Acoustic waves

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Piezoelectric Film Waveguides for Surface Acoustic Waves

Piezoelectric Film Waveguides for Surface Acoustic Waves

The paper presents results of mathematical modeling of piezoelectric film waveguide structures for surface acoustic waves (SAW). Piezoelectric ZnO film is supposed to be placed on a fused quartz substrate. The analytical ratios and numerical results allow to determine the design parameters of the waveguide structures to provide a single-mode SAW propagation mode. The results of amplitude and phase experi- mental studies of the SAW in the waveguide structures that were carried out on the laser optical sensing set up confirm the theoretical calculations.
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Determinação da Resistência à Compressão do Concreto Por Meio da Propagação de Ondas Acústicas / Determination of Concrete Compressive Strength by Propagating Acoustic Waves

Determinação da Resistência à Compressão do Concreto Por Meio da Propagação de Ondas Acústicas / Determination of Concrete Compressive Strength by Propagating Acoustic Waves

This aim of this work to present a non-destructive methodology for verifying the compressive strength of concrete by using acoustic waves generated with hammer strikes. For to analyze the feasibility of the proposed method, specimens with compression strengths of 15 MPa, 40 MPa and 50 MPa were obtained. The acoustic signals generated with the hammer were captured using a free software that simulates a digital oscilloscope. The analyzes carried out in the time and frequency domain showed a relationship between the amplitude intensity and the compressive strength of the specimens. However, the relationship between signal amplitudes and resistance to compression proved to be very dependent on the propagation surface of the acoustic wave, with regard to the degree of porosity.
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Angular oscillation of solid scatterers in response to progressive planar acoustic waves: do fish otoliths rock?

Angular oscillation of solid scatterers in response to progressive planar acoustic waves: do fish otoliths rock?

Fish can sense a wide variety of sounds by means of the otolith organs of the inner ear. Among the incompletely understood components of this process are the patterns of movement of the otoliths vis-a`-vis fish head or whole-body movement. How complex are the motions? How does the otolith organ respond to sounds from different directions and frequencies? In the present work we examine the responses of a dense rigid scatterer (representing the otolith) suspended in an acoustic fluid to low-frequency planar progressive acoustic waves. A simple mechanical model, which predicts both translational and angular oscillation, is formulated. The responses of simple shapes (sphere and hemisphere) are analyzed with an acoustic finite element model. The hemispherical scatterer is found to oscillate both in the direction of the propagation of the progressive waves and also in the plane of the wavefront as a result of angular motion. The models predict that this characteristic will be shared by other irregularly-shaped scatterers, including fish otoliths, which could provide the fish hearing mechanisms with an additional component of oscillation and therefore one more source of acoustical cues.
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Utilização de ondas acústicas para avaliação da corrosão superficial em barras de aço / The use of acoustic waves to evaluation surface corrosion in steel bars

Utilização de ondas acústicas para avaliação da corrosão superficial em barras de aço / The use of acoustic waves to evaluation surface corrosion in steel bars

The aim of this study was to develop a simple methodology, capable of characterizing different surface corrosion state in the steel bars through the acoustic waves propagation. For this, was used the gravitational potential energy caused by the impact of a steel ball in free fall on the surface of bars etched. After this, the acoustic signal was captured using computer and free software. The results obtained showed a possibility of a non-destructive method for investigating the corrosion of steel bars used in reinforced concrete structural elements.
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Nonlinear electron acoustic structures generated on the high-potential side of a double layer

Nonlinear electron acoustic structures generated on the high-potential side of a double layer

Abstract. High-time resolution measurements of the elec- tron distribution function performed in the auroral upward current region reveals a large asymmetry between the low- and high-potential sides of a double-layer. The latter side is characterized by a large enhancement of a locally trapped electron population which corresponds to a significant part (∼up to 30%) of the total electron density. As compared to the background hot electron population, this trapped com- ponent has a very cold temperature in the direction paral- lel to the static magnetic field. Accordingly, the differential drift between the trapped and background hot electron pop- ulations generates high frequency electron acoustic waves in a direction quasi-parallel to the magnetic field. The den- sity of the trapped electron population can be deduced from the frequency where the electron acoustic spectrum maxi- mizes. In the auroral midcavity region, the electron acoustic waves may be modulated by an additional turbulence gen- erated in the ion acoustic range thanks to the presence of a pre-accelerated ion beam located on the high-potential side of the double layer. Electron holes characterized by bipolar pulses in the electric field are sometimes detected in correla- tion with these electron acoustic wave packets.
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UAN: underwater acoustic network

UAN: underwater acoustic network

Abstract—Acoustic networks are for underwater what wifi is for terrestrial networks. The ocean is a nearly perfect media for acoustic waves in which regards long range propagation but poses a number of challenges in terms of available bandwidth, Doppler spread and channel fading. These limitations originate in the physical properties of the ocean, namely its anisotropy and boundary interaction which are particularly relevant in coastal waters where acoustic propagation becomes predominantly de- pendent on seafloor and sea surface properties. The acoustic communication channel is therefore multipath dominated and time and Doppler spread variable. The problem is aggravated when involving moving receivers as for instance when attempting to establish communication with or between moving autonomous underwater vehicles. The EU-funded project UAN - Underwater Acoustic Network aims at conceiving, developing and testing at sea an innovative and operational concept for integrating in a unique communication system submerged, surface and aerial sensors with the objective of protecting off-shore and coastline critical infrastructures. UAN went through various phases, including the development of hardware and software specific components, its testing independently and then in an integrated fashion, both in the lab and at sea. This paper reports on the project concept and vision as well as on the progress of its various development phases and the results obtained herein. At the time of writing, a final project sea trial is being planned and will take place two weeks before the conference so, although here we will concentrate on the progress obtained so far, the presentation at the conference may include additional results depending on the outcome of the sea trial.
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Wideband and wide beam polyvinylidene difluoride (PVDF) acoustic transducer for broadband underwater communications

Wideband and wide beam polyvinylidene difluoride (PVDF) acoustic transducer for broadband underwater communications

Acoustic communication systems have been widely used in underwater environments, since acoustic waves have low attenuation at low frequencies (up to tens of kHz), reaching large distances. Acoustic waves propagate more easily in an underwater environment [1] than the radio frequency (RF) and optic waves, but attenuation, ambient noise, Doppler Effect, low and variable sound speed, multipath and sound refraction (scattering) air bubbles and particles in suspension represents a considerable obstacle in underwater wireless communications [2]. One solution for higher data rates is to increase the carrier frequency [3]. However, increasing the frequency also will increase the attenuation and this represents a major drawback. To give some perspective, an acoustic signal at 1 MHz is attenuated around 280 dB/km considering only the attenuation by absorption [4].
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Lat. Am. j. solids struct.  vol.11 número10

Lat. Am. j. solids struct. vol.11 número10

The Laser-Ultrasonic technique uses laser energy to generate ul- trasound waves in various solids. This technique allows inspecting large structures. The generated ultrasound wave form is affected by features of laser pulse (wavelength, pulse duration, power density). The goal of this paper is to study the effects of laser parameters (rise time and beam radius of laser) on the laser generated surface acoustic waves in an aluminum plate. The results obtained from the finite element model of laser generated ultrasound are presented in terms of temperature and displacement. At first, the transient temperature field can be precisely calculated by using the finite element method. Then, laser generated surface acoustic wave forms are calculated in aluminum plate. Results from numerical simula- tion are compared with other references; the accuracy of the met- hod is proved accordingly. In this simulation the sequential field coupling is used. Simulation results show that the laser parameters have a significant influence on the ultrasound waves and will be able to be utilized to choose best experimental parameters of laser.
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Anomalous width variation of rarefactive ion acoustic solitary waves in the context of auroral plasmas

Anomalous width variation of rarefactive ion acoustic solitary waves in the context of auroral plasmas

Similar structures have also been observed by POLAR satel- lite at higher altitudes (Cattell et al., 2001). These elec- tron solitary waves were first identified by GEOTAIL satel- lite as the constituents of the broadband electrostatic noise (BEN) (Muschietti et al., 1999a) and were found to be as- sociated with electron beams (Crumley et al., 2001). The theoretical interpretations of these electron solitary waves mostly describe them as BGK (Bernstein-Greene-Kruskal) electron phase space holes (Turikov, 1984; Muschietti et al., 1999a,b, 2002; Maslov and Schamel, 1993; Schamel, 1982) while Dubouloz et al. (1991) has described them as elec- tron acoustic waves. Ion mode solitary waves, on the other hand, were associated with up-flowing ion beams (Bounds et al., 1999) and move with a velocity of the order of ion sound wave (Dombeck et al., 2001). They are observed com- paratively at lower altitudes of auroral zone (Cattell et al., 2001). The structures were found to show density depletion in the form of a symmetric potential well and are referred to as solitary waves (SW) but frequently they also display a net potential drop constituting weak double layers (WDL) (Temerin et al., 1982; B¨ostrom et al., 1989). Initial interpre- tations of such solitary waves were based on the theory of nonlinear evolution of coherent potential pulses from the lin- ear ion acoustic waves (Lotko, 1983). Later the work was extended to include H + and O + beams (Qian et al., 1989). The problem of the formation of weak double layers was also addressed on the basis of the theory of ion acoustic waves (Gray et al., 1991) and was suggested as the result of the evolution of ion acoustic solitary waves (Berthomier et al., 1998). The possible existence of solitary waves in the ion acoustic frequency range triggered several theoretical and numerical investigations (Qian et al., 1988; Koskinen et al., 1990; Gray et al., 1991; Yadav and Sharma, 1990; Reddy and Lakhina, 1991; Reddy et al., 1992
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Study of the Impact of Non-linear Piezoelectric Constants on the Acoustic Wave Propagation on Lithium Niobate

Study of the Impact of Non-linear Piezoelectric Constants on the Acoustic Wave Propagation on Lithium Niobate

In this paper, the wave equation is obtained by us- ing the linearized constitutive equations and incorpo- rating the stress in the equation of motion and taking account of the published set linear and nonlinear mate- riel constants. A new method is proposed to select and separate between the different modes of propagation of acoustic waves, by regarding only to the attenuations coefficients. Numerical simulations and results for Lithium Niobate are presented.

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Cluster observations and theoretical identification of broadband waves in the auroral region

Cluster observations and theoretical identification of broadband waves in the auroral region

Abstract. Broadband waves are common on auroral field lines. We use two different methods to study the polarization of the waves at 10 to 180 Hz observed by the Cluster space- craft at altitudes of about 4 Earth radii in the nightside auro- ral region. Observations of electric and magnetic wave fields, together with electron and ion data, are used as input to the methods. We find that much of the wave emissions are con- sistent with linear waves in homogeneous plasma. Observed waves with a large electric field perpendicular to the geo- magnetic field are more common (electrostatic ion cyclotron waves), while ion acoustic waves with a large parallel electric field appear in smaller regions without suprathermal (tens of eV) plasma. The regions void of suprathermal plasma are in- terpreted as parallel potential drops of a few hundred volts.
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Analog Model for Quantum Gravity Effects: Phonons in Random Fluids

Analog Model for Quantum Gravity Effects: Phonons in Random Fluids

In summary, we have constructed a condensed matter analog model for fluctuations of the geometry of spacetime due to quantum gravity effects. The model leads to the interpretation that such classical background fluctuations induce effective interactions on free fields. We expect that such sound cone fluctuations can be tested in suspensions like colloids since excitations of acoustic modes in these environments are described by random wave equations such as the one we discussed in this Letter [19]. A possible course of action is to remember Ref. [14], where it is shown that a nonlinear dispersion relation generated by a random wave equation induces peaks in the density of states. Another direction is the analysis of localization of acoustic waves. Such an issue is related to the problem of how sound cone fluctuations in our analog model can change the variation of flight of pulses. The study of wave locali- zation using diagrammatic perturbation method was pre- sented in Refs. [20–23]. It is known that in one dimension any disorder is strong enough to induce exponential locali- zation of eigenmodes. On the other hand, a random fluid with a supersonic acoustic flow is also an analog model that opens the possibility to discuss the effect of the fluctuation of the geometry in the Hawking radiation. Specific ex- amples studying Anderson localization in the analog model of the present Letter as well as the implementation of randomness in an acoustic black hole will be reported elsewhere.
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Detecção de danos em estruturas guiadas usando ondas de alta frequência

Detecção de danos em estruturas guiadas usando ondas de alta frequência

This Chapter summarizes the work done in this dissertation and presents the main conclusions obtained as well as the recommendations for further work. The principal objectives in this dissertation were to develop a wave propagation model of a one-dimensional structure with symmetric damage coupled with PZT actuator and sensor in two configurations to sense reflected and transmitted waves and to analyse the effects of the size of piezoelectric and symmetric damage both in frequency and time domain. To achieve these objectives the dissertation was organized as follows:
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Fado' Voice Acoustic Features

Fado' Voice Acoustic Features

104 Fado singers participated on this study: 47 males, 57 females; 90 amateur and 14 professional, with ages from [18–67]. Fado singers produced spoken tasks consisting on sustained [a,i,u,s,z] plus reading aloud and sung tasks consisting on sustained [a,i,u] of the song “Nem ´as paredes confesso”. Acoustic voice parameters were compared between males vs. females, professionals vs. amateurs and young vs. older voices a two independent t-test with an α at .05.

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Acoustic modem for underwater communications

Acoustic modem for underwater communications

The final channel property that bears discussing is the frequency shift and spread from Doppler effect, caused by relative transmitter-receiver motion. The magnitude of this effect is determined by the ratio a = v/c of relative velocity to propagation speed. While in radio communication channels the Doppler effect is only relevant for transmitters or receivers moving at high speed (such as Low Earth Orbit satellites or jet aircraft), the low speed of sound in water means that even platforms just drifting with the current can be affected. An added difficulty of underwater channels is the existence of Doppler effect from time-varying multipath, as discussed previously, since reflections from surface waves behave as additional emitters with their own independent velocities [26, p. 52]. Another undesirable coupling between the two effects occurs when the Doppler spread on each path differs.
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Lat. Am. j. solids struct.  vol.11 número7

Lat. Am. j. solids struct. vol.11 número7

These phenomena have been investigated for the simple isotropic semi-space as well as the complicated systems of multilayered anisotropic media. A detailed review in this respect is given by Nayfeh (1995). Qi (1994) investigated the influence of viscous fluid loading on the propagation of leaky Rayleigh waves in the presence of heat conduction effects. Wu and Zhu (1995) suggested an alternative approach to the treatment of Qi (1994). They presented solutions for the dispersion relations of leaky Rayleigh waves in the absence of heat conduction effects. Zhu and Wu (1995) used this technique to study Lamb waves in submerged and fluid coated plates. Nayfeh and Nagy (1997) formulated the exact characteristic equations for leaky waves propagating along the inter- faces of systems which involve isotropic elastic solids loaded with viscous fluids, including half- spaces and finite thickness fluid layers.
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A typical wave wake from high-speed vessels: its group structure and run-up

A typical wave wake from high-speed vessels: its group structure and run-up

Even though the significant effect of waves from high- speed vessels on low-energy coasts has been demonstrated for different basins and environments, the reason of its such strong impact still remains unclear. It can be partially con- nected to the net transport of water, excited by ships sail- ing at transcritical speeds, which may produce water level set-up under groups of high vessel waves and result in a rapid reaction of the coast (Soomere et al., 2011). This ef- fect may also be reinforced by the specific group structure of vessel-induced waves, when the largest, the longest and the most asymmetric waves come first and more symmetric waves of smaller amplitude and period come after. The char- acteristic properties of these groups are experimentally stud- ied in this paper for Pikakari beach in Tallinn Bay, the Baltic Sea.
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Acoustic barriers as an acoustic deterrent for native potamodromous migratory fish species

Acoustic barriers as an acoustic deterrent for native potamodromous migratory fish species

The use of acoustic barriers depends on the hearing capabilities of target species. Fish present a continuum of hearing capabilities associated with the evolution of hearing structures (Popper & Fay, 2011). Fish that present morphological specializations connecting air- filled cavities, such as the swimbladder, to the inner ear have enhanced hearing capabilities and can detect sound pressure in addi- tion to the kinetic component of sounds, i.e. particle motion. The Cyprinidae, are notably sensitive to sound and can detect a wide fre- quency range (up to thousands of Hz) (Popper & Fay, 2011, Popper & Schilt, 2008). Species with no hearing specializations, such as Salmoni- dae, are only able to detect particle motion and their hearing sensitiv- ity is restricted to low frequency sounds of up to a few hundred Hertz; e.g.,400 Hz in the Atlantic salmon Salmo salar L. 1758 (see fig- ure 2.1 in Popper & Schilt, 2008). Due to the large variation in hearing structures, different species may react differently to an acoustic bar- rier, emphasizing the need for species-dedicated behavioural evalua- tion tests.
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ACOUSTIC EMISSION ANALYZER

ACOUSTIC EMISSION ANALYZER

In this paper appears a solution for acoustic emission analysis commonly known as noise. For the accomplishment of this work a personal computer is used, besides sensors (microphones) and boards designed and built for signal conditioning. These components are part of a virtual instrument used for monitoring the acoustical emission. The main goal of this work is to develop a virtual instrument that supplies many important data as the result of an analysis allowing to have information in an easy and friendly way. Moreover this information is very useful for studying and resolving several situations in planning, production and testing areas.
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Rev. Bras. Reumatol.  vol.49 número3

Rev. Bras. Reumatol. vol.49 número3

Immune-mediated inner ear disease (IMIED) produces neu- rosensorial deafness. The patients complain about the reduction of acoustic acuity or reduction of sound discrimination. In general, it is bilateral, rapidLy progressive. It may be associated with vestibular symptoms. The syndrome mechanism is not completely clear, but it is accepted as an immunologic nature. It is known that the endolymphatic sac is an immunocompetent organ, and circulating antibodies, against antigens of the inner ear, as well as viral endolymph antigens, are found in this con- dition. However, specificity and sensibility and the role of those autoantibodies in the pathologic process are poorly explained. Generally, early use and high doses of corticotherapy solve or reduce the problem. In case of persistence of manifestations resistant to corticotherapy, another option should be metho- trexate, with a good, regular and, sometimes, inefficient result, according to several papers published.
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