromagnetic waves. The results indicate that the electromagnetic wave absorption phenomenon involves generation of real power, a real part of the time averaged Poynting vector, which moves horizontally along the pattern surface after the incident wave has irradiated the pattern conductor from the vertical direction, and the direction of power ?ow changes to enter the polymer layer from the pattern interval, causing an accumulation of power inside the polymer layer, followed by absorption, which is converted into heat due to the loss factor.
关键词： Electromagnetic wave absorbers,Absorption layers,Power flow,Frequency selective surfaces,Poynting vectors
更新于2025-09-04 15:30:14