Currently, one of the key challenges in many different fields of science and engineering is the development of methods capable of distinguishing noise signals from chaotic ones. Analysis of the nature and structure of temporal data series can predict many adverse events before they occur: heart or epileptic attacks, various engine breakdowns, changes in financial markets, etc. The problem of distinguishing between signals of random nature (noise signals) and signals whose nature is determined by complex non-periodic (chaotic) dynamics, is not yet completely solved. This work was aimed to create a method of time series analysis based on forbidden permutations patterns, which will be able to distinguish the appearance of atypical dynamics. Preliminary results demonstrate the ability forbidden permutations patterns analysis method to distinguish between chaotic and noisy dynamics.
A method for preparation of luminescent silicon coatings applicable to both rigid glass substrates and flexible nonwoven polymeric electrospun mats is proposed. This technique allows for synthesis of nanosized silicon crystallites that fluoresce in visible and near-IR light. Proposed approach to preparation of nanostructured fluorescent fibrous materials seems promising for applications in biosensing.
Currently, methods of laser micromachining of various kinds of microsized structures are actively developed by scientists and engineers in a variety of fields. Particularly, laser micromachining allows for selective ablation of thin metal films on dielectric substrates in order to create planar conductive structures with rather complex patterns. Meander-like structures on dielectric substrates can serve as a slow-wave structure in perspective compact millimeter band vacuum electronic devices such as traveling-wave tubes. Thus, the aim of this work was to prepare conductive planar structures from thin metal coatings based on a copper-molybdenum alloy. Copper-molybdenum thin films were deposited onto dielectric substrates by magnetron co-sputtering. Then the coatings were micromachined using a nanosecond pulsed laser to form a series of planar structures in the shape of strips of varied width. Deposited coppermolybdenum thin films after laser micromachining suffer from lack of adhesion to the substrates. Possible way to overcome this issue is use of an adhesion sublayer such as titanium or chromium.
Ongoing active development of modern radiofrequency electronic devices operating in the millimeter (V) band, such as 5th-generation wireless communications demands new materials to control electromagnetic interference, compatibility and reliability of such systems. Here we present a follow-up of studies on antireflective and absorptive micrometer-thick film coatings for operation in V-band using simultaneous magnetron co-deposition of silicon and aluminum. In this system graded segregation was observed under certain regimes, resulting in a depth gradient of aluminum content. Further investigations on the morphology of the obtained films were performed. Inhibition of electromagnetic waves reflection in 50-70 GHz range by up to 27 dB (at least 10 dB throughout the whole range) was achieved through variation of Al content in coatings by the ratio of sputtered atoms fluxes. Surface morphology of films as well as optical properties of those in visible and near IR bands were investigated. It was found that electrophysical properties of resulting samples are severely influenced by the amount and homogeneity of aluminum distribution in the coating. Optical spectroscopy suggests that variation of aluminum content in the film allows for control over resulting film material kind that can be adjusted from dielectric through semiconductive to almost metal-like. Non-homogeneous aluminum distribution in the depth of the film, particularly existence of a two-layered semiconductive optical structure in samples prepared at particular deposition regime was confirmed by measuring optical reflection spectra from the coating side and in reverse. Segregation of aluminum towards the surface of the film in course of silicon recrystallization was confirmed by AFM and surface roughness measurements.
Scalable and cost-effective microfabrication approaches are highly demanded for manufacturing of RF and millimeterwave circuits such as transmission structures for flexible electronic devices. Flexible electronics play a key role in wearable and wireless technologies applicable in personalized medicine, sensing, energy harvesting, and communication areas. Here we report the results of thin copper films patterns micromachining using nanosecond-pulsed laser on flexible dielectric substrates. Thin copper films were deposited by magnetron sputtering onto 100 μm thick polyimide films that were used as dielectric substrates. Then, patterns were created through film ablation using a CNC laser micromachining system with a 1064 nm ytterbium 8 ns pulse duration fiber laser to chisel away the superfluous material just as it have been done in sculputure for ages. Several regimes of laser micromachining were studied. The most important issue in the laser micromachining of the metal films on the flexible dielectric substrate is flexible substrate thermal damage due to overheating. Optimal regimes of laser micromachining were found that allow to prevent this. These regimes will be used in the future to fabricate flexible transmission lines for RF and millimeter-wave signals. The schematic and design of the transmission line are considered. Results of numerical simulations made by ANSYS HFSS are presented.
Traveling-wave tubes (TWT) with microstrip planar slow wave structures (SWS) have attracted an increasing interest thanks to low operating voltage and size of the tube, as well as compatibility with modern microfabrication technologies. In this work, we report the results of design, fabrication, and experimental cold-test study of planar meander-line SWSs for millimeter-band TWTs (V-, W-, and D-band). SWS samples have been fabricated using the technology based on magnetron sputtering and subsequent laser ablation.
Design and preliminary numerical simulations of D-band planar microstrip meander-line slow wave structure for lowvoltage tubes with sheet electron beam were carried out. An original approach based on magnetron sputtering and laser ablation methods was utilized for microstrip meander-line slow wave structure microfarication. An application of nanosecond and picosecond laser ablation for microfabrication of D-band (110-170 GHz) planar microstrip meander-line slow wave structure was considered. We have verified our original approach for planar slow wave structures microfabrication by using different CNC precision laser machines operating with different values of laser pulse duration (100 ns, 8 ns, 4 ns and 10 ps). Samples of slow wave structures were fabricated and characterized by scanning electron microscopy and profilometry methods. It was shown that each considered CNC precision laser machine allows fabricating D-band microstrip meander-line slow wave structure with required dimensions, but picosecond laser ablation has such advantages as the absence of ablation products (droplets, and etc.) on the slow wave structure surface. As the next step, we are going to study S-parameters of microfabricated D-band microstrip meander-line slow wave structure samples experimentally by using vector network analyzer with D-band frequency converters.
In this paper, we consider a short review of existing technologies of flexible antenna fabrication and propose our original approach for flexible antenna fabrication. Review of existing technologies of flexible antenna fabrication includes photolithography, screen printing, pad printing, gravure printing, inkjet printing, micro-dispensing, micro-jetting, and aerosol-jet technology. Advantages and disadvantages of each mentioned above technologies were noted. In the second part of this study, we consider our original technology for antenna fabrication on flexible substrates utilizing magnetron sputtering and laser ablation methods. Samples of flexible antennas are formed on a flexible dielectric substrate in a technology process comprising following basic stages: 1) deposition a conductive coating onto the dielectric substrate with help of magnetron sputtering, 2) formation the pattern of the antenna structure on the conductive coating by laser ablation. In the final stage, the substrate is divided into individual samples of specific sizes. A number of test flexible antennas fabricated by our original approach are shown.
We consider the results of dielectric properties study in millimeter band of thin-films based on silicon nitride compositions. Silicon nitride thin-film coatings were deposited on a substrate by DC magnetron sputtering. As a substrate for silicon nitride thin-film coatings a quartz plate were utilized. The ratio of argon and nitrogen in the working gas mixture was chosen as the variable parameter to control the composition of the deposited thin-film coating. Several samples of silicon nitride thin-film coatings with about 1 um thickness were fabricated. Radiophysical and dielectric properties of the fabricated SiN-type thin-film coatings were studied in millimeter wave frequency band of 50-70 GHz (V-band) with help of free space measurement method. The obtained results have shown that by controlling the resistive thin-film coating composition one can only slightly vary the radiophysical and dielectric properties of coating in millimeter-band.
We consider the results of modern scientific literature review on the experience and possibilities of using resistive thinfilm layers in vacuum electron devices (resistive wall amplifier). Such thin-film layers can be used as analogue of conventional slow wave structures in vacuum microwave amplifiers. The disadvantages of conventional slow wave structures in millimeter and submillimeter wavelength ranges are discussed. The main advantages and features of resistive thin-film layers, which could be serve as slow wave structures in amplifying devices of vacuum microwave electronics of millimeter and submillimeter wavelength range, are revealed. The proposed review covers the period from 1953, when the idea of a resistive wall amplifier was first introduced, to 2018. It was shown that the majority of literature consist only theoretical results, only a few papers consider the experimental results. Also it is noted that the focus of modern study shifts to the using of metamaterials as a resistive thin-film layer, very promising theoretical results and some cold measurements were obtained only in the GHz region.
Microfabricated vacuum power amplifiers and oscillators operating at millimeter and submillimeter (THz) bands are of great interest for applications in high-speed communication, radar, security and military systems, electronic warfare, etc. In this work, we report the results of numerical simulation and cold-test measurements of electromagnetic parameters of the V-band (50-70 GHz) planar meander-line SWS. The microstrip meander-line SWS is suitable for using in a millimeter-band TWT amplifiers. Several samples of copper microstrip meander-line SWS on a quartz substrate consisting of 50 meander periods with input and output couplers were designed, microfabricated and optimized. The SWS was microfabricated by using magnetron sputtering and laser ablation processes. This technique is a more facile, flexible and lower cost as compared to photolithography method. Transmission and reflection of proposed SWS were measured experimentally and calculated numerically. The results of the experimental cold-test measurements are verified by numerical simulations. Electromagnetic parameters of the SWSs were simulated using the finite-element ANSYS HFSS and COMSOL Multiphysics software packages. The results obtained with these two codes are in excellent agreement with each other and good agreement between experimental and numerical results is also observed.
Encapsulation of various nanoparticles in nanofibers has become one of the most interesting topics in the field of electrospinning and SERS. Literature review shows that several main approaches can be distinguished for the preparation of electrospun nanofibers with embedded metal nanostructures. However, there is no information about the comparison of various methods of metal nanoparticles introduction into nanofiber-based SERS-platforms. Three main approaches were used here for preparation of SERS-platforms based on electrospun nanofibers with embedded silver nanoparticles: synthesis of metal nanostructures inside fibers prepared with incorporated precursor, metal nanostructures synthesis via their nucleation in prepared nanofibers and sorption of metal nanostructures onto ready-made nanofibers. SERS-platforms based on polyacrylonitrile nanofibers containing various concentrations of Ag nanoparticles were obtained using techniques described above and tested.
We have propose an original approach for fabrication of flexible antennas for biomedical-related applications. The technology is based on magnetron sputtering and laser ablation methods. The magnetron sputtering method is used to deposit a thin layer of metal (copper) on a flexible substrate (polyimide film). Then laser ablation is utilized to remove excess copper thus forming an antenna pattern on the metal layer. ISM band flexible design with microstrip feeding structure was chosen for testing this technique. Results of numerical simulation are presented. A number of test flexible antennas were fabricated by our original approach. Similar flexible antennas were also fabricated via photolithography process. A comparison of the experimental results of return loss (S11) measurements of antennas with different fabrication approach was carried out. The obtained experimental data is in a good agreement with the numerical modeling results. Proposed technology has significant advantages in cost, speed, and flexibility over photolithography processes commonly utilized for such applications.
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