Spectral Characteristics of Needle Array-Plate Dielectric Barrier Discharge Plasma and Its Activated Water

The plasma-activated water (PAW), as a new environmentally friendly nonthermal processing technology, has attracted wide attention for its applications in agriculture, food, and biomedical fields. This paper used the needle array-plate dielectric barrier discharge (needle array-plate DBD) device to activate deionized water and prepare PAW simply and efficiently. It was found that the concentration of reactive oxygen and nitrogen species (RONS) generated in the process of needle array-plate DBD was large and varied. Especially in the wavelength range of 600–770 nm, the spectral intensity is stronger. And, the ionic wind is more likely to interact with the deionized water. The changes in PAW parameters and UV/Vis spectra with treatment time were measured under different voltages and needle-dielectric plate distances. Results show that increasing discharge voltage or decreasing needle-dielectric plate distance increases the concentration of RONS, ionic wind speed, water evaporation, and conductivity of the PAW and decreases pH. UV/Vis spectra results show that prolonged treatment time results in increased total absorbance and concentrations of H2O2 and NO 3 − and that a new absorption peak appears at 210 nm in the UV/Vis spectra. When the wavelength is larger than 210 nm, a redshifted new peak and color enhancement are observed. The seeds of Astragalus adsurgens Pall were treated by discharge plasma, PAW, and the combination of plasma and PAW. It was found that high voltage and long-time activated PAW could significantly increase the ROS level of seeds and seedlings after germination for 3 days, resulting in oxidative stress damage. The survival rate of seeds was lower than that under the half lethal dose. This paper provides a feasible device design for treating activated water in large quantities with high efficiency, which is important for the application of PAW and mutation breeding of A. adsurgens Pall.

All-Dielectric Huygens’ Metasurface for Wavefront Manipulation in the Visible Region

All-dielectric Huygens’ metasurfaces have been widely used in wavefront manipulation through multipole interactions. Huygens’ metasurfaces utilize the superposition between an electric dipole and a magnetic dipole resonance to realize transmission enhancement and an accumulated 2π phase change. Benefiting from this unique property, we design and numerically investigate an all-dielectric Huygens’ metasurface exhibiting high-efficiency anomalous refraction. To suppress the substrate effect, the metasurface structure is submerged in a dielectric plate. We strategically placed two elements in four short periods to form a unit cell and adjusted the spacing between the two elements to effectively inhibit the interaction between elements. At the operating wavelength of 692 nm, the obtained anomalous transmission efficiency is over 90.7% with a diffraction angle of 30.84°. The performance of the proposed structure is far superior to most of the existing phase-gradient metasurface structures in the visible region, which paves the way for designing efficient beam deflection devices.

AN ANTENNA BASED ON A HYBRID METAL–DIELECTRIC STRUCTURE

Purpose: Nowadays, in the millimeter frequency range, the dielectric waveguides of various modifications have certain advantages over the standard metal waveguides, primarily due to the possibility of creating functional units based on them. This is due to the relative simplicity and low cost of manufacturing the dielectric waveguides and functional units using them, the high degree of their integration with active elements, the use in their manufacture of different dielectrics and polymers with a wide range of material constants and a variety of mechanical properties (in particular, some materials have a significant flexibility). After making a series of physical experiments we have found the possibility of implementing the frequency selection and radiation into free space of electromagnetic waves by a hybrid metal-dielectric structure. Design/methodology/approach: The studied electrodynamic structure belongs to the class of hybrid metal-dielectric structures. It includes a modified inverted dielectric waveguide with a periodic sequence on the dielectric plate of fifteen dielectric rods with metallized coating on one of the faces placed outwards. The structure efficiency was estimated by the voltage standing-wave ratio (VSWR) values and power attenuation in the duct. The measurements were made with the reflectometer method. To estimate the degree of electromagnetic field concentration near the rod inhomogeneities in the near zone, the mobile probe method was used. The field structures were visualized with the method of isolines. Findings: The results of a series of experimental investigations showed the possibility of matching the structure with the external waveguides in the frequency range of 26.5-32.5 GHz with the voltage standing-wave ratio (VSWR) less than 1.8. The frequency dependence of attenuation is oscillatory with clearly expressed frequency ranges with small and large attenuation values. Moreover, the dependence is almost periodic, which is typical of periodic structures. The frequency response slope in the transition zones can be quite high and reach values of 41.26 dB/GHz. The degree of concentration of the electric field near the waveguide dielectric rod and the degree of excitation of the dielectric inhomogeneities was found by directly measured electric field strength in the near zone. Measurements of energy characteristics made under the short-circuit conditions for the main guide and in the mode of matched load of the main guide showed both the ability to control the polarization characteristics and the ability to change the appearance of the pattern and its orientation in space. Conclusions: It has been experimentally proven that a hybrid metal-dielectric structure, being a modified inverted dielectric waveguide with a periodic sequence on the dielectric plate of fifteen dielectric rods with metalized coating on one of the faces placed outwards, can be effectively integrated into a standard transmission line. It is found that this structure can be matched with the external circuits in a fairly wide frequency range. It is also found that in different frequency ranges this hybrid metal-dielectric structure shows the possibility of both efficient frequency selection and radiation in free space. Antenna measurements have shown the beam pattern shape controllability. Key words: inverted dielectric waveguide, periodic sequence, voltage standing-wave ratio (VSWR), attenuation, reflectometer method, mobile probe method, directivity pattern

Dielectric Coupler for General Purpose Q-Band EPR Cavity

Here, we report on a robust and efficient mechanism for tuning the microwave coupling of a Q-band (34 GHz), general purpose, cylindrical EPR cavity operating in the TE011 mode. This novel mechanism allows for both the adjustment of the cavity’s coupling over a wide frequency range, as well as its bandwidth from that of a high-Q cavity (about 10 MHz), to a broadband cavity (above 1 GHz). The coupling element consists of a dielectric plate fixed onto a movable waveguide short that allows for two modes of operation. In the first mode, the dielectric plate does not influence the resonance properties of the coupling iris and allows for precise, critical coupling of the high-Q cavity. In the second mode, the dielectric plate is positioned in front of the coupling iris, varying the iris’ resonance properties and allowing very strong overcoupling to be achieved. This mechanism can be generalized for other types of EPR cavities, in particular at high microwave frequencies.

A Novel Multiband Fractal Antenna for Wireless Application

This paper proposes a novel multiband antenna using circle and triangle fractals for wireless application. By cutting a triangle slot in the circular monopole, a novel fractal method of the circular nested triangle structure is presented. The above structure is iterated four times, which forms the proposed fractal antenna. The antenna adopts the microstrip feeding method. In order to improve out band rejection and expand bandwidth, a ring resonator is designed on the back of the dielectric plate. The designed antenna covers 1.8 GHz–2.9 GHz applied to Bluetooth, TD-SCDMA, WCDMA, CDMA2000, and LTE33-41, 3.4 GHz–4.6 GHz applied to LTE 42/43 and WiMAX, and 5 GHz–5.6 GHz applied to WLAN. The substrate is FR4 with a dielectric constant of 4.4 and a loss tangent of 0.02. The size of the fabricated antenna is 87.5 × 61 × 1.6 mm. The measured pick gain achieves 2.98 dBi, 2.58 dBi, and 3.34 dBi at 2.6 GHz, 3.8 GHz, and 5.3 GHz, respectively. The measurement and simulation results are in good agreement, which verifies the rationality of the design.

Radiators of scalar modes of a circular waveguide.

The frequency characteristics of the radiators of ТМ01 and ТЕ01modes of a circular metal waveguide are investigated. Radiators in the form of an open end of a circular waveguide with a stepped cut, including those with a cylindrical mirror, as well as an open end of a waveguide with an inhomogeneous anisotropic dielectric plate are considered. Numerical simulation and optimization of parameters were carried out using finite element and finite differences in time domain methods.

Research of the Possibilities of Matching the Multi-element Receiving-Transmitting Irradiator Aperture

Currently, aperture antennas with spatial excitation, such as reflector antennas and phased array antennas, are widely used in radar. The composition of such an antenna includes an irradiator, which can be made in the form of a small-element array of radiators to form a set of necessary radiation patterns. Monopulse irradiators are often used, which form both total and difference directional patterns. When performing an irradiator based on waveguide parts, radiators in the form of horns or open ends of waveguides are installed in its aperture. Waveguide irradiators with four and twelve horns are widely used. One of the main electrical characteristics of such an irradiator when used as part of a receiving-transmitting antenna is the isolation of the transmitting and receiving paths. Matching the aperture of the transmitting and receiving irradiator has a significant effect on the isolation of its waveguide channels. With small transverse dimensions of the radiators in the form of open ends of waveguides, it is not possible to obtain high isolation of waveguide channels without the use of additional matching elements. The task of research the effect of matching the aperture of a waveguide multi-element irradiator on the isolation of its transmitting and receiving channels, as well as the ways of matching its radiators, is set.The article considers a four-horn irradiator, the aperture of which contains radiators in the form of open ends of a square waveguide. Each radiator has the radius rounding required for the manufacture of the product using the available technological processes. To match the emitter, a dielectric plate is installed inside it. During the research the thickness of the plate and its location relative to the aperture plane changed. The characteristics of matching the radiators with a plate made of teflon, polyethylene and ST-4 material based on polymers filled with titanium dioxide are presented.The proposed method of matching the opening of a multi-element irradiator with a transverse emitter size of 0,68λ (λ is the wavelength in free space corresponding to the average frequency of the operating band) makes it possible to improve the isolation of the receiving and transmitting waveguide channels by at least 4 dB in the frequency band of up to 3%.