Frequency Acoustic Waves Research Articles

Measurement of acoustic wave frequency by Bragg light diffraction.

The new technology is offered for measurement of acoustic wave frequency. The method is based on using the Bragg light diffraction on the hypersonic transversal acoustic wave in a gyrotropic crystal. As is well known, the intensity of diffracted light in this case is strongly dependent from the quantity of specific rotation of polarization vector. As a result, using the standard calibration of light intensity it is possible to measure the changes of acoustic wave frequency. Measurements of the diffracted light intensity have been carried out in several points along the direction of the acoustic wave propagation. The applied sample of LiNbO3 was oriented along the crystallographic axis of the third order with the accuracy of 10′. The plane‐polarized transverse acoustic waves were excited in the frequency range from 900 MHz to 1.2 GHz. The results obtained at the average frequency 1.0 GHz were shown, that the intensity of diffracted light intensity is sensitive parameter to the change of the transverse acou...

Measuring method using surface acoustic wave device, and surface acoustic wave device and biosensor device

A measuring method using a surface acoustic wave device, with which even in a case where a target substance having a different viscosity is added to a buffer liquid on the surface acoustic wave device it is possible to measure a mass load accurately without suffering an effect of this viscous load, and it is also possible to shorten the time taken for the temperature of the buffer liquid to stabilize and thereby shorten the time taken for the measurement. The measuring method provided is a method for exciting a surface acoustic wave on a substrate and measuring a property of a target substance placed on a detecting part on the substrate on the basis of a change in a characteristic of the surface acoustic wave, with the characterizing feature that a viscous load of the target substance is evaluated on the basis of fluctuations of at least two different frequencies among frequencies of the surface acoustic wave excited on the substrate, and a mass load of the target substance is measured by being separated from this viscous load.

Modulation of electroactive polymer film dynamics by metal ion complexation and redox switching

The viscoelastic properties of [Ni(salen)(crown ether)] conducting polymer films were characterized using high frequency acoustic wave resonators. Shear moduli values respond to film redox state and barium ion complexation. The variations in storage and loss moduli are significant, but always such that the films are viscoelastic, i.e. a soft material. Both components are increased by polymer oxidation, the loss modulus to a greater extent. In the absence of Ba2+, the similarity of shear moduli- and nanogravimetric-potential signatures (for acoustically thick and thin films, respectively) provides a compositional explanation for changes in film dynamics. Ba2+ uptake restricts the extent of film redox switching. In the presence of Ba2+ the pattern of redox driven shear modulus changes is unaltered, but the values of both components are systematically higher. These changes are interpreted in terms of (i) space limited accommodation of counter ions (ii) crown-Ba2+-crown crosslinking between polymer chains, and (iii) decreased free volume for plasticizing solvent. We suggest that the first of these is the origin of the restricted charge injection (controlled by electroneutrality), the second of the increased storage moduli, and the third of the increased loss moduli. Observations at different time scales, via acoustic wave resonator harmonics, reveal increases in both shear moduli components with increasing frequency; these are considered in the light of simple mechanical models for polymer dynamics.

Deposition of ZnO thin films on SiO 2/Si substrate with Al 2O 3 buffer layer by radio frequency magnetron sputtering for high frequency surface acoustic wave devices

ZnO films with c-axis (0002) orientation have been grown on SiO 2/Si substrates with an Al 2O 3 buffer layer by radio frequency magnetron sputtering. Crystalline structures of the films were investigated by X-ray diffraction, atomic force microscopy and scanning electron microscopy. The center frequency of the surface acoustic wave (SAW) device with a 4.8 μm thick Al 2O 3 buffer layer was measured to be about 408 MHz, which was much higher than that (265 MHz) of ZnO/SiO 2/Si structure and approaches that (435 MHz) of ZnO/sapphire. It is a possible way as an alternative for the sapphire substrate for the high frequency SAW device applications, and is also useful to integrate the semiconductor and high frequency SAW devices on the same Si substrate.

Nonlinear parameter estimation in water-saturated sandy sediment with difference frequency acoustic wave

Difference frequency acoustic wave from nonlinear interaction of two primary acoustic waves at frequencies of 76 and 114 kHz was utilized with a parametric acoustic array theory to estimate the nonlinearity parameter of water-saturated sandy sediment. Such nonlinearity parameter can be used as background information for the nonlinear acoustic investigation of bottom or sub-bottom profiling in the ocean sandy sediments. Because of its lower attenuation the difference frequency acoustic wave method can be usefully applied to estimate the nonlinearity parameter of ocean sediment in the ocean as well as under laboratory conditions. The nonlinearity parameter β for the water-saturated sandy sediment used as a reference in this study was estimated as β = 80.5 ± 5.1 at the difference frequency of 38 kHz. It was agreed very well with that estimated at the difference frequency of 67 kHz, when two primary frequencies were 137 and 204 kHz. The estimated nonlinearity parameter of water-saturated sandy sediment in this study was also compared and analyzed with those estimated in previously published literatures. It was suggested that the difference frequency wave method used to estimate the nonlinearity parameter of water-saturated sandy sediment can be employed as a good method to estimate the nonlinearity parameters of fluid-like granular media.

Elementary excitations, electronic correlation functions and sum rule in noble-metal chalcogenides

Noble-metal chalcogenides are known as both electronic and ionic conductors. Physics in superionic conductors is investigated on the basis of the idea of elementary excitations. First, the semiconducting properties of noble-metal chalcogenides are investigated by preparing the full Hamiltonian for conduction electrons and phonons. The influence of electron interactions on the longitudinal acoustic wave frequencies and the matrix element for the electron–phonon interaction are investigated. Three cases of ω >> kυ F , ω < kυ F and ω = 0 are investigated for polar semiconductors like noble-metal chalcogenides. Next, the structure factors, and the f-sum rule of conductivity are investigated in silver chalcogenides by making use of a continuum model. The structure factors S ee, S Ae and S Be with which electrons are connected are expressed symmetrically in terms of the structure factors S AA, S BB and S AB of ions in the long-wavelength limit using the fluctuation–dissipation theorem and the Kramers–Kronig relation. The obtained conductivity satisfies the f-sum rule.

Flight systems aeroelastic‐acoustics simulation.

Many practical problems, such as flight vehicles, are often characterized by complex interactions among a number of primary disciplines as structures, fluids, controls, and propulsion, among others. In some critical flight regimes as transonic flow, the dynamics behavior of fluids tend to be highly complex, needing computational fluid dynamics (CFD)‐based modeling, rather than linear aerodynamic methods, for accurate prediction of unsteady flow. Such unsteady pressure values, generated by the interaction of fluids and elastic structures, could then be conveniently used to compute acoustic wave frequencies and sound levels. For accurate simulation of complex engineering problems such as advanced aircraft, it is necessary to employ unstructured grids to model the fluid discipline, such being mostly the case for structure modeling. Effective CFD‐based aeroelastic modeling, using finite element discretization of both fluids and structures, employing unstructured grids, have been efficiently utilized for simulation of Hyper‐X and F‐18 aircraft. In connection with a current ongoing project Stratospheric Observatory For Infrared Astronomy, evaluation of acoustic activities in the cavity of the modified Boeing 747SP aircraft, housing the telescope, became a crucial issue. The multidisciplinary code STARS7 was recently extended to include the acoustic effects.

Acoustic waves in hydrogels: A bi-phasic model for ultrasound tissue-mimicking phantom

In the present paper a continuum poroelastic model for high frequency acoustic waves in hydrogels has been developed. The model has been used to obtain the acoustic longitudinal wave equation for ultrasound. In order to obtain a satisfactory model for hydrogels, a viscoelastic force describing the interaction between the polymer network of the matrix and the bounded water is introduced. The model is validated by means of ultrasound (US) wave speed and attenuation measurements in polyvinylalcohol (PVA) hydrogel samples as a function of their water volume fraction “β” and polymer matrix cross-linking. The model predicts that the law ∝ ν (1 + δ) for ultrasound attenuation can be applied as a function of the frequency ν, where δ is the frequency exponent of the polymer-bounded water viscosity. This outcome can well explain the attenuation of the US frequency in natural gels where δ is typically about 0.25÷0.50 while the value for pure water is 1. The theory and experiments show that US attenuation in hydrogels decreases steadily with the increase of its water volume fraction β in a linear. The new proposed dissipative mechanism leads to a US wave speed c that follows the law: c = c w( β − ϕ) − 3/2 , where c w is the US wave speed in water and ϕ is the volume fraction of the bounded water. Since 0 < β < 1 and ϕ > 0, the hydrogel US velocity is always higher than that of pure water. If β tends to 1 (100% water), then the US speed in hydrogels converges to a higher value than that of pure water. The US speed gap at β = 1, between hydrogels and water, is the direct consequence of the introduction of the polymer network-bounded water interaction. This is in line with the experimental results that show that the US speed gap at β = 1 decreases in the gel samples with a more cross-linked polymer matrix that has a lower bounded water volume fraction. On the contrary, if the water content is very low (i.e., β < 0.4), the measured US speed converges to that of the dry hydrogel matrix which increases in the samples with a higher degree of network cross-linking with greater elastic moduli.

Nonlinear frequency shift in surface acoustic wave resonator operating as a gas sensor

The shift in the resonance frequency of a two-port quartz surface acoustic wave (SAW) resonator operating as a gas sensor without a selective layer is studied versus the power of an SAW excited in the resonator. At working frequencies of the resonator (≈389 MHz) placed in the flow of moisture-containing nitrogen gas, an anomalously large positive shift of the resonance frequency is observed as the SAW power exceeds 1 mW. This shift is one order of magnitude larger than that due to the nonlinear amplitude-frequency effect, which is known for quartz SAW resonators. Possible physical mechanisms underlying this phenomenon are analyzed. Experimental data indicate that such a shift is associated with the influence of a powerful SAW on sorption processes taking place on the active surface of the resonator rather than being a direct consequence of heating of the SAW substrate by the powerful SAW.

Interfacial destabilization and atomization driven by surface acoustic waves

Surface acoustic wave atomization is a rapid means for generating micron and submicron aerosol droplets. Little, however, is understood about the mechanisms by which these droplets form due to the complex hydrodynamic processes that occur across widely varying length and time scales. Through experiments, scaling theory, and simple numerical modeling, we elucidate the interfacial destabilization mechanisms that lead to droplet formation. Using a millimeter-order fluid drop exposed to surface acoustic waves as it sits atop a single-crystal lithium niobate piezoelectric substrate, large aerosol droplets on the length scale of the parent drop dimension are ejected through a whipping and pinch-off phenomenon, which occurs at the asymmetrically formed crest of the drop due to leakage of acoustic radiation at the Rayleigh angle. Smaller micron order droplets, on the other hand, are formed due to the axisymmetric breakup of cylindrical liquid jets that are ejected as a consequence of interfacial destabilization. The 10μm droplet dimension correlates with the jet radius and the instability wavelength, both determined from a simple scaling argument involving a viscous-capillary dominant force balance. The results are further supported by numerical solution of the evolution equation governing the interfacial profile of a sessile drop along which an acoustic pressure wave is imposed. Viscous and capillary forces dominate in the bulk of the parent drop, but inertia is dominant in the ejected jets and within a thin boundary layer adjacent to the substrate where surface and interfacial accelerations are large. With the specific exception of parent drops that spread into thin films with thicknesses on the order of the boundary layer dimension prior to atomization, the free surface of the drop is always observed to vibrate at the capillary-viscous resonance frequency—even if the exciting frequency of the surface acoustic wave is several orders of magnitude larger—contrary to common assumptions used in deriving subharmonic models resulting in a Mathieu equation for the capillary wave motion, which has commonly led to erroneous predictions of the droplet size.

Nanoscale objects as promising high frequency acoustic transducers in picosecond acoustics

Twenty year ago, H. Maris opened up the field of nanoscale acoustics by demonstrating the opportunity of using ultrashort optical pulses for generating and detecting high frequency acoustic waves. Roughly, an optical pulse is converted in a picosecond acoustic pulse through the optical absorption in a thin metallic layer. Since then, this so-called picosecond ultrasonics has known a larger and larger success all around the world. Up to now, picosecond ultrasonics meets two main limitations. First it is difficult to reach the THz range using the usual way of producing the acoustic pulse. Second, in the common geometry only longitudinal waves are excited by the laser. Here we present some results showing that nanoscale objects could help in overcoming both difficulties. We first show that semiconductor quantum dots can be a very efficient emitter of coherent phonons whose frequency can be higher than those obtained in metallic thin films. Second we show that 2D arrays of nanosize metallic dots offers a way of generating and detecting high frequency surface acoustic waves.

Experimental studies of generation and propagation of high frequency acoustic waves in various solid materials using ultraviolet picosecond laser pulses

The generation of high frequency acoustic waves by picosecond laser pulses in the ultraviolet region and their detection by optical interferometric schemes, is presented. The two main acoustical modes, longitudinal and shear are clearly apparent in the time resolved spectra of solid materials, for various absorbing energies, extending from the thermoelastic to the ablative regime. The ultraviolet light is strongly absorbed by insulator materials like Pyrex and thus strong elastic waves are produced. From the time separation of the longitudinal waves we have deduced values for the speed of sound in various materials and of different thickness, that are in very good agreement with those reported in the literature. Also the time bandwidth of the sound waves is measured and significant differences, originating from different sample thickness, are apparent.

Splitting of the resonance frequencies of acoustic waves in a rotating compressible fluid

In a rotating compressible fluid bounded by cylindrical walls, the resonance frequencies of acoustic waves propagating along and against the direction of rotation exhibit splitting into two components. The magnitude of such splitting in a model case that can be realized in experiment has been calculated. The results can be of interest for the acoustics of rotating technical devices and for the measurement of velocities of rotating fluids.

Alignment of particles in microfluidic systems using standing surface acoustic waves

We report on the use of standing surface acoustic waves, formed on a single-crystal piezoelectric substrate, to organize micron-scale latex particles into an array comprising a series of lines in an adjacent microfluidic system. The lines of particles are formed parallel to the substrate surface and perpendicular to the surface acoustic wave vector. They extend across the width of the acoustic beam aperture, with a periodicity of one-half the surface acoustic wavelength. The position and spacing of the particle arrays can be altered by adjusting the acoustic wave frequency within the device passband. We discuss the mechanism responsible for the formation of the lines, which could be widely applicable to the alignment of microscopic objects held in suspension.

Method of manufacturing potassium niobate single crystal thin film, surface acoustic wave element, frequency filter, frequency oscillator, electronic circuit, and electronic apparatus

A method of manufacturing potassium niobate single crystal thin film on a single crystal substrate that epitaxially grows orthorhombic potassium niobate single crystal at a temperature near room temperature at a high deposition rate. A surface acoustic wave element, frequency filter, frequency oscillator, electronics circuit, and electronic device employ the thin film manufactured by the method, and are high in k 2 , wideband, downsized, and economical in power consumption. The method includes the steps of coating liquid drops of a potassium niobate solution on a SrTiO 3 single crystal substrate by a liquid drop emission method, and precipitating potassium niobate single crystal layer by epitaxial growth from the liquid drops.

Modulation of the extraordinary optical transmission by surface acoustic waves

The numerical study of the acoustic (elastic) effect in periodically nanostructured metallic films exhibiting extraordinary optical transmission (EOT) deposited onto the top of a piezoelectric material is reported. Surface acoustic waves are generated in the piezoelectric substrate and their influence in the transmission spectrum of the EOT structure is studied. It is shown that low frequency acoustic waves can significantly tune the resonance frequency of the EOT structure and modulate the transmitted intensity. Acoustic waves appear as an interesting route to realize controllable EOT devices and other active plasmonic components.

Can High Frequency Acoustic Waves Heat the Quiet Sun Chromosphere?

Abstract We use Hinode/SOT Ca II H-line and blue continuum broadband observations to study the presence and power of high frequency acoustic waves at high spatial resolution. We find that there is no dominant power at small spatial scales; the integrated power using the full resolution of Hinode ($0\rlap{.}^{\prime\prime}05$ pixels, $0\rlap{.}^{\prime\prime}16$ resolution) is larger than the power in the data degraded to $0\rlap{.}^{\prime\prime}5$ pixels (TRACE pixel size) by only a factor of 1.2. At 20 mHz the ratio is 1.6. Combining this result with the estimates of the acoustic flux based on TRACE data of Fossum and Carlsson (2006, ApJ, 646, 579), we conclude that the total energy flux in acoustic waves of frequency 5–40 mHz entering the internetwork chromosphere of the quiet Sun is less than 800 Wm$^{-2}$, inadequate to balance the radiative losses in a static chromosphere by a factor of five.

High frequency oscillations in the solar chromosphere and their connection with heating

AbstractHigh frequency acoustic waves have been suggested as a source of mechanical heating in the quiet solar chromosphere. To investigate this, we have observed intensity oscillations of several lines in the frequency interval 1.64-70mHz using data from the VTT Tenerife and the Dunn Solar Telescope at the National Solar Observatory. Our analysis of Fe i 543.45 nm, Fe i 543.29 nm and the G-band, indicate that the majority of oscillations are connected with the magnetic fields and do not provide sufficient mechanical flux for the heating of the chromosphere. This correlation is also observed in quiet Sun areas.

Laser induced short plane acoustic wave focusing in water

Laser induced high frequency acoustic wave generation, propagation, and focusing in water are studied. A large area, flat, and short duration acoustic wave was generated by the thermoelastic interaction of a homogenized short pulsed laser beam with the liquid-solid interface and propagated at the speed of sound. Laser flash Schlieren photography was used to visualize the transient interaction of the flat acoustic wave with a cylindrical concave lens and the subsequent acoustic wave focusing. Numerical simulations showed the acoustic wave could be focused to several tens of microns in size and 7bars in pressure.

Experimental investigation of cavitational bubble dynamics under multi-frequency system

Acoustic emission spectra measurements have been carried out under mono and multi-frequency acoustic sources to understand the fundamental difference in bubble/cavity dynamics. The effect of introducing the dual and triple frequency acoustic waves of different frequency on the sono-chemical yield has also been investigated experimentally. The introduction of a second wave has increased the number of cavitating bubbles and as well as the collapsing intensity of cavities resulting into higher sono-chemical yield, and better effective utilization of reactor volume with a large number of resonating cavitating bubbles. To get the information about the intensity of each of the cavity oscillating events, decomposition of the pressure signal measured by the hydrophone in the frequency domain of the FFT power spectrum has been carried out. Inverse fourier reconstruction technique, has been used to elaborate the dynamics of the cavitating bubbles in the multi-frequency system.