The characteristics of relative permittivity and reflectance for poly (methyl methacrylate) (PMMA) films prepared by spin-coating were investigated and an excellent wideband terahertz (THz) metamaterial absorber (MA) had been fabricated by employing PMMA film as the dielectric layer. XRD and AFM indicated that all the PMMA films with thicknesses from 11 to 17 μm were amorphous and extremely smooth with roughness about 0.203 nm. Raman results demonstrated that vibration strength of the same covalent bonds tends to be consistent with an increase in film thickness. The dual beam laser interferometer (DBLI) was employed to study the influence of applied frequency and thickness on the relative permittivity, and the results exhibited dielectric constants increased from 2.88 to 4.04 with the thickness increasing from 9 to 14 μm. And the dielectric constants for PMMA films with a certain thickness (8 μm) gradually declined when the applied frequency increased from 100 to 105 Hz; besides, the dielectric constant in THz band was forecasted approximately 2.5. The terahertz time domain spectrometer (THz-TDS) results revealed that the THz reflectance was of gradual degradation from 80 to 58% at 3.2 THz, as the thickness increased from 11 to 17 μm. In addition, the UV-VIS spectrum showed that thickness had little effect on reflectance and transmittance in visible region, leading to the almost same Eg (energy gap) about 3.7 eV. At last, by employing PMMA film as the dielectric layer, a highly wideband metamaterial absorber with absorption > 80% from 4.1 to 7.4 THz was fabricated.

Optically Transparent Microwave Metamaterial Absorber (OTMMA) is of significant use in both civil and military field. In this paper, equivalent circuit model is adopted as springboard to navigate the design of OTMMA. The physical model and absorption mechanisms of ideal lightweight ultrathin OTMMA are comprehensively researched. Both the theoretical value of equivalent resistance and the quantitative relation between the equivalent inductance and equivalent capacitance are derived for design. Frequency-dependent characteristics of theoretical equivalent resistance are also investigated. Based on these theoretical works, an effective and controllable design approach is proposed. To validate the approach, a wideband OTMMA is designed, fabricated, analyzed and tested. The results reveal that high absorption more than 90% can be achieved in the whole 6~18 GHz band. The fabricated OTMMA also has an optical transparency up to 78% at 600 nm and is much thinner and lighter than its counterparts.

The ITO film with visible light transparence, and high terahertz (THz) reflectivity is a promising material for the commercial and engineering applications in the THz field. This study investigates the terahertz optical performance and electrical properties of ITO films prepared by DC magnetron sputtering in the presence of oxygen at different annealing temperatures. By comparing the XPS spectra of ITO films before and after the annealing, the doping theory is employed to explain why and how the ratio of Sn4+/Sn2+ can be changed because of annealing, and it is concluded that Sn with low valence (Sn2+) can result in a lower visible transmission. In the THz region, the ITO film has high reflectance that observes the Hagen-Rubens (HR) relationship to some extent. According to the HR relation, the THz reflectance of the ITO film is mainly affected by the conductivity which can be controlled by adjusting the annealing temperature and the oxygen flow in the process of preparation. Applying the prepared ITO film with high THz reflectance into our proposed metamaterial absorber, the experimental result proves that the maximum absorptivity of 94.66%. can. be achieved at 4.26 THz. (C) 2017 Elsevier Ltd. All rights reserved.