Experimental identification of the features of sound propagation in a shallow pond with a system of four vertical antennas
Experimental identification of the features of sound propagation in a shallow pond with a system of four vertical antennas
K.V. Dmitriev, A. S. Lipavskiy, I.A. Pankov, S.N.Sergeev, E.A. Fadeev
The experiment of the sound propagation in a shallow pond in a natural environment was made. The pond surface was covered with a layer of ice. The signals were recorded synchronously by the system of four vertical antennas located at different distances from the source. The waves propagating in the water layer and in the pond bottom were detected and its velocities were obtained.
Show AbstractNumerical modeling of axially symmetric focused fields generated by ultrasound surgery transducers using a wide-angle parabolic approximation
Numerical modeling of axially symmetric focused fields generated by ultrasound surgery transducers using a wide-angle parabolic approximation
I. S. Mezdrokhin, P.V. Yuldashev, V. A. Khokhlova
A numerical algorithm for calculating ultrasound fields radiated from axially symmetric focused sources was developed on the basis of a wide-angle parabolic approximation of the Helmholtz equation. A numerical solution for the field of an axially symmetric spherical radiator with an aperture of a = 5cm, focal length F = 9cm, and the frequency f = 1MHz was obtained. The solution was compared to those obtained using the full diffraction formulation and with conventional parabolic equation. The results showed that the relative error in pressure amplitude at the focus was 1–2% for a wide-angle parabolic approximation and 10–12% for the conventional parabolic approximation comparing to the exact Rayleigh integral solution. Calculation time for a wide-angle model was comparable to conventional parabolic model, and was an order of magnitude less than calculating the exact solution using the Rayleigh integral.
Show AbstractComparison of thermal ablation criteria for nonlinear regimes of ultrasound irradiation of biological tissue using a multi-element phased array
Comparison of thermal ablation criteria for nonlinear regimes of ultrasound irradiation of biological tissue using a multi-element phased array
Y. S. Andriyakhina, I.V. Sinilschikov, P.V. Yuldashev, V. A. Khokhlova
In this paper different criteria of thermal ablation induced by high intensity focused ultrasound in clinically significant volumes of biological tissue were compared. Sonications using a multi-element ultrasound array and various nonlinear focusing regimes were considered in numerical experiment. Sonication of tissue was maintained until thermal dose reached a threshold value at the circle of a certain radius. The threshold temperature was chosen so that the sonication stopped at the same time when using the criteria of temperature or dose. Threshold temperatures equivalent to the thermal dose threshold achieved at the end of the heating were obtained. Volumes of thermal lesions in tissue were calculated using both the criteria of thermal dose and temperature. It was shown that the use of the threshold temperature criterion corresponded with good accuracy to the thermal dose criterion in case of the uniform heating of the tissue volume.
Show AbstractMethod to determine maximal values of acousto–optic figure of merit in optically isotropic media
Method to determine maximal values of acousto–optic figure of merit in optically isotropic media
P.A. Nikitin
A method to determine optimal values of acousto-optic (АО) figure of merit was developed. Its advantages are clarity and high performance. Results can be used for development high-efficient AO devices based on optically isotropic media.
Show AbstractQuasi–orthogonal and quasi–collinear acoucto–optic interaction in absorbing medium
Quasi–orthogonal and quasi–collinear acoucto–optic interaction in absorbing medium
P.A. Nikitin, V.B. Voloshinov
A theory of acousto–optic interaction (AOI) in anisotropic medium, taking into account absorption of electromagnetic waves and attenuation of acoustic waves, has been developed. Expressions for optimal length and bandwidth of the AOI were derived. A non–reciprocal effect inherent only in the backward collinear diffraction was discovered.
Show AbstractMathematical model of rectangular waveguide system with impedance wall
Mathematical model of rectangular waveguide system with impedance wall
A. I. Erokhin, I.E. Mogilevsky, V.E. Rodyakin, V.M. Pikunov
Mathematical model for rectangular waveguide with impedance wall on which impedance Schukin–Leontovich boundary conditions are implemented is considered. Using these boundary conditions complete electromagnetic field in the waveguide is not divided into TE and TM fields and hybrids modes have to be taken into account. A new basis to represent components of complete electromagnetic field of a rectangular waveguide is suggested using witch impedance boundary conditions are satisfied exactly. Stiff system ODEs for amplitudes of this representation is a result.
Show AbstractEstimate of geometrical–phase corrections for transducers of ring antenna
Estimate of geometrical–phase corrections for transducers of ring antenna
V.A. Burov, D.I. Zotov, O.D. Rumyantseva
Algorithm of estimating the geometrical and phase corrections for receiving–transmitting transducers of ring antenna array of ultrasound tomograph is discussed. These corrections should be taken into account during reconstruction of spatial distributions of sound velocity and absorption of an investigated object, in order to avoid a deterioration of tomogram quality.
Show AbstractSecond harmonic generation in regular domain structures with fluctuations of the thickness of intermediate layers
Second harmonic generation in regular domain structures with fluctuations of the thickness of intermediate layers
A.M. Vyunishev$^{1,2}$, I.V. Timofeev$^{1,2}$, A.S. Chirkin$^{3}$
The second optical harmonic generation in quadratic nonlinear crystal structure is theoretically investigated. The structure consists of regularly modulated inhomogeneous layers that are divided by homogeneous layers of random thickness. The dependence of the process efficiency on the layer number and dispersion of the layer thickness is determined.
Show AbstractNumerical simulation of new technique of forming virtual cathode in relativistic electron beam in coaxial drift space with attached external magnetic field
Numerical simulation of new technique of forming virtual cathode in relativistic electron beam in coaxial drift space with attached external magnetic field
A.A. Koronovskiy, S.A. Kurkin, A.A. Badarin, A.E. Hramov
In this paper is considering dynamics of electron beam in coaxial drift space in external inhomogeneous magnetic field. Numerical simulation, which was conducting, show possibility forming of virtual cathode with help of compression relativistic beam by external magnetic field.
Show AbstractOn Electron Beam Grouping in Non–Uniform Magnetic Fields
On Electron Beam Grouping in Non–Uniform Magnetic Fields
D.A. Mikheev, V. L. Savvin
A new principle of the electron beam grouping with cyclotron rotation in inhomogeneous magnetic fields is proposed. It is shown that the electron 3D grouping may not be accompanied by an increase in space charge density in contrast to the electron bunching during the one-dimensional motion of the electrons.
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