Digital library of Brno University of Technology

    Tungsten wire surface cleaning using electropolishing process

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    This article deals with the preparation of tungsten wires surface for electrochemical etching process via electropolishing process. Cleaning of the wire surface is very important for obtaining field emission cold cathodes with sharp tips and low contamination on its surface which are made from these tungsten wires. There are many ways to clean wire surface such as heating it in a ultra vacuum, using solutions and acids, mechanical cleaning etc. Each of these methods has advantages and disadvantages and due to electropolishing process quickness this method was selected for futher usage

    Comparison of Dry and Wet Oxidation Process during Low Pressure Boron Diffusion with BBR3 in Solar Cell Production

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    This paper deals with replacing a dry oxidation with a wet oxidation process during low pressure diffusion using boron tribromide (BBr3) in solar cell production. Because the liquid boron trioxide (B2O3), a product of a chemical reaction during diffusion, condenses apart from wafers on walls of quartz tube, it is essential to clean the tube after diffusion. This could be done by evaporation of water into the tube after unload or, in order to make the production time shorter, by replacing the dry oxidation with wet oxidation process. In this paper a comparison of the wet and dry oxidation is given with regard to the solar cell production

    Foundations of Fractional Calculus on Time Scales

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    Bakalářská práce pojednává o zlomkovém kalkule na časových škálach, přesněji - zavádí zlomkový kalkulus na časových škálach a taktéž vyšetřuje jednoznačnost axiomatické definice zavádějící mocninné funkce. Po zavedení základních pojmů je předmětem diskuze hlavně zobecněná Laplaceova transformace a důkaz jednoznačnosti zobecněné Laplaceovy transformace, která je použita jako nástroj pro dokázání jednoznačnosti zlomkových mocniných funkcií na časových škálach.The bachelor thesis concerns fractional calculus on time scales, more precisely, it introduces fractional calculus on time scales and also investigates the property of uniqueness of the axiomatic definition of the power functions. After introducing basic concepts, the subject of discussion is mostly generalized Laplace transform as well as proof of uniqueness of generalized Laplace transform, which is used as a tool to proving the uniqueness of fractional power functions on time scales.

    Controlling and Evaluation of Laser Micromanipulation Experiments

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    Tato práce je zamerena na vytvorení uživatelsky prívetivého softwarového rozhraní v programovém prostredí LabViewTM, které zjednoduší realizaci nejruznejších experimentu využívajících laserových mikromanipulací a laserové spetroskopie živých organismu. Obe tyto rychle se rozvíjející techniky umožnují bezkontaktní a nedestruktivní manipulaci a diagnostiku jednotlivých jednobunecných organizmu, bakterií ci viru. V rámci této práce jsme vytvorili komunikacní protokoly k rízení rozlicných periferií, kalibraci snímané vizuální scény, zpracování obrazu v reálném case, automatickou detekci bunek (mikroobjektu) ve snímané scéne, snímání a zpracování Ramanovského spektra z živých organismu. Cílem našeho snažení je plne automatický laserový systém, který trídí živé bunky na základe jejich chemického složení. Tato práce byla vypracována v Ústavu prístrojové techniky AV CR, v.v.i., pod vedením prof. RNDr. Pavla Zemánka, Ph.D.This work is focused on the development of a user friendly software interface using the LabViewTM environment that simplifies running of various experiments using laser micromanipulations and laser microspectroscopy of living microorganisms. Both techniques have been developing very fast for the last decade and belong to the growing group of contact-less and nondestructive techniques for manipulation and diagnostics of individual living microorganisms, cells, or viruses. Within this project we mastered the driving of peripheries, calibration of CCD scene, real-time image processing of the CCD scene, automatic selection of the cell for further laser processing, acquisition and processing of the Raman spectrum from living microorganisms. The final goal of our activity is fully automatic laser-based sorter of living cells depending on their chemical compositions. This work has been elaborated at the Institute of Scientific Instruments of the ASCR, v.v.i. under the supervision of prof. Pavel Zemanek.

    Power losses in optical part of the link working in free space

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    Tato diplomová práce pojednává o charakteristikách laserových diod, difrakcí a o vlastnostech gausovského svazku. Je určen útlum vazby vysílací dioda - vysílací apertura v závislosti na velikostech apertury a na velikosti svazku v programu MATLAB. Jsou stanoveny optimální parametry vazby apertura-dioda.This master's thesis deals with the characteristics of the laser diode, diffraction and the properties of the gaussian beam. The coupling attenuation of the laser diode and the transmitting aperture is calculated depending on the sizes of the aperture and on the size of the beam in program MATLAB. The optimal parameters of the coupling diode-aperture are determined.

    Degenerate RFID Channel Modeling for Positioning Applications

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    This paper introduces the theory of channel modeling for positioning applications in UHF RFID. It explains basic parameters for channel characterization from both the narrowband and wideband point of view. More details are given about ranging and direction finding. Finally, several positioning scenarios are analyzed with developed channel models. All the described models use a degenerate channel, i.e. combined signal propagation from the transmitter to the tag and from the tag to the receiver

    Design of Compact Planar Diplexer Based on Novel Spiral-Based Resonators

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    A miniaturized planar diplexer utilizing the novel spiral-based resonators is proposed. The given cell which is initially proposed in this article is composed of two separated rectangular spirals which are asymmetrical to each other and thus, it is called as ‘asymmetrical separated spirals resonator’ (ASSR). ASSR has more superior transmission property than the previous prototype and extremely compact dimension is also achieved. It is demonstrated that ASSR can exhibit bandpass performance with high frequency selectivity and good transmission property within the relatively low frequency band. Based on the given characteristic, one planar diplexer composed of T-junction and two ASSRs is synthesized and the fabricated prototype with compact dimension is achieved, thanks to ASSRs explored. Simultaneously, the transversal dimension of each channel is extremely compact because ASSRs are completely embedded in the feed lines. Both the simulated and measured results indicate that satisfactory impedance matching and high isolation between two channels are achieved. Furthermore, the proposed diplexer is uniplanar and no defected ground structure is introduced

    Wideband Tunable PIFA Antenna with Loaded Slot Structure for Mobile Handset and LTE Applications

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    A compact planar inverted F antenna (PIFA) with a tunable frequency response is presented. Tuning of the resonant frequency is realized by loading a varactor on an embedded slot of the proposed antenna structure without further optimizing other antenna geometry parameters. The antenna exhibits a wide frequency range from 1570 to 2600 MHz with a good impedance matching (S11 ≤-10 dB) covering the GPS, PCS, DCS, UMTS, WLAN and LTE systems. To validate the theoretical model and design concept, the antenna prototype was fabricated and measured. The compact size of the antenna is 15mm × 8mm × 3mm, which makes this antenna a good candidate for mobile handset and wireless communication applications

    Antenna Miniaturization Based on Supperscattering Effect

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    Antennas are essential components of all existing radio equipments. The miniaturization of antenna is a key issue of antenna technology. Based on supperscattering effect, we found that when a small horn antenna is located inside of a dielectric core and covered with a complementary layer, its far field radiation pattern will be equivalent to a large horn antenna. The complementary layer with only axial parameters varying with radius is obtained using coordinate transformation theory. Besides, the influence of loss and perturbations of parameters on supperscattering effect is also investigated. Results show that the device is robust against the perturbation in the axial material parameters when the refractive index is kept invariant. Full-wave simulations based on finite element method are performed to validate the design
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