307 research outputs found
A Theoretical Model of the Holographic Formation of Controllable Waveguide Channels System in Photopolymer Liquid Crystalline Composition
Rapid development of the integrated optics and photonics makes it necessary to create cheap and simple technology of optical waveguide systems formation. Photolithography methods, widely used for these tasks recently, require the production of a number of precision amplitude and phase masks. This fact makes this technology expensive and the formation process long. On another side there is a cheap and one-step holographic recording method in photopolymer compositions. Parameters of the waveguide system formed by this method are determined by recording geometry and material’s properties. Besides, compositions may contain liquid crystals that make it possible to create elements, controllable by external electric field. In this chapter, the theoretical model of the holographic formation of controllable waveguide channels system in photopolymer liquid crystalline composition is developed. Special attention is paid to localization of waveguides in the media caused by light field attenuation during the formation process
Reconfigurable antennas and radio wave propagation at millimeter-wave frequencies
For the last decades we have been witnessing the evolution of wireless radio networks. Since new devices appear and the mobile traffic, as well as the number of users, grows rapidly, there is a great demand in high capacity communications with better coverage, high transmission quality, and more efficient use of the radio spectrum. In this thesis, reconfigurable antennas at micro- and millimeter-wave frequencies and peculiar properties of radio wave propagation at mm-wave frequencies are studied.
Reconfigurable antennas can improve radio link performance. Recently, many different concepts have been developed in the reconfigurable antenna design to control the antenna bandwidth, resonant frequency, polarization, and radiation properties. In the first part of the thesis, we investigate mechanically tunable antennas operating at microwave frequencies with the ability to change the shape of the conductor element and, consequently, to control the radiation properties of the antenna. Also in the first part, we study conformal antenna arraysfor 60 GHz applications based on cylindrical structures. Beam switching technology is implemented by realizing several antenna arrays around the cylinder with a switching network.Scanning angles of +34˚/-32˚ are achieved.
Moreover, it is vital to study radio wave propagation peculiarities at mm-wave frequencies in indoor and outdoor environments to be able to deploy wireless networks effectively. The propagation part of the thesis focuses on several aspects. First, we investigate how the estimation of optimum antenna configurations in indoor environment can be done usingrealistic propagation models at 60 GHz. Ray tracing simulations are performed and realistic human blockage models are considered. Second, we present the results from a measurement campaign where reflection and scattering properties of two different built surfaces are studied in the millimeter-wave E-band (71-76 and 81-86 GHz). Next, we present a geometry based channel model for a street canyon scenario, using angular-domain measurement results to calculate realistic power angular spectra in the azimuth and elevation planes. Then, we evaluate propagation effects on the radio channel on the rooftop of the buildings bymeasurements and simulations. We have used unmanned aerial vehicles and photogrammetrytechnique to create a highly accurate 3D model of the environment. Based on a comparison of the measured and simulated power delay profiles, we show that the highly accurate 3D modelsare beneficial in radio wave propagation planning at mm-wave frequencies instead of using simple geometrical models
Conformal Antenna Array for Millimeter-Wave Communications: Performance Evaluation
In this paper, we study the influence of the radius of a cylindrical
supporting structure on radiation properties of a conformal millimeter-wave
antenna array. Bent antenna array structures on cylindrical surfaces may have
important applications in future mobile devices. Small radii may be needed if
the antenna is printed on the edges of mobile devices and in items which human
beings are wearing, such as wrist watches, bracelets and rings. The antenna
under study consists of four linear series-fed arrays of four patch elements
and is operating at 58.8 GHz with linear polarization. The antenna array is
fabricated on polytetrafluoroethylene substrate with thickness of 0.127 mm due
to its good plasticity properties and low losses. Results for both planar and
conformal antenna arrays show rather good agreement between simulation and
measurements. The results show that conformal antenna structures allow
achieving large angular coverage and may allow beam-steering implementations if
switches are used to select between different arrays around a cylindrical
supporting structure.Comment: Keywords: conformal antenna, millimeter-wave communications, patch
antenna array. 11 pages, 10 figures, 1 tabl
NUMERICAL SIMULATION OF LOW LIQUID FLOW THROUGH COAXIAL SWIRL MIXTUR
The paper describes the numerical simulation methodology of operating fluid (water) discharge into air environment through the mixer hydraulic paths composed of two low-flow coaxial centrifugal injectors. The results of liquid mixing modulation within those paths and beyond them are presented
Magnetic Structures of Some Multiferroics
We studied crystal and magnetic structures of some composite and single-phase multiferroics: (x)MFe2O4 + (1-x)BaTiO3, Ni3-yCoyV2O8, and Bi0.9Ba0.1Fe0.9Ti0.1O3. Composite multiferroics (x)MFe2O4 + (1-x)BaTiO3 with x = (0.2; 0.3; 0.4) and M = (Ni, Co) have ferrimagnetic structure, which is described by the propagation vector k = 0. Oxides Ni3-yCoyV2O8 with y = (0.1; 0.3; 0.5) possess a modulated magnetic structure, described by the vector k = (δ, 0, 0), where δ = 0.283 and 0.348 at 7.4 K for y = 0.1 and 0.5, respectively. In the Bi0.9Ba0.1Fe0.9Ti0.1O3 multiferroic a magnetic order is destroyed at 600 K and the Fe-ion magnetic moment decreases from µ = 3.46(5) μB at 300 K to zero at 600 K
Path Loss Characterization for Intra-Vehicle Wearable Deployments at 60 GHz
In this work, we present the results of a wideband measurement campaign at 60
GHz conducted inside a Linkker electric city bus. Targeting prospective
millimeter-wave (mmWave) public transportation wearable scenarios, we mimic a
typical deployment of mobile high-end consumer devices in a dense environment.
Specifically, our intra-vehicle deployment includes one receiver and multiple
transmitters corresponding to a mmWave access point and passengers' wearable
and hand-held devices. While the receiver is located in the front part of the
bus, the transmitters repeat realistic locations of personal devices (i) at the
seat level (e.g., a hand-held device) and (ii) at a height 70 cm above the seat
(e.g., a wearable device: augmented reality glasses or a head-mounted display).
Based on the measured received power, we construct a logarithmic model for the
distance-dependent path loss. The parametrized models developed in the course
of this study have the potential to become an attractive ground for the link
budget estimation and interference footprint studies in crowded public
transportation scenarios.Comment: 4 pages, 8 figures, 1 table, accepted to EuCAP 201
Millimeter Wave Channel Modeling via Generative Neural Networks
Statistical channel models are instrumental to design and evaluate wireless
communication systems. In the millimeter wave bands, such models become acutely
challenging; they must capture the delay, directions, and path gains, for each
link and with high resolution. This paper presents a general modeling
methodology based on training generative neural networks from data. The
proposed generative model consists of a two-stage structure that first predicts
the state of each link (line-of-sight, non-line-of-sight, or outage), and
subsequently feeds this state into a conditional variational autoencoder that
generates the path losses, delays, and angles of arrival and departure for all
its propagation paths. Importantly, minimal prior assumptions are made,
enabling the model to capture complex relationships within the data. The
methodology is demonstrated for 28GHz air-to-ground channels in an urban
environment, with training datasets produced by means of ray tracing.Comment: Submitted to IEEE GLOBECOM 2020 Workshop on Wireless Propagation
Channels for 5G and B5
Features of Magnetocaloric Effect in Er(Co-Fe)2 Laves Phases
In this work the results of measurements of heat capacity (CP) and magnetocaloric effect (MCE) in Er(Co1-хFeх)2 system in the concentration range 0.07 ≤ x ≤ 0.80 are presented. Phase composition was controlled by X-ray difraction analysis. Heat capacity was measured in the temperature range 77-320 K. MCE has been studied within the temperature range 5-670 K in magnetic fields up to 70 kOe. It was found that Fe concentration increase caused the table-like (plateau) MCE temperature dependence for both magnetic entropy change date and direct ∆T-effect measurements independently on Fe concentration. The possible reasons of such behavior are discussed
Characterizing the UAV-to-Machine UWB Radio Channel in Smart Factories
In this work, the results of Ultra-Wideband air-to-ground measurements carried out in a real-world factory environment are presented and discussed. With intelligent industrial deployments in mind, we envision a scenario where the Unmanned Aerial Vehicle can be used as a supplementary tool for factory operation, optimization and control. Measurements address narrow band and wide band characterization of the wireless radio channel, and can be used for link budget calculation, interference studies and time dispersion assessment in real factories, without the usual limitation for both radio terminals to be close to ground. The measurements are performed at different locations and different heights over the 3.1-5.3 GHz band. Some fundamental propagation parameters values are determined vs. distance, height and propagation conditions. The measurements are complemented with, and compared to, conventional ground-to-ground measurements with the same setup. The conducted measurement campaign gives an insight for realizing wireless applications in smart connected factories, including UAV-assisted applications
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