Number of found documents: 172
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Hidden Problems in Precise Calibration on Microstrip
Raboch, Jiří; Hoffmann, Karel; Škvor, Zbyněk; Hudec, Přemysl
2008 -
A study of calibration problems on microstrip with respect to interaction of electromagnetic fields around SMA to microstrip launcher and microstrip short was carried out in frequency band up to 26 GHz. Omni Spectra SMA to microstrip launcher, 50 Omega microstrip line on Arlon CuClad 223 0.508 mm thick substrate and microstrip shorts with reflective wall above the upper side of substrate as a calibration elements were used for simulations in CST Microwave Studio. Strong influence of dimensions of shorts and distance between the shorts and the launcher on simulated calibration data was observed. Reasonable dimensions of the short and the distance between the short and the launcher making possible correct precise calibration were determined. Available in digital repository of ČVUT.
Hidden Problems in Precise Calibration on Microstrip

A study of calibration problems on microstrip with respect to interaction of electromagnetic fields around SMA to microstrip launcher and microstrip short was carried out in frequency band up to 26 ...

Raboch, Jiří; Hoffmann, Karel; Škvor, Zbyněk; Hudec, Přemysl
České vysoké učení technické v Praze, 2008

A Double H-Shaped Resonator for an Isotropic ENG Metamaterial
Macháč, Jan; Rytíř, Martin; Protiva, Pavel; Zehentner, Jan
2008 -
This paper presents a new planar particle showing negative effective permittivity under irradiation by an electromagnetic wave. The response of this particle, aimed to be sensitive to an electric field, is strongly anisotropic. The particle is used to design an isotropic epsilon-negative metamaterial in two forms. Firstly, a unit cell of the metamaterial consists of a cube bearing six proposed particles on its faces, located with specific orientations. The experiments showed that this unit cell is suitable for manufacturing an isotropic epsilon-negative metamaterial obtained by arranging these cells in a 3D cubic periodic system. The second form of an epsilon negative metamaterial with an isotropic response consists of the proposed planar particles themselves, distributed quasi-randomly, composing a 2D system and/or of particles placed in spherical shells and distributed fully randomly in a hosting material composing a 3D system. The isotropy of these systems was verified by measurements in a rectangular waveguide. Available in digital repository of ČVUT.
A Double H-Shaped Resonator for an Isotropic ENG Metamaterial

This paper presents a new planar particle showing negative effective permittivity under irradiation by an electromagnetic wave. The response of this particle, aimed to be sensitive to an electric ...

Macháč, Jan; Rytíř, Martin; Protiva, Pavel; Zehentner, Jan
České vysoké učení technické v Praze, 2008

Electrically Conductive Adhesive Filled with Mixture of Silver Nano and Microparticles
Mach, Pavel; Radev, Radoslav; Pietriková, Alena
2008 -
Electrically conductive adhesive with isotropical electrical conductivity modified with addition of silver nanoparticles has been investigated. The electrical resistance, nonlinearity of a current vs. voltage characteristic and the tensile strength of adhesive joints formed of this adhesive have been measured. The specimens have also been aged at the temperature of 125degC and at the combined climate 80degC/80 % relative humidity for 700 hours. It has been found that silver nanoparticles added into the electrically conductive adhesive cause decrease of its conductivity, increase of its nonlinearity and increase of the tensile strength. Available in digital repository of ČVUT.
Electrically Conductive Adhesive Filled with Mixture of Silver Nano and Microparticles

Electrically conductive adhesive with isotropical electrical conductivity modified with addition of silver nanoparticles has been investigated. The electrical resistance, nonlinearity of a current vs. ...

Mach, Pavel; Radev, Radoslav; Pietriková, Alena
České vysoké učení technické v Praze, 2008

Testing of Techniques for Improvement of Conductivity of Electrically Conductive Adhesives
Mach, Pavel; Richter, Lukáš; Pietriková, Alena
2008 -
The paper presents methods, which have been used for improvement of electrical conductivity of electrically conductive adhesives with isotropical electrical conductivity. Conductivity level depends, among other things, on level of aggregation of filler particles. The research has been focused on improvement of electrical properties by better aggregation of filler particles in adhesive. Following methods have been tested with the goal to support aggregation: ultrasound mixing for 60s, rotary mixing for 60 s, and addition of a small amount of AgNO3. The goal of addition of this salt has been to decrease Coulomb forces between particles of filler. Four types of formulations have been used for experiments. One-component formulations: adhesives bisphenol epoxy resin with 75 % (wt.) silver flakes, bisphenol epoxy resin with 75 % (wt.) silver flakes + 10 % (wt.) silver nanoparticles, bisphenol epoxy resin with 65 % (wt.) silver flakes + 20 % (wt.) silver nanoparticles. Two component formulation: bisphenol epoxy resin with 55 % (wt.) silver flakes. It has been found that ultrasound mixing has low influence only to the value of the electrical conductivity of adhesive, rotary mixing before application of the adhesive improves electrical conductivity significantly; addition of AgNO3 into the adhesive has improved electrical conductivity of two formulations and has had almost no effect for two other formulations. As a part of this work the course of electrical conductivity of adhesives during the curing time has also been investigated. Available in digital repository of ČVUT.
Testing of Techniques for Improvement of Conductivity of Electrically Conductive Adhesives

The paper presents methods, which have been used for improvement of electrical conductivity of electrically conductive adhesives with isotropical electrical conductivity. Conductivity level depends, ...

Mach, Pavel; Richter, Lukáš; Pietriková, Alena
České vysoké učení technické v Praze, 2008

Efficient Sequential Correspondence Selection by Cosegmentation
Čech, Jan; Matas, Jiří; Perd’och, Michal
2008 -
In many retrieval, object recognition and wide baseline stereo methods, correspondences of interest points are established possibly sublinearly by matching a compact descriptor such as SIFT. We show that a subsequent cosegmentation process coupled with a quasi-optimal sequential decision process leads to a correspondence verification procedure that has (i) high precision (is highly discriminative) (ii) good recall and (iii) is fast. The sequential decision on the correctness of a correspondence is based on trivial attributes of a modified dense stereo matching algorithm. The attributes are projected on a prominent discriminative direction by SVM. Waldpsilas sequential probability ratio test is performed for SVM projection computed on progressively larger co-segmented regions. Experimentally we show that the process significantly outperforms the standard correspondence selection process based on SIFT distance ratios on challenging matching problems. Available in digital repository of ČVUT.
Efficient Sequential Correspondence Selection by Cosegmentation

In many retrieval, object recognition and wide baseline stereo methods, correspondences of interest points are established possibly sublinearly by matching a compact descriptor such as SIFT. We show ...

Čech, Jan; Matas, Jiří; Perd’och, Michal
České vysoké učení technické v Praze, 2008

Dense Linear-Time Correspondences for Tracking
Obdržálek, Štěpán; Perd’och, Michal; Matas, Jiří
2008 -
A novel method is proposed for the problem of frame-to-frame correspondence search in video sequences. The method, based on hashing of low-dimensional image descriptors, establishes dense correspondences and allows large motions. All image pixels are considered for matching, the notion of interest points is reviewed. In our formulation, points of interest are those that can be reliably matched. Their saliency depends on properties of the chosen matching function and on actual image content. Both computational time and memory requirements of the correspondence search are asymptotically linear in the number of image pixels, irrespective of correspondence density and of image content. All steps of the method are simple and allow for a hardware implementation. Functionality is demonstrated on sequences taken from a vehicle moving in an urban environment. Available in digital repository of ČVUT.
Dense Linear-Time Correspondences for Tracking

A novel method is proposed for the problem of frame-to-frame correspondence search in video sequences. The method, based on hashing of low-dimensional image descriptors, establishes dense ...

Obdržálek, Štěpán; Perd’och, Michal; Matas, Jiří
České vysoké učení technické v Praze, 2008

Coupling of split ring resonators in a mu-negative volumetric metamaterial
Macháč, J.; Zehentner, J.; Bláha, M.
2008 -
This paper presents an experimental and theoretical study of the coupling of split ring resonators, and aims to show ways to widen the frequency band of the response of mu-negative metamaterials. The behaviour of these metamaterials is theoretically described in terms of coupled resonant circuits theory. In particular the coupling is studied on pairs of split ring resonators and systems containing the greater number of resonators. Widening of the metamaterial response frequency band is caused primarily by dispersion of the resonant frequencies of the particular resonators, and to a minor extent by mutual coupling. The more particles participate in the tested system, the wider the frequency band of the system response. The requirement to obtain an isotropic medium is taken into account. Keywords: split ring resonator; coupled resonators; mu negative metamaterial; isotropic metamaterial; widening frequency band Available in digital repository of ČVUT.
Coupling of split ring resonators in a mu-negative volumetric metamaterial

This paper presents an experimental and theoretical study of the coupling of split ring resonators, and aims to show ways to widen the frequency band of the response of mu-negative metamaterials. The ...

Macháč, J.; Zehentner, J.; Bláha, M.
České vysoké učení technické v Praze, 2008

Modification of Electrically Conductive Adhesives for Better Mechanical and Electrical Properties
Mach, Pavel; Richter, Lukáš; Pietriková, Alena
2008 -
The goal of the work has been to check a possibility of improvement of electrical properties of electrically conductive adhesives with isotropic electrical conductivity to edge these properties toward to properties of solders. The electrical resistance and nonlinearity of I-V characteristic have been investigated. Two ways have been used for electrically conductive adhesive modification: addition of small amount of silver nanoparticles (grains) of three different dimensions into adhesive, and substitution of a part of filler flakes with the same amount of nanoparticles. It has been found that addition of silver nanoparticles increases the resistance and nonlinearity of adhesive. It has also been found that adhesives modified with nanoparticles have lower sensitivity to combined climatic ageing in comparison with adhesives without nanoparticles. The reason is other quality of contacts between flakes and contacts between nanoparticles. Available in digital repository of ČVUT.
Modification of Electrically Conductive Adhesives for Better Mechanical and Electrical Properties

The goal of the work has been to check a possibility of improvement of electrical properties of electrically conductive adhesives with isotropic electrical conductivity to edge these properties toward ...

Mach, Pavel; Richter, Lukáš; Pietriková, Alena
České vysoké učení technické v Praze, 2008

Failure Mode and Effects Analysis of a Process of Reflow Lead-Free Soldering
Mach, Pavel; Duraj, Aleš
2008 -
There are many methods usable for production process optimization. The paper describes the use of failure mode and effects analysis (FMEA of a process type) for the process of lead-free soldering improvement. The schedule of FMEA has been set. Then a flow chart of a process has been drawn and critical failures including their consequences for the final product have been described. Criteria for significance of failures characterization have been defined and have been used for evaluation of significance of failures. Diagnostic methods for critical failures have been proposed and corrective actions have been realized. Available in digital repository of ČVUT.
Failure Mode and Effects Analysis of a Process of Reflow Lead-Free Soldering

There are many methods usable for production process optimization. The paper describes the use of failure mode and effects analysis (FMEA of a process type) for the process of lead-free soldering ...

Mach, Pavel; Duraj, Aleš
České vysoké učení technické v Praze, 2008

A Planar Version of A Slotline Leaky Wave Antenna with a Stacked Substrate
Macháč, J.; Pavliš, A.; Houška, M.; Zehentner, J.
2008 -
This paper presents a new version of a leaky wave antenna based on a conductor-backed slotline with a stacked substrate. The advantage of this new structure is its flat top surface, due to the antenna being fed from the rear side via an SMA connector. The antenna radiates into a single main beam above the substrate. A bi-directional antenna radiating symmetrically both forwards and backwards was obtained by mirroring the structure. Available in digital repository of ČVUT.
A Planar Version of A Slotline Leaky Wave Antenna with a Stacked Substrate

This paper presents a new version of a leaky wave antenna based on a conductor-backed slotline with a stacked substrate. The advantage of this new structure is its flat top surface, due to the antenna ...

Macháč, J.; Pavliš, A.; Houška, M.; Zehentner, J.
České vysoké učení technické v Praze, 2008

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