Abstract
A new, transparent, metal-free absorber, based on the use of multilayer graphene/dielectric laminates (GLs), is proposed for applications in the low-terahertz frequency range. The designed absorber has a total thickness of around 70 µm and consists of a front matching dielectric layer followed by a GL, a dielectric spacer and a back GL. The laminates are periodic structures constituted of graphene sheets separated by 50-nm-thick polyethylene terephthalate (PET) interlayers, while the matching layer and the spacer are one-quarter-wavelength thick and made of PET. The GLs are modeled as homogeneous-equivalent single layers (ESLs) characterized by their sheet resistances Rs. An innovative analytical method is proposed in order to select Rs values optimizing the electromagnetic wave absorption either in low-gigahertz or low-terahertz frequency range. The frequency spectra of the absorption, reflection and transmission coefficients are computed in the range up to 4 THz by using different values of Rs. Then, realistic Rs values of chemically doped graphene monolayers over PET substrates are considered. The designed absorbers are characterized by an absorption coefficient with a peak value of about 0.8 at the first resonant frequency of 1.1 THz, and a 1.4 THz bandwidth centered at 1.5 THz with reflection coefficient below - 10 dB. Moreover, the optical transmittance of the proposed absorbers are computed by means of the optical matrix theory and it is found to be greater than 86% in all the visible ranges.
Highlights
In the last decade, the exponential growth of wireless communications and data traffic has fueled the research in technologies operating at terahertz (THz) and low-THz frequency ranges [1]
The development of new absorbers operating in the low-THz and THz frequency range is generally recognized as an urgent challenge to be addressed, since high absorption is crucial for several applications such as modulators, sensors and solar cells [3,4]
Resonance-based metamaterial absorbers have aroused intensive interest [5,6], since they can offer near unity absorption
Summary
The exponential growth of wireless communications and data traffic has fueled the research in technologies operating at terahertz (THz) and low-THz frequency ranges [1]. The complexity of these structures leads to difficulties in fabrication because most of them employ metals, classified as critical raw materials and characterized by electrical and electromagnetic properties hardly tunable, especially when thin films are required [4,7]. Most of these structures are not transparent in the visible frequency range, reducing their applications. The optical transmittances of the backside reflector and of the overall proposed absorbers are computed by means of the well-known matrix theory for the analysis of multilayer systems [23] It results that the optical transmittance of the designed absorber is greater than 88% in all the visible ranges
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