A complex shear modulus of colloidal suspensions of silica nanoparticles in the liquid polymer PES-2 are measured depending on the angle of shear deformation using acoustical resonance method. A piezoelectric crystal with the resonance frequency of 73 kHz as vibrator is applied in study. The changing of the viscoelastic properties of the suspensions depending on the concentration and size of nanoparticles is shown according to the comparison with the base liquid.
It is numerical investigated of dynamics of the state of a liquid on decompression by SPH. Tne two statement is demonstrated reflection shock wave from free surface and shock wave loading of a liquid droplet. A numerical analysis shows that focusing of the shock wave reflected from the free surface of the droplet leads to the formation of a dense, but rapidly expanding cavitation cluster at the droplet center. It is shows tnat SPH can be used to a investigation of a fluid structure of a cavitating liquid witn high volume of a gas phase and to describe the process of inversion of the two-phase state of this medium: transition from a cavitating fluid to a system consisting of a gas and particles.
Results of experiments on influence of low-frequency vibration on acoustic emission (AE) are presented. Experiments were carried out on the hollow thin-walled pipe with the artificial crack which has been filled by epoxide. At joint action of mechanical pressure and low-frequency vibration the effect of amplitude modulation of AE signals was observed. Simple hardware realization of modulating component extraction is proposed. Besides the effect of intensification of AE by the influence of extraneous vibration on the sample has been experimentally registered.
T.S. Dembelova, D.N. Makarova, .B.B. Badmaev, B.V. Badarkhaev
Memoirs of the Faculty of Physics 2014. N 5.
Experimentally established, that the real shear modulus and the effective viscosity of liquid decrease with the increasing of the amplitude of shear deformation. Measurements carried out at small gradients of flow velocity showed that the viscosity of liquid increases with flow velocity decreasing. It is probably due to the structuring of the liquid.
Two interesting effects in the ideal medium are considered. The first one consists in the following. When body moves in an ideal
medium, the medium has energy and momentum, defined through the attached mass and velocity of body. It turns out that the
energy of the medium is concentrated around the body, while the momentum is placed at infinity. The second effect is concerned
to acoustical streaming. The surface oscillations in an ideal medium can generate acoustical streaming - stationary flows of fluid.
Yu.R. Aleshin, D.M. Ksenofontov, M.A. Choba, V.N. Platonov, Yu.V. Anufriev
Memoirs of the Faculty of Physics 2014. N 5.
Amorphous metallic film in terms of technology is the most environmentally friendly and allow you to use the materials in a wide range of applications. The change of the phase composition of these glasses and the possibility of non-destructive measurement of acoustic characteristics is the theme for this experimental study.
The weakening of one-dimensional transverse viscous waves, their phase velocities, the spatial and frequency dispersion in free space by analytical and numerical methods were researched. The dispersion of the phase velocity in a cylindrical wave in a free half-space is negative. The gradient of the phase velocity is greater when the source wave size is less. With the increase in its size dispersion vanishes in the limit and the phase velocity approaches the value of the plane wave phase velocity. The weakening both flat and cylindrical viscous waves in a gap, the magnitude of their phase velocities, the dispersion laws depend on the wave width of a gap and on the boundary conditions on the source opposite the wall.
This paper presents the results of a non-contact diagnostics of materials with low acoustic impedance and solid plates with air ultrasound. For generating and receiving acoustic waves in the air in the frequency range from 0.08 to 2 MHz ultrasound was developed automated measuring system and measurement technique in pulse mode. Generating and receiving ultrasound air carried with focused acoustic transducer. Determination of elastic properties of thin plates of solid work was carried out using a zero anti-symmetric Lamb wave modes. For diagnostic materials with low acoustic impedance used longitudinal acoustic wave. Was measured density expanded polystyrene and the velocity of longitudinal waves in it, calculated impedance and coefficient of elasticity of the material.
The difference between strongly nonlinear waves and waves with strongly displayed weak nonlinearity is pointed out. The classification of strongly nonlinear systems is given. The simplest structural features of meta-materials having high nonlinearity are described. Examples of mathematical models having sufficient generality and interesting for nonlinear wave physics are given. Particle-like properties of singular solutions, as well as some unusual phenomena are pointed out. Accretion, self-trapping and self-splitting can exemplify such phenomena.
Results of theoretical researches of nonlinear propagation of a sound in the crystallizing liquid containing the crystallization centers are presented. The abnormal behaviour of frequency and concentration dependences of the parameter of the acoustic nonlinearity, essentially differing on the character from those in case of a liquid with particles without phase transformations is revealed. It is shown, that phase transformations make strong influence on dynamics of the crystallization centers with the sizes, characteristic for experiments with crystallizing liquids in porous environments in which anomalies in behaviour of absorption and a dispersion of sound speed have been earlier experimentally established at crystallization and melting. It is shown, that feature of the parameter of acoustic nonlinearity in crystallizing water at monodisperse crystallization centers is sharp nonlinearity increase at the small sizes from ten to hundred nanometers. It is noticed, that the important feature is the failure at the sizes in some hundreds nanometers when compressibility of crystallization center owing to phase transformations become negative. Nevertheless, as a whole phase transformations increase acoustic nonlinearity of crystallizing liquids. It is revealed, that the most considerable influence of phase transformations is observed on rather low frequencies and at the small sizes of the crystallization centers.
It is the result of comparison of experimental researches of a field of viscosity wave current near to several spheres with the surfaces possessing various adhesive properties. The liquid is glycerol with kinematic viscosity ν =6,4 sm2/s under normal conditions. Here as a measure of the adhesion force is the contact angle. With increase in value of oscillatory velocity of a sphere in case of the waterproof surface (graphite, paraffin) the observable field of current velocity of becomes essentially distinct from a field near to a surface possessing hydrophilic properties (the metal, the painted surface) with other things being equal. This difference of the velocity field for the hydrophobic surface currents can be explained by a slippage of the liquid.
Numerical solutions of the Rayleigh-Plesset equation of gas bubble pulsations under slow increasing pressure amplitude of acoustic pump wave were thoroughly investigated. 3D diagrams of transformation of discrete spectrum of periodic pulsations in a continuous spectrum with broad spectral lines have been obtained. Dynamics of behavior of these broad lines and of conversion of continuous spectrum in a discrete one at the confluence of these broad lines has been investigated. Spectra that corresponded to almost periodic oscillations were detected and subharmonics under 1/8 were found.
Nonlinear generation of an acoustic wave by two pump sound waves is studied in a three-phase marine sediment that consists of a solid frame and the pore water with air bubbles in it. To avoid generation of harmonics the interaction is studied in the frequency range where there is a considerable wave velocity dispersion. Nonlinear equations are obtained to describe the interaction of acoustic waves in the presence of air bubbles. An expression for the amplitude of the generated wave is obtained and its dependence on distance and on resonance frequencies of bubbles is numerically analyzed.
Many modern medical applications of high intensity focused ultrasound rely on nonlinear acoustic effect of shock formation in the pressure waveform at the focus. The problem arises to determine parameters of the transducer that allow to obtain a certain value of the shock amplitude at the focus required for a specific application. It was proposed that the main transducer parameter, which determines the shock amplitude, is the transducer F-number. This hypothesis was tested using multi parameter numerical calculations of nonlinear ultrasound fields generated by such transducers. Khokhlov-Zabolotskaya-Kuznetsov equation was used in the modeling. The method to determine characteristic focal waveform with fully developed shock front was proposed. The approach was developed for calculating the shock amplitude between the time points at the specified level of the waveform time derivative. The magnitude of this level as relative to the maximum value of the derivative was determined by comparing heat deposition at the focus, calculated numerically and analytically using the weak shock theory. Characteristic shock amplitudes in the focal waveforms were calculated for transducers operating at 1 MHz frequency within the range of F-numbers from 0.8 to 2. It was shown that fully developed shock fronts of 80 MPa amplitudes correspond to transducers with F-number close to unity, which is a typical value for therapeutic transducers.
The results of experimental studies of the influence of defect structure changes in a D16 polycrystalline aluminum alloy on its linear and nonlinear elastic properties are presented. The change of defect structure in the sample is caused by application of static cyclic stress (tension- compression - tension – compression) to it. Studies of the elastic properties of the test specimen during the application of variable loads were carried out using static, quasi-static and dynamic methods. Ultrasonic measurements were conducted using the pulse method. Investigation of nonlinear elastic properties of the test material were done using two methods: a dynamic spectral method according to the efficiency of generation of the second harmonic in the acoustic wavefield of finite amplitude at a frequency of 5 MHz and quasistatic method by measuring the change of velocity of acoustic waves in the sample as a function of the applied static pressure to it.
Keywords: defects, nonclassic elastic nonlinearity, plastic deformation, spectral method, second harmonic.
The results of the experimental studies of the temperature dependence of the normalized Gruneisen parameter for cadmium diphosphide single crystal in the field of commensurate-incommensurate phase transition are presented. Measurements were made using laser photoacoustic method with harmonic excitation and piezoelectric registration in the temperatures interval of 280-330 K. Anomalies of the temperature dependence of the amplitude of the photoacoustic signal is proportional to the Gruneisen parameter were observed in the temperature range of 305-322 K. These anomalies are associated with the occurrence of phase transitions from commensurate to incommensurate phase. The estimation of the temperature dependence of the normalized Gruneisen parameter using literature data and comparison with experimental data were made.
Forced vibrations of the oscillator with dry (Coulomb) friction are studied. Earlier the class of asymmetrical decisions describing the steady-state nonlinear vibrations of the oscillator was found. Asymmetry of vibrations is exhibit in distinction of amplitudes in opposite directions. The specified class of decisions is received on the following assumptions: duration of one cycle of vibrations is equal to the period of force exciting vibrations, duration of half-cycles (time of movement in opposite directions) are equal, there are no stops of nonzero duration and change of the movement direction on each of the half-cycles. In this work the question of the possibility of the specified class decisions expansion due to refusal of a condition of equality of half-cycles is investigated. It is shown that there can be only two types of decisions. The first decision is received in an explicit form, however numerical modeling for rather representative set of parameters showed that it doesn't meet a condition of the absence of the movement direction change on each of the half-cycles. For the second type of decisions the transcendental equation determining duration of half-cycles is established.
We measured the linear and nonlinear elastic moduli of polymer material plastisol. The layer of material was polymerized between two coaxial solid cylinders with diameters 6-8 times greater than the thickness of the layer. During the polymerization process mechanical stresses arose within the material. Comparing the measured values of the elastic parameters of the material, polymerized between the cylinders, to the values measured in the material, polymerized between flat parallel plates, under uniaxial compression it became possible to evaluate these stresses. Measurements in the flat and cylindrical geometry have been carried out by the method of static shear deformations up to 0.4-0.6 of the layer thickness. Nonlinear effects are well pronounced under such deformations, which allows to estimate their contribution to the elastic properties exhibited by the material and measure the nonlinear Landau parameters. Shear strain was created by certain tension applied to one of the plastisol boundaries in plane geometry. The second boundary was fixed and could not move in the direction of shear deformation. However, bindings allowed this boundary to move in the direction perpendicular to the direction of shear deformation. The shear strain in a cylindrical geometry was created by the rotation of one of the cylinders applying a certain stress tangentially to the lateral surface. The pattern of stress-strain curves and the measured values of static shear modulus appeared to be significantly different in cylindrical geometry and planar geometry, whereas the thickness of plastisol was the same. Landau parameter A, measured in plane geometry with the uniaxial compression applied, was equal to -392 kPa.
Analysis with heterogeneous form of localized structures acoustic waves. In certain conditions, the process of wave propagation is accompanied in the course of motion of a continuous nonlinear decay of the amplitude of the displacements, and the emission of the bulk waves, which allows to distinguish them as a new class of waves of low intensity with heterogeneous structure. Discovered a new physical phenomenon, unknown in the technical literature. Identified a specific type of waves with a complex structure, extending along the edges on a sustainable trajectory.
V.V. Moshkin, A.V. Moshkina, V.L. Preobrazensky, P. Pernod
Memoirs of the Faculty of Physics 2014. N 5.
The cascade process of generation of the second acoustic harmonics accompanied by its simultaneous parametric wave phase conjugation in α-Fe2O3 antiferromagnetic crystal under transversal electromagnetic field is studied experimentally and theoretically. The necessary conditions for generation at variations of the magnetization direction relatively to the crystallographic axes and direction of propagation of transversal sound wave are defined. The observed effect is caused by the magnetoelastic interaction and is described in the framework of the theory of giant effective elastic anharmonicity.
The spectrum of the composite acoustic resonator (HBAR) is a multimode, and may contain several thousand resonance peaks. We have developed a set of programs that allows recording the spectrum scans with arbitrary frequency step within the whole frequency range of the network analyzer. Due to the high degree of automation of the processing of scans we obtain data on the parameters (frequency and width) of each resonance peak. Proposed method increases the accuracy of the previously known method of measuring the velocity of an acoustic wave (AW) of the material by comparing the spectra HBAR before and after developing the test layer. For the layers with the thickness of a few wavelengths the new method allows to obtain information about the velocity from only one AW spectrum.
It has been theoretically and experimentally shown that in contrast to other waves type the electromechanical coupling coefficient, power flow angle, external effects sensitivity and properties anisotropy of plate acoustic waves can be changed only due to changing plate thickness at the constant crystallographic orientation of plate material. The behavior of pointed dependencies is various for modes with different orders. The amount of modes n in piezoelectric plates more bigger than ones in the isotropic plates with the same thickness.
A modified quasifield method of surface acoustic waves (SAW) interdigital transducers (IDT) electrical characteristics simulation without any phenomenological parameters was proposed. It allows simulating with high accuracy and operatively of the perspective SAW devices on the microwave frequency band for any IDT electrodes configurations with the consideration of the finite thickness of the electrodes, including taking into account of the layered structure of the electrodes with the adhesive sublayer. The results obtained by this method are in good agreement with the experimental data that were described in the literature.
In this paper it is experimentally demonstrated that in the composite resonator structure with ferromagnetic and piezoelectric films magnetic oscillations can be excited and detected directly by means of an electroacoustic transducer of bulk acoustic waves. Excitation of nonuniform ferromagnetic resonance occurs at frequencies close to those of the magnetoelastic resonance in a magnetic material, and appears as a frequency rearrangement of the multimode resonator, which depends resonantly on the external magnetic field. The rearrangement for the resonator with the ZnO film and YIG in the whole intermodal interval 3.6 MHz was experimentally observed. The observed effect is of interest to: a) the practical application of a tunable frequency control elements and microwave filters, b) study the magnetic dynamics in ferromagnetic films, c) new applications of microwave acoustic resonators.
Availability of a thin liquid layer on the surface of the piezoelectric acoustic duct leads to perturbation conditions of propagation of surface acoustic waves (SAW). Analytical expressions for describing of the attenuation and the relative change in the SAW velocity as a function of the normalized thickness of the liquid layer were obtained. It is shown that dielectric and acoustic components of perturbation of SAW propagation conditions caused by the liquid layer can be considered independently.
I.A. Borodina, B.D. Zaitsev, I.E. Kuznetsova, A.A. Teplykh, A.M. Shikhabudonov
Memoirs of the Faculty of Physics 2014. N 5.
Piezoelectric resonators with lateral electric field cause a great interest of designers of multi-channel acoustic sensors. The electrodes of such resonator are deposited on one side of the plate that allows to separate resonators and analyzable objects. The main problem of the design of resonators matrix is the suppression of the unwanted oscillations, which worsen resonant properties and lead to the strong acoustic coupling between them. The method of the solution of such problem is described in the present paper. The matrix including two resonators placed on the plate of lithium niobate of X cut with thickness of 0.5 mm was experimentally investigated. The electrodes of rectangular shape with dimensions of 5×10 mm and width of gap between them of 2 mm provided the lateral electric field, which was oriented along axis Y. It has been shown that the resonance was achieved on the longitudinal acoustic wave propagating along axis X between electrodes. For suppression of unwanted oscillations the area around resonators and parts of electrodes were covered by damping layer. We measured the frequency dependencies of real and imaginary parts of electrical impedance /admittance of each resonator and determined the resonant frequency and Q-factor for series and parallel resonances. We also measured the frequency dependence of the parameter S12, which in all cases did not exceed 50 dB. It meant that resonators under study were acoustically decoupled. Thus it has been shown that damping layer provides the good quality of each resonator as well as total acoustic decoupling between them.
B.D. Zaitsev, A.M. Shikhabudinov, A.A. Teplykh, I. E. Kuznetsova
Memoirs of the Faculty of Physics 2014. N 5.
The possibility of measuring the surface conductance of thin films has been shown by using shear –horizontal plate acoustic wave of zero order (SH0), which propagates in the delay line based on the plate of Y –X lithium niobate. This delay line including two interdigital transducers (IDT) was connected to meter of S – parameters E5071C, which allowed to measure the insertion loss and phase of output signal. It has been found that the dielectric plate with thin conducting layer placed above the delay line between IDTs leads to the change the insertion loss and phase of output signal. At that the degree of this change decreases with increasing the width of the gap between delay line and plate. As conducting thin films of chromium and aluminum were used. The conductance of these films changed in the range 1 – 10-6 S and was determined with the help of four-probe method. The experimental data allowed to build the calibration dependence of the shift of output signal phase on surface conductance of films for the fixed width of gap between the plate and delay line (~ 100 microns). This calibration curve turned out close to linear dependence with the slope of 120 degree/S. The developed method may be used for measuring the conductance of such films, the contacts for which cannot be made or these contacts may significantly act on the result of the measurement.
The method of calculation of characteristics of acoustic oscillations existing in piezoelectric electric field excited resonator was developed. The resonator represents thin piezoelectric plate with two rectangular electrodes on one its side. The developed method is based on the finite element analysis and allows to find the distribution of the mechanical displacement components in piezoelectric plate and electrical potential in piezoelectric plate and surrounding vacuum for the given value of frequency of excited field. At that this method allows to consider various boundary conditions on different areas of surface plate including the presence of damping layers. This allows to calculate the real and imaginary parts of electrical impedance as function of frequency. The resonator under study represented the plate of $X$ – cut lithium niobate with thickness of 0.5 mm. Two rectangular electrodes with width of 5 mm were deposited on one side of the plate in such a way that excited electric field was oriented along crystallographic axis $Y$. The calculations were carried out for different values of width of the gap between electrodes in a range 1 – 3 mm. It has been shown that the increase in the width of gap leads to insignificant increase in resonant frequency and the use of damping layers on outside parts of electrodes allows significantly increase its $Q$-factor. The obtained results are in a satisfactory agreement with experimental data.
During last years the disigners of acoustic liquid sensors concentrate special attention on piezoelectric resonators with lateral electric field. The main problem of their development is the supression of unwanted oscillations. For achievement of this aim there exist at least two variants. Firstly, the choice of optimal shape of electrodes and exact their orientation respectively to crystallographic axes of plate. However the shape and dimensions of electrodes depend on shape of plate and its sizes. Secondly, the deposition of the damping layer around the electrodes including the certain part of electrodes. The paper is devoted to the experimental study of the influence of width of gap between electrodes and width of area of electrodes covered by damping layer on the frequency and $Q$ - factor of series and parallel resonances and electromecanical coupling coefficient. Electrodes of rectangular shape with dimensions 5 $\times$ 10 mm were deposited on the plate of lithium niobate of $X$ – cut with thickness of 0.5 mm. The width of the gap between electrodes and width of their coating area were changed from 1 to 5 mm. The lateral electric field was oriented along axis $Y$. It has been shown that the resonance was achieved on the longitudinal acoustic wave propagating along axis $X$ between electrodes. It has been found that changes in width of gap between electrodes and width of coating area vary frequencies of series and parallel resonances in the range of $\sim$1\%. At that the values of $Q$ – factor of series and parallel resonances change in ranges 500 - 13000 and 500 - 1800, respectively. The change in electromechanical coupling coefficient lies in range 1 - 4\%.
B.D. Zaitsev, A.M. Shikhabudinov, A.A. Teplykh, I.A. Borodina, I.E. Kuznetsova
Memoirs of the Faculty of Physics 2014. N 5.
The paper is devoted to the possibilities of the applications of piezoelectric resonators with lateral electric field for analysis of liquid properties and measurement of microdisplacements. It has been shown that the sensitivity of liquid sensors may be significantly increased by using the module of electrical impedance or admittance on the fixed frequency near the resonance as informative parameter. The change of pointed parameters may achieved 30% and 70% for the change in viscosity from 1 to 1000 mPa×s and for the change in conductivity in range 100 -10000 μS/cm. The second application is based on the fact that electric field of the resonator penetrates outside of piezoelectric plate. The experiments concerning with influence of the gap between free side of resonator and conductive and dielectric plate on the frequencies of series and parallel resonances were carried out. Obtained results have shown the possibility of development of meters of microdisplacements which may be used for permanent monitoring of deformations and crack opening of various constructions, elements of bridges and building, and also for measuring small displacements of two objects respectively each other. It has been demonstrated that the frequency of parallel resonance is unambiguously determined by the width gap in ranges 0 – 0.3 mm and 0 – 2.5 mm for conducting plate and plate of corundum, respectively. The frequency of series resonance does not depend on width of gap but is defined by the temperature. So the frequency of series resonance allows to determine the temperature and to perform the needed corrections.
As known, anomalous resisto-acoustic effect is a fundamental property for weakly inhomogeneous piezoactive waves (Bleustein - Gulyaev, Love, and some leaky waves). It consists in that the velocity of aforementioned waves first increases, achieves its maximum, and only then decreases with growing conductance of a layer placed at the surface of piezoelectric half-space. In this paper we continue to study the peculiarities of the effect occurence and the influence of different electrical boundary conditions on its characteristics. Conditions have been found under which the said effect occurs and, respectively, dissappears. The magnitude of positive change in velocity with growing layer conductance is demonstrated to be reduced up to zero as a layer with arbitrary conductance has been removed from the piezoelectric surface. The positive change in velocity is, respectively, increased with removing an perfectly conducting screen from the “piezoelectric half-space – conducting layer” structure. As piezoelectric the potassium niobate has been used. The obtained results are useful for a more deep understanding the physical bases of propagation of weakly inhomogeneous piezoactive acoustic waves.
Results of theoretical and experimental investigation of acoustic beam walk-off influence on acousto-optic characteristics in a paratellurite single crystal are presented. Variants of isotropic and anisotropic diffraction are analyzed. Angular and frequency characteristics of acousto-optic interaction are calculated on the basis of modified Raman–Nath equations in wide ranges of Bragg angles and acoustic frequencies. It is established that the acoustic walk-off can change essentially the width of acousto-optic range. Therefore this effect should be taken into consideration at designing acousto-optic instruments. Experimental verification of the numerical calculations is fulfilled with an acousto-optic cell made of paratellurite cut.
F.R. Akhmedzhanov, Z.T. Azamatov, A.F. Boltaboev, E.T. Rahimov
Memoirs of the Faculty of Physics 2014. N 5.
Propagation velocity and attenuation coefficient of acoustics waves in paratellurite crystals were measured by Bragg diffraction of light in the frequency range 0.4 1.6 GHz. Based on these results the real and imaginary components of the complex tensor of elastic constants have been calculated. The analysis of the attenuation anisotropy was carried out for the acoustic waves with different polarization propagating in the crystallographic planes, which are orthogonal to symmetry axes of the second and fourth order. It is shown that strong anisotropy of acoustic attenuation observed for the transverse wave propagating in the plane (1-10), mainly due to the anisotropy of its phase velocity.
The main tasks of facing the engineering industry is to reduce the weight and material-specific products. The main way to achieve this goal is the production of parts and components made of aluminum. However, the industrial application of the aluminum is limited due to its low strength characteristics and low durability. The analysis of the existing problems in this area, as well as the results of research on the effects of various ultrasonic processes of metal showed that currently the main way to improve the properties of aluminum parts is to change the properties of the surface layer by etching parts. Work described in this paper aims to explore the prospects for the application of ultrasound to enhance the effectiveness of chemical treatment of aluminum.
It is shown that the method of pulsed acoustic microscopy can detect hidden defects in the multilayer crystal chips during the process of their build-up. The proposed methods allow identifying the adhesion defects at intercrystalline layer, defects of electrical contacts soldering, distribution and deformation of the heat-sinking layer (polyimide grid), and internal crystals cracks. The operating frequency of 50-100 MHz allows to perform acoustic imaging with a resolution of 30-50 mkm at the depth of two crystalline layers (2690 microns). Visualization of the structure at a greater depth is difficult because of the strong refractive index in silicon, and also because of the numerous internal structure elements forming the shadows in the images of the lower layers.
Internal microstructure of dense ceramics based on zirconia has been investigated by impulse acoustic microscopy technique. The dependence between porosity of ceramic material and its elastic moduli was studied.
V.M. Levin, Yu.S. Petronyuk, E.S. Morokov, S. Bellucci, P.P. Kuzhir
Memoirs of the Faculty of Physics 2014. N 5.
There is a common representation of the uniform distribution of the filler particles over the composite bulk, regardless of the continuous cluster formation. However, in practice, the effective interaction between nanoparticles is often implemented with fractal their agglomeration to conglomerates of micron size and higher. The emergence of conglomerates reduces the expected physical and chemical properties of nanocomposites transfer them to the category of conventional composites with fine structure. Moreover, depending on the method of composite fabrication conglomerates may include air and gas bubbles.
Ipulse acoustic microscopy technique allows investigating three-dimensional structure with micron resolution and studying the elastic properties of miniature specimens. Currently, the method is relevant for characterization of advanced composites with micro and nanostructures. In the paper the investigation results of the composites with different carbon fillers (graphite, graphite, nanotubes) are presented.
The short transverse viscous waves induced in a thin liquid layer placed on a solid surface cause the appearance of non-linear effects such as currents, the radiation force and the hydrodynamic cavitation by analytical and numerical methods in the present research were shown. These effects during ultrasonic metallization provide wetting by melt of solid surface and create a developed relief of surface and intensify the physical-chemical interaction for the liquid melt and solid phase.
The hardness of steel is one of the most important properties that determine its durability. To increase the hardness of the surface hardening technology used, nitriding and surface plastic deformation, which is based on a fundamentally different processes. The application of the combined method can improve the hardness of the surface layer of the material and increase the depth of hardening. This paper presents the results of studies of the properties of coatings obtained by nitration followed by ultrasonic hardening treatment.
In internal combustion engines pollution exposed parts of different sizes, shapes and designs. Of particular difficulty is the removal of contaminants case products, due to their large size, the presence of a large number of holes, pockets and other hard to reach places. One of the most effective ways to clean parts is ultrasound. The article describes the technology and equipment for automated ultrasonic cleaning of body parts moving emitter.
The values of the blood flow and heat sources in the human forearm under the physical load were obtained with acoustothermometry. The probe of the multichannel acoustothermograph developed in IAP of RAS was used to measure the thermal acoustic radiation. The frequency band of the acoustothermograph was 1.2-2.7 МГц, the threshold sensitivity was 0.3 K at the integration time 10 s. Human volunteers clenched - unclenched the fists during 100 s. They made 120 5 movements for this time. To decrease the blood flow in the forearm a tourniquet was applied on the volunteer's shoulder. The experimental results showed that the forearm temperature increased and reached the maximum value after 100 s of work without the tourniquet and after 200 s of work with the tourniquet and thereafter decreased. The acoustobrightness temperature increased on about 1.5 К without the tourniquet and on about 0.7 К with the tourniquet. The results allowed to estimate the blood flow: 0.023 1/min. This value is confirmed with literature data 0.02-0.07 1/min. The blood flow was increased 7.5-fold under the physical load. The heat source was 0.0043 K/s. The heat equation with the blood flow (Pennes equation) was used to calculate the temperature in the depth of the forearm. The calculation showed that the forearm temperature maximum was 36°С in the rest. Under the physical load the additional heat sources increased the temperature up to 37°С and the blood flow increased the temperature up to 38°С.
In many current medical applications of high intensity focused ultrasound it is necessary to take into account additional energy losses due to the presence of natural obstacles like ribs. In this study the feasibility of using phased arrays with different number of elements to reduce overheating ribs when focusing through the intercostal spaces was studied. Geometric approach to switch off the array elements that are in the shadow of ribs was used to minimize the exposure of the ribs to the ultrasound energy. The effect of the number of the array elements on the value of the power losses of the focused beam at the ribs and the level of intensity in the focal region behind the ribs was studied.
V.A. Khokhlova, Y.-N. Wang, S.V. Buravkov, A.D. Maxwell, T.D. Khokhlova, D.W. Lin, O.A. Sapozhnikov, M.R. Bailey, G.R. Schade
Memoirs of the Faculty of Physics 2014. N 5.
Most current clinical applications of high intensity focused ultrasound in noninvasive surgery (HIFU) rely on the rapid heating of the propagation medium caused by absorption of the ultrasound wave energy, which results in thermal denaturation of tissue in the focal region of ultrasound beam. Recently, scientists from the University of Washington and Moscow State University have developed a new method to mechanically destroy tissue using pulse-periodic focused waves with high amplitude shock fronts. Such millisecond duration pulses cause ultrafast heating of tissue at the focus and explosive boiling in tissue during each of the pulses. Interaction of shock fronts with millimeter size vapor-gas cavity leads to mechanical disintegration of tissue into subcellular fragments. The efficiency of the method has already been shown in ex-vivo tissues of bovine liver and heart, as well as in porcine kidney in-vivo. In this paper, mechanically disintegrated lesions obtained in ex-vivo human and porcine kidney tissues were analyzed histologically. The results of comparative histological studies are discussed.
The results of the authors on the sonodynamic therapy of cancer with the use of nanoparticles as sonosensitizers are summarized in this article. Cavitational and thermal effects of ultrasound in aqueous and gel model media containing the modifiers of different nature have been studied by various methods. Some provisions defining the selection criteria of promising sonosensitizers on model systems were formulated. Apparatus for preclinical and clinical research has been established. The original method for the synthesis of nanoparticles and their aggregates (solid phase sonosensitizers) directly in a tumor has been proposed. Range of biophysical and physicochemical problems related to solid phase sonosensitization was formulated.
A method is presented for nonlinear acoustic holography for the study of powerful ultrasound sources and the corresponding radiated fields. The approach is based on measuring two-dimensional distributions of amplitude and phase of acoustic pressure for harmonics present in the signal spectrum. The obtained distributions are used to calculate the back-propagation of the acoustic field for a mathematical reconstruction of the vibrational velocity on the surface of the source. Calculation of the nonlinear propagation is based on the numerical solution of the Westervelt wave equation. The developed method of nonlinear acoustic holography is an effective tool for the characterization of therapeutic ultrasound sources operating at high power levels, when the source vibration characteristics may differ significantly from the vibration characteristics at low power levels. The paper presents the basis of a numerical model for the calculation of the nonlinear propagation of the time-reversed acoustic field. Physical experiments on nonlinear holography of real therapeutic sources are also described.
П.В Юлдашев, А. Максвелл, В. Крайдер, О.А. Сапожников, М. Бэйли, Л. Крам, В.А. Хохлова
Memoirs of the Faculty of Physics 2014. N 5.
Во многих современных приложениях мощного фокусированного ультразвука (HIFU) в неинвазивной хирургии, например, при гистотрипсии, возникает необходимость генерации мощных ультразвуковых полей с амплитудой ударного фронта в фокусе до 120 МПа на значительной глубине в ткани. Для экспериментального исследования возможности создания таких полей и генерации механических разрушений в ткани был создан прототип системы, состоящий из усилителя и излучателя с рабочей частотой 1 МГц. Излучатель состоит из семи отдельных элементов круглой формы, расположенных на сферической чашке диаметром 14.7 см и радиусом кривизны 14 см. Цель настоящей работы состояла в характеризации поля указанного излучателя в воде с помощью гидрофонных измерений и численного моделирования. Моделирование поля было выполнено на основе трехмерного уравнения Вестервельта с начальными условиями, полученными экспериментально методом акустической голографии. В эксперименте профили волны в фокусе были измерены оптоволоконным гидрофоном. Измерения проводились при различной амплитуде акустического давления на поверхности источника. Было показано, что результаты измерений и расчетов хорошо согласуются между собой. Найдены максимально достижимые значения для пиковых давлений и амплитуды ударного фронта. Таким образом, в работе было показано, что численное моделирование на основе трехмерного уравнения Вестервельта является важным инструментом для прогнозирования характеристик ультразвуковых полей, создаваемых мощными терапевтическими HIFU излучателями.
Experimental results on heating of an absorbing medium by parametrically conjugated ultrasound beam are reported. A polymer with acoustic parameters close to those of biological tissues was used for heating. Advantages of the developed method due to phase conjugation phenomenon are demonstrated by means of thermocouple measurements: automated targeting of an ultrasonic beam on the area of heating, and weak impact of the sample’s position or its movement in some limits on the warming process. The value of heating achieved 8С within about 100 s.
A comparative study of two methods of measuring the acoustic absorption coefficient is performed - a standard one based on registering the amplitude of wave transmitted through a test sample and of its modification with application of phase conjugate ultrasonic waves. The insert-substitution technique was used as an example of the standard method. It is shown that wave front distortions of probing beam due to structure heterogeneities and scattering objects in test samples provoke significant errors in measurements by the standard method. At the same time, usage of phase conjugate waves permits to almost completely eliminate the errors for the measurements in the presence of phase heterogeneities of test samples. This is also the case for low concentrations of scatterers with sizes comparable to the acoustic wavelength. In the other cases, including measurements in biological tissues, the phase conjugation method permits to obtain more reliable estimations of dissipative losses than the standard one.
Overview of the current state of problems connected with some general principles of sounds coding of in auditory system is presented. It is emphasized that after transformation in the cochlea an auditory signal is presented only as a pulse activity in a population of auditory nerve fibers. Statistical independence of firing in different fibers is urgently required in order to encode spectro-temporal features of the sound in very big frequency and dynamic ranges. Complex mechanism of frequency analysis in cochlea as well a specific system of synaptic transmission between inner hair cells and auditory nerve fibers serve to ensure this independence. The presence of independent noise components in each fibers also serves the same aim. These properties allow to code in a population of fibers such time intervals which are considerably shorter than duration of a single neuron's pulse (spike). On the following levels of the auditory pathway this information is processed by several different methods. As a consequence a sharp increase in the number of single neurons takes place along the auditory pathway. Starting from the auditory midbrain center the plasticity of the nervous tissue is becoming increasingly important. Virtually every nerve cell could be considered as a self-learning element, which internal properties are determined mainly by its prior experience. The experimental data which serves to justify the expressed provisions are discussed.
Causes of deterioration and facilitation of discrimination of changes in the intensity of short high-frequency sounds (pulses) presented in silence, with noise, and after noise exposure were analysed by comparing the results of simulation and psychoacoustic experiments. In the simulation experiments we studied the characteristics of peripheral coding of changes in the intensity of pulses; searched for the conditions when the response of the ensemble can store information about the amplitude-temporal structure (conditions for the implementation of the volley principle); and analysed the statistical characteristics of responses of the ensemble of auditory nerve fibres (ANF) to pulse and composite sound containing long noise masker and pulse (“noise–pulse complex”). Coding should be understood as the conversion from the analogous receptor potential of the inner hair cell to the sequence of action potentials (spikes) generated by the ensemble of ANFs. Simulation experiments have shown that changes in masker level may cause changes in the properties of peripheral coding of both pulse and noise–pulse complex. Auditory experiments have shown that an appreciable effect of discrimination improvement occurs when the average intensity pulse is presented along with or after the noise masker, the level of which is almost equivalent to the threshold of pulse masking. Furthermore if the delay between pulse and end of masker is 50–60 ms, increase in the masker level causes alternation of the effects of deterioration and facilitation of discrimination of changes in the pulse intensity. There are grounds for believing that the observed effects are based on the variability of properties of the peripheral coding of both pulses and noise–pulse complexes.
The process of accumulating empirical data in scientific research on acoustic communication of cetaceans is entering the stage of actual experiment. We analysed ‘emotional’ signals of bottlenose dolphin (Tursiops truncatus) and beluga whale (Delphinapterus leucas) represented with non-equidistant sequences of short pulses ranging from 1.8 to 6 ms within the bursts of pulses 80 – 600 ms long. Broadband recording of ‘emotional’ signals of beluga whale revealed that spectral density of the recorded pulses could be up to 500 kHz and even more, which contradicts the common frequency-threshold characteristics of the receiving system of toothed whales.
New multi-channel complexes of registration marine mammals’ bioacoustic activity on digital medium have greatly increased the possibilities of the researcher. When planning up-to-date laboratory experiment or conducting ethological acoustic observations in the open sea the researcher needs facilities for storage and further processing of data recorded during field studies. The created database is designed for classification of measurement results, storage and minimization of large amount of hydroacoustic data and its subsequent use in computational experiments.
Interference of articulation patterns in different languages is a major obstacle to mastering accent-free foreign-language pronunciation. Database of Russian speech, developed at the Laboratory of Phonetics and Speech Communication of the Philological Faculty of Moscow State University, comprises two similar parts: the correct orthoepic one and Russian pronunciation with the accent: patterns produced by people with different native languages (including reading of isolated words and sentences, and spontaneous utterances). The variety of articulation mouth shapes necessary for the sound production in different languages can be represented as a cross-language space of articulation postures in which these postures may mismatch those in Russian. Such a mismatch requires complete restructuring the articulation bases of the native language with the aim of mastering the accent-free Russian pronunciation.
Keywords: foreign language accent, Russian language, interference, database.
Keywords: foreign-language accent, Russian, interference , database.
The research describes proposed model of information transformations taking place in auditory system. Drawing an analogy between processes of transformation information in auditory system and proposed model. This model is built on foundations of the theory of active perception (TAP) proposed for information processes modeling in visual perception. Based on proposed model were created several methods of processing of sound signals: computing method of human voice pitch frequency, method of useful signal extraction. Effectiveness of the proposed methods was confirmed by the conducted experimental researches.