Microwave absorption in radar stealth technology is faced with challenges in terms of its effectiveness in low-frequency regions.Herein,we report a new laser-based method for producing an ultrawideband metamaterial-ba...Microwave absorption in radar stealth technology is faced with challenges in terms of its effectiveness in low-frequency regions.Herein,we report a new laser-based method for producing an ultrawideband metamaterial-based microwave absorber with a highly uniform sheet resistance and negative magnetic permeability at resonant frequencies,which results in a wide bandwidth in the L-to S-band.Control of the electrical sheet resistance uniformity has been achieved with less than 5%deviation at 400Ωsq^(-1)and 6%deviation at 120Ωsq^(-1),resulting in a microwave absorption coefficient between 97.2%and 97.7%within a1.56–18.3 GHz bandwidth for incident angles of 0°–40°,and there is no need for providing energy or an electrical power source during the operation.Porous N-and S-doped turbostratic graphene 2D patterns with embedded magnetic nanoparticles were produced simultaneously on a polyethylene terephthalate substrate via laser direct writing.The proposed low-frequency,wideband,wide-incident-angle,and high-electromagnetic-absorption microwave absorber can potentially be used in aviation,electromagnetic interference(EMI)suppression,and 5G applications.展开更多
Biochar has trigged increasing attention in the last decade due to its multiple functionalities,in which,color is not only the visual appearance,but also a useful indicator of relevant properties as well as an importa...Biochar has trigged increasing attention in the last decade due to its multiple functionalities,in which,color is not only the visual appearance,but also a useful indicator of relevant properties as well as an important tool to predict biochar’s properties.However,biochar color characterization remains challenged currently.In this work,three different feedstock-derived biochars were produced and basic color information(from color spaces RGB,HSB and CIE L^(*)a^(*)b^(*))of their scanned images was extracted.Then principal component analysis(PCA)and nonmetric multidimensional scaling analysis(NMDS)were employed on the combinations of different color indexes to cluster biochars.With the assumption that clusters from both PCA and NMDS were as consistent as possible with that of visual intuition of biochar color,we identified feedstock-independent color indexes[(R+G-B)/(R+G+B),(R+B-G)/(R+G+B),(G+B-R)/(R+G+B),L,a,b]to characterize color of bio-char,which can in microscopic perspective elucidate color differences with respect to pyrolysis temperature and feedstock type.Finally,prediction ability of color indexes with biochar yield as model property was explored and good performance was observed for both partial least squares regression(R2=0.8653)and neural network regression(R^(2)=0.9720)with the latter being more powerful.The proposed color indexes will find more applications in prediction of biochar properties and functions in future.展开更多
文摘Microwave absorption in radar stealth technology is faced with challenges in terms of its effectiveness in low-frequency regions.Herein,we report a new laser-based method for producing an ultrawideband metamaterial-based microwave absorber with a highly uniform sheet resistance and negative magnetic permeability at resonant frequencies,which results in a wide bandwidth in the L-to S-band.Control of the electrical sheet resistance uniformity has been achieved with less than 5%deviation at 400Ωsq^(-1)and 6%deviation at 120Ωsq^(-1),resulting in a microwave absorption coefficient between 97.2%and 97.7%within a1.56–18.3 GHz bandwidth for incident angles of 0°–40°,and there is no need for providing energy or an electrical power source during the operation.Porous N-and S-doped turbostratic graphene 2D patterns with embedded magnetic nanoparticles were produced simultaneously on a polyethylene terephthalate substrate via laser direct writing.The proposed low-frequency,wideband,wide-incident-angle,and high-electromagnetic-absorption microwave absorber can potentially be used in aviation,electromagnetic interference(EMI)suppression,and 5G applications.
基金This work was financially supported by National Natural Science Foundation of China(31760165,41661095,51969008)Outstanding Scholarship of Jiangxi Scientific Committee(20192BCBL23014)+6 种基金Natural Science Foundation of Jiangxi Province(20202BABL203024)Education Department of Jiangxi Province(GJJ190540)Foundation of Key Laboratory of Yangtze River Water Environment Ministry of Education(Tongji University)(YRWEF201907)Foundation for postdoctoral research in Jiangxi Province(2018KY48)Foundation of President of the Zhongke-Ji’an Institute for Eco-Environmental Sciences(ZJIEES-2020-05)College student innovation and entrepreneurship project of China(202010419023)College student innovation and entrepreneurship project of Jiangxi Province(S202010419039).
文摘Biochar has trigged increasing attention in the last decade due to its multiple functionalities,in which,color is not only the visual appearance,but also a useful indicator of relevant properties as well as an important tool to predict biochar’s properties.However,biochar color characterization remains challenged currently.In this work,three different feedstock-derived biochars were produced and basic color information(from color spaces RGB,HSB and CIE L^(*)a^(*)b^(*))of their scanned images was extracted.Then principal component analysis(PCA)and nonmetric multidimensional scaling analysis(NMDS)were employed on the combinations of different color indexes to cluster biochars.With the assumption that clusters from both PCA and NMDS were as consistent as possible with that of visual intuition of biochar color,we identified feedstock-independent color indexes[(R+G-B)/(R+G+B),(R+B-G)/(R+G+B),(G+B-R)/(R+G+B),L,a,b]to characterize color of bio-char,which can in microscopic perspective elucidate color differences with respect to pyrolysis temperature and feedstock type.Finally,prediction ability of color indexes with biochar yield as model property was explored and good performance was observed for both partial least squares regression(R2=0.8653)and neural network regression(R^(2)=0.9720)with the latter being more powerful.The proposed color indexes will find more applications in prediction of biochar properties and functions in future.
