This article investigates the dichroic properties of aligned γ-Al2O3 nanofibers coated with graphene in the terahertz (THz) regime, revealing significant variance in absorption based on the orientation of the electric field in relation to the nanofibers, arising from the anisotropic nature of the material. Samples are prepared in a hot-wall chemical vapor deposition reactor with varying growth times, resulting in 5 samples with increasing graphene content. Compositional characterization is carried out using scanning electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. The samples are characterized electromagnetically using two distinct measurement techniques. First, a novel waveguide measurement setup is deployed, wherein square waveguide cassettes are used to capture the anisotropic behavior of the material and equally measure both polarization states in 67–500 GHz. Then, the samples are characterized using terahertz time-domain spectroscopy up to 4 THz. Both techniques highlight absorption enhancement when the electric field is parallel to the fibers, opening new possibilities for THz devices using polarization filtering.

One of the challenges of using carbon nanotubes electronics is achieving precise control of the conductivity type. It is particularly difficult to obtain the n-type conductive nanotubes. One of the most common methods of CNTs modification allowing to change their conductivity type is chemical functionalization. This paper describes the results of studies on non-covalent modification of randomly oriented single-walled carbon nan-otubes (SWCNT) layers with methyl viologen (MV), which allows for the change of the conductivity of SWCNT from p- to n-type. The properties of pristine and MV-modified SWCNT have been compared using Scanning Electron Microscopy, Raman spectroscopy, and X-ray Photoelectron Spectroscopy. The SWCNT conductivity type change was confirmed by photo-conductance under ultraviolet illumination and measurements in the field effect transistor configuration.

Materials with tunable dielectric properties are highly relevant for terahertz (THz) applications. Herein, the tuning of the dielectric response of single‐walled carbon nanotube layers by light illumination is studied for applications to THz phase shifters. The dependence of the length of individual nanotubes on the THz photoconductivity of the network is experimentally investigated in the frequency range of 0.2–1 THz by time‐domain spectroscopy (TDS). The effective conductivity of the networks is described by a theoretical model that fits the measured dielectric function. Terahertz phase shifters are realized with the carbon nanotube layers as the optically tunable element deposited on the wall of rectangular dielectric waveguides. The phase of the electromagnetic wave propagating in the waveguide is shown to be tunable by illuminating the nanotubes. A linear phase shift with the frequency is measured between 75 and 500 GHz with a low change in amplitude due to the illumination.

This work presents the preparation and the frequency domain measurements of graphene augmented inorganic nanofibers oriented across the longitudinal axis of the fibers, embedded in a hollow WR-10 waveguide cassette. A simple measurement setup is employed, allowing for rapid, broadband characterization of the material under test. Due to the orientation of the fibers, highly anisotropic behavior is revealed.

Dielectric waveguides are a potential platform for future integrated THz electronics but are still challenging to interface with standard measurement equipment. The commonly used tapered transition to hollow metallic waveguides involves manual alignment, leading to measurement inaccuracies. In this paper, we report the effects of misalignment between a dielectric and a metallic waveguide in the W-band. The results indicate the excitation of unwanted high-order modes in the dielectric waveguide that are expected to degrade the performance, especially at higher frequencies.

This article presents the preparation, compositional and electromagnetic characterization of modified few-walled carbon nanotubes/nanofibrillar cellulose (FWCNT/NFC) aerogels integrated in a standard terahertz hollow waveguide and studies their operation as absorbers of electromagnetic waves in the WR-3.4 band (220-330 GHz). Hybrid aerogels consisting of different weight ratios of NFC and modified FWCNT are prepared by freezedrying and characterized through scanning electron microscopy and Raman spectroscopy, and then placed within waveguide cassettes in a simple, low-cost and efficient way that requires no special equipment. A broadband measurement setup is employed for examining the electromagnetic response of the materials. It is found that the materials are excellent absorbers with an average shielding efficiency of 66 dB in the best case and return loss above 10 dB across the band with a flat frequency response. FWCNT aerogels are assessed as a promising candidate for terahertz waveguide terminations.

The ongoing development of sub-THz systems and applications has created a need for new absorbing materials which can be integrated in a simple, low-cost manner. Here, we investigate the properties of CNT-based aerogels in the range of 67-110 GHz and develop a simple technique for their integration. The aerogels are synthesised using standard techniques and then shaped using a laser cutter to allow for direct integration. The S-parameters of a total of four aerogel absorber samples are measured. The absorbers offer a return loss of up to 12 - 14.5 dB across the measurement band, with a maximum absorption 2.54 of 5 dB/mm The observed performance makes CNT aerogels extremely promising candidates for use in sub-THz waveguide systems and applications.

This article presents novel graphene-based absorber materials which can be directly integrated in terahertz waveguide systems. A simple, low-cost integration method is developed, allowing graphene augmented inorganic nanofibers to be embedded inside a metallic waveguide. In contrast to existing absorbers, the ability to embed such materials in a metallic waveguide allows them to be integrated into complete terahertz systems for large-scale applications. The electromagnetic properties of such materials are then examined using standard network analysis techniques. A wideband measurement setup is developed to enable measurement of a single sample from 67 to 500 GHz, eliminating the need to fabricate multiple samples. The porosity of the integrated material leads to excellent electromagnetic performance across a wide range of frequencies. The samples are found to have a reflection coefficient less than −10 dB for frequencies above200 GHz, while their attenuation per unit length exceeds 35 dB mm⁻¹. The low reflectivity of the material allows it to be used in systems applications where undesired reflections must be avoided. The electromagnetic shielding effectiveness of the material is assessed, with a total effectiveness of 20–45 dB observed for 0.84 mm thick samples.