Transparent Thermally Tunable Microwave Absorber Prototype Based on Patterned VO2 Film

Transparent microwave absorbers that exhibit high optical transmittance and microwave absorption capability are ideal,although having a fixed absorption performance limits their applicability.Here,a simple,transparent,and thermally tunable microwave absorber is proposed,based on a patterned vanadium dioxide(VO_(2))film.Numerical calculations and experiments demonstrate that the proposed VO_(2)absorber has a high optical transmittance of 84.9%at 620 nm;its reflection loss at 15.06 GHz can be thermally tuned from–4.257 to–60.179 dB,and near-unity absorption is achieved at 523.750 K.Adjusting only the patterned VO_(2)film duty cycle can change the temperature of near-unity absorption.Our VO_(2)absorber has a simple composition,a high optical transmittance,a thermally tunable microwave absorption performance,a large modulation depth,and an adjustable temperature tuning range,making it promising for application in tunable sensors,thermal emitters,modulators,thermal imaging,bolometers,and photovoltaic devices.

Tunable VO_(2) cavity enables multispectral manipulation from visible to microwave frequencies

Optical materials capable of dynamically manipulating electromagnetic waves are an emerging field in memories,optical modulators,and thermal management.Recently,their multispectral design preliminarily attracts much attention,aiming to enhance their efficiency and integration of functionalities.However,the multispectral manipulation based on these materials is challenging due to their ubiquitous wavelength dependence restricting their capacity to narrow wavelengths.In this article,we cascade multiple tunable optical cavities with selective-transparent layers,enabling a universal approach to overcoming wavelength dependence and establishing a multispectral platform with highly integrated functions.Based on it,we demonstrate the multispectral(ranging from 400 nm to 3 cm),fast response speed(0.9 s),and reversible manipulation based on a typical phase change material,vanadium dioxide.Our platform involves tandem VO_(2)-based Fabry–Pérot(F-P)cavities enabling the customization of optical responses at target bands independently.It can achieve broadband color-changing capacity in the visible region(a shift of~60 nm in resonant wavelength)and is capable of freely switching between three typical optical models(transmittance,reflectance,and absorptance)in the infrared to microwave regions with drastic amplitude tunability exceeding 0.7.This work represents a state-of-art advance in multispectral optics and material science,providing a critical approach for expanding the multispectral manipulation ability of optical systems.

Effect of Unit Cell Shape on Switchable Infrared Metamaterial VO_(2)Absorbers/Emitters

Metamaterial absorber/emitter is an important aspect of infrared radiation manipulation.In this paper,we proposed four simple switchable infrared metamaterial absorbers/emitters with Ag/VO_(2)disks on the Ag plane employing triangle,square,hexagon,and circle unit cells.The spectral absorption peaks whose intensities are above 0.99 occur at~4μm after structure optimization when VO_(2)is in insulating state and disappear when VO_(2)becomes metallic state.The simulated electromagnetic field reveals that the spectral absorption peaks are attributed to the excitation of magnetic polariton within the insulating VO_(2)spacer layer,whose values exceed 1.59 orders of magnitude higher than the incident magnetic field.Longer resonant wavelength would be excited in square arrays because its configuration is a better carrier of charges at the same spans.For absorption stability,the absorbers/emitters with square and circular structures do not have any change with the polarization angles changing from 0°to 90°,due to the high rotational symmetric structure.And four absorbers/emitters reveal similar shifts and attenuations under different incident angles.We believed that the switchable absorber/emitter demonstrates promising applications in the sensing technology and adaptive infrared system.

MgF_(2) as abundant and environmentally friendly electrolytes for high performance electrochromic devices

Electrochromic devices(ECDs)can regulate the indoor solar radiation by adjusting optical transmissive properties,showing great commercial potential and important social value of green energy saving.However,the unsafety and high cost of Li^(+) based electrolyte hinder the large-scale and industrialized production of ECDs.Other metal ions have been used as electrolyte ions,but they are rarely reported in all solid state ECDs.In this study,MgF_(2) film is used as the solid electrolyte to construct all solid state ECD with the structure of glass/ITO/WO_(3)/MgF_(2)/NiO/ITO.The ECD shows the large optical modulation(~83%at 820 nm,with 100 s durations)and fast response(19.2 s for bleaching and 8.3 s for coloring,with 25 s durations).Moreover,the ECD achieves the extreme transmittance value of colored states Tc=0%,which can give an absolute private state.This work not only indicates that MgF_(2) film can be an alternative to Lit based electrolyte in all solid state ECDs,but also broadens the applications of all solid state EC smart windows to private buildings.