Emission Of Sound Waves Research Articles

Electrothermal sound receivers

An analysis of the physical processes occurring during the emission of sound waves by electrothermal sound sources (thermophones) showed that a thermophone is a reversible physical system. This made it possible to determine the conditions under which the convertion of an acoustic signal into an alternating electric current can be carried out on the thermophone active element and, hence, the system will respond to an external acoustic field. Keywords: acoustic signal, active element, metal film, electric current, electrothermal receiver.

Электротермические приемники звука

An analysis of the physical processes occurring during the emission of sound waves by electrothermal sound sources - thermophones, showed that a thermophone is a reversible physical system. This made it possible to determine the conditions under which the process of converting an acoustic signal into an alternating electric current can be carried out on the active element of the thermophone, and, consequently, the system will respond to an external acoustic field.

Develpoment and Characterization of Novel Probes for Photoacoustic Microscopy

The photoacoustic effect (PA) is a physical phenomenon based on the emission of sound waves following light absorption in material samples. The photon absorption and subsequent non-radiative depletion of the chromophores rapidly rises the temperature within the sample, increasing the pressure and inducing a thermoelastic expansion, leading to the emission of a pressure wave called photoacoustic wave. The reduced scattering of acoustic waves enables high-resolution, deeply penetrating imaging in biological tissues. The difference among the absorption coefficients of tissue components or suitable transgene labels in the sample gives the base of contrast in PA imaging but the few number of probes showing high PA efficiency reduces the applications to living systems and processes at the cellular and subcellular levels. The development of reversibly switchable fluorescent proteins (rsFPs) has revolutionized the life science imaging contributing to optical nanoscopy as agents able to improve contrast-to-noise ratio and spatial resolution. The competiveness between light and heating emission in rsFPs optimized for fluorescence imaging considerably reduces the acoustic emission efficiency making them not suitable for PA microscopy. The aim of this project is the development of a novel approach in photoacoustic microscopy inspired by the toolbox of knowledge we have for fluorescence imaging. The key point lies in the probes, belonging to two different families of photochromic proteins, which will be characterized and applied in the novel photoacoustic microscope: GAF3, and two new mutants of GFPs obtained adding a fluorescence-decreasing mutation to wildQ and wildQT proteins.

Zero-point excitation of a circularly moving detector in an atomic condensate and phonon laser dynamical instabilities

We study a circularly moving impurity in an atomic condensate for the realisation of superradiance phenomena in tabletop experiments. The impurity is coupled to the density fluctuations of the condensate and, in a quantum field theory language, it serves as an analog of a detector for the quantum phonon field. For sufficiently large rotation speeds, the zero-point fluctuations of the phonon field induce a sizeable excitation rate of the detector even when the condensate is initially at rest in its ground state. For spatially confined condensates and harmonic detectors, such a superradiant emission of sound waves provides a dynamical instability mechanism leading to a new concept of phonon lasing. Following an analogy with the theory of rotating black holes, our results suggest a promising avenue to quantum simulate basic interaction processes involving fast moving detectors in curved space-times.

Free and forced bending vibrations of a thin plate in a perfect compressible fluid with energy dissipation taken into account

AbstractA refined statement of stationary dynamic acoustoelasticity problems of thin isotropic plates surrounded from both sides by acoustic media assumed to be perfect compressible fluids has been studed. The problem statement takes into account the energy dissipation in the material of the plate and fluid on the basis of the Kelvin‐Voigt hysteresis model. The refinement of the fluid behavior is based on the assumption that the pressure increment is proportional not only to volumetric strain, but also to the rate of its volumetric strain. This assumption allows us to obtain the generalized Helmholtz wave equation by introducing Skudrzyk's complex sound velocity into consideration to take account of the energy dissipation. The motion equations of the plate are based on the classical Kirchhoff‐Love model and are obtained in two versions. In the first version unsimplified three‐dimensional wave equations are used to determine the aerohydrodynamic load acting on a plate. The second version is based on simplifying the equations of fluid motion by the introduction of the well‐known hypothesis of plane reflection and emission of sound waves. On the basis of the derived equations, exact analytical solutions of two types of problems are obtained. The first type is related to the problem of free vibrations of a rectangular plate hinged around the contour when complex eigenfrequencies were defined. The second type is related to the problem of forced vibrations of the plate under the action of a flat mono‐harmonic incident sound wave when sound transmission loss, the stress‐strain state parameters of the plate as well as the laws of change in sound pressure in a fluid were determined. It is shown that correct and more meaningful solutions of acoustoelasticity problems of the considered class are possible only in case of describing the behavior of a fluid with unsimplified three‐dimensional wave equations with consideration of the energy dissipation.

First-principle description of acoustic radiation of shear flows.

As a methodology complementary to acoustic analogy, the asymptotic approach to aeroacoustics seeks to predict aerodynamical noise on the basis of first principles by probing into the physical processes of acoustic radiation. The present paper highlights the principal ideas and recent developments of this approach, which have shed light on some of the fundamental issues in sound generation in shear flows. The theoretical work on sound wave emission by nonlinearly modulated wavepackets of supersonic and subsonic instability modes in free shear flows identifies the respective physical sources or emitters. A wavepacket of supersonic modes is itself an efficient emitter, radiating directly intensive sound in the form of a Mach wave beam, the frequencies of which are in the same band as those of the modes in the packet. By contrast, a wavepacket of subsonic modes radiates very weak sound directly. However, the nonlinear self-interaction of such a wavepacket generates a slowly modulated mean-flow distortion, which then emits sound waves with low frequencies and long wavelengths on the scale of the wavepacket envelope. In both cases, the acoustic waves emitted to the far field are explicitly expressed in terms of the amplitude function of the wavepacket. The asymptotic approach has also been applied to analyse generation of sound waves in wall-bounded shear flows on the triple-deck scale. Several subtleties have been found. The near-field approximation has to be worked out to a sufficiently higher order in order just to calculate the far-field sound at leading order. The back action of the radiated sound on the flow in the viscous sublayer and the main shear layer is accounted for by an impedance coefficient. This effect is of higher order in the subsonic regime, but becomes a leading order in the transonic and supersonic regimes. This article is part of the theme issue 'Frontiers of aeroacoustics research: theory, computation and experiment'.

Elastic precursor wave decay in shock-compressed aluminum over a wide range of temperature

The effect of temperature on the dynamic flow behavior of aluminum is considered in the context of precursor wave decay measurements and simulations. In this regard, a dislocation-based model of high-rate metal plasticity is brought into agreement with previous measurements of evolving wave profiles at 300 to 933 K, wherein the amplification of the precursor structure with temperature arises naturally from the dislocation mechanics treatment. The model suggests that the kinetics of inelastic flow and stress relaxation are governed primarily by phonon scattering and radiative damping (sound wave emission from dislocation cores), both of which intensify with temperature. The manifestation of these drag effects is linked to low dislocation density ahead of the precursor wave and the high mobility of dislocations in the face-centered cubic lattice. Simulations performed using other typical models of shock wave plasticity do not reproduce the observed temperature-dependence of elastic/plastic wave structure.

Noise emissions from highway with the use of measuring and modeling

Due to population growth in major cities, many issues and problems bother related governors. Due to noise pollution, diseases like psychiatric, hearing problems and sleep disorders increased dramatically. In conclusion, this issue has to be studied and controlled by authorities in order to increase health care of area. This paper is case study of sound wave emission of one of the most crowded highways in Tehran city. In result, in rush hours, when the volume of vehicles is in its most and their speed in low, noise pollution of the area increases. But when the road in clear and speed in high and volume is low, sound level reaches its lowest value. Average sound level of this highway is 97.23 (dB).

Analogue Hawking radiation in an exactly solvable model of BEC

Hawking radiation, the spontaneous emission of thermal photons from an event horizon, is one of the most intriguing and elusive predictions of field theory in curved spacetimes. A formally analogue phenomenon occurs at the supersonic transition of a fluid: in this respect, ultracold gases stand out among the most promising systems but the theoretical modelling of this effect has always been carried out in semiclassical approximation, borrowing part of the analysis from the gravitational analogy. Here we discuss the exact solution of a one-dimensional Bose gas flowing against an obstacle, showing that spontaneous phonon emission (the analogue of Hawking radiation) is predicted without reference to the gravitational analogy. Long after the creation of the obstacle, the fluid settles into a stationary state displaying the emission of sound waves (phonons) in the upstream direction. A careful analysis shows that a precise correspondence between this phenomenon and the spontaneous emission of radiation from an event horizon requires additional conditions to be met in future experiments aimed at identifying the occurrence of the Hawking-like mechanism in Bose-Einstein condensates.

Matter-wave dark solitons in boxlike traps

Motivated by the experimental development of quasi-homogeneous Bose-Einstein condensates confined in box-like traps, we study numerically the dynamics of dark solitons in such traps at zero temperature. We consider the cases where the side walls of the box potential rise either as a power-law or a Gaussian. While the soliton propagates through the homogeneous interior of the box without dissipation, it typically dissipates energy during a reflection from a wall through the emission of sound waves, causing a slight increase in the soliton's speed. We characterise this energy loss as a function of the wall parameters. Moreover, over multiple oscillations and reflections in the box-like trap, the energy loss and speed increase of the soliton can be significant, although the decay eventually becomes stabilized when the soliton equilibrates with the ambient sound field.

Study on the measurement speed and signal to noise ratio of multi tone burst wave for high speed non-contact acoustic inspection method

The non-contact acoustic inspection method using an air-borne sound can detect the cavity defect and crack near the measurement surface by using flexural resonance. By this method which uses the conventional single tone burst wave, since only one frequency was used for one sound wave emission, the length of measurement time had become a problem. Therefore, the multi-tone burst wave was devised for high speed improvement. However, measurement time and signal to noise (S/N) ratio change with the parameters in which a multi-tone burst wave is contained at the time of one sound wave emission, such as the number of frequency, the arranging method, pulse length, and the average number of times. Therefore, the experiment using the concrete test object having the styrofoam which imitated the cavity defect was conducted and a multi-tone burst wave was used, it was investigated how the measurement time and the S/N ratio of this method would change. From the experimental result, it became clear that the improvement in the measurement speed of several or more times was realizable maintaining a comparable S/N ratio as compared with the conventional single tone burst wave.

High speed non-contact acoustic inspection method using multi tone burst wave

The non-contact acoustic inspection method using an air-borne sound can detect the cavity defect and crack near the measurement surface by using flexural resonance. By this method using a single tone burst wave, the length of the measurement time of a two-dimensional scan was a practical problem. This is because only one frequency was used for one sound wave emission so that a high signal to noise (S/N) ratio could be obtained with the laser Doppler vibrometer (LDV) of a weak laser power (e.g., He-Ne 1mW). However, two or more frequency can be used at the time of one sound wave emission (multi tone burst wave) by taking into consideration the difference of the propagation velocity of a sound wave and laser light. That is, it becomes possible to perform high-speed measurement as compared with the conventional method, using effectively the time & frequency gate for raising a S/N ratio by terminating measurement before the reflective sound wave reaches a laser head from the measurement surface. The experiment using a concrete test object was carried out and the validity of this multi tone burst wave as high-speed measurement was confirmed from the experimental result.

On the Problems of Emission of Sound Waves in the Dynamic Process of Deformation of Plates with Regard for External and Internal Damping

To describe the dynamic process of deformation of a plate, we construct the corresponding equation of motion for small strains and displacements with regard for the internal and external aerodynamic damping. This equation is based on the Kirchhoff–Love kinematic hypotheses, the generalized Kelvin–Voigt constitutive model, and the solutions of hydrodynamic wave equations for the acoustic media surrounding the plate obtained in the one-dimensional approximation within the framework of the well-known hypothesis of plane reflection and emission of acoustic waves. By using the constructed equation, we find the exact analytic solutions of the problem of damped vibrations of a rectangular plate, preliminarily bent and hingedly supported over its contour and of the emission of sound waves by the plate after its liberation from constraints. We also solve the problem of emission of sound waves caused by the shock of the plate by a transverse load.

Dark soliton decay due to trap anharmonicity in atomic Bose-Einstein condensates

A number of recent experiments with nearly pure atomic Bose-Einstein condensates have confirmed the predicted dark soliton oscillations when under harmonic trapping. However, a dark soliton propagating in an inhomogeneous condensate has also been predicted to be unstable to the emission of sound waves. Although harmonic trapping supports an equilibrium between the coexisting soliton and sound, we show that the ensuing dynamics are sensitive to trap anharmonicities. Such anharmonicities can break the soliton-sound equilibrium and lead to the net decay of the soliton on a considerably shorter time scale than other dissipation mechanisms. Thus, we propose that small realistic modifications to existing experimental setups could enable the experimental observation of this decay channel.

Non-linear saturation of g-modes in proto-neutron stars: quieting the acoustic engine

Abstract According to Burrows et al.'s acoustic mechanism for core-collapse supernova explosions, the primary, l= 1, g-mode in the core of the proto-neutron star is excited to an energy of ∼1050erg and damps by the emission of sound waves. Here we calculate the damping of the primary mode by the parametric instability, i.e. by non-linear, three-mode coupling between the low-order primary mode and pairs of high-order g-modes. We show that the primary mode is strongly coupled to highly resonant, neutrino damped pairs with n≳ 10; such short wavelength interactions cannot be resolved in the simulations. We find that the parametric instability saturates the primary mode energy at ∼1048erg, well below the energy needed to drive an explosion. We therefore conclude that acoustic power is unlikely to be energetically significant in core-collapse supernova explosions.

A simple model of the magnetic emission from a dust devil

A simple Rankine‐like vortex model of the dust devil behaving as a magnetic solenoid has been constructed. It is augmented with a one‐dimensional model describing steady vertical distribution of the electric charge in the dust devil. For terrestrial dust devils, the model permits uniform vertical distribution of the negatively charged dust within the main vortex flow. For higher electric conductivity of air on Mars, the model hints on a rapid decay with altitude of the dust electrification, with e‐folding height order of several tens of meters, which is much less than the total dust column height. It is shown that some characteristic features of recently discovered ULF magnetic emission from the terrestrial dust devil can be interpreted in terms of interaction between negatively charged smaller‐scale vortex filaments inside the main vortex. It is conjectured that such ULF magnetic emission should be accompanied by the emission of sound waves of approximately doubled frequency.

Statistical Modeling in the Problem of Excitation of Fields by Random Sources on a Surface

We develop a method for statistical modeling of the emission of noise fields by sources located on a surface and consider the problem of sound-wave emission by the ocean surface. We also construct a model of distribution of the pressure and vibrational velocity of the sound field in a medium on the basis of randomization of the spectral density of pressure fluctuations on the surface. The obtained samples are exact solutions of the wave equation. The behavior of some statistical moments of the simulated field is studied.

Influence of electromagnetic radiation on molecular solitons.

The soliton model of charge and energy transport in biological macromolecules is used to suggest one of the possible mechanisms for electromagnetic radiation influence on biological systems. The influence of the electromagnetic field (EMF) on molecular solitons is studied both analytically and numerically. Numerical simulations prove the stability of solitons for fields of large amplitude, and allow the study of emission of phonons. It is shown that in the spectra of biological effects of radiation there are two characteristic frequencies of EMFs, one of which is connected with the most intensive energy absorption and emission of sound waves by the soliton, and the other of which is connected with the soliton photodissociation into a delocalized state.

Tri-chamber speaker box

A speaker box with improved low frequency response. Three chambers of specified proportion are provided which allow vibration of both front-cone and rear-cone sound waves projected from an internally installed low frequency speaker. Housing is provided for one or more higher frequency speakers, further providing rear covers to protect the speakers from low frequency sound wave interference. Ports are also provided for rear-cone sound wave emission.

Dynamics of Excess Electron Localization in Liquid Helium and Neon

In this paper, we address the relations between the structure, electronic level structure, energetics, and localization dynamics of an excess electron in a bubble in liquid 4He, 3He, and Ne. Our treatment of the dynamics of formation for the electron bubble rests on a quantum mechanical Wigner−Seitz description of the excess electron in conjunction with a hydrodynamic picture for the liquid. The dynamics of electron localization is described in terms of the initial formation of an incipient bubble of radius 3.3−3.5 Å followed by adiabatic bubble expansion in the ground electronic state. The hydrodynamic model for bubble expansion considers the expansion of a spherical cavity in an incompressible liquid with the energy dissipation being due to the emission of sound waves. This model predicts the bubble expansion time ( ) in liquid 4He to be = 8.5 ps at P = 0, exhibiting a marked pressure dependence (decreasing by a numerical factor of 4 at P = 16 atm) and revealing a small isotope effect of (4He)/ (3He) = 0.83 in liquid 3He, while for liquid Ne, ≅ 1 ps. The collapse times of the empty bubble formed by vertical photoionization of the electron bubble are τc = 19.8 ps for 4He and τc = 34 ps for 3He, with τc being considerably longer than , reflecting the effect of the kinetic electron energy on the fast electron bubble expansion. The interrogation of the electron bubble localization dynamics by femtosecond absorption spectroscopy is explored by the analysis of the temporal evolution of the electronic excitation energies.