For biomedical applications in the terahertz band, composites such as macromolecule compounds, biotissues and phantoms are studied. A description of dielectric properties of composite materials using mathematical models has its own fundamental and technological importance. In this work, we present an iterative effective medium theory for multi-component materials. The model has good performance in describing composite materials with more than two components. The theory is evaluated by comparing with the complex permittivity of three different composite materials. A comparison with other commonly used models is given in the form of relative errors.

Terahertz (THz) technology has been applied in many scientific areas, such as explosive detection, quality control, and medical diagnostics.^{1 – 9} Compared with other medical diagnosis methods, THz technology has many advantages. THz radiation does not cause ionization in biotissues because it has very low photon energy.^{2 – 6} Since THz radiation is very sensitive to water and the hydration state of the object, which leads to good contrast between the normal and diseased tissues, THz has great promise in medical applications, especially for cancer diagnosis and tumor resection.^{4,5,8 – 10}

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.

Typical waveplates are limited to specific frequencies. We propose a general design of a series of THz achromatic quarter-wave plates that work for different frequency range. The simplified formulas and the basic parameters that are used to calculate the thicknesses and rotating angles with the possibility of choosing the frequency range are provided. The main feature of the design is that the number of the x-cut quartz plates is equal to the frequency expansion factor (f _max /f _min ) of the resulting waveplate, and by altering the thicknesses of quartz plates following a specific pattern only, the frequency range of the waveplate can be shifted. Two achromatic waveplates working in the frequency range of 0.2-0.6 THz and 0.2-1.2 THz were manufactured for testing. The measurement result demonstrates the reliability of the proposed design.

EPJ Web of Conferences, open-access proceedings in physics and astronomy

Subject of Research. The paper presents qualitative analysis of terahertz time-domain spectroscopy application for cancer diagnosis by measurement of the optical properties and spectral characteristics of cancer cells. For this purpose, the cultivation of two cancer cells, U-251 (glioblastoma brain) and A549 (lung adenocarcinoma), were carried out, then their refractive index, absorption coefficient and dielectric constant were measured, and the optical properties of tumor cells were compared with the optical properties of healthy cells (fibroblasts). Tumor cells contain more OH-components in comparison with healthy cells. Since terahertz radiation is heavily absorbed by water, there are differences in the spectra of healthy and oncological cells. Because of the demand for rapid and effective diagnostics of oncology (including intraoperative), the obtained results show that terahertz time-domain spectroscopy can be used for this purpose in the present time.Method. To obtain the optical properties and spectral characteristics of the researched objects, a terahertz time-domain spectroscopy method in the transmission mode was used. The researched cell lines were cultured in vitro. Optical properties and spectral characteristics of the samples were calculated by the thin film method and Fourier transform.Main Results. The results show the differences of refractive index, absorption coefficient and dielectric permittivity between the oncological cell lines U-251, A549 and the healthy cells in the frequency range 0.2-1 THz. It was found that cancer cells have higher values of refractive indices and absorption coefficients than those of healthy cells. Brain glioblastoma (U-251) has a transmission peak at the frequency of 0.24 THz.Practical Relevance. The results obtained in this work can form the basis for the intraoperative diagnosis of brain and lung cancer with the use of terahertz time-domain spectroscopy, and it is also useful in the other studies, for example, the development of biotissue phantoms in the THz frequency range