Denis V. Ponomarev

Background and Objectives: One promising direction for developing environmentally friendly electromagnetic wave absorbers involves using structures that incorporate polar liquids, such as water. This is because water in the microwave range exhibits both a significant real part and a significant imaginary part of the complex permittivity. Such structures can be either continuous water layers or composite surfaces comprising individually arranged periodic droplets. Compared to more traditional materials, electromagnetic radiation absorbers based on composite water-containing structures offer several advantages, such as biocompatibility, availability, ease of fabrication, and optical transparency. One example of such a composite is cellulose paper acting as a matrix, filled with distilled water. Composite structures based on cellulose and its derivatives with inclusions of carbon nanotubes and silver nanowires are already known to be used as absorbers. Using an absorber made of such a composite material as an interface layer in a photonic crystal enables the observation of various resonance effects arising from the specific properties of the interface. Altering the electromagnetic characteristics of this interface layer leads to changes in the frequency and amplitude of the photonic Tamm resonance. Therefore, it is of interest to study the emergence of Tamm resonances within the band gap of a microwave photonic crystal that utilizes an electromagnetic energy absorber based on water-containing cellulose paper as the interface layer. Furthermore, this study aims to demonstrate interface control by varying the mass fractions of distilled water. Materials and Methods: The experimental structure was fabricated as a photonic crystal comprising alternating layers of two different dielectric materials inside a rectangular waveguide. A layer of cellulose paper containing distilled water was sandwiched between two Teflon films and placed immediately adjacent to the last layer of the photonic crystal. A vector network analyzer was used to measure the frequency characteristics in the 7–13 GHz frequency range. Numerical calculations for the layered structures were performed using the transfer matrix method. Results: As the thickness of the cellulose paper containing distilled water (with a mass fraction of more than 51%) increases, damped oscillations of the Tamm resonance frequencies have been observed within the first and second band gaps. Increasing the cellulose paper thickness has also led to damped oscillations of the reflectivity coefficients in these band gaps. For greater cellulose paper thicknesses, these values have been stabilized, becoming constant. The final values depend on both the mass fraction of water and the size of the air gap between the last layer of the photonic crystal and the cellulose paper layer. Conclusion: Adjusting the interface parameters by regulating the air gap between the photonic crystal and the cellulose layer allows for control over the Tamm resonance amplitude. For each fixed cellulose layer thickness with a specific mass fraction of distilled water, a particular air gap value must be selected to achieve the maximum Tamm resonance amplitude.

The appearance of Tamm resonances in forbidden bands of 1-D microwave photonic crystal with dielectric filling adjacent to monolithic metal nanolayer or to a nanolayer in the form of parallel metal strips has been investigated. The reflection and transmission coefficients in the microwave range were calculated using the transfer matrix method and the finite element method in the ANSYS HFSS software. The experimental data confirmed the calculation results and demonstrated the appearance of Tamm resonances in the X-band at certain thicknesses and electrical conductivities of metal nanolayers. It has been established that the amplitude in the antinodes of the standing electromagnetic wave at the Tamm resonance frequency in the first forbidden band increases monotonically with the distance from the depth of the photonic crystal to its boundary with conducting layer almost linearly. At the frequency of Tamm resonances in the higher-order forbidden bands the amplitude increases stepwise. The method for measuring the electrical conductivity of metal nanolayers contacting the photonic crystal has been theoretically justified and experimentally confirmed. The measurement technique is based on the fitting procedure to minimize by the least squares method the difference between the experimental and calculated frequency dependences of the reflection and transmission coefficients in the vicinity of the Tamm resonance.

A method for the measurement of the complex permittivity of insulators using a microwave coaxial photonic crystal is proposed and implemented. The method is based on a solution to an inverse problem using minimization of the difference of experimental and calculated frequency dependences of the transmission and reflection coefficients at the defect-mode frequency in the band gap of a photonic microwave crystal containing a structure with the parameters that must be determined. An unambiguous solution to the inverse problem can be obtained using a defect mode in the band gap at the frequency of which a maximum of the standing wave is obtained in the region of the structure under study.

— A feasible design of a system with an allowed band with near-unity frequency-independent transmission utilizing the reflective properties of photonic crystals with dielectric filling and...

The influence of continuous microwave fields with the average power level on the characteristics of a square-pulse RC-generator with a multichannel buffer decoupling network and matching...

A compact broadband waveguide matched load based on Bragg structures has been developed. It contains alternating nanoscale metal and dielectric layers designed for the frequency range of 140–210 GHz....

Novel, small-sized broadband matched loads in the form of disordered photonic crystals containing nanometer metallic and insulating layers have been developed. It has been proposed to form insulating layers with different permittivities and low dissipation factors in both centimeter and millimeter wavelength ranges from the composites that consist of insulating matrices filled with air inclusions.

A method is proposed for the measurement of the electrophysical characteristics of semiconductor structures: the electrical conductivity of the n layer, which plays the role of substrate for a semiconductor structure, and the thickness and electrical conductivity of the strongly doped epitaxial n⁺ layer. The method is based on the use of a one-dimensional microwave photonic crystal with a violation of periodicity containing the semiconductor structure under investigation. The characteristics of epitaxial gallium-arsenide structures consisting of an epitaxial layer and the semi-insulating substrate measured by this method are presented.