We apply terahertz time-domain spectroscopy for the quantitative non-invasive assessment of the water content in biological samples, such as tree leaves and pork muscles. The developed experimental terahertz time-domain spectroscopy system operates both in transmission and reflection modes. The Landau-Looyenga-Lifshitz-based model is used for the calculation of the water concentration within the samples. The results of the water concentration measurements are compared with the results of the gravimetric measurements. The obtained results show that the water content in biological samples can be measured non-invasively, with a high accuracy, utilizing terahertz waves in transmission and reflection modes.

Materials with tunable dielectric properties are valuable for a wide range of electronic devices, but are often lossy at terahertz frequencies. Here we experimentally report the tuning of the dielectric properties of single-walled carbon nanotubes under light illumination. The effect is demonstrated by measurements of impedance variations at low frequency as well as complex dielectric constant variations in the wide frequency range of 0.1-1 THz by time domain spectroscopy. We show that the dielectric constant is significantly modified for varying light intensities. The effect is also practically applied to phase shifters based on dielectric rod waveguides, loaded with carbon nanotube layers. The carbon nanotubes are used as tunable impedance surface controlled by light illumination, in the frequency range of 75-500 GHz. These results suggest that the effect of dielectric constant tuning with light, accompanied by low transmission losses of the carbon nanotube layer in such an ultra-wide band, may open up new directions for the design and fabrication of novel Terahertz and optoelectronic devices.

We report results of galvanomagnetic and terahertz time-domain spectroscopy measurements on thin films of Bi 1−x Sb x on polyimide and mica substrates with various antimony concentrations (x from 0 to 15 %) and film thickness (70, 150 nm). The resistivity, Hall coefficient and magnetoresistivity of the films were measured experimentally in the magnetic field of 0.65 T at room temperature. Mobility and concentration of electrons and holes in the film plane were calculated using the transport coefficients. The terahertz time-domain spectroscopy is used to measure the complex conductivity and permittivity of Bi 1−x Sb x thin films on the dielectric substrates in the frequency range from 0.2 to 1 THz. The plasma frequency, relaxation time, DC conductivity and effective carrier mass were extracted from these data and evaluated as functions of the Sb concentration for different film thickness and substrate. We observed that the film magnetoresistivity decreases with increasing the Sb concentration and for most of the films the Hall coefficient is negative and depends on the external factors insignificantly. We show that the mobility of charge carriers weakly depends on Sb concentration, which confirms the assertion about the scattering of carriers on themselves and not on defects in the structure. It was revealed that film static and dynamic resistivity (conductivity) as well as dielectric permittivity depend on Sb content and the film thickness. The results may be used for development of various thermoelectric, electronic and optical devices, such as THz detectors or components which can control the properties of THz radiation.

The optical properties of whole human blood with the different glucose level were studied by terahertz time-domain spectroscopy at frequencies ranging from 0.3 -0.5 THz. The increasing of refractive index of blood at the glucose level growth was shown for series of experiments. The dispersion of complex refractive index of human nails was obtained. Based on these data, the non-invasive glucose measuring technique was proposed which utilizes the reflection of the THz pulse from nail plate/nail bed interface.

In recent times, terahertz (THz) technologies have been actively applied in many biomedical research work, including gastric cancer diagnosis. In order to provide an effective removal of tumor during surgery, it is necessary to clearly distinguish it from different membranes of the stomach. In this work, we reported an investigation of various normal and cancer fresh gastric tissues using terahertz time-domain spectroscopy in the reflection mode. Refractive index and absorption coefficient of moderately differentiated and poorly differentiated gastric adenocarcinomas, as well as both serosa and mucosa were obtained in the frequency range from 0.2 to 1 THz. All cancer tissues were distinguishable from normal ones. The influence of the morphology of the investigated tissues on the obtained optical properties is discussed. The obtained results demonstrated a potential of THz time-domain spectroscopy to discriminate a tumor from normal serous and mucous gastric membranes. Thus, this method might be applied to gastric cancer diagnosis.

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A room-temperature terahertz (THz) detector based on a thermoelectric frequency selective surface (FSS) has been numerically simulated, designed, fabricated, and tested. The FSS has been fabricated from a 150 nm thin Bi88Sb12 thermoelectric film with the engraved periodic Greek crosses. The detector prototype has been tested under the 0.14 THz radiation exposure and showed a voltage response due to the photo-thermoelectric effect up to 0.13–0.18 mV, and voltage responsivity equal to 14–20 mV/W. The detector based on the FSS has shown voltage responsivity up to three times higher in comparison with the detector based on the continuous film. Thermal imaging has shown a temperature increase in the FSS up to 1.5 K under the THz exposure. The obtained results demonstrate prospects for utilization of the Bi88Sb12 FSS detector as a low cost, compact, high-speed, highly sensitive room-temperature THz detector.

The optical properties of the polymer composites consisting of polyvinyl chloride nanofibers and polypropylene films in the frequency range of 0.2–1.0 THz were studied, and the mechanical properties of polyvinyl chloride nanofibers and the structure porosity were investigated. An iterative mathematical model based on effective medium theory was used to describe the effective refractive index and absorption coefficient of the polymer composites. The permittivity tensors of the composites were calculated using the Rytov method. We found that the refractive indices of the composites increased with the increase of polypropylene contents, while absorption coefficients remained the same. The polarization-dependencies of THz optical properties of the composites were relatively low. The proposed composites have the potential to be used as materials for terahertz optical components.