Wednesday, 15 October 2014

Assignment of the Terahertz Spectra of Crystalline Copper Sulfate and Its Hydrates via Solid-State Density Functional Theory

Michael Thomas Ruggiero , Tiphaine Bardon , Matija Strlic , Phil F. Taday , and Timothy Michael Korter


Terahertz (THz) vibrational spectroscopy is a promising tool for the non-destructive and potentially non-invasive characterization of historical objects, which can provide information on the materials used for their production as well as identify and monitor their chemical degradation. Copper sulfate (CuSO4) has drawn interest due to its inclusion in the preparation of iron gall inks found in historical artwork and documents. Copper sulfate rapidly forms hydrates which contribute to the formulation of these ink species, and may influence their corrosive nature. In this study, copper sulfate has been studied using a combination of THz time-domain spectroscopy, powder X-ray diffraction (PXRD), and solid-state density functional theory (DFT) in order to better understand the spectral absorbances in the THz region. The results have revealed that the THz spectrum of commercially available “anhydrous” copper sulfate results from the presence of not only the anhydrous form, but also the monohydrate (CuSO4⋅H2O) and trihydrate (CuSO4⋅3H2O) forms. Complete assignment of the experimental spectrum was achieved through a comparison of density functionals and extensive investigation of the influence of basis set polarization functions on the bonding interactions, lattice parameters, and low-frequency motions in these crystalline solids.

Thursday, 9 October 2014

Polarization-insensitive metamaterial absorber of selective response in terahertz frequency range

B Grześkiewicz, A Sierakowski, J Marczewski, N Pałka and E Wolarz


We present an experimental and numerical analysis of a planar metamaterial that selectively absorbs terahertz radiation. The metamaterial is produced as a planar two-dimensional network of electromagnetic resonators and is characterized by electric and magnetic responses in a narrow frequency range. The unit cell of the metamaterial has fourfold symmetry about the axis perpendicular to the planes containing the metallic resonators. Such a planar metamaterial is polarization-insensitive to the electromagnetic waves. A good agreement of the absorption characteristics obtained from the numerical simulations and from the spectroscopic experiments is shown. The analysis of wave impedance, refractive index, permittivity and permeability of the metamaterial allows the identification of the characteristic electromagnetic resonance and antiresonance in the system. It is shown that the absorption is mostly the result of the electric field energy accumulation in the metamaterial absorber.

Thursday, 2 October 2014

THz Metal Mesh Filters On Electrically Thick Fused Silica Substrates

William Otter, Fangjing Hu, Stepan Lucyszyn, Jonathan Hazell,


This paper shows simulated and measured results of ultra-low cost metal mesh filters on electrically thick substrates for millimeter-wave and THz bands. It provides a broad overview of metal mesh filters currently available and suggest why it is worth moving to an electrically thick substrate for ultra-low cost applications. We demonstrate scalable traditional metal mesh filters on 525 µm thick fused silica substrates. In addition, trapped-mode excitation is exploited to improve out-of-band rejection at higher frequencies. The measured results prove that these filters are scalable in the THz range using cost-effective micromachining manufacturing. This work opens up the possibility of using electrically thick metal mesh filters for ultra-low cost applications.