ACCELERATING OF THE ELECTRONS OF ELECTRON BUNCHES IN A WAVEGUIDE LOADED DIELECTRIC STRUCTURE

The paper presents some results of experimental studies of the excitation of wake fields and the acceleration of electrons in waveguide-dielectric structures (DS) upon injection of a sequence of electron bunches into them. Exper-iments have shown an increase in the amplitude of the wake wave and the acceleration of a small fraction of elec-trons when the wavelength of the excited field is equal to the doubled bunch length. A simple physical model of the observed phenomenon is given. Also, the paper proposes a method for accelerating a part of each electron bunch in the steady-state mode of the resonator dielectric structure. Some of the electrons are “cut out” by the collimator and enter the accelerating phase of the previously excited wake wave. The wave is displaced due to the difference in the distances traveled by the wave and the accelerated part of the electrons.

Towards structured SPP manipulation of light at the nanoscale

Surface plasmon photonics is a rapidly developing area of physics, optics, and nanotechnology. The unique ability of meso- and nano-structures to manipulate light in the subwavelength range down to nanoscale volumes stimulated their use in a vast research endeavours. The investigations are driven by interests in both fundamental and practical applications aspects where plasmonic light concentrators elegantly interface mesoscale dielectric structure with thin metal films. The effects of a photonic nanojet and a photonic hook, discovered by Minins, have been studied in sufficient detail in the literature, but only recently have they been able to be confirmed experimentally for low-dimensional systems – in-plane surface plasmon waves. The nature of these phenomenas lies in the dispersion of the phase velocity of waves inside the dielectric structure, which leads to constructive interference of the transmitted, diffracted, and near-field waves. Our results set the grounds for in-plane plasmonic wavelength scaled optics with unprecedented control of the energy flow at the nanoscale, and shown a way toward realizing the densely packed optical elements needed for future plasmonic and optical devices.

Diffraction limited photonic hook via scattering and diffraction of dual-dielectric structures

Photonic hooks have demonstrated to be great candidates for multiple applications ranging from sensing up to optical trapping. In this work, we propose a mechanism to produce such bent structured light beams by exploiting the diffraction and scattering generated by a pair of dielectric rectangles immersed in free space. It is shown how the photonic hooks are generated away from the output surface of the dielectrics by correctly engineering each individual dielectric structure to generate minimum diffraction and maximum scattering along the propagation axis. Different scenarios are studied such as dual-dielectric structures having different lateral dimensions and refractive index as well as cases when both dielectrics have the same lateral dimensions. The results are evaluated both numerically and theoretically demonstrating an excellent agreement between them. These results may open new avenues for optical trapping, focusing and sensing devices via compact and simple dual-dielectric structures.

Model of Е-polarized wave propagation in a multilayer dielectric structure

This paper addresses the determination of the dielectric constant of multilayer dielectric structures by radiowave interferometry. In the general case, in interferometry measurements to one measured value of the reflection coefficient there may correspond an infinity of dielectric constants. This ambiguity may be resolved by first determining the effect of different parameters of the probing electromagnetic wave on the reflection coefficient. In particular, it is important to have a preliminary estimate of the effect of the incidence angle and the polarization on the range of variation of the reflection coefficient with the variation of one of the structure parameters. This paper considers the case where a plane E-polarized electromagnetic wave, i.e. a wave whose magnetic field is perpendicular to the incidence plane, is incident on a multilayer dielectric structure. The aim of this work is to develop a model of the propagation of an E-polarized electromagnetic wave through a multilayer dielectric structure at an arbitrary incidence angle and to determine the range of variation of the reflection coefficient with the variation of the dielectric constants of the layers. The paper presents a model of the propagation of an E-polarized electromagnetic wave in a two-layer dielectric structure. A metal base, which is an ideal conductor, underlies the structure. The electromagnetic wave is incident from the air at an arbitrary incidence angle. Based on the model, a method is proposed for measuring the relative dielectric constant and the dielectric loss tangent. It is shown that at a normal incidence the reflection coefficient magnitude is the same both for H- and E-polarization. Because of this, determining the relative dielectric constant and the loss tangent from the measured reflection coefficient magnitude calls for measurements not only at a normal incidence, but also at an oblique incidence, at which the reflection coefficient magnitudes will be different for H- and E-polarization.

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

A method to detect the content of substance in solution by using spectral position information of photonic crystal

Photonic crystal is a dielectric structure arranged according to certain rules, and its excellent electromagnetic wave characteristics can be used to manufacture a lot of kinds of photonic crystal devices. In this paper, a defect is introduced into the photonic crystal, and the transfer matrix method is used to study the relationship between the liquid concentration and the peak value of the liquid transmission at the electromagnetic wave length when the defect is a mixture of ethanol and glycol. The results show that by observing and measuring the position of the peak transmittance of the mixed liquid, the substance content of the liquid mixture, that is, the concentration, can be inferred. The accuracy of this method is compared with the experimental results, which shows that this method has high accuracy. This method is simple and easy to operate. This result opens up a new direction for the application of photonic crystals.

Backlobe Radiations Reduction with Patch Antenna Using Multilayered Dielectric Structure

Backlobe radiations are the key stumbling block to using microstrip patch antennas in wireless communication, but they can be minimised by using a slot-coupled feeding technique. This paper proposes a microstrip patch antenna with a multilayer structure. The Ansoft High Frequency Structure Simulation is used to describe and model this slot-fed antenna, which has an improved gain of 5.6dB and directivity of 5.9dB and resonates at a frequency of 2.25GHz.