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    Wyświetlanie 1-8 z 8
    Tytuł:
    Laboratory model of high frequency sonar
    Autorzy:
    Buszman, K.
    Szymczak, W.
    Powiązania:
    https://bibliotekanauki.pl/articles/331519.pdf
    Data publikacji:
    2008
    Wydawca:
    Polskie Towarzystwo Akustyczne
    Tematy:
    laboratory model
    sonars
    hydroacoustic
    Opis:
    This article contains the construction and laboratory application of high frequency sonar model. In view of working in laboratory conditions, they must be fulfilled succeeding parametric cases: very narrow beam, low level of side lobes and low acoustic power of transmitted impulse sounding. When all of these conditions are fulfilled, it makes possible the explanation to students some terms like depth, angular resolution and making clear, that water is the best environment to acoustic waves transmission. Furthermore, there is used automatic component, namely rotary antenna, which make possibility to precision area scanning.
    Źródło:
    Hydroacoustics; 2008, 11; 39-46
    1642-1817
    Pojawia się w:
    Hydroacoustics
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    High frequency ship radiated noise in shallow water
    Autorzy:
    Carbó, R.
    Molero, A. C.
    Powiązania:
    https://bibliotekanauki.pl/articles/332483.pdf
    Data publikacji:
    1999
    Wydawca:
    Polskie Towarzystwo Akustyczne
    Opis:
    The stationary acoustic field in a two pIane parallel medium, sea surface and sea boftom, when a source near to the sea surface radiates, is characterized by the thickness of the medium and the reflectivity of the boundary surfaces. It is known that the maxima and minima of pressure are produced at same given depths depending on the radiated frequency and distance. Considering the ship noise as an acoustical source, the frequency spectrum of the acoustic pressure at certain depth, is nof only the spectrum of the acoustic ship noise but it is also modified by the wave field originated by consecutive reflections at the boundary surfaces. As a consequence, over the free field spectrum of (he ship noise, a series of minima appears. The corresponding frequencies are those for which the receiver is located at the nodes of the stationary wave field.
    Źródło:
    Hydroacoustics; 1999, 2; 213-218
    1642-1817
    Pojawia się w:
    Hydroacoustics
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    PC-based high frequency imaging system with coded excitation
    Autorzy:
    Lewandowski, M.
    Nowicki, A.
    Powiązania:
    https://bibliotekanauki.pl/articles/331588.pdf
    Data publikacji:
    2008
    Wydawca:
    Polskie Towarzystwo Akustyczne
    Tematy:
    coded transmission
    SNR
    FPGA
    Opis:
    Coded transmission is a technique that gives significant improvement in SNR and enables higher contrast imaging without sacrificing the resolution. A novel HF (20-35 MHz) ultrasound real-time imaging system for research and evaluation of the coded transmission was developed. The digital programmable coder-digitizer module based on the field programmable gate array (FPGA) chip supports arbitrary waveform coded transmission and RF echoes sampling up to 200 MSPS. A novel balanced software architecture supports real-time RF processing and display at rates up to 30 frames/sec. The system was used to gather data for sine burst and 16-bit Golay code excitation using a single element scanning head with thick film focused spherical transducer 25 MHz center frequency and 56% system bandwidth. SNR gain for the Golay codes (referenced to single burst) of 15 dB for 20 MHz and 16 dB for 35 MHz were obtained. In water the axial resolution for both single burst and the Golay codes was the same FWMH=20 ns at 20 MHz and FWMH=15 ns at 35 MHz. The presented system is a practical and low cost implementation of coded excitation technique in HF ultrasound imaging.
    Źródło:
    Hydroacoustics; 2008, 11; 239-247
    1642-1817
    Pojawia się w:
    Hydroacoustics
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Estimation of radial artery reactive response using high frequency ultrasound
    Autorzy:
    Nowicki, A.
    Secomski, W.
    Trawiński, Z.
    Lewandowski, M.
    Trots, I.
    Szubielski, M.
    Olszewski, R.
    Powiązania:
    https://bibliotekanauki.pl/articles/332584.pdf
    Data publikacji:
    2016
    Wydawca:
    Polskie Towarzystwo Akustyczne
    Tematy:
    thick film transducers
    atherosclerosis
    flow mediated vasodilation
    Opis:
    Background: There is a growing interest in the application of non-invasive clinical tools allowing one to assess the endothelial function, preceding atherosclerosis. The precision in estimating of the artery Flow Mediated Vasodilation (FMD) using standard 10-12 MHz linear array probes does not exceed 0.2 mm, far beyond that required. Methods: We have introduced a wide-band, high frequency 25-30 MHz, Golay encoded wobbling type imaging to measure dilation of the radial artery instead of the brachial one. 18 young volunteers, and 4 volunteers with cardiac events history, were examined. In the second approach 20 MHz linear scanning combined with 20 MHz pulsed Doppler attached to the linear array was used. The radial artery FMD was normalized using shear rate at the radial artery wall. Results and Conclusions: For the “healthy” group, the FMD resulting from reactive hyperemia response was over 20%; while in the “atherosclerotic” group, the FMD was at least twice as small, not exceeding 10%. The shear rate (SR) normalized FMDSR was in the range from 7.8 to 9.9 in arbitrary units, while in patients with minor cardiac history FMDSR was clearly lower, 6.8 to 7.6. The normalized FMDSR of radial artery RARR can be an alternative to the brachial FMD where the precision of measurements is lower and the diameter dilation does not exceed 7-10%.
    Źródło:
    Hydroacoustics; 2016, 19; 297-306
    1642-1817
    Pojawia się w:
    Hydroacoustics
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Statistics of envelope of high frequency ultrasound signal backscattered in human dermis
    Autorzy:
    Piotrzkowska, H.
    Litniewski, J.
    Szymańska, E.
    Lewandowski, M.
    Nowicki, A.
    Powiązania:
    https://bibliotekanauki.pl/articles/331987.pdf
    Data publikacji:
    2010
    Wydawca:
    Polskie Towarzystwo Akustyczne
    Opis:
    The scattering of ultrasonic waves depends on the size, shape, acoustical properties and concentration of scatterers in tissue. In these study K distribution of the ultrasound backscatter envelope was used to assess the structural properties of the skin tissue. The custom-designed high frequency ultrasonic scanner was applied to obtain RF B-scans of the skin in vivo at the frequency of 20 ÷ 30MHz. The results are encouraging. The K distribution models the envelope statistics very well. The parameters of the K-distribution, namely, the effective number of scatterers may be useful for the skin characterization.
    Źródło:
    Hydroacoustics; 2010, 13; 205-214
    1642-1817
    Pojawia się w:
    Hydroacoustics
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Experimental evaluation of high frequency side scan sonar as object search and identification tool
    Autorzy:
    Łukaszewicz, D.
    Rowiński, L.
    Powiązania:
    https://bibliotekanauki.pl/articles/332364.pdf
    Data publikacji:
    2006
    Wydawca:
    Polskie Towarzystwo Akustyczne
    Opis:
    Paper presents initial results o laboratory tests of the sonar selected as a short range tool for an underwater vehicle. It is intended for bottom located object search and identification. To evaluate sonar imaging capability expressed by its resolution, several parameters were investigated. First group of parameters regards the sonar itself, while the second regards an object material and dimensions and shape. Their cross-influence was investigated for different distances from hydrophone to an object of interest and different hydrophone elevation angles. Experiments were performed in a shallow water laboratory tank.
    Źródło:
    Hydroacoustics; 2006, 9; 109-118
    1642-1817
    Pojawia się w:
    Hydroacoustics
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Distribution and discrimination of anchovy, and sprat in the Black Sea from high frequency sound records
    Autorzy:
    Mutlu, E.
    Powiązania:
    https://bibliotekanauki.pl/articles/332447.pdf
    Data publikacji:
    1999
    Wydawca:
    Polskie Towarzystwo Akustyczne
    Opis:
    High frequency (200 kHz) was used to identify anchovy, and sprat schools from over the entire trackline of broad-scale acoustical survey over a period of 4 years (1991-1994) in the Bleak Sea. Analysis of color enhanced echograms as well as trawl catches provided detailed morphological descriptions to discriminate aggregations of anchovy, and sprat together with characteristics of their habitat. Sprat showed fish school scattered in relatively, a thin layer near the bottom like semi-pelagic fish made up. Anatomy of the aggregation did not change between day and night, and there was 110 diet shift in the habitat. Anchovy formed the pole shaped schools as well as compact aggregation arising from bottom around the shelf break area to that as much high up as 30-70 m, during the day. Additionally, a striking point is that the anchovy in an appearance, of what looked to be pole shape school, stand ready on top of submarine steep cliff to escape down immediately in case of any disturbance to the school. There is a sharp discrimination between the schools of sprat and anchovy.
    Źródło:
    Hydroacoustics; 1999, 2; 27-31
    1642-1817
    Pojawia się w:
    Hydroacoustics
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Low- and high-frequency elastic scattering analysis of fluid-filled, flat-endcapped cylindrical shells proud on a sandy seabed
    Autorzy:
    Tesei, A.
    Groen, J.
    Powiązania:
    https://bibliotekanauki.pl/articles/331639.pdf
    Data publikacji:
    2008
    Wydawca:
    Polskie Towarzystwo Akustyczne
    Tematy:
    sandy seabed
    at-sea scattering data
    hydroacoustics
    Opis:
    This work presents the analysis of at-sea scattering data by a man-made target which supports the excitation of strong structural waves or resonances, not only at low but even at high frequency (ka>100). The object is a water-filled, flat-endcapped, 2m-long, steel cylindrical shell, measured both at low frequency (2-10 kHz) and at high frequency (120 kHz), where different elastic phenomena are supported and identified. In particular, in the high-frequency sonar images obtained with an AUV-mounted synthetic aperture sonar, significant elastic effects clearly appear, which are interpreted as echoes of a shear wave travelling axially along the cylindrical shell. For interpretation of sonar images it is crucial to understand and predict these supplementary scattering mechanisms.
    Źródło:
    Hydroacoustics; 2008, 11; 388-400
    1642-1817
    Pojawia się w:
    Hydroacoustics
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
      Wyświetlanie 1-8 z 8

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