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    Wyświetlanie 1-4 z 4
    Tytuł:
    The Shielding Effectiveness of a Magnetic Fluid in Radio Frequency Range
    Autorzy:
    Dolník, B.
    Rajňák, M.
    Cimbala, R.
    Kolcunová, I.
    Kurimský, J.
    Džmura, J.
    Petráš, J.
    Zbojovský, J.
    Kosterec, M.
    Kopčanský, P.
    Timko, M.
    Powiązania:
    https://bibliotekanauki.pl/articles/1030481.pdf
    Data publikacji:
    2018-03
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    41.20.Jb
    41.20.Gz
    75.50.Mm
    81.70.Ex
    07.50.Hp
    Opis:
    This article builds on the previous work and describes the interaction of transformer oil-based magnetic fluid (MF) with the radio frequency (RF) magnetic near-field. Three prepared samples of the MF used as a barrier to magnetic near-field, consist of transformer oil and dispersed magnetite nanoparticles coated with oleic acid. We pay attention to the important area related to the electromagnetic field shielding by the MF. Such sample of the MF may be a good candidate for applications where it is necessary to simultaneously electrically isolate, remove the excess of heat and to shield electromagnetic interference (EMI). We present a method for the determination of shielding effectiveness (SE) of the MF under RF excitation conditions ranging from 500 MHz to 3 GHz. We report the effect of magnetic volume fraction in the MF and the effect of the sample thickness on the SE.
    Źródło:
    Acta Physica Polonica A; 2018, 133, 3; 585-587
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    The Response of a Magnetic Fluid to Radio Frequency Electromagnetic Field
    Autorzy:
    Dolník, B.
    Rajňák, M.
    Cimbala, R.
    Kolcunová, I.
    Kurimský, J.
    Balogh, J.
    Džmura, J.
    Petráš, J.
    Kopčanský, P.
    Timko, M.
    Briančin, J.
    Fabián, M.
    Powiązania:
    https://bibliotekanauki.pl/articles/1032825.pdf
    Data publikacji:
    2017-04
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    41.20.Jb
    41.20.Gz
    75.50.Mm
    81.70.Ex
    07.50.Hp
    Opis:
    Electromagnetic pollution generated by the electrical devices has been regarded as a new form of pollution, harmful to the society as air and water pollution. The operation of electronic devices in a polluted electromagnetic environment has caused electromagnetic interference to become important concerns. Devices that are vulnerable to interference must often be shielded to protect them from the effects of electromagnetic interference. In this work we describe an interaction of a magnetic fluid based on transformer oil with alternating magnetic field. The magnetic fluid was composed of a transformer oil and dispersed magnetite nanoparticles coated with oleic acid. Among the wide range of topics covered, we pay attention to an important field related to the absorption of electromagnetic field by magnetic fluid as a suitable candidate for applications where it is necessary to electrically isolate, remove excess of heat, and to shield electromagnetic fields. We present a method for the determination of shielding effectiveness of the magnetic fluid under high-frequency excitation conditions from 750 MHz to 3 GHz by means of magnetic near field measurements and analysis. Herein, we report the effect of magnetic volume fraction in the magnetic fluid and the effect of the sample thickness on the shielding effectiveness. We have found that the magnetic fluid has a frequency dependent "windows", characterized that either absorb the magnetic field, or facilitate penetration of the magnetic field through the barrier.
    Źródło:
    Acta Physica Polonica A; 2017, 131, 4; 946-948
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Ultrasound Frequency Analysis of a Magnetic Fluid in Low-Intensity External Magnetic Field
    Autorzy:
    Kurimský, J.
    Rajňák, M.
    Cimbala, R.
    Dolník, B.
    Tóthová, J.
    Paulovičová, K.
    Timko, M.
    Kopčanský, P.
    Kolcunová, I.
    Petráš, J.
    Džmura, J.
    Balogh, J.
    Powiązania:
    https://bibliotekanauki.pl/articles/1032764.pdf
    Data publikacji:
    2017-04
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    43.58.+z
    43.60.+d
    47.65.Cb
    82.70.Dd
    83.80.Hj
    Opis:
    This work deals with an interaction of a magnetic fluid of a dielectric nature with a magnetic field by means of ultrasound waves measurements and analysis. Ultrasound analysis is known as a non-destructive inspection tool often used in technical diagnostics, moreover, it has numerous applications in medicine and biology, too. We report the low-frequency ultrasound analysis of a dielectric magnetic fluid in a low-intensity external static magnetic field. The studied magnetic fluid was composed of a transformer oil and dispersed magnetite nanoparticles coated with oleic acid. Experiments were carried out by using an ultrasonic testing cell. The cell was exposed to a magnetic field of 50 mT in both parallel and perpendicular direction to the waves propagation. A through-transmission mode measurement was applied, where two fixed narrow-band transducers with completely shielded crystal for maximum RFI/EMI immunity (Physical Acoustic R15I-AST, the resonant frequency 150 kHz) served as a transmitter and a receiver. In this way we carried out the measurement of the frequency-dependent ultrasonic response to a rectangle calibrating signal of 5 μs pulse width. Digitized signals were recorded for further analysis. We present the frequency domain analysis of the low-frequency ultrasound in magnetic fluid. The frequency spectrum in magnetic fluid colloidal system was calculated by the Fourier transformation method. Results show that there is a frequency shift in the amplitude-frequency spectrum caused by the step-up magnetic field. The higher the magnetic field, the higher the frequency of the peaks. The effect of particle aggregation in magnetic field on the ultrasound wave propagation is discussed in the paper.
    Źródło:
    Acta Physica Polonica A; 2017, 131, 4; 910-912
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Height-diameter models for mixed-species forests consisting of spruce, fir, and beech
    Autorzy:
    Petras, R.
    Bosela, M.
    Mecko, J.
    Oszlanyi, J.
    Popa, I.
    Powiązania:
    https://bibliotekanauki.pl/articles/38691.pdf
    Data publikacji:
    2014
    Wydawca:
    Instytut Badawczy Leśnictwa
    Tematy:
    height-diameter model
    mixed-species forest
    tree
    spruce
    fir
    beech
    Abies alba
    Picea abies
    Fagus sylvatica
    Opis:
    Height-diameter models define the general relationship between the tree height and diameter at each growth stage of the forest stand. This paper presents generalized height-diameter models for mixed-species forest stands consisting of Norway spruce (Picea abies Karst.), Silver fir (Abies alba L.), and European beech (Fagus sylvatica L.) from Slovakia. The models were derived using two growth functions from the exponential family: the two-parameter Michailoff and three-parameter Korf functions. Generalized height-diameter functions must normally be constrained to pass through the mean stand diameter and height, and then the final growth model has only one or two parameters to be estimated. These “free” parameters are then expressed over the quadratic mean diameter, height and stand age and the final mathematical form of the model is obtained. The study material included 50 long-term experimental plots located in the Western Carpathians. The plots were established 40–50 years ago and have been repeatedly measured at 5 to 10-year intervals. The dataset includes 7,950 height measurements of spruce, 21,661 of fir and 5,794 of beech. As many as 9 regression models were derived for each species. Although the “goodness of fit” of all models showed that they were generally well suited for the data, the best results were obtained for silver fir. The coefficient of determination ranged from 0.946 to 0.948, RMSE (m) was in the interval 1.94–1.97 and the bias (m) was –0.031 to 0.063. Although slightly imprecise parameter estimation was established for spruce, the estimations of the regression parameters obtained for beech were quite less precise. The coefficient of determination for beech was 0.854–0.860, RMSE (m) 2.67–2.72, and the bias (m) ranged from –0.144 to –0.056. The majority of models using Korf’s formula produced slightly better estimations than Michailoff’s, and it proved immaterial which estimated parameter was fixed and which parameters were free.
    Źródło:
    Folia Forestalia Polonica. Series A . Forestry; 2014, 56, 2
    0071-6677
    Pojawia się w:
    Folia Forestalia Polonica. Series A . Forestry
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
      Wyświetlanie 1-4 z 4

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