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Modification of the Measurement Setup for Examination of Acoustic Field Distribution Inside Cylindrical Ducts for Axisymmetric Excitation

100%
Gorazd Ł., Jurkiewicz J., Raab S., Snakowska A.
Acta Physica Polonica A
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2013
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vol. 123
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issue 6
1085-1089
EN
The aim of the paper is to present results of examination of the acoustic pressure field inside a model of a cylindrical duct. Measurements of the root mean square acoustic pressure were carried out using a new measurement setup, first in conditions allowing for propagation of the plane wave only, and next - by increasing the excitation frequency - with successive higher modes also taken in account. Two types of hard-walled cylindrical ducts were examined corresponding to mathematical models known as the infinite duct and the semi-infinite duct. A dedicated measurement setup is presented as well as the successive stages of its modification. In order to verify the modified measuring system, the first stage of the research work consisted in excitation of the axisymmetric modes only and assessing the degree of symmetry represented by the measurement data Significant improvement of the compatibility of the obtained measurement results with theoretical predictions was observed in the explored frequency band 800-5500 Hz that for the duct inside radius of a=0.077 m corresponded to the reduced frequency range 1.13
2
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Acoustic Impedance of Outlet of a Hard-Walled Unbaffled Cylindrical Duct for Multimode Incident Wave

100%
Jurkiewicz J., Snakowska A., Smolik D.
Acta Physica Polonica A
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2011
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vol. 119
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issue 6A
1061-1067
EN
In the paper, the specific acoustic impedance of outlet of an unbaffled duct for incident wave composed of one or many circumferential cut-on duct modes has been derived and presented on graphs. When considering the multimode excitation the equal energy per mode principle and random phases have been assumed. Experimentally verified assumption on equal energy per mode allows for quantitative analysis of the sound field and thus provides more physical insight into the in-duct and out-duct phenomena. The assumption of random phase was implemented by means of the Monte Carlo method and so the expected value, the standard deviation and the percentile curves of the impedance were presented. Numerical data obtained according to the derived theoretical formulae for single and multimode incident wave manifest strong modal character and dependence on the modes phases. The assumption of multimode incident wave has brought the theoretical model closer to what is being observed in practice, especially when ducts of large radius, such as heating and air conditioning systems or turbojet engines, are considered.
3
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Open End Correction for Arbitrary Mode Propagating in a Cylindrical Acoustic Waveguide

100%
Snakowska A., Jurkiewicz J., Smolik D.
Acta Physica Polonica A
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2011
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vol. 120
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issue 4
736-739
EN
The paper presents a method of theoretical derivation and numerical calculation of the open-end correction coefficient for an arbitrary cut-on mode propagating in acoustic waveguide. Actually, the so-called open-end correction coefficient of acoustic tube, frequently discussed in literature, refers to specific conditions, when the wave heading the outlet is the plane wave. It follows from the fact that the plane wave is a commonly applied approximation when considering phenomena in duct-like devices or systems (tubes, musical instruments, heating or ventilation systems). The aim of the paper is to extend the concept of the open-end correction on the so-called higher Bessel modes, that under some conditions can also propagate in a duct. Theoretical results, forming the basis for numerical calculations, were obtained by considering diffraction at the duct end and applying the Wiener-Hopf factorization method. As a result, the formula for the acoustic field inside the duct was derived. For each Bessel mode present in the incident wave the reflected wave is composed of all cut-on modes of the same circumferential order. Each mode present in the reflected wave is characterized by the complex reflection/coupling coefficient, argument of which describes phase change at the duct end and therefore the open-end correction coefficient can be attributed to each coupled pair of modes.
4
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Electromagnetic Wave Behaviour in Uniaxial Magnetodielectric Media of 1+1>2 Type

80%
Kapelewski J., Dukata A.
Acta Physica Polonica A
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2009
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vol. 116
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issue 3
331-334
EN
In the paper a phenomenological approach is proposed to polarized electromagnetic wave propagation in magnetodielectric media, composed of piezoelectric and magnetostrictive anisotropic monolayers. The composite materials consisting of a system of such bimorph films have recently attracted much interest, because they can exhibit a much stronger magnetoelectric effect in a wide temperature range than the single phase multiferroic materials. In the paper dispersion equations given in a common form for both TE and TM modes are derived for long wave approximation. The equations can be of use in evaluation of directional dependence for particular polarizations, which is of particular interest in designing substrate for miniaturized polarimetric antenna, especially useful for modern synthetic aperture radar systems.
5
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Coupled Waves in Two-Phase Periodic Planar Multilayers

80%
Kapelewski J.
Acta Physica Polonica A
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2011
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vol. 120
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issue 4
647-650
EN
In the paper a consequently dynamic model approach to the magnetoelectric coupling is proposed. As opposed to the static case the approach includes both the elastic equation of motion and the full set of the Maxwell equations for effective composite medium. The analytical treatment is performed from two layers of ∞_m symmetry and results in closed relations for propagation characteristics of coupled elasto-electrodynamic waves for millimeter-length range.
6
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New Approach to Rayleigh Wave Propagation in the Elastic Halfspace - Viscoelastic Layer Interface

80%
Pasternak M.
Acta Physica Polonica A
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2008
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vol. 114
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issue 6A
A-169-A-174
EN
The Rayleigh wave propagation problem in the elastic halfspace - viscoelastic layer interface was analysed in the paper. The problem was formulated in the Fourier-Laplace space using the Biot viscoelastic solid model. The characteristic equation has taken the Rayleigh equation form with correction term describing viscoelastic layer properties influence on the wave velocity. The approach presented here seems to be useful for surface acoustic waves gas sensors modelling because many chemisensitive coatings applied to the sensors exhibit viscoelastic properties.
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