Abstract-Investigation of multiband plasmonic metamaterial perfect absorbers based on graphene ribbons by the phase-coupled method

Hongju Li, Chuansheng Ji, Yongze Ren, Jigang Hu, Meng Qin, Lingling Wang,

https://www.sciencedirect.com/science/article/pii/S0008622318309138

We develop an original phase-coupled method to realize multispectral metamaterial near-unity absorbers based on spatially separated graphene ribbon arrays with mid-infrared plasmonic resonances. The results both from the coupled-mode theory and finite-difference time-domain simulations reveal that in addition to the single-band absorption enabled by the bi-layer identical ribbon arrays, the outstanding dual-band perfect absorption is observed with the change in the phase between bi-layer ribbons only by varying the spacer thickness. The spectral positions of absorption peaks are tuned handily by small changes in ribbon widths and chemical potentials of graphene. Moreover, the triple-band absorber is achieved handily by the same principle and such absorbers are robust for nor-normal incident angles. The transfer matrix method is also utilized to uncover further the underlying physics of the phased-coupled-induced multispectral absorbers. Theoretical analysis are in excellent agreement with numerical calculations. The phase-coupled method thus provides new opportunities for obtaining multi-channel metamaterial perfect absorbers.

Abstract-Multispectral UV imaging for determination of the tablet coating thickness

• Anna Novikova^a, 
• Jens M. Carstensen^b, 
• J. Axel Zeitler^c, 
• Thomas Rades^d, 
• Claudia S. Leopold^a, , 

• ^a Division of Pharmaceutical Technology, Department of Chemistry, University of Hamburg, Bundesstraße 45, 20146 Hamburg, Germany
• ^b Department of Applied Mathematics and Computer Science, Technical University of Denmark, Richard Petersens Plads Building 321, 2800 Lyngby, Denmark
• ^c Department of Chemical Engineering, University of Cambridge, New Museums Site, Pembroke Street, Cambridge, CB2 3RA, United Kingdom
• ^d Department of Pharmacy, University of Copenhagen, Universitetsparken 2, 2100 Copenhagen, Denmark

http://www.sciencedirect.com/science/article/pii/S0022354917300886

The applicability of off-line multispectral ultraviolet (UV) imaging in combination with multivariate data analysis was investigated to determine the coating thickness and its distribution on the tablet surface during lab scale coating. The UV imaging results were compared with the weight gain measured for each individual tablet and the corresponding coating thickness and its distribution measured by terahertz pulsed imaging (TPI). Three different tablet formulations were investigated, two of which contained UV active tablet cores. Three coating formulations were applied: Aquacoat^®ECD (a mainly translucent coating) and Eudragit^® NE (a turbid coating containing solid particles). It was shown that UV imaging is a fast and non-destructive method to predict individual tablet weight gain as well as coating thickness. The coating thickness distribution profiles determined by UV imaging correlated to the results of the TPI measurements. UV imaging appears to hold a significant potential as a PAT tool for determination of the tablet coating thickness and its distribution resulting from its high measurement speed, high molar absorptivity and a high scattering coefficient, in addition to relatively low costs.