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Fundamentals of Physical Acoustics

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... In the ultrasonic ranging system, the transducers can be used as either the transmitter, the receiver or both depending on the configurations. The sound field established by the transducer in the medium is related to the shape and size of the transducer, the vibration mode, the working parameters such as frequency and the types of the medium [76]. ...
... The sound field established by the transducer in the medium is related to th and size of the transducer, the vibration mode, the working parameters such as fr and the types of the medium [76]. ...
... Attenuation is a result of several fact interaction with medium and interfaces, including scattering, absorption, reflec diffraction. In the ultrasonic ranging system where the transducer operates in pu mode, the transducer emits the ultrasonic wave and is reflected by the target obst ultrasonic overall loss formula can be expressed as shown in Equation (4), inclu attenuation contribution from the propagation path [76] α -2 = = 10 4 r r ac t P a G G P r As shown in Figure 3, there are the main lobe and sidelobes in the acoustic field [77], with the main lobe mainly could be used for ranging. In applications where the ranging direction is fixed, the transducer is generally configured in an orientation to align with its main lobe's direction. ...
Article
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Ultrasonic ranging has been widely used in automobiles, unmanned aerial vehicles (UAVs), robots and other fields. With the appearance of micromachined ultrasonic transducers (MUTs), the application of ultrasonic ranging technology presents a more extensive trend. This review focuses on ultrasonic ranging technology and its development history and future trend. Going through the state-of-the-art ultrasonic ranging methods, this paper covers the principles of each method, the signal processing methodologies, the overall system performance as well as key ultrasonic transducer parameters. Moreover, the error sources and compensation methods of ultrasonic ranging systems are discussed. This review aims to give an overview of the ultrasonic ranging technology including its current development and challenges.
... We present the general framework used to describe acoustic eigen-frequencies of a cavity. We describe the classic problem formulation, following Blackstock (2000), where we remind the useful equations for our problem, the set of approximations we take, as well as the boundary conditions. We also present the resolution method we use (perturbation theory) as well as the full resolution of the problem for the reference model we choose. ...
... The description of a fluid behaviour breaks down to the conservation and constitutive equations. The conservation equations for mass, momentum and energy write (Blackstock, 2000) ∂ρ ∂t ...
... In the acoustic framework, the sound waves cause disturbances in the medium (here defined as the fluid with its background state, possibly in motion) that can be considered small if |v| c 0 or M S = |v|/c 0 1 with M S the (sonic) Mach number. In this smallsignal limit, the conservation equations can be linearized into (Blackstock, 2000) ...
Thesis
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Zonal flows are expected to play a major role in the heat transfer mechanism of geophysical bodies such as the Earth's core of Jupiter's atmosphere.However due to the turbulent regime the systems are in, and the specific force balance, dominated by rotation, it is very hard to accurately model zonal flows. This causes their formation and dynamics to still not be well understood.Experimental studies propose a complementary approach where all scales of structures coexist. However most of the experimental set-up remain far from the relevant regimes found in the natural systems.We present a new laboratory experiment to study zonal flows induced by thermal convection, called ZoRo. The originality of this new apparatus resides in the fast that all balances, forcings and geometry are closest to the geophysical bodies. In order to match those, ZoRo is a rapidly rotating spheroid (flattened sphere) filled with air.In order to experimentally study zonal flows, all physical ingredients are reunited in the apparatus, and we measure the flow field. Since the working fluid is air, so gaseous, it is very challenging to accurately measure its velocity.To tackle to this problem, we developed a new velocimetry technique based on the acoustic resonances of the fluid cavity, the modal acoustic velocimetry (MAV).As the quantity of interest is velocity, we develop theoretical predictions that take into account the other effects that influence the acoustic spectrum (cavity's geometry, fluid's diffusions, container elasticity etc).Once the velocity contribution is isolated, it is possible to retrieve the flow field using acoustic frequencies through an inverse problem. We test this method against both synthetic cases and real experimental flows measured in ZoRo.MAV is a well-technique for measuring global azimuthal flows such as zonal flows. It is very sensitive to variations in the flow structure, down to a few centimetres.We were able to image the internal flow velocity with non-intrusive sensors thanks to MAV.This thesis is a first landmark towards realistic zonal flows laboratory experiments. The velocimetry technique is fully developed, allowing accurate non-intrusive measurements of zonal flows.
... Lumped element modeling is a low frequency approximation applicable when the characteristic length scales of the physical phenomena are much larger than the largest geometric dimension of the system. In acoustics, this corresponds to an acoustically compact device, in which the largest dimension of the device in question are significantly smaller than the acoustic wavelength [10]. A common rule of thumb is that a device is acoustically compact when its largest dimension is about one eighth of the acoustic wavelength. ...
... which is accurate for 1. This approximation assumes no sound radiation into the cavity and only accounts for the end that radiates into an open medium, [10]. The total acoustic resistance of the neck, , is found by adding and or = + . ...
... The acoustic mass of the neck, , is given in Blackstock [10] by ...
Conference Paper
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Acoustic liners are noise reduction devices inside aircraft engines to mitigate noise radiation. A conventional single degree of freedom (SDOF) acoustic liner is comprised of a perforated facesheet, honeycomb cells, and a rigid backing. In the current study, a dielectric elastomer (DE) membrane is inserted between the facesheet and rigid backing, creating an adaptive 2DOF liner. This configuration is referred to as a DE acoustic liner (DEAL). A DE is an electroactive polymer material capable of changing shape when subjected to an electric field. In the present configuration, an initial tension is imposed on the membrane causing an in-plane tensile stress. When subjected to an electric field, the stress is reduced, and the membrane becomes more compliant. In turn, this reduces the resonance frequency of the acoustic liner, thus enabling tuning of its acoustic impedance. The tunability of the DEAL is demonstrated experimentally in a normal incidence impedance tube using the two-microphone method. A lumped element model (LEM) is also developed to enable modeling and future design optimization.
... La mayor parte de la información fue obtenida del libro "The Physics of Musical Instruments" escrito por Neville H. Fletcher y Thomas D. Rossing [9], así como del libro "Fundamentals of Physical Acoustics" de David T. Balckstock [4]. ...
... Para encontrar la nota que tenga un intervalo de quinta ascendente se multiplica la frecuencia f por 3 2 ; para una quinta descendente se divide por 3 2 , muliplicando (o dividiendo) este resultado por 2 para obtener sonidos dentro de los límites dentro de la escala. Por ejemplo, al buscar una quinta descendente con el método descrito se obtiene 2 3 f y para ubicar esta nota dentro de la octava se multiplica por 2 y se obtiene 4 3 f , que es el cuarto grado de la escala: F a. Pero si se multiplica f por 3 2 se obtiene el quinto grado de la escala: Sol. Luego al multiplicar 3 2 f × 3 2 = 9 4 f y dividirlo por 2 (y ubicarlo así dentro de la octava) se obtiene 9 8 f que corresponde al segundo grado: Re. ...
Thesis
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In Spanish. Afinaciones y temperamentos Históricos Historial tunings and temperaments.
... Here we use the "wide-tube approximation" modeling, which comes from the results of Kirchhoff (1868). Absorption is related only to interaction with the pipe wall, which takes place in a narrow boundary layer, with respect to the pipe radius (Blackstock, 2000). The absorption coefficient  and the phase velocity are functions of the angular frequency , the pipe radius b, and the fluid physical properties (density  f , speed of sound in the free medium , dynamic viscosity , specific heats ratio  and Prandtl number Pr): ...
... The model is applicable when the pipe rigidity is much higher than the fluid rigidity. In order to take into account pipe elasticity, we replace the free medium fluid sound speed with the celerity of water-hammer pressure waves in pipelines, which depends on the ratios between the pipe radius and the wall thickness b/w t , and between the fluid and pipe compressibility B f /E (Blackstock, 2000), , ...
Article
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Pipeline Inspection Gauges (PIGs) are widely used for monitoring and managing pipeline integrity. During a pigging operation it is fundamental to have a continuous measurement of the PIG position and movement, in order to achieve the best inspection and to have an early warning in the case the device is stuck. Currently, the tracking is performed by installing on the PIG “active” systems (e.g. acoustic pingers or electromagnetic emitters) that communicate with a set of receivers, making it possible the localization of the travelling gauge. Another solution is the deployment of an appropriately dense network of sensors along the pipe track, or the utilization of a dedicated system/crew that moves close to the pipe, so to physically perceive the vibrations generated by the nearby passage of the device. In fact, the moving PIG produces pressure transients and vibro-acoustic noise due to the velocity fluctuations, to the friction against the internal walls and to the crossing of the welding dents. It is important to mention that the conduit acts like an acoustic waveguide and the “sound” generated by the PIG, in many practical situations, can be sensed within the fluid at several kilometres from the originating point. This paper presents three different tracking procedures that exploit the noise generated by the PIG to locate it, remotely and passively, without requiring any additional equipment to be mounted on the gauge. The key points of the procedures are the availability of pressure measurements at a small number of positions along the pipeline, at relative distances of tens of kilometres, an accurate synchronization of the measurements, the real time transmission and multichannel processing of the data. The first method locates the PIG by performing a crosscorrelation analysis between the acoustic signal recorded on opposite sides of the moving gauge, the second method is based on the counting of the transients generated at known positions, the third one describes the pipe section between the PIG and the arrival terminal like a resonant structure, and obtains the length of this section (the distance of the PIG to the arrival) from the resonance frequency. All the methods are presented starting from real examples, in order to highlight their effective applicability. Moreover, the localization results are in agreement with the output of more sophisticated technological solutions.
... Let us first discuss how far a human speaker can be heard intelligibly (without amplification) in different conditions [6]. A similar exercise was done for Julius Caesar's battlefield speeches [7] with overall results similar to ours. ...
... On the setting at the Horns of Hattin, see Section 5.2, Maria Valtorta writes (170. [2][3][4][5][6][7][8][9][10][11][12][13][14]: "The people sit on the stones scattered in the little valley between the two crests, but some wait for the sun to dry the grass, wet with dew, so that they may sit down on the earth". On this occasion, people do not seem to be so packed because there is plenty of room. ...
Article
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We have studied Jesus Christ’s speeches contained in The Gospel as revealed to me by Maria Valtorta to assess: (i) similarities and differences of the speeches delivered to diverse audiences, through deep-language statistics; (ii) duration of the speeches delivered in different occasions; (iii) whether the setting of the speeches is realistic. Mathematically, the speeches can be divided into two sets: (a) two apparently well-planned and coordinated series of speeches delivered at “Clear Water” and at the Horns of Hattin (Sermon of the Mountain); (b) extempore speeches delivered in many localities (parables, speeches to people or to disciples, in Synagogues, at the Temple). By converting sequences of words into intervals, through a suitable reading/speaking speed, the speeches’ durations were found to be realistic. The setting of the speeches allows the assessment of the likelihood of the places and occasions for delivering them. Maria Valtorta wrote extraordinary speeches that she attributed to the alleged Jesus of Nazareth. In addition to their theological and doctrinal contents (whose study is far beyond the scope of this paper), the speeches are so realistic in whatever mathematical parameter, or setting, we study them, that she is either a great literary author, or—as she claims—an attentive “eyewitness” of what she reports.
... Using experimental values for ν and c 0 result in a compact equation solely in terms of frequency. For sound attenuation in fresh water at 20 • C, the bulk thermoviscous absorption coefficient can be written as[4]:α tv ≈ 2.17 × 10 −13 f 2 dB/m (2.36)For the BRP, the maximum length of any side is 8.54 m. Therefore, if each pressure wave travels two lengths of the pool, and there is only 0.1 dB of attenuation over that distance, the lowest frequency to achieve that amount of loss is approximately 164 kHz. ...
... Accordingly, frequencies below 160 kHz experience less than 0.1 dB of loss over two lengths of the longest side of the pool. And at frequencies below 20 kHz in fresh water at 20 • C, thermoviscous attenuation can be entirely neglected[4].Conversely, sound waves in large enclosures filled with water experience dissipation governed primarily by wall losses. Equation 2.23 defines the equivalent absorptive area, ...
Technical Report
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Laboratory experiments have suggested that thermoacoustic engines can be incorporated within nuclear fuel rods. Such engines would radiate sounds that could be used to measure and acoustically-telemeter information about the operation of the nuclear reactor (e.g., coolant temperature or fluxes of neutrons or other energetic particles) or the physical condition of the nuclear fuel itself (e.g., changes in temperature, evolved gases) that are encoded as the frequency and/or amplitude of the radiated sound [IEEE Measurement and Instrumentation 16(3), 18-25 (2013)]. For such acoustic information to be detectable, it is important to characterize the vibroacoustical environments within reactors. Measurements will be presented of the background noise spectra (with and without coolant pumps) and reverberation times within the 70,000 gallon pool that cools and shields the fuel in the 1 MW research reactor on Penn State’s campus using two hydrophones, a piezoelectric projector, and an accelerometer. Several signal-processing techniques will be demonstrated to enhance the measured results. Background vibrational measurement were also taken at the 250 MW Advanced Test Reactor, located at the Idaho National Laboratory, using accelerometers mounted outside the reactor’s pressure vessel and on plumbing will also be presented. The detectability predictions made in the thesis were validated in September 2015 using a nuclear fission-heated thermoacoustic sensor that was placed in the core of the Breazeale Nuclear Reactor on Penn State’s campus. Some features of the thermoacoustic device used in that experiment will also be revealed. [Work supported by the U.S. Department of Energy.]
... However, if absorption coefficient as a function of frequency ( () f  ) of materials is known, exact acoustic pressure waves could be obtained. Since the absolute value of acoustic pressure reflection coefficient ( [18,19], the exact acoustic pressure in the silo may be further derived. ...
Article
This work presents an approach for measuring material volumes in a closed cylindrical silo by using acoustic waves and resonance frequency analysis of silo’s acoustic systems. With an assumption that the acoustical systems were linear and time-invariant, frequency responses of the systems were identified via measurement. A sine sweep was generated, amplified and fed to a loudspeaker inside the silo. Acoustic waves were picked up by a microphone and processed to yield the silo's frequency response. Resonance frequencies and wave mode numbers of standing waves in the frequency range below 900 Hz were analyzed and used for calculation of air-cavity lengths. With known silo's dimension, the material volume estimations were achieved. Sets of experiments for estimating volumes of sand, cement, water, rice grain, and stone flakes in a closed silo, were done. It was found that the approach could successfully estimate the volumes of sand, cement, and water with a satisfactory accuracy. Percent errors of the estimations were less than 3% from the actual volumes. However, the approach could not estimate the volume of rice grain and stone flakes, since their sound refractions were neither resulted in standing waves nor acoustical modes in the silo.
... As noticed in Figure 4.11, 0% NR sample nearly similar like the sample of Ijuk and Kenaf 0% NR. The wave pattern with a slender drop at midrange frequency illustrates that this sample under the porous category which damps the travelling sound wave [14]. The results of the past study by Hosseini Fouladi et al. [15] using Coir at 50mm gives the parallel result with Coir 0% NR sample in this study. ...
... Le modèle linéaire de propagation acoustique auquel nous nous intéressons, prend en compte la diffraction du faisceau acoustique et l'atténuation. Le transducteur est caractérisé par le modèle de vibration harmonique d'un piston plan d'amplitude U ac et de pulsation ω = 2π f (Blackstock, 2001) dont chaque point émet une onde de pression sphérique atténuée supposée égale à : ...
Thesis
Le brassage acoustique présente une alternative prometteuse pour l'amélioration des procédés de purification pendant la solidification du silicium photovoltaïque. Dans cette étude, on s'intéresse à la caractérisation de l'efficacité d'un brassage par acoustic streaming pour favoriser le phénomène de ségrégation. Nous avons ainsi développé une approche expérimentale originale basée sur des démonstrateurs en eau des phénomènes présents lors de la solidification. Cette démarche s'appuie sur une analogie entre d'une part la diffusion solutale des impuretés à travers la couche limite, au niveau du front de solidification, pendant le processus de croissance cristalline dans les fours de solidification, et d'autre part la diffusion des ions à travers la couche limite à la surface de l'électrode dans une cellule électrochimique. En effet, l'application des méthodes d'électrochimie analytique (polarographie), nous a permis de caractériser le transfert de masse au voisinage d'une paroi et de suivre son amélioration sous l'effet d'un jet impactant généré par une source acoustique continue au sein du fluide. La cohérence des résultats expérimentaux avec des simulations hydrodynamiques a été également examinée. En vue d'étendre les résultats obtenus dans l'eau à d'autres fluides notamment les métaux en phase liquide, on présente, dans la dernière partie de ce manuscrit, les différents paramètres de similitude permettant une description complète de l'expérience en fonction du fluide choisi : la géométrie, l'acoustique et l'hydrodynamique. Nous présenterons ensuite, le cas particulier d'un dispositif expérimental utilisant du galinstan.
... During the measurement, temperature (23±1 • C) and humidity (52±1 RH%) were monitored, both to comply with the instrumentation operating conditions, and to take into account their influence on the ultrasounds [30], [31], [32]. ...
Article
An ultrasonic heading measurement method, working under magnetic interference prohibitive for magnetometers, was prototyped, validated, and metrologically characterized. Two capacitive ultrasonic transducers convert the mechanical rotation in two correspondingly time-delayed electrical sine waves. Then, the time delay is estimated using the standard tree parameter sine-fitting algorithm. The prototyped goniometer achieves the same repeatability level (< 36 mrad) of a magnetometer-based heading in the range [-437 mrad, 437 mrad]. Simultaneously, a throughput of 505 Sa/s is proved on an STM32F303xC Arm® Cortex® -M4 32-bit micro-controller. An interference analysis revealed the experimental deterministic error well explained by the combined effect of beacon and receiver directivity, as well as by the relative position of beacon, receiver, and reflective surfaces. Noise robustness was assessed in case of SNR decayed to 9.1 dB from the initial value of 36.6 dB: the maximum deterministic error in the range [-437 mrad, 437 mrad] increased less than 10% (from 21 mrad to 23 mrad in absolute value).
... We demonstrate here that attenuation measurements (validated by PIG tracking) prove to be a valuable feature for assessing the inner status of the pipeline. For single-phase fluids, the specific attenuation ˛ of acoustic waves propagating within the pipe can be expressed as follows (Blackstock and Atchley 2001): ...
Article
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The formation of deposits is a very common issue in oil and gas pipeline transportation systems. Such sediments, mainly wax and paraffine for crude oil, or hydrates and water for gas, progressively reduce the free cross-sectional area of the pipe, leading in some cases to the complete occlusion of the conduit. The overall result is a decrease in the transportation performance, with negative economic, environmental, and safety consequences. To prevent this issue, the amount of inner deposits must be continuously and accurately monitored, such that the corresponding cleaning procedures can be performed when necessary. Currently, the former operation is still dictated by best-practice rules pertaining to preventive or reactive approaches, yet the demand from the industry is for predictive solutions that can be deployed online for real-time monitoring applications. The paper moves toward this direction by presenting a machine learning methodology that leverages pressure measurements to perform online monitoring of the inner deposits in crude oil trunklines. The key point is that the attenuation of pressure transients within the fluid is dependent on the free cross-sectional area of the pipe. Pressure signals, collected from two or more distinct locations along a pipeline, can therefore be exploited to estimate and track in real time the presence and thickness of the deposits. Several statistical indicators, derived from the attenuation of such pressure transients between adjacent acquisition points, are fed to a data-driven regression algorithm that automatically outputs a numeric indicator representing the amount of inner pipe debris. The procedure is applied to the pressure measurements collected for one and a half years on discrete points at a relative distance of 40 and 60 km along an oil pipeline in Italy (100 km length, 16-in. inner diameter pipes). The availability of historical data prepipe and postpipe cleaning campaigns further enriches the proposed data-driven approach. Experimental results demonstrate that the proposed predictive monitoring strategy is capable of tracking the conditions of the entire conduit and of individual pipeline sections, thus determining which portion of the line is subject to the highest occlusion levels. In addition, our methodology allows for real-time acquisition and processing of data, thus enabling the opportunity for online monitoring. Prediction accuracy is assessed by evaluating the typical metrics used in the statistical analysis of regression problems.
... For a traditional local-reacting acoustic liner, it is defined as the ratio of the acoustic pressure and the normal component of the acoustic velocity at the surface of the liner. 26 The acoustic impedance is normalized by the characteristic impedance of air. It is a function of frequency, liner design and geometry, and the aeroacoustic environment in which the liner is installed. ...
Article
The emphasis on increased turbofan fuel efficiency requires advanced turbofan designs that will integrate higher engine bypass ratios and shorter nacelles. The resulting acoustic signature of these designs will have a more broadband character as well as a smaller available area for liner installation. This two-fold impact compels a need for an improvement in the state of the art in liner technology. Increasing the acoustic absorption efficacy over a broader frequency range is a means to address this need. An acoustic liner development and optimization process was conceived and employed to achieve and demonstrate an improved broadband liner design concept. A series of increasing technology readiness level liner studies were conducted to enhance the optimization methodology while validating the concept. This progression spanned several NASA Aeronautics Research Mission Directorate programs/projects due to its relevance. This article reviews the development and evaluation process of the multi-degree-of-freedom liner technology concept from formation through simple experimental models to a flight test over an approximate 10-year period, focusing on the discrete tests comprising the development.
... We first verified our ability to measure distances, as well as the signal decay due to attenuation in air given that ultrasound signal attenuation is significant at MHz frequencies [14]. We used a setup consisting of a pair of transducers aimed at a flat target attached to a linear translation stage (Test bench 1, Figure 2A). ...
Article
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Most eye tracking methods are light-based. As such, they can suffer from ambient light changes when used outdoors, especially for use cases where eye trackers are embedded in Augmented Reality glasses. It has been recently suggested that ultrasound could provide a low power, fast, light-insensitive alternative to camera-based sensors for eye tracking. Here, we report on our work on modeling ultrasound sensor integration into a glasses form factor AR device to evaluate the feasibility of estimating eye-gaze in various configurations. Next, we designed a benchtop experimental setup to collect empirical data on time of flight and amplitude signals for reflected ultrasound waves for a range of gaze angles of a model eye. We used this data as input for a low-complexity gradient-boosted tree machine learning regression model and demonstrate that we can effectively estimate gaze (gaze RMSE error of 0.965 ± 0.178 degrees with an adjusted R2 score of 90.2 ± 4.6).
... As already explained, the main advantage of an annular ring is its capability to be axially focused; focus depth tunability, beam diameter at the focus point, and range of achievable pressure are its main parameters. The focus depth, F d , is defined by Equation (1), where S is the transducer area (whatever its shape), λ is the wavelength, f is the frequency, and c is the sound velocity in the propagation medium [18]. It is evident that transducers with the same area will produce a greater focus depth with higher frequency. ...
Article
This paper presents a multielement annular ring ultrasound transducer formed by individual high-frequency PMUTs (17.5 MHz in air and 8.7 MHz in liquid) intended for high-precision axial focalization and high-performance ultrasound imaging. The prototype has five independent multielement rings fabricated by a monolithic process over CMOS, allowing for a very compact and robust design. Crosstalk between rings is under 56 dB, which guarantees an efficient beam focusing on a range between 1.4 mm and 67 µm. The presented PMUT-on-CMOS annular array with an overall diameter down to 669 µm achieves an output pressure in liquid of 4.84 kPa/V/mm2 at 1.5 mm away from the array when the five channels are excited together, which is the largest reported for PMUTs. Pulse-echo experiments towards high-resolution imaging are demonstrated using the central ring as a receiver. With an equivalent diameter of 149 µm, this central ring provides high receiving sensitivity, 441.6 nV/Pa, higher than that of commercial hydrophones with equivalent size. A 1D ultrasound image using two channels is demonstrated, with maximum received signals of 7 mVpp when a nonintegrated amplifier is used, demonstrating the ultrasound imaging capabilities.
... For more than 50 years, nonlinear acoustics have been used in a variety of industries; from medical ultrasound to underwater detection, microfluidics to acoustic levitation [51,52]. These applications are governed by a well characterized set of physical wave equations [53,54]. In broad terms, acoustics can be precisely and intelligently controlled to coalesce and remove particles from a carrier fluid in a continuous, non-fouling, scalable process. ...
Chapter
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The biopharmaceutical industry is maturing, which is leading to increased competition and regulatory expectations. We discuss these pressures on the biopharmaceutical industry and the drive to reduce cost and improve quality and flexibility. In this context, the pros and cons of the continuous bioprocessing have been addressed and a compelling case has been made for the adoption of continuous bioprocessing. The transformative technologies showcased in this chapter include Acoustic Wave Separation (AWS), Multicolumn chromatography, virus inactivation and single-pass tangential flow filtration (SPTFF). Recent efforts by the companies invested in the continuous platform have been presented along with the prospects of this exciting new technology.
... These terms are named based on their mathematical description: no divergence operator for the monopole term, the single divergence operator for the dipole term, and the double divergence operator for the quadrupole term. Although these source terms resemble those with the same names in classical acoustics [66], here the sources are modeled by flow field properties and are typically moving. Therefore, the monopole, dipole, and quadrupole terms do not have the expected directivity patterns that are well known in classical acoustics. ...
Thesis
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https://etda.libraries.psu.edu/catalog/19898zug117 This thesis makes contributions to two important aspects of computing the time-varying rotor noise of electrical vertical take-off and landing (eVTOL) aircraft for urban air mobility (UAM) applications: the time variation of rotor broadband noise, and noise due continuously-varying rotor angular speed. The noise prediction software PSU-WOPWOP was updated to compute the broadband noise spectrum as a function of observer time within a rotor period. Time-varying broadband noise spectra and directivity computations for helicopter main rotors in forward flight show significant modulation with the blade passage frequency, due to convective amplification and retarded-time effects. Qualitative agreement between noise predictions and flight test data was obtained. The noise prediction software PSU-WOPWOP was also updated to compute the discrete frequency noise of rotors with continuously-varying rotational speed, which may require accepting input kinematics and aerodynamic loading data at unevenly-spaced source time intervals. Order of magnitude analysis and numerical simulations demonstrated that thickness noise modulations caused by variable rotor speed are primarily due to the time variation of instantaneous rotor speed, rather than angular acceleration, for typical rotor speed variations expected for manned eVTOL aircraft.
... Once ( ) is specified, the storage modulus and loss modulus can be obtained from the real and imaginary parts of ( ), respectively. Furthermore, the complex wavenumber ̂ is related to the bulk modulus (Blackstock 2000;Carstensen and Parker 2014) as: ...
Preprint
The quantification of liver fat as a diagnostic assessment of steatosis remains an important priority for noninvasive imaging systems. We derive a framework in which the unknown fat volume percentage can be estimated from a pair of ultrasound measurements. The precise estimation of ultrasound speed of sound and attenuation within the liver are shown to be sufficient for estimating fat volume assuming a classical model of the properties of a composite elastic material. In this model, steatosis is represented as a random dispersion of spherical fat vacuoles with acoustic properties similar to those of edible oils. Using values of speed of sound and attenuation from the literature where normal and steatotic livers were studied near 3.5 MHz, we demonstrate agreement of the new estimation method with independent measures of fat. This framework holds the potential for translation to clinical scanners where the two ultrasound measurements can be made and utilized for improved quantitative assessment of steatosis.
... Conversely, thermal and viscous effects are significant in the narrow slits. The sound propagation is then governed by linearized Navier Stokes equations [14]. The mesh density along the horizontal walls of the slits is increased in order to improve the resolution of acoustic boundary layers. ...
Conference Paper
Acoustic test fixtures (ATFs) can be used to measure the insertion loss (IL) of earplugs. Reliable numerical modeling of the occluded artificial ear canal of the ATF could be helpful for optimizing the earplug performance during the design phase. This requires the simulation of the IEC 60318-4 occluded ear simulator which is usually based on the classical lumped parameter model (LPM) or complete 3D numerical model. Lumped models are generally accepted to have inherent frequency limitations and cannot properly deal with the thermal and viscous phenomena in certain areas of the simulator. 3D numerical models based on the finite element (FE) or boundary element method are capable of accurately describing the simulator behavior taking thermo-viscous effects into consideration but many dimensional details related to the published numerical models of the IEC 60318-4 simulator remain unspecified. This study proposes a transfer matrix (TM) model of the IEC 60318-4 simula-tor whose geometry is determined using Computed Tomography scan images. The specific acoustic impedance of certain elements in the simulator model is deduced using the low reduced frequency (LRF) model which has been proved satisfactory to account analytically for thermo-viscous energy losses. The TM model is validated using a 3D FE model of the simulator based on the same geometric dimensions. It is then coupled to a 2D axisymmetric FE model of an ATF ear canal occluded or not by a silicone earplug to simulate the earplug IL. The coupled FE/TM method is found to provide satisfactory IL prediction compared to a complete 3D FE model of the corresponding system. The proposed TM model is also shown to better capture the simulator behavior compared to the classical LPM.
... In this follow-up study, the cavity length was varied from 0.2 mm to 30 mm. For comparison, the viscous boundary layer thickness was 69.3 µm at 1 kHz, room temperature, and standard pressure [29]. To illustrate the size effect and provide a validation for the experimental study, an FEM model was developed using the Pressure Acoustics (PA) module or the Thermoviscous Acoustics (TA) module, in combination with the acoustics-structure interaction module in COMSOL 5.3a. ...
Article
Full-text available
An air-backed diaphragm is the key structure of most dynamic pressure sensors and plays a critical role in determining the sensor performance. Our previous analytical model investigated the influence of air cavity length on the sensitivity and bandwidth. The model found that as the cavity length decreases, the static sensitivity monotonically decreases, and the fundamental natural frequency shows a three-stage trend: increasing in the long-cavity-length range, reaching a plateau value in the medium-cavity-length range, and decreasing in the short-cavity-length range, which cannot be captured by the widely used lumped model. In this study, we conducted the first experimental measurements to validate these findings. Pressure sensors with a circular polyimide diaphragm and a backing air cavity with an adjustable length were designed, fabricated, and characterized, from which the static sensitivities and fundamental natural frequencies were obtained as a function of the cavity length. A further parametric study was conducted by changing the in-plane tension in the diaphragm. A finite element model was developed in COMSOL to investigate the effects of thermoviscous damping and provide validation for the experimental study. Along with the analytical model, this study provides a new understanding and important design guidelines for dynamic pressure sensors with air-backed diaphragms.
... The medium-resolution analytical model finds the transmission loss by calculating a transmission coefficient for the structure given an incident sound wave. The transmission coefficient accounts for the structure's mass density (m), stiffness (D), damping (η), and incident angle (φ) as seen in Eq. (10) (Blackstock 2000). The stiffness (or structural rigidity) is estimated by adding the stiffness of the concrete panel with that of the concrete rib . ...
Article
In many buildings, structural concrete systems have a large impact on the building's overall weight, embodied energy, and embodied carbon. Efficient structural components could result in building weight reductions, leading to material savings and a reduced carbon footprint. Shaping of concrete slabs through structural optimization has recently seen significant interest due to advancements in digital fabrication and the potential for more sustainable and architecturally expressive designs. However, many promising optimization-based approaches to shaping slabs do not consider secondary design aspects during computational exploration, including acoustics. This paper presents a computational investigation of trade-offs between structural and acoustic objectives using a multiobjective optimization framework while designing concrete slabs with curved ribs. A series of Pareto front approximations and constrained optimization runs at specific acoustic performance levels were used to explore optimal designs, while evaluating how a computational search for competing objectives distributes structural material. Shaped slabs were then compared to conventional floor assemblies. The study shows how slab shaping impacts sound insulation and suggests how designers could incorporate structural-acoustic optimized concrete slabs in building design.
... It should be noted that the problem of the frequency dependence of the Debye potential in a wide frequency range has never been a subject of a special study. The authors of [17] pointed out the virtual independence (NB!) of the IVP amplitude from the ultrasound frequency in the common measurement range (100 kHz-1 MHz), and this is well explained by the fact that the amplitude of the vibrational velocity does not depend on the frequency [20]. To check this prediction, we have attempted [1] to detect IVP appearance at as low a sound frequency as possible. ...
Preprint
In this paper, we considered two phenomena in acoustically excited aqueous solutions of a strong electrolyte. These are the well-known Debye ionic vibrational potential (IVP), and radiofrequency anisotropy we discovered earlier , apparently, for the first time. Since both occur due to the accelerated motion of the solution, we have tried to combine them in one simple model. We have established that for a polarized UHF radio wave passed through a NaCl aqueous solution excited by an acoustic pulse the rotation angle of its vector E is proportional to the integral of the square of the observing IVP over time. An equivalent electrical circuit simulating the observed phenomena has been proposed and tested for physical feasibility. Several arguments are given in favour of the fluid-gyroscopic mechanism of RF anisotropy-related effects. We also found out that the IVP is practically independent of the vibrational velocity for frequencies below 10 kHz and it tends to zero at zero frequency. The latter is consistent with the law of conservation of energy but contradicts the incomplete existing theory.
... where is the maximum pressure without attenuation, which, for a baffled piston (as a transducer), is given as a function of equilibrium density, sound speed, and velocity amplitude as = 2 0 [36]. Basically, as mentioned in [51], factor 2 comes from the fact that the sound source is baffled and that all the radiation emitted by the source is forced into only half of the space (the free space ahead of the piston). In our case, we only consider the forward emission of the radiation inside the enclosure and this factor 2 has not to be introduced. ...
Article
This paper implements the lattice Boltzmann method to simulate the propagation of sound waves in three dimensions. The numerical model is exercised on the lid-driven cavity flow. Tests are then proposed on acoustic situations. The results are first confronted with analytical solutions of the spherical waves emitted by a single point source inside a cubic cavity. Then, we studied the case where the waves are emitted from a circular sound source placed at the center of the left boundary of a parallelepipedic cavity filled with water. With the circular source discretized as a set of point sources, we were able to simulate the wave propagation in 3D and calculate the sound pressure amplitude. Tests using different emission conditions and LBM relaxation times finally allowed us to get good comparisons with analytical expressions of the pressure amplitude along the source axis, highlighting the performance of the lattice Boltzmann simulations in acoustics.
... We can calculate the transmitted incident wave intensity based on the fact that particle velocity and local particle pressures must be continuous across the boundary. When the acoustic impedances of the materials on both sides of the boundary are known, the fraction of the incident wave intensity that is transmitted through the boundary can be calculated as [5]: ...
... A sketch of MCL modeled are shown in Figures 2-4. The solid MCLs are modeled using shell elements and the surrounding air is modeled using Thermoviscous Acoustics and Pressure Acoustic [58]. When vibration waves propagate in a fluid bounded by the surface of MCL, so-called viscous and thermal boundary layers are created at the MCL surfaces. ...
Article
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Micro-Cantilever (MCL) is a thin film structure that is applied for aerosol particle mass sensing. Several modifications to the rectangular MCL (length-to-width ratio, slots at the anchor, serrations at its side edges) are made to deduce the role and influence of the shape of rectangular MCL-based aerosol mass sensors and reduce gas damping. A finite element fluid-structure interaction model was used to investigate the performance of MCL. It is found that (I) the mass sensitivity and quality factor decline with the increasing of length-to-width ratio which alters the resonant frequency of the MCL. The optimum conditions, including the length-to-width ratio (σlw = 5) and resonant frequency (f0 = 540.7 kHz) of the MCL, are obtained with the constant surface area (S = 45,000 μm2) in the frequency domain ranging from 0 to 600 kHz. (II) The slots can enhance the read-out signal and bring a small Q factor drop. (III) The edge serrations on MCL significantly reduce the gas damping. The results provide a reference for the design of aerosol mass sensor, which makes it possible to develop aerosol mass sensor with high frequency, sensitivity, and quality.
... PVDF or PVDF-TrFE were used as the material for preparing an artificial cochlear sensory epithelium with trapezoidal and curved membranes because of its biocompatibility (its toxicity tests have been demonstrated in our previous study [25]). PVDF or PVDF-TrFE are designated as a linear elastic material, and the numerical analysis of the oscillation characteristics for the experimental devices employs the following equation [38]: ...
Article
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Based on the modern microelectromechanical systems technology, we present a revolutionary miniaturized artificial cochlear sensory epithelium for future implantation tests on guinea pigs. The device was curved to fit the spiral structure of the cochlea and miniaturized to a maximum dimension of <1 mm to be implanted in the cochlea. First, the effect of the curved configuration on the oscillation characteristics of a trapezoidal membrane was evaluated using the relatively larger devices, which had a trapezoidal and a comparable curved shape designed for high-precision in vitro measurements. Both experimental and numerical analyses were used to determine the resonance frequencies and positions, and multiple oscillation modes were clearly observed. Because the maximum oscillation amplitude positions, i.e., the resonance positions, differed depending on the resonance frequencies in both trapezoidal and curved membrane devices, the sound frequency was determined based on the resonance position, thus reproducing the frequency selectivity of the basilar membrane in the organ of Corti. Furthermore, the resonance frequencies and positions of these two devices with different configurations were determined to be quantitatively consistent and similar in terms of mechanical dynamics. This result shows that despite a curved angle of 50–60°, the effect of the curved shape on oscillation characteristics was negligible. Second, the nanometer-scale oscillation of the miniaturized device was successfully measured, and the local resonance frequency in air was varied from 157 to 277 kHz using an experimental system that could measure the amplitude distribution in a two-dimensional (2D) plane with a high accuracy and reproducibility at a high speed. The miniaturized device developed in this study was shown to have frequency selectivity, and when the device was implanted in the cochlea, it was expected to discriminate frequencies in the same manner as the basilar membrane in the biological system. This study established methods for fabricating and evaluating the miniaturized device, and the proposed miniaturized device in a curved shape demonstrated the feasibility of next-generation cochlear implants.
Article
In many acoustic components, strong directional response exerts considerable influence on sound wave energy transmission, restricting their widespread applications. Here, we report new designs of an inclined metamaterial channel that enable improved transmission behaviors and broadband performance under variable-angle incident radiation. For the two-dimensional sound wave guide, the tilt angle is tuned to cater for oblique incidences. The inclined metamaterial is modified based on the normal space-coiling sound wave guide with impedance matching layers. At different incident angles, the inclined waveguides are capable of providing proper gradient parameter distributions to match the impedance value of the outside environment and the inner structure. Both experimental and numerical results show that the inclined metamaterial designs improve the broadband transmission efficiency for 2 kHz with specific incident angles. The anomalous refraction behaviors are demonstrated based on the inclined metamaterial units, showing a huge potential for wavefront engineering and acoustic transparency.
Article
Full-text available
In this paper, we focus on two-dimensional solid/fluid phononic crystal in megahertz range. The case of Ethanol rods embedded in a ceramic lattice has been computed. The plane wave expansion method is used to calculate the dispersion relations which are in good agreement with the transmitted sound pressure level spectra established by the finite element method. Results show that this structure exhibit some absolute bandgaps with suitable bandwidth. So with the help of adding suitable defects, and by introducing methyl nonafluorobutyl ether as a defect inclusion, perfect modes were obtained among bandgaps region. Also, by designing a quasi-periodic structure and with the help of coherent cavities, a distinct frequency was obtained. So, by combining a row of defect rods as a moderate waveguides and designed quasi-periodic structure, we led to the design of acoustic add/drop filter. The designed filter receives the frequencies range from f=1.47MHz to f=1.51MHz and send them in to one distinct output with high confinement and due to the quasi-periodic structure frequency f=1.498MHz is use as the add-drop frequency.
Article
Materials with properties that can be described by a near-zero index of refraction have received significant attention in the fields of electromagnetics, optics, and acoustics, due to their extraordinary capabilities in wave manipulation. It was recently demonstrated theoretically and experimentally that acoustic waves could manifest near-zero-index propagation based on the effective compressibility of a waveguide channel approaching zero. In turn, this allows tunneling of acoustic waves with nearly infinite wavelength (or equivalently, uniform phase) when the channel cross section is much larger than the feeding lines. Here, we show that these concepts can be leveraged to realize an acoustic power divider and multiplexer offering tunneling of sound to an arbitrary number of output ports, with phase shifts equal to 0° or 180° and robust response to variations in the port position. We present analytical and numerical models describing the properties of this device and study limitations and trade-offs that occur in the presence of losses as the device size is scaled.
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Cuando una superficie vibra comprimiendo el medio que tiene delante, genera ondas acústicas. Este es el caso de los altavoces, que generan ondas acústicas a frecuencias audibles mediante una superficie móvil. En este trabajo presentamos un tutorial para modelizar la radiación acústica de superficies vibrantes, diferenciando entre geometrías circulares planas y curvadas. En primer lugar, derivaremos los modelos que describen la radiación de superficies móviles, y obtendremos soluciones analíticas para los casos más simples. Para los más complejos, se integrará numéricamente. Ambas soluciones se han incorporado a una interfaz gráfica sencilla, con las que se puede visualizar el campo acústico generado por las distintas superficies al variar sus características de radiación. La metodología propuesta permite profundizar en el análisis de la radiación de ondas acústicas, y presentar un ejemplo de modelización para estudiantes de Acústica, desde la modelización hasta la obtención de soluciones analíticas y numéricas.
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The aim of this study is to investigate the effect of morphologies and the structure of polyurethane-based coatings created by different colour pigments, on sound transmission loss properties. To achieve this goal, coatings were created in different concentrations of 5%, 7% and 9% with red, green, orange and yellow pigments. The coatings were applied on glass surfaces and the sound transmission loss was measured by an experimental arrangement containing a microphone and a decibel meter. The effect of surface tension energy, surface roughness, reflection percentages and concentration of pigments were found to be negligible on the sound transmission loss, whereas the LAB colour codes have a determining effect. In the scope of this study, a new method and mathematical model were created to help measure the sound transmission loss on a surface, in which sound signal was carried with a laser beam via a system created in the laboratory.
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In the arc welding and arc additive manufacturing processes, utilizing self-induced ultrasound has attracted widespread attention for obtaining intensive arc plasma and optimizing metallurgical characteristics of molten pool, featuring with increased penetration, suppressed dendrites and refined grains in the deposited layer and weld joint of metal. However, the ultrasound emitting mechanism remains unclear and process optimization remains limited by incomplete understanding of ultrasound in the arc plasma and molten pool. In our work, Multiscale experiments and modeling (MHD and MHD waves modeling at meso scale, coupled phase-field and fluid flow modeling and fluid-structure modeling at micro scale) are proposed to reveal the physical essence of ultrasound generation, ultrasound induced streaming, suppressed dendrites growth and dendrites fragmentations. It demonstrates the effectiveness and efficiency of utilizing self-induced ultrasound in controlling microstructures of 316 stainless steel with a maximum of 24% decrease in grain size and transition from anisotropy orientation to isotropy orientation, and concrete directions of process optimization arc identified for facilitating the successful industrial use. We expect introducing self-induced ultrasound energy could be a more efficient and cost effective technology for controlling of microstructure in the arc metal processing related fields.
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The quantification of liver fat as a diagnostic assessment of steatosis remains an important priority for non-invasive imaging systems. We derive a framework in which the unknown fat volume percentage can be estimated from a pair of ultrasound measurements. The precise estimation of ultrasound speed of sound and attenuation within the liver is found to be sufficient for estimating fat volume assuming a classic model of the properties of a composite elastic material. In this model, steatosis is represented as a random dispersion of spherical fat vacuoles with acoustic properties similar to those of edible oils. Using values of speed of sound and attenuation from the literature in which normal and steatotic livers were studied near 3.5 MHz, we describe agreement of the new estimation method with independent measures of fat. This framework holds the potential for translation to clinical scanners with which the two ultrasound measurements can be made and used for improved quantitative assessment of steatosis.
Conference Paper
View Video Presentation: https://doi.org/10.2514/6.2022-2562.vid Safety earmuffs and earplugs are often worn by personnel exposed to high sound pressure levels, such as flight deck crews on aircraft carriers, in order to prevent noise-induced hearing loss. Personal protective equipment, specifically earplug-style hearing protection, are not typically molded to the ear of the wearer. As a result, small spaces, which serve as flanking paths or leakage for sound, can exist between the ear canal wall and earplug due to differences in geometry between individual ear canals. The purpose of this work is to model and study the frequency-dependent acoustic transmission loss (TL) of these flanking paths by varying their diameter and shape using quantified representative small orifices in 3D printed plates, and investigating how flanking paths can affect the noise blockage performance of three commercial earplugs made of silicone putty, soft foam, or rubber silicone sealed with and without a petroleum jelly (Vaseline). The frequency-dependent acoustic TL is measured utilizing a two-sided, two-microphone TL tube using an impulse method. Analytical modeling predictions based on circular axisymmetric models of the flanking paths are compared with computed COMSOL numerical modeling and experimental results.
Article
This work describes the development of an acoustic sensor based on piezoelectric ZnO thin film to be utilized for aero-acoustic measurements. The design of the device was carried out through CAD tool Coventorware. The backside of the device consists of the microtunnel and diaphragm structures. The Si-diaphragm thickness of the device was optimized for high sound pressure level (SPL) (upto 180 dB) using Coventorware. A microtunnel connects the cavity, created after diaphragm formation to the outside environment. The designed device has been fabricated using standard Si-fabrication technology. Microtunnel and diaphragm structures have been fabricated in a single step using wet etching technique which results in reduced cost as well as fewer number of process steps and increased yield of the device. The front side consists of a piezoelectric sensing layer of ZnO sandwiched between two sputter deposited electrode layers of Au covered with PECVD oxide on a thermally oxidized Si-diaphragm. The low cut-off frequency, bandwidth, resonance frequency and flat band sensitivity of the device have been found to be 35.2 Hz, 15 kHz, 78 kHz and 136.5 μV/Pa respectively. The fabricated device can be used for the SPL measurement in aircrafts, aerospace and similar applications.
Conference Paper
The aeroacoustic properties of porous fabrics are investigated experimentally in an effort to find a porous fabric as an ideal interface between wind tunnel flow and quiescent conditions. Currently, the commercially available Kevlar type 120 fabric is widely used for similar applications, such as side-walls in hybrid anechoic wind tunnels or as a cover of phased microphone arrays. A total number of 8 fabrics were investigated, namely, four glass fiber fabrics, two plain weave Kevlar fabrics, and two modified plain Kevlar fabrics with their pores clogged. Two, custom-made rigs were used to quantify the transmission loss and self-noise of all eight fabrics. It was found that the pores serve as a low-resistance gateway for sound waves to pass through, hence enabling a low transmission loss. The transmission loss was found to increase with decreasing open area ratio while other fabric properties had a minor impact on transmission loss. The self-noise of the fabrics has also been evaluated and it was found that the thread density (thread per inch) is a primary factor of determining the frequency range of self-noise with the open area ratio potentially playing a secondary role in the self-noise levels. For both metrics, the mass per unit area seemed to play a minor role in the aeroacoustic performances of the fabrics. Finally, surface pressure measurements revealed that the commercially available plain Kevlar (type 120) has no quantifiable effect on the hydrodynamic pressure field passing over the fabric, suggesting that Kevlar behaves as a no-slip wall from the flow's perspective when no pressure difference is present on the two sides of the fabric.
Article
High-density acoustic energy harvesting is one of the power solutions for wireless sensor network nodes in the Internet of Things. In this paper, we present a novel metamaterial and Helmholtz coupled resonator (MHCR) to enhance the sound energy density by energy focusing and pressure amplification. Metamaterial refers to a type of structural composite material, usually periodic. The local modification of the material by introducing a defect can make the wave at the defect band frequency be confined to the defect area to achieve acoustic energy focusing. The Helmholtz resonator is added to the defect of the metamaterial to amplify the focused sound waves. The variation in channel pressure causes the plug of the air in the neck to oscillate in and out, producing adiabatic compression and expansion of the air in the cavity to amplify sound pressure. The mathematical models of band structure, resonant frequency, vibration amplitude with vibroacoustic coupling and output voltage with electromechanical coupling are developed to design MHCR. The maximum voltage of the coupled energy harvester was about 3.5 times that of the maximum voltage of the metamaterial energy harvester. Field tests illustrated the effectiveness of the proposed MHCR with the maximum transmission ratio of 30.83 mV/Pa in mechanical noise environment, which was 48 times the maximum transmission ratio of the metamaterial energy harvester in the chirping of cicadas.
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The emphasis on increased turbofan fuel efficiency requires advanced turbofan designs that will integrate higher engine bypass ratios and shorter nacelles. The resulting acoustic signature of these designs will have a more broadband character as well as a smaller available area for liner installation. This two-fold impact compels a need for an improvement in the state of the art in liner technology. Increasing the acoustic absorption efficacy over a broader frequency range is a means to address this need. NASA investigated over-the-rotor acoustic liners for turbofan applications as a potential solution. This type of liner represents a significant advance over traditional liners due to placement in close proximity to the rotor. An advantage of placing treatment in this region is a modification of the acoustic near field, thereby inhibiting noise generation mechanisms. This can result in higher attenuation levels than could be achieved by the conventional sound absorption means. In addition, there is potential to integrate the liner with fan rub-strip and containment components, reducing engine components and thus weight, enabling a systematic enhancement in noise reduction and engine performance. This article reviews the development and evaluation process of three unique over-the-rotor concepts focusing on the discrete tests conducted across the Technology Readiness Level span.
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Therapists’ struggle to construct the meaning of their patients’ communications includes listening to their musical aspects such as intonations and rhythms. Similarly, supervisors listen to the musical aspects of their supervisees’ therapeutic narratives to construct their unsymbolized meanings and to identify the patients’ voices concealed in the supervisees’ voices. To describe supervisors’ listening processes, I propose the echo chamber metaphor along with the metaphors of evenly hovering attention and dreaming. The metaphoric echo chambers help supervisors in their listening processes by magnifying the sound signals in the supervisees’ voices and by highlighting their richness and uniqueness. Two main devices of echo chambers—adjusting the reverberation time of sounds and using specific surfaces to reflect these sounds can be effectively compared to inner devices used by supervisors while listening to their supervisees’ discourses.
Article
Silica nanoparticle-impregnated Kevlar (SNK) fabric has better specific ballistic performance in comparison to its neat counterparts. For multifunctional structural applications using lightweight composites, combining this improved ballistic functionality with an acoustic functionality is desirable. In this study, acoustic characterization of neat and SNK samples is conducted using the normal-incidence impedance tube method. Both the absorption coefficient and transmission loss (TL) are measured in the 60–6000 Hz frequency range. The influence of parameters such as number of layers of neat or treated fabric, percentage by weight of nanoparticle addition, spacing between fabric layers, and residual porosity is examined. It is found that while absorption decreases with an increase in nanoparticle addition for frequencies above about 2500 Hz, increasing the number of layers shifts peak absorption to lower frequencies. By introducing an air-gap behind the fabric layer, dominant low-frequency (1000–3000 Hz) absorption peaks are obtained that correlate well with natural modes of mass-equivalent thin plates. Examining the influence of residual porosity by laminating the SNK samples reveals that it contributes to about 30–50% of the total absorption. Above about 1500 Hz, 3–5 dB of TL increase is obtained for SNK samples vis-à-vis the neat samples. TL is found to increase beyond that of the neat sample above a threshold frequency when an air-gap is introduced between two SNK layers. With an increase in the weight of nanoparticle addition, measured TL tends to be closer to mass law predictions. This study demonstrates that SNK fabric could provide improved acoustic performance in addition to its ballistic capabilities, making it suitable for multifunctional applications and could form the basis for the development of simplified models to predict the structural acoustic response of such nanoparticle–fabric composites.
Article
Full-text available
We derive an analytical solution for the acoustic streaming inside a rigid tube resulting from a pseudo-standing wave field, generated by two counterpropagating travelling waves. We solve the second-order axisymmetric problem that follows from the perturbation expansion of the governing equations. In the process, we impose no restriction on the diameter of the tube with respect to the thickness of the viscous boundary layer and acoustic wavelength. The derived solution is then used to study the evolution of streaming patterns inside the tube when geometrical and material parameters are varied. We show how the Schlichting streaming torus at the wall bounds the Rayleigh streaming near the axis of the tube. Decreasing the ratio (Ξ) of the tube radius to the viscous boundary layer thickness gradually expands the Schlichting streaming, suppressing the Rayleigh streaming. Considering the average mass transport velocity, the Rayleigh streaming vanishes at the critical ratio Ξ_S=6.2. The critical ratio is independent of fluid properties in the limit of large acoustic wavelength relative to the radius of the tube (Λ). When Λ decreases towards unity, large-scale Eckart-like streaming develops near the axis, superseding the Rayleigh streaming, while the Schlichting streaming remains at the wall. In addition, we demonstrate the relevance of the compressibility of the streaming flow and of the full inclusion of the spatial variation of the Reynolds stress that acts as the streaming source. The study is especially relevant for microfluidic systems, wherein the viscous boundary layer can reach significant thicknesses.
Chapter
The fluid mechanics equations, from which the acoustics equations and results may be derived, are quite complicated. The most important equation, the wave equation, is presented in this chapter together with some of its solutions. Such solutions give the sound pressure explicitly as functions of time and space, and the general approach may be termed the wave acoustics approach. The chapter presents some of the useful results of this approach but also briefly discusses some of the other alternative approaches, sometimes termed ray acoustics and energy acoustics, that are used when the wave acoustics approach becomes too complicated. Some of the basic concepts of sound wave propagation are also discussed. Three‐dimensional wave equation is useful if sound wave propagation in rectangular spaces such as rooms is being considered. Standing‐wave phenomena are observed in many situations in acoustics and the vibration of strings and elastic structures.
Article
Focused ultrasound (FU) is a hyperthermia-induced method for the treatment of thyroid tumors. FU has the privilege of ablating the cancer tissue, while preserving the healthy tissue from undesired damage. Inaccuracies in the temperature evaluation reduces the treatment effectiveness; therefore, the present study through experimental and numerical analysis of FU presents a new approach to increase the accuracy of temperature estimation. Our study encompasses novelty by conducting a thermal analysis based on the porous structure of thyroid nodule. The thyroid tumor specimens are exposed to the ultrasound wave irradiation while the temperature elevation is accurately monitored and measured at the focal point. To numerically model the problem, the thyroid tumors are considered as porous media. The sample porosities are determined using Field Emission Scanning Electron Microscopy (FESEM) imaging system. The thermal properties are averaged over vascular and extravascular regions as the fluid and solid phases, respectively. It is observed that the focal point temperature can be predicted numerically with results being within 0.06% of those measured experimentally. The use of classical bio-heat transfer model, to predict the focal point temperature, has also been tested with results within 0.39% of the experimental data. The structural-based bio-heat transfer model is used to determine the extent of the necrotic area at different transducer powers. Results show that based on a porous medium approach, an irreversible necrosis does not occur at 5 W ultrasound power, while more than half of the thyroid tumor would be destructed when the power is increased to 10 W.
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