Liquid crystal (LC) cells that are coated with metamaterials are fabricated in this work. The LC directors in the cells are aligned by rubbed polyimide layers, and make angles θ of 0°, 45°, and 90° with respect to the gaps of the split-ring resonators (SRRs) of the metamaterials. Experimental results display that the resonance frequencies of the metamaterials in these cells increase with an increase in θ, and the cells have a maximum frequency shifting region of 18 GHz. Simulated results reveal that the increase in the resonance frequencies arises from the birefringence of the LC, and the LC has a birefringence of 0.15 in the terahertz region. The resonance frequencies of the metamaterials are shifted by the rubbing directions of the polyimide layers, so the LC cells coated with the metamaterials are passively tunable terahertz filters. The passively tunable terahertz filters exhibit promising applications on terahertz communication, terahertz sensing, and terahertz imaging.

The paper deals with the preparation of cobalt nanoparticles dispersed multi walled carbon nanotube buckypaper by the dispersion and filtration method to study the electromagnetic (microwave) absorption properties. From the X-ray diffraction the crystallite size of the cobalt nanoparticles of 33.04 nm was calculated. FESEM image clearly indicates the presence of cobalt nanoparticles in the buckypaper. Microwave-absorbing properties were investigated in terms of measuring the transmission coefficient (S21) with MWCNT-buckypaper as the absorber using microstrip line in a frequency range of 2–20 GHz. Compared to the pure buckypaper the absorption peak of the Co-CNT composites move to the lower frequency by dispersing the Co nanoparticles into the MWCNT-BP.

The frequency and temperature dependence of the surface resistance of metallic films was measured by a microwave micro-strip method under a T-junction structure. Numerical analysis of micro-strips made of silver-tin (Ag-Sn) alloy, or good conducting niobium (Nb) films reveals the surface resistances behaving as nearly a one-half power law dependence on the frequency, which is in congruence with the results derived from the free-electron model in simple metals. In addition, we have specifically investigated the electron transport with a strong localization effect on the DC temperature-dependent resistivity in abnormal and normal Nb films. The results indicate a deviation from a one-half power law may occur in the abnormal film. This work can be further exploited to measure the conductivity and penetration depth of metals in multilayered structure or of superconducting films.

A liquid crystal (LC) layer that is too thick exhibits a small terahertz birefringence due to the limited long-range force of the alignment layers that exert on it. An LC layer that is too thin has a small terahertz birefringence due to its invisibility to incident terahertz waves. Therefore, an LC layer may have a large terahertz birefringence at a specific thickness. It is well known that the birefringence of an LC layer dominates the shift of the resonance frequency of the metamaterial imbedded into the LC layer. As a result, this work studies the effect of the thicknesses of LC layers on the shift of the resonance frequencies of metamaterials. LC layers with various thicknesses ranging from 310 µm to 1487 µm are deposited on terahertz metamaterials, and each of the layers is aligned by two polyimide layers that are rubbed in a direction. The terahertz metamaterials have a maximum frequency shifting range of 21 GHz as 710 µm thick LC layers with mutually orthogonal rubbing directions are deposited on them. The maximum frequency shifting range arises from the competition between the long-range force of the polyimide layers and the interaction between the LC layers and their incident terahertz waves.

This study investigated the complex dielectric permittivity of freestanding multiwalled carbon nanotube buckypaper (MWCNT-BP) and a synthesized hybrid alumina-filled buckypaper (Al 2 O 3 -BP) composite with different alumina loadings (5-30 wt%). The non-destructive microwave transmission technique for complex permittivity determination involving cavity perturbation was employed to characterize a set of Al 2 O 3 -BP sheets. This was done by filling a rectangular cavity resonator with a standard dielectric Teflon sample and then performing permittivity measurements for the buckypaper (BP) samples in the X-band frequency range (7-12 GHz). Field-emission scanning electron microscopy (FESEM) was used to analyze the morphology of the MWCNT-BP and the aluminaloaded BP composites. DC electrical resistivity measurements clearly demonstrated conductor-insulator transition. The effect of alumina loadings on the dielectric properties of the synthesized hybrid Al 2 O 3 -BP sheet is discussed.