A FABRY-PEROT METARESONATOR SUPPORTING TRAPPED-MODE RESONANCES

Purpose: Investigation of the electrodynamic properties of a Fabry-Perot metaresonator formed by two parallel perfectly conducting, two-dimensionally periodic, two-element screens of finite thickness with rectangular holes. The resonator is excited by a plane linearly polarized electromagnetic wave. The basic cell of each of the screens used as the metaresonator mirrors contains two lengths of rectangular waveguides of different transverse sections. Design/methodology/approach: An operator method for solving the 3D problems of electromagnetic wave diffraction by multielement two-dimensionally periodic structures is used in the study. The computation algorithm uses the partial domain technique and the method of generalized scattering matrices. Findings: As follows from the results of the numerical modeling made, the magnitude of the plane wave reflected from the metaresonator turns to zero at fixed frequencies lying below the cutoff frequencies for the rectangular waveguide sections embedded in the resonator mirrors. The effect of the total electromagnetic wave transmission through the metaresonator at the first lower frequency is characterized by a strong localization of the electromagnetic field in the resonator volume. The reason is excitation of the metaresonator by the exponentially descending field penetrating inside the resonator through the evanescent holes at the resonance frequency. The second low-frequency resonance of the total electromagnetic wave transmission through the metaresonator is associated with the trapped-mode resonance, which is observed in multielement two-dimensionally periodic structures. This case is characterized by a strong localization of the electromagnetic field from both sides near the metaresonator mirror surfaces. Conclusions: The unique electrodynamic properties of the metaresonator can find application in the devices for measuring the electrophysical parameters of composite materials with high losses. The effect of strong localization of the electromagnetic field both in the resonator volume and near the mirror surfaces can be used for monitoring the gaseous substances in crowded places. Key words: two-dimensionally periodic screen; rectangular waveguide; Fabry-Perot metaresonator; reflection factor; evanescent waveguide; trapped-mode resonance

High-frequency acoustic impedance tube based on MEMS microphones

Acoustic impedance tubes are commonly used to measure a test specimen's acoustic characteristics, such as reflection factor, absorption coefficient, or acoustic impedance, in combination with one or two condenser measurement microphones according to associated standards. In the development process of an impedance tube, the microphone diaphragm's size has an important role in the measurement quality. On the one hand, the microphone diameter has to be large enough to ensure the possibility of measuring at low sound pressure levels (SPLs), but on the other hand, the size of the microphone diaphragm should be small in order not to influence the sound propagation through the impedance tube due to the microphone coupling. Micro-Electro-Mechanical Systems (MEMS) microphones are recently widely applied in various acoustic applications due to their small size and high sensitivity. This paper proposes the development of an acoustic impedance tube equipped with 16 MEMS microphones and an inner diameter of 8 mm with an operating frequency range between 60 Hz and 16 kHz. The bottom port MEMS microphones are connected via a 1 mm hole to the tube. The system evaluation is based on standard test specimens like empty probe adapters, rigid termination, and porous absorbers.

Return Stroke Process Simulation Using TCS Model

The Traveling Current Source (TCS) model describes the electrical processes during the lightning return stroke phase. The TCS model assumes that the lightning current is injected at the top of the increasing return stroke channel represented by a transmission line. The electric and magnetic field is calculated based on the spatial and temporal distribution of the lightning current along the return stroke channel. It is shown that the main characteristics of the measured electric and magnetic fields can be reproduced with the TCS model. These are the Initial Peak of the electric and magnetic fields for near intermediate and far distances, the Ramp (up to the maximum) of the near electric field, the Hump of the near magnetic field after the initial peak, and the Zero Crossing of the far distant electric and magnetic fields. The fundamentals of the model are presented, and the model is extended to consider the current reflections occurring at the ground and the upper end of the return stroke channel. To this end, the ground reflection factor ρ and the top reflection factor R are introduced. Due to the increasing return stroke channel, the top reflection factor is a function of the return stroke velocity. The total current is composed of the source current according to the TCS model and the reflected currents. It is shown that the ground reflection causes significant variation in the waveform of the channel-base current and the electric and magnetic fields.

BANDWIDTH AND GAIN ENHANCEMENT OF MICROSTRIP ANTENNA USING DEFECTED GROUND STRUCTURE AND HORIZONTAL PATCH GAP

This research proposed microstrip antenna design using the Defected Ground Structure (DGS) and horizontal patch gap (HPG) for bandwidth and enhancement purposes. This design is to reduce the weakness of a microstrip antenna, which has small gain and narrow bandwidth. The design was simulated in CST Microwave Studio with a working frequency of 2.4 GHz. The design consists of three stages model, i.e., conventional design, DGS modification, and the combination DGS using a Horizontal Patch Gap (DGSHPG). The radius of the conventional circular patch is 16.7 mm. The substrate has 4.6 of dielectric constant, 1.6 of substrate height, and 0.025 of the loss tangent. The simulation results show that the DGS design produces more bandwidth and gain than a conventional design, where the bandwidth and gain improvement are 421.2 MHz and 1.73 dB, respectively. The DGS model is combined with a gap that separates the circular patch (DGSHPG) to achieve the optimum design. The results show the bandwidth and gain improvement of more than 50% and 18.1% compared to the DGS design, respectively. Other parameter performance also shows improvement, such as a reflection factor with -53.3 dB at the center frequency. The physical change also influences the patch’s radius, where it is reduced around 1.4 mm or 8.4% from the original design. Overall, the proposed design has succeeded in achieving bandwidth and gain enhancement and reducing the patch dimension.

Designing Franklin’s Microstrip Antenna with Defected Ground Structure at MMwave Frequency

The development of telecommunication technology is very rapid at this time has entered into 4G technology. Soon, the 5G technology has a fast data access speed of at least 1 Gbps. To support 5G technology is carried out in-depth research, especially in 5G antennas. This study aims to increase the bandwidth of Franklin's five array microstrip antennas using the DGS (Defected Ground Structure) method for 5G antenna applications at an operating frequency of 28 GHz. The research was conducted by doing rectangular defects in the ground field. This research produced an enhanced bandwidth by 1.707 GHz from 1.196 GHz without DGS (Defected Ground Structure) to 2.9 GHz with DGS (Defected Ground Structure). It means a bandwidth enhancement of 142.47%. At the same time, the design achieved a gain enhancement of 141.7 %. Franklin's microstrip antenna output with DGS (Defected Ground Structure) method from the research simulation results are the bandwidth of 2.9 GHz, reflection factor of -52.95 dB, and Gain 11.80 dB. In comparison, the results of antenna measurements that have been fabricated produce bandwidth of 2 GHz, reflection factor -27.72 dB on frequency 26.6 GHz. The deviation between the simulation and measurement may result in inaccuracies during the fabrication process.

Effect of climatic factors on energy loss of millimeter range electromagnetic wave in passing through a precipitation layer on the mirror antenna reflector

Problem statement. Communication systems transition to the millimeter wavelength range, as well as known theoretical studies on higher electromagnetic energy losses in precipitation in this range compared with the centimeter range have necessitated a scientific justification of an antenna protection method against climatic factors. This makes the chosen research topic relevant. Objective. Analysis of the climatic factors effect on the electromagnetic energy losses in the precipitation layer on the reflector of the millimeter wave range mirror antenna. Results. It is shown that the estimation of electromagnetic energy losses in the precipitation layer on the metal reflector of the mirror antenna should be carried out with the use of the basic statements of meteorological electromagnetism, which unites the statements of electrodynamics and statistical meteorology. Thus, to estimate the electromagnetic energy losses in the precipitation layer on the metal reflector of the millimeter wavelength reflector antenna, the model of the flat multi-layer dielectric coating on the metal screen can be used, which allows to relate the reflection factor to the layer parameters: the electrical parameters of the precipitation (value of the relative permittivity and the tangent angle of dielectric losses) and the layer thickness. Analysis of the known methods of finding the electrical parameters of meteorological precipitation showed that, firstly, it is difficult to measure the imaginary component of the relative permittivity of rain, ice, and snow in the millimeter frequency range. Secondly, there is no approved calculation methodology for the electrical parameters of snow, and the known models depend on random factors - the specific density of snow at the time of measurement and the electrical parameters of the ice and water that make up the snow and their concentrations. Third, finding the electrical characteristics of any type of precipitation characteristic of a given location of the mirror antenna depends on the air temperature. To justify the thickness of precipitation layer on the antenna reflector, the following statistical data are also necessary: the intensity of rain in a given location with a given probability, the daily rate of snow layer and the thickness of ice, which can form in a given climatic region on the metal elements of the mirror structure, including the reflector. Obtained results of electromagnetic energy losses in precipitation layer for different cases of meteorological conditions for millimeter band and their comparison with data for centimeter wavelength range have shown that the greatest losses (from 12-13 dB to 92 dB) in millimeter wavelength range, especially at frequencies above 60 GHz are caused by snow precipitation. In the centimeter wavelength range the maximum losses (up to 10 dB) can be observed in rain.

Типологія Одеси в Есеїстиці Б. Херсонського

The article analyzes the topological peculiarities of Odessa embodiment in B. Khersonsky’s essays from the perspective of the ”essay of place” as a peculiar variation of the writer’s literary platform in topological format, which is a continuation of verbal searches, established in other practices, the ones that are already traditional for the writer. Odessa is outlined through the important topographic accents made by the means of reflection, the author’s personal attachment to topological realities rooted in the past, and their experience, attraction to theorizing the phenomenon of space itself as an object of reflection, factor of identity. Attention is drawn to the artistic and intellectual side of experiencing the problems of Odessa and the people who represent it or are associated with it in the collection of B. Khersonsky ”The Patched Blanket”. The complex socio-cultural, mythological, political, historical, religious, ethnic, linguistic and other inclusions of a city with more than 200 years of history are the levers of this experience, thus creating images and essays whose nature is cultural, historical, mythological and individual-existential at the same time.