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International audience; Although it can be transformed by various electronic devices, the sound of the solid body electric guitar originates from, and is strongly linked with, the string vibration. The coupling of the string with the guitar alters its vibration and can lead to decay time inhomogeneities. This paper implements and justifies a framework for the study of decay times of electric guitar tones. Two damping mechanisms are theoretically and experimentally identified: the string intrinsic damping and the damping due to mechanical coupling with the neck of the guitar. The electromagnetic pickup is shown to not provide any additional damping to the string. The pickup is also shown to be far more sensitive to the out-of-plane polarization of the string. Finally, an accurate prediction of the decay time of electric guitar tones is made possible, whose only requirements are the knowledge of the isolated string dampings and the out-of-plane conductance at the neck of the guitar. This prediction can be of great help for instrument makers and manufacturers.

The acoustic transmission coefficient of a resonant sonic crystal made of hollow bamboo rods is studied experimentally and theoretically. The plane wave expansion and multiple scattering theory (MST) are used to predict the bandgap in transmission coefficient of a non-resonant sonic crystal composed of rods without holes. The predicted results are validated against experimental data for the acoustic transmission coefficient. It is shown that a sonic crystal made from a natural material with some irregularities can exhibit a clear transmission bandgap. Then, the hollow bamboo rods are drilled between each node to create an array of Helmholtz resonators. It is shown that the presence of Helmholtz resonators leads to an additional bandgap in the low-frequency part of the transmission coefficient. The MST is modified in order to account for the resonance effect of the holes in the drilled bamboo rods. This resonant multiple scattering theory is validated experimentally and could be further used for the description and optimization of more complex resonant sonic crystals.

It has been suggested that the first spectral peak and the first two spectral notches of head-related transfer functions (HRTFs) are cues for sound localization in the median plane. Therefore, to examine the mechanism for generating spectral peaks and notches, HRTFs were calculated from four head shapes using the finite-difference time-domain method. The comparison between HRTFs calculated from the whole head and the pinna-related transfer functions calculated from the segmented pinna indicated that the pinna determines the basic peak-notch pattern of the HRTFs. An analysis of the distribution patterns of pressure nodes and anti-nodes on the pinna computed in the steady state for sinusoidal excitations confirmed that the first three peaks correspond to the first three normal modes of the pinna. The analysis also revealed that at the first spectral notch frequencies, one or two anti-nodes appeared in the cymba and the triangular fossa, and a node developed in the concha. Furthermore, according to changes in the instantaneous pressure distribution patterns on the pinna, three types of mechanisms were hypothesized for inducing the node in the concha depending on the source elevation angle.

Measurements of signals generated over the New England mud patch, an area of ocean roughly 70 m deep characterized by a 10 m thick surficial mud-layer, by the Intensity Vector Autonomous Recorder (IVAR) are presented. IVAR is a bottom deployed system that measures both potential and kinetic energy roughly 1.2 m above the seafloor. Data originate from signals generated by a towed J15 source (transmission in the 50–500 Hz band), and signal underwater sound (SUS) MK-64 explosive sources, both part of the SCE17 signal set, and individual modes are identified by their unique Doppler shifts and/or through time-frequency analysis of dispersion. The density contrast between water and mud manifests a concentration kinetic energy in the water column, specifically when the water/mud interface intersects a node of the vertical mode functions. Following the work of Tolstoy (JASA 28(6), 1182–1192, 1956), data observations are fit to a representative sediment model through coupling two reduced waveguides, one representing the water column and the other the layered sediment, at their lattice points. The persistence of a resonance, which occurs at intersecting lattice points, is examined in terms of the range dependence in water depth and sediment structure.

Stable acoustical tweezers and particle manipulation using vortex beams have recently been accomplished in air [Nature Commun. 6: 8661 (2015)] and in water [Phys. Rev. Lett. 116: 024301 (2016)]. In both configurations, a particle is trapped along the propagation axis of a focused vortex, where the acoustic field exhibits a pressure node. More recently, a stable orbital motion of a particle trapped off-axis was achieved by alternating between two counter-rotating vortices [Phys. Rev. Lett. 120: 044301 (2018)]. However, this kind of orbital motion had not been possible so far with a steady helical field having a single angular momentum state. In this work, we present the first experimental evidence of the simultaneous 3D trapping and stable orbiting of millimeter-sized particles in air due to angular momentum transfer in a standing wave trap created by the interference of two vortices. In contrast with previous work, the two vortices have the same helicity with respect to the laboratory reference frame, and thus the angular momentum of this field is well-defined. A description of the particle kinematics as a function of different control parameters is presented, along with a comparison between experimental measurements of the field and theoretical simulations.

Acoustic streaming in ultrasonic (1.4–3.0 MHz) circular and rectangular resonators of path length approximately one-half or one quarter wavelength (λ) has been characterized by particle image velocimetry (PIV) using fluorescent 1 μm diam latex markers. Particles of all diameters examined (1, 24, 80 μm) moved into pressure node planes within 4 s of initiation of sonication. The larger particles then moved within that plane to one or more preferred positions. 1 μm particles in a λ/2 cylindrical resonator with a single nodal concentration region for larger particles were convected by Rayleigh-type streaming from the center of the node plane to its edge. In contrast, particles concentrated at many loci in two planes of a second cylindrical and a rectangular chamber. Small scale wall-associated Rayleigh-type vortices occurred in a λ/4 chamber. More unexpectedly, wall-independent bulk suspension vortices, with circulation planes parallel to the transducer radiating surface, were recorded in both resonators. Tracer particles experienced radial forces that drove them towards or away from the center of the vortices to be concentrated at its center or entrained in a vortex perimeter ring. These different outcomes are discussed in terms of lateral radiation force distribution in the node planes.

Traveling and standing waves are produced in an open-tube resonator in a controlled ratio. A regenerator/heat-exchanger assembly is placed at the velocity node of the standing wave. The quality factor, Q, and acoustic power along the resonator are measured as the standing wave ratio (SWR), porosity, length, temperature gradient, and position of the regenerator are varied. The results agree qualitatively with the predictions of a simple model. Higher acoustic impedance in the regenerator improves the acoustic gain-to-viscous-loss ratio. Positive power amplification across the regenerator is observed, maximized by an optimum combination of standing and traveling waves.

During the production of diphthongs, acoustic waves propagate along a time-varying three-dimensional (3D) vocal tract of complex geometry. The shape of the vocal tract walls does not only change because of the action of the articulators to produce a given sound, but also experience an elastic back reaction to the inner acoustic pressure. In this work the Finite Element Method (FEM) is used to simulate these phenomena. The mixed wave equation for the acoustic pressure and acoustic particle velocity expressed in an Arbitrary Lagrangian-Eulerian (ALE) frame of reference is solved to account for acoustic wave propagation in moving domains. The flexibility of walls is considered by solving a mass-damper-stiffness auxiliary equation for each boundary node. Dynamic vocal tract geometries are generated from the interpolation of static 3D vocal tract geometries of vowels, obtained from Magnetic Resonance Imaging (MRI). Some diphthong sounds are generated as examples

The fundamental azimuthal modes of a constricted annular resonator are investigated. It is found that a given mode of an unconstricted resonator splits into two separate modes in the constricted resonator. One mode is of a higher frequency and has a pressure antinode centered in the constricted region. The other mode is of a lower frequency and has a pressure node centered in the constricted region. The resonance frequency of the higher-frequency modes increases linearly with a decrease in the constricted to unconstricted area ratio, whereas the lower frequency drops nonlinearly. Measurements and theory match to within 0.5% when end corrections and thermo-viscous losses are included in the system model. It was found that end correction impedances derived by mode-matching techniques were the only ones accurate enough to match the measurements and computation to within the error bounds.

This analysis consists of the development of the fluid flow about a spherical particle placed at the velocity node of a standing wave. High-frequency acoustic fields are being used to levitate particles in Earth gravity, and to stabilize particles in low-gravity situations. While a standing wave in an infinite medium may be purely oscillatory with no net flow components, the interaction with particles or solid walls leads to nonlinear effects that create a net steady component of the flow. In the present development, the perturbation method is employed to derive the flow field for the situation when a spherical particle is positioned at the velocity node. As found in an earlier analysis [Riley, Q. J. Mech. Appl. Math 19, 461 (1966)] applicable to a solid sphere at the velocity antinode, there is a thin shear-wave region adjacent to the spherical boundary. However, this thin Stokes layer does not cover the entire sphere in the same manner as in the previous case. In the polar regions flow reversal takes place but the Stokes layer opens to the surrounding field. On an equatorial belt region there are closed streamlines.

A method for separating particles in liquid by exploiting the competition between acoustic radiation force and electrostatic force is investigated. The displacement of particles from the pressure node of an ultrasound standing wave varies according to the effective charges, radii, and stiffness of the particles, and the particles of different radii can thus be separated even when they consist of the same material. When the particles are of different materials, they can also be separated in relations to their effective electric charges or their stiffness. In this study, the efficacy of this method was theoretically estimated and demonstrated by an experiment, with a mixture of polystyrene spheres of different radii in water, using 500‐kHz ultrasound and a 3.3‐V/mm electric field. The measured ratio of the displacements of polystyrene spheres 10 and 20 μm in diameter from the pressure node was 2:3, which is consistent with the value predicted theoretically. Radiation forces on the polystyrene spheres were also measured by using this technique.

A deoxyribonucleic acid (DNA) concentration method using acoustic radiation force is proposed. Ethanol was added to an aqueous DNA sample in order to initiate clustering of the DNA molecules of 2686 bps. The change in the distribution of the DNA clusters induced by a standing wave ultrasound irradiation was observed with an optical microscope. The observable DNA clusters gathered on the pressure node in the ultrasonic standing wave field and formed larger clusters that did not break apart after the irradiation was stopped. Without ultrasound irradiation, no significant change in the cluster distribution was observed. This method may have a potential use for concentrating and collecting biomaterials such as nucleic acids and proteins.

The theoretical treatments of nonlinear standing waves had been hampered for years by the simultaneous nonlinear partial differential equations of Riemann. It is suggested that the situation may become encouraging if attention is concentrated on the motion of a particle at a point fixed in space, or on the waveform of the standing wave with fixed alternating values of the particle velocities. It is shown that the motion of a particle at a point fixed on the waveform of a standing wave is readily soluble from the Riemann equations, and an exact, stable solution of the nonlinear standing wave is obtained, which differs from that in linear acoustics only in containing an additional term proportional to the particle displacements in the arguments of the time and space functions. These implicit functions are readily developed into explicit power series, and the field parameters of the standing wave result in terms representing the harmonics. The properties of the nonlinear standing waves thus obtained have been confirmed by experiments. A standing‐wave tube has been built and equipped with a high power loudspeaker driver as the source of excitation. The gradual spectral variation of the standing wave with increasing excitation has been observed. Experimental results agree well with the theoretical predictions and further uncover a number of interesting phenomena. Under certain conditions, saturation and bifurcation appear at a high sound level.

The Polynesian nose flute is found in two versions that are blown in a similar manner but fingered and tuned differently. The Eastern Polynesian flute, known in Hawai'i as 'ohe hano ihu, but is found also to Tahiti and Niue. The tube is closed by a segment node at one end but with a hole for blowing and open at the other end. It typically has two or three finger holes along the tube and three or four playable notes. Being similar to other flutes, the scale tunings can be calculated from hole and tube dimensions by analytic expressions. In Fiji, New Zealand, Samoa, and Tonga, where it is known as fangufangu, both ends of the Western Polynesian flute are closed by segment nodes. There are five holes are placed along the top, usually evenly spaced from one end to the other, with a sixth hole in the middle underneath, giving a variety of fingering options with four to six notes and two registers. The scale tunings are determined by first calculating the frequency response using a lumped-element method.

An experimental study of sound scattering by a thin‐walled cylindrical shell stiffened by an internal lengthwise rib is presented. The results show that, in the explored frequency band, the positions of the resonance frequencies of the wave S0 are not affected much by the presence of a stiffener. Measurements made during the transient state after the quasiharmonic excitation of the stiffened shell have shown that, at the S0 wave resonance frequencies, backscattering is at its maximum when the rib is located at the vibration node of the shell. On the other hand, when in the total backscattered pressure, forced vibration is also taken into account, the maxima are detected when the rib is located at the vibration antinodes. In the stiffened shell other additional resonances appear which are not excited in the case of an unstiffened shell. These resonances are attributed to the propagation of the flexural type waves which are not detected in an unstiffened shell. In a stiffened shell these resonances appear a...

We have examined the effect of the no-slip boundary condition on the steady streaming around a radially pulsating bubble, located at the velocity node of a standing sound wave. The no-slip condition can take place on the bubble surface under many circumstances, especially if the surface is contaminated or otherwise coated. We applied the singular perturbation analysis with the oscillation amplitude, e=U 0/(aω)<

In the experiment, a nichrome wire is suspended between a metal bridge and a pulley with a weight hanger and standard weights that supply a constant tension. The 28 gauge wire has a diam = 0.32 mm and a mass/length = 0.66 g/m. For a 2 m long wire with a 0.43 kg mass providing tension, the standing wave resonant frequencies are integer multiples of 20 Hz (neglecting the wire’s stiffness). An AC current from a variable autotransformer is used to heat the wire (from the bridge to the pulley) until it glows. Near the bridge, a variable gap neodymium magnet is positioned with its poles on either side of the wire. The wire will glow at the nodes, but due to cooling (by the air vibration) the antinodes do not glow. The experiment is described in [C. A. Taylor, The Art and Science of Lecture Demonstration, Taylor & Francis, 1988]. Replace the magnet with an oscillator and audio power amplifier for frequency control [Sabatier and Drewrey, J. Acoust. Soc. Am. 104, 1793 (1998)]. One can also demonstrate glowing node...

The vibrational modes of an almond‐shape bell, having the profile of a church bell, were studied using holographic interferometry. The noncircular shape results in mode pairs, one pair member having a node at the end of the bell, the other an antinode. Frequency ratios between the mode pairs range from 0.94 to 1.21.

Ultrasonic manipulation is widely used as a noncontact technology and recently small particles rotating on a vibrating substrate has been observed. In this report,a novel methodology which compounds the procedures of ultrasonic trapping, transporting and rotating micro-particles in fluid using a single device is investigated. Irregular micro-particles in a standing wave field experience both acoustic radiation force and torque, which drive the particles to pressure nodes and keep them in a balance posture. A prototype device has also been built according to this theory, which six phase-controlled piezoelectric transducers whose sound beam axes are arranged with an angle of 60 deg in the x-y plane are used to generate ultrasonic standing waves with arbitrary node. The transducers are divided to two groups, so the wave field can be rotated by switching between the two groups. The synthesized sound field is scanned using a needle hydrophone and 200 μm irregular SiO2 particles are used to perform the compound...

A dust-screening member is shaped like a plate as a whole, and has at least one side that is symmetric with respect to a virtual axis on a surface of the member. A vibrating member is adjacent to one side of the dust-screening member, arranged on the surface along the one side, and configured to produce, at the surface, vibration having a vibrational amplitude perpendicular to the surface. A drive unit is configured to drive the vibrating member to produce the vibration on the surface, such that peak ridges of the vibration form a closed loop and an area including a center of the closed loop is surrounded by a node area having almost no vibrational amplitude. When a thickness of the dust-screening member is assumed to be tg and a thickness of the vibrating member is assumed to be tp, tg/tp has a dimension of 0.8.

The present invention provides methods and apparatuses for an audio transducer. The audio transducer is excited by driving a paddle of a diaphragm. A plurality of node regions of a paddle is determined for the higher-order modal components, which correspond to resonance frequencies and have an order greater than one. An intersection region of at least two higher-order modal components is identified, in which an excitation point is located with the intersection region. The diaphragm of the audio transducer includes a frame, at least one hinge, and a paddle. The paddle connects to the frame by the at least one hinge and is excited by a signal source at an excitation point to produce an acoustic signal.

A basic understanding of the production of sound waves can be obtained by studying standing waves and resonance frequencies. A vibrating string will settle into a steady, standing wave pattern when it is driven at one of its resonance frequencies. The resonance frequencies depend on the string's length and the tension applied to the string. Similarly the resonance frequencies of tubes are determined by the tube's length and whether the ends are open or closed. In a series of hands-on demos, we will explore the factors that influence the creation of standing waves by exciting the resonances of strings, tubes, rods, a metal plate, slinky, and a wine glass. These simple models provide insight into how musical instruments produce sound.

Pitch bending on the vibraphone is an extended performance technique called for by modern composers dating back to the 1960s. After first striking the middle of a bar with a soft mallet in the normal manner, the pitch bend is obtained by pressing a hard mallet onto the bar at a nodal point and then sliding it away from the node as the note sustains. The audible result is a descending pitch, typically of about one semitone. Experimental data showing frequency vs location of the hard mallet al.ong the bar are presented and interpreted with the use of time‐averaged electronic speckle‐pattern interferograms showing the vibrational modes of the vibraphone bar. Frequency vs mallet mass data are also presented and discussed. In addition, it is shown that for some combinations of mallet type and vibrational mode this technique can produce an increase in frequency.

A basic understanding of the production of sound waves can be obtained by studying standing waves and resonance frequencies. A vibrating string will settle into a steady, standing wave pattern when it is driven at one of its resonance frequencies. The resonance frequencies depend on the string length and the tension applied to the string. Similarly the resonance frequencies of tubes are determined by the tube length and whether the ends are open or closed. In a series of hands‐on demos, we will explore the factors that influence the creation of standing waves by exciting the resonances of strings, tubes, rods, a metal plate, slinky, and a wine glass. These simple models provide insight into how musical instruments produce sound.

Most sounds are made up of many waves added together. These waves, called harmonics, are all related to each other because their frequencies are integer multiples of the lowest frequency, the fundamental. Adding together different amounts of each harmonic is part of what makes different sounds unique. The individual harmonics of a vibrating string are easy to see, one at a time, by creating a standing wave on the string and adjusting the driving frequency. The frequency where the fundamental, one‐looped standing wave appears on the string depends on the string’s length, mass, and tension, but if these factors are all kept constant while the driving frequency is increased, a new loop will be added to the standing wave for each multiple of the original frequency. This is an exciting way to see waves, observe their properties, and really understand how frequency, wavelength, and other properties are all interrelated.

Standing waves, or resonances, will occur in an open‐ended tube when the air in the tube is excited at a particular frequency or its harmonics. The resonant frequencies are a function of the tube length. The first standing wave, fundamental mode or first harmonic, is set‐up with antinodes at each end of the tube, as the air is free to move at the ends, with one node in the middle of the tube. Each successive standing wave has an additional anti‐node and node, with the second harmonic containing three, antinodes and two nodes, the third containing four and three, respectively, and so on. This phenomenon of an air column resonance will be demonstrated using corrugated tubes. By spinning the tube overhead at a particular speed, the resonance frequencies will be excited. For slower speeds, lower frequencies will be heard, while the pitch will increase for faster speeds. Instrumental examples of open‐ended tubes include the flute and organ pipes.

The vibraphone is a member of the keyboard (or mallet) percussion family, with tuned aluminum bars typically spanning three chromatic octaves (F3–F6). Extended performance techniques include the use of harmonics and bowing of bars, as well as the pitch bending effect discussed here. After first striking the middle of a bar with a soft mallet in the normal manner, the pitch bend is obtained by pressing a hard mallet onto the bar at a nodal point and then sliding it away from the node as the note sustains. The audible result is a descending pitch, typically of about one semitone. Experimental data on frequency versus location of the hard mallet along the bar are presented. The mass, hardness, and orientation of the sliding mallet relative to the bar are discussed. Interferograms of the lower frequency modes of the bar are also shown. Results are interpreted using a mass perturbation model.

There is presently much interest in understanding the hydrophysical parameters in a shallow estuary. The importance of predicting the currents in Hudson River was demonstrated during rescue and recovery of the USAirways aircraft crashed in the river on January 15, 2009. Usually hydrophysical parameters are measured by fixed location sensors that cannot provide high spatial resolution. Acoustic tomography, on the other hand, can map the hydrophysical parameters. Recently, Stevens Institute of Technology using their fully equipped underwater facility including two surface vessels has conducted the first feasibility test on acoustic tomography. The test was conducted in the Hudson River, a shallow estuary that is connected to New York Harbor. The test used an estimate of the differential time of flight of an acoustical signal in opposite directions between two nodes. One node was at a fixed location, while the other was on a research vessel drifting on the other side of the river. An application of a frequen...

Standing waves on a string are a popular classroom demonstration which helps students understand such fundamental acoustic concepts as wavelengths, interference, and resonances. The close connection between this demonstration and stringed musical instruments helps bridge the gap between the science classroom and other interests they may have. In this version of the demonstration, we replace the string with a copper wire and add a permanent magnet. This allows the vibrations in the string to be directly translated into an electrical signal which can be broadcast through a standard stereo amplifier and speakers similar to an electric guitar pickup. The effects of string tension and length can then be explored. Alternatively, an ac can be driven through the wire creating a periodic driving force from the magnetic field of a precise frequency allowing standing waves to be established on the string. More advanced students can also examine the Fourier transform of the signal produced when the wire is struck and find peaks at the resonant frequencies.

In a dynamic damper including: a torque transmissible tube member; a mass member housed within an inside of the tube member concentrically to the tube member; and a pair of elastic members, both ends of the mass member in a center axis direction of the tube member are coupled to the tube member via the pair of elastic members, the mass member includes a large mass section interposed between the pair of elastic members, a length of the mass member in the center axis direction of the tube member is longer than a diameter of the large mass section, and, from among two different bending resonance vibration modes of the tube member, a node of a higher order bending resonance vibration mode is placed at a position between the pair of elastic members.

The invention provides a piezoelectric substrate in the form of a rectangular plate in which a Rayleigh wave is propagated, and an IDT and a reflector are provided by forming interdigital electrodes on the piezoelectric substrate. At least an end face on a shorter side of the piezoelectric substrate on a top side thereof is formed as a vertical smooth surface that is substantially in parallel with a conductor strip at an end of the reflector in the position of an imaginary node of a stress wave exiting the conductor strip, thereby providing a reflecting end face to reflect the stress wave.

A method and apparatus for generating ultrasound pulses comprises producing a multi-level pulse sequence including a series of pulses. The series of pulses includes at least three pulses having three different amplitudes, respectively. The amplitudes are at least one of a positive non-zero voltage, a negative non-zero voltage, and an intermediate level voltage. The multi-level pulse sequence may be produced by a switch network having at least three different input voltage levels. The switch network outputs the multi-level pulse sequence at an output node to a transducer within a probe. Echo signals based on the series of pulses are received, and an ultrasound image is produced based on the received echo signals.

The acoustic guitar produces tones by transferring energy from the strings, through the bridge to the top plate, back, and air cavity of the guitar. The vibrations are ultimately radiated into the air as sound. The air‐cavity and body resonances of the guitar play an important role in both the tone and the sustain (the time it takes notes to decay) produced by the guitar. To study the relationship between resonances of the guitar and the sustain of notes, the resonance frequencies were measured using a mechanical shaker attached to the body of the guitar and laser Doppler vibrometer to measure its vibration. A string was tuned to different frequencies and plucked. The decay of the note was measured with an electromagnetic pickup that measured the vibration of the string, a vibrometer to measure vibration of the top plate, and microphones located inside and outside the guitar. As expected, when the fundamental frequency of the string was near one of the resonances of the guitar, the decay rate was faster (shorter sustain) than when the string was between resonances. The relationship between the decay rates of the different parts of the system will also be discussed.

This work presents an extensive analysis of the properties of the heterogeneous blankets (HGs) and their effectiveness in controlling the vibration of the base structures. The HG blankets act as a distributed vibration absorbers consisting of mass inhomogeneities inside a layer of porous media (acoustic foam). To asses the effectiveness of these HG blankets in controlling the vibration of the base structure (plate), detailed finite element (FE) models of the foam, the HG blanket, and the plate have been developed. The foam has been dicretized using the eight node hexahedral elements. The HG blanket model consists of the foam model with point masses attached to the nodes of the elements. The structural (plate) domain is discretized using four node rectangular plate elements. Each of the FE models has been individually validated by comparing the numerical results with their respective analytical and experimental results. The structural and the HG blanket FE models were then combined into a larger FE model comprised of a base plate with the HG treatment on its surface. The results from this numerical model have shown that there is a significant reduction in the vibration levels of the base plate due to the HG treatment on it.

A tubular resonant mechanical horn having a contoured inner surface such that, under vibration, an output radial displacement is obtained on the outer surface of horn that is substantially uniform over its entire surface, for producing effects useful in continuous processes. The horn does not contain a node of motional displacement.

The acoustic radiation force operating on a cell in a 0.5‐MPa pressure amplitude 3‐MHz standing wave field equals that experienced in a 250‐g gravitational field. Consequently, cells may be driven rapidly to preferred points in the sound field. Acoustic radiation pressure can drive bacteria, flowing by an acoustic reflector (prepared as an immunosensor surface), onto that surface where they are then captured. Animal cells have been driven onto the fabric of wide‐gauge filters to form, a basis for a supported bioreactor. Real standing wave fields do not have the ideal plane‐wave form, particularly when the transducer diameter is much larger than a wavelength (typical transducer diameter of 20 mm, wavelength of 0.5 mm at 3 MHz in water). Pressure variations within a node plane then give rise to regions towards which cells migrate and may be held against flow in potential traps. These traps are exploited commercially to retain cells in fermentors in the pharmaceutical industry. Most recently, ultrasound trap...

The generation of multiphonic sounds in blown musical instruments is modeled by an eigenvalue finite‐element‐method (FEM) calculation. A common technique for the production of multiphonic tones is the use of complex sound‐hole closing techniques, where more than one overtone spectrum appears, with fundamental frequencies being in inharmonic relations. Eigenfrequencies of a tube with both ends open are compared to eigenfrequencies of a tube with at least one sound hole open. It shows up that the tube with one open sound hole leads to additional eigenfrequencies in the tube for each node number. This is because of two possibilities of pressure curves within the tube for each node number, the pressure right and left of the hole being in phase or in opposite phase. The frequencies of equal phase form a new overtone structure which is harmonic within itself and so forms a new tone, a multiphonic. So the multiphonic model is in agreement with the Backus formula of multiphonic sounds as a combination of the tube...

We have studied nearly degenerate pairs of vibrational modes in a C4 handbell. Manufacturers seek to eliminate the beating of these modes by careful choice of the clapper position but this can’t always be done satisfactorily. Using electronic holography, we are studying the effects of small, localized mass changes on the frequency and orientation of these mode pairs. One expects one mode of the pair to rotate until it has an anti‐node at the point of the added mass and the other to rotate until it has a node there. Then adding further mass should only change the frequency of the first mode. We find some mode pairs respond in just the expected manner but others behave more strangely. [Work supported by an NSF MRI grant.]

A golf club having suppressed vibration modes is disclosed. The club comprises a shaft, a golf club head, a grip and a plurality of discrete shaft stiffeners. The shaft stiffeners are strategically located along the shaft so as to shift the nodes of at least the second and third flexural vibration modes of the club shaft such that a node of each of the second and third flexural vibration modes occurs both at the club face and within the region underlying the golf club grip. Preferably, the stiffeners are made of a shape memory alloy that can be shrunk onto the outside surface of the shaft, then expanded to permit the position of the stiffeners to be adjusted to suit the boundary conditions imposed by the human user.

Ultrasonic standing waves can be used to generate radiation forces on particles within a fluid. A number of authors have derived detailed representations of these forces but these are most commonly applied using an approximation to the energy distribution based upon an idealized standing wave within a mode based upon rigid boundaries. An electro-acoustic model of the acoustic energy distribution within a standing wave with arbitrary thickness boundaries has been expanded to model the radiation force on an example particle within the acoustic field. This is used to examine the force profile on a particle at resonances other than those predicted with rigid boundaries, and with pressure nodes at different positions. A simple analytical method for predicting modal conditions for combinations of frequencies and layer thickness characteristics is presented, which predicts that resonances can exist that will produce a pressure node at arbitrary positions in the fluid layer of such a system. This can be used to design resonators that will drive particles to positions other than the center of the fluid layer, including the fluid/solid boundary of the layer, with significant potential applications in sensing systems. Further, the model also predicts conditions for multiple subwavelength resonances within the fluid layer of a single resonator, each resonance having different nodal planes for particle concentration.

Finite element formulations based on Biot’s poroelasticity equations have been used extensively throughout recent years. The most common are Biot’s displacement (u_,U_) and mixed displacement‐pressure (u_,p) formulations. They are used to predict the structural and acoustical behavior of poroelastic mediums within multilayered structures. These models, while accurate, lead to the resolution of large linear systems: they need, respectively, six and four degrees of freedom per node in order to efficiently describe the poroelastic medium’s vibroacoustic behavior in 3‐D problems. In this paper, a simplified displacement (u_) formulation is presented. It is also based on Biot’s equations, but requires only three degrees of freedom per node, related to the solid phase displacement field, to describe the behavior of poroelastic mediums in 3‐D problems. The development of the governing (u_) equations for the equivalent solid poroelastic formulation is detailed. The limitations of this approach are also discussed....

A strong sound field can (1) trap a bubble of gas at a velocity node, (2) maintain the bubble against diffusion, and (3) at sufficient intensity cause it to emit flashes of light that have intensities over 30 mW and widths less than 50 ps. The flashes are emitted in a clocklike fashion with a jitter that is also less than 50 ps. The spectral intensity of the sonoluminescence (SL) increases into the ultraviolet. The mechanism for this effect is still unknown but light scattering experiments have resolved the bubble motion—radius versus time—on a scale of nanoseconds and indicate that the light is emitted by a supersonic collapse. The emitted intensity is a strong function of ambient temperature and varies by a factor of 200 between 1 and 40 C. Light scattering measurements of temperature‐dependent SL therefore provide data that can critically test any proposed theory such as imploding shock waves [C. C. Wu and P. H. Roberts, Phys. Rev. Lett. (May 1993)]. [Work supported by the US DOE Division of Advanced E...

The transfer line method (TLM) can be regarded as a discretized version of Huygen’s principle. Wave energy propagates along a system of lines connecting regularly spaced node points. An energy packet reaching a node along a certain line will at the next time step be split up and reradiated into all the lines connected to that node. Wave propagation is therefore regarded as a discretized process in space and time with local updating rules. Special rules are applied for reflecting, absorbing, and partially absorbing surfaces. The method has been used for some time in electromagnetic wave propagation, but not so much in acoustic studies. The present study is a 2‐D investigation of the scattering of sound pulses from objects having different shapes: circular, triangular, and rectangular. Performing this in the time domain allows the following of the scattering process in detail.

A device for producing thrust has a variety of uses, such as pumping liquid, compressing or blowing air, or powering an aircraft. The device has a chamber with a sound driver located therein. The sound driver creates a compression standing wave in the chamber which will have at least one low pressure node and at least two high pressure peaks. An intake port extends through the chamber and is located adjacent the low pressure node for drawing in a fluid into the chamber. A discharge port extends through the chamber and is located adjacent the high pressure peak for discharging fluid from the chamber.

The application of the BEM (direct form) for the external domain, with a lineal combination of Helmholtz’s equation integral and their derivative (Burton, Miller) makes possible the calculation of the unique solution for each number of waves. The fundamental characteristics of this model that works with lineal sound source are: (1) The calculation surface is the topographical profile adapted with adjacent plans, discertizated in elements defined by two extreme nodes and one central node. (2) The acoustic impedance of each element is determined starting from the Delany equation. (3) The unknowns are the sound field in each node φi. (4) A form function φ is determined starting from the φi of each node. (5) Helmholtz’s operators are obtained by integrating the φ function in each element. (6) By solving the equation system with these operators, the values of the φi, and the function φ, are obtained. (7) By integrating Helmholtz’s equation integral starting from φ, the value of the sound field in each point of...

There is described an apparatus for inclusion in a ship comprising a mass (10), means (16) for vibrationally coupling the mass (10) to the ship's hull (12) and means (28) for damping the movement of the mass (10), the mass (10) being so sized and located as to, when in use, reduce the fundamental and/or harmonics of a transverse two node mode of wave-induced vibration in the ship's hull (12). There is also described an apparatus for inclusion in a ship comprising a mass (10) made up in part of the tackle or fitments of the ship, means (16) for vibrationally coupling the mass (10) to the ship's hull (12) and means (28) for damping the movement of the mass (10) so as to thereby, when in use, reduce vibrations in the ship's hull (12). In a preferred embodiment the mass (10) is in part comprised of a chain locker and that portion of the chain stored therein. By reducing vibrations in the ship's hull (12) significant stresses may be relieved and the performance of the ship enhanced. A ship incorporating the apparatus and a method of reducing vibrations in a ship's hull are also described.

A resonance torsional vibration damping system includes a member having at least one node location along its length. An energy exchanging device, such as a fly wheel and eddy current brake, is operably connected to the member at a damping location that is a distance away from the at least one node location. The energy exchanging device is capable of imparting a plurality of successive torsional impulses to the member. A suitable sensor, such as an angular amplitude sensor or a torsional stress sensor, is utilized to detect the presence of a resonance torsional vibration in the member. A computer is in communication with the energy exchanging device and the sensor, and is capable of controlling the energy exchanging device.

In a filling machine for carbonated drinks, many bubbles are generated, causing the vessels to overflow. As a result, only a small volume of drink is left in the vessel, and the vessel is dirtied. For breaking these bubbles, some bubble breaking methods were investigated experimentally. Finally, it was discovered that the method using aerial ultrasonic waves was the best of all for the filling machines. A bubble breaking machine utilizing aerial ultrasonic waves has been developed. It consists of an ultrasonic vibrator, a metallic horn, a rectangular plate, partition plates, and a reflection plate. The rectangular plate is designed to vibrate in the stripes mode, which is the most efficient radiation mode. The partition plates are set perpendicular to the node lines of the stripes mode, so many pistons are produced by the partition plates. The reflection plate concentrates sound radiation from one piston at one particular point. The equipment was applied to a filling machine of carbonated drinks and the desired results were obtained.

A typical thermoacoustic prime mover has a well‐defined acoustic impedance in at least one place. For instance, many prime movers have a rigid end which forces the acoustic velocity to be zero at that point. Such ‘‘built‐in’’ boundary conditions serve as convenient starting points for computational analysis of the performance of a device. They also serve to place the stack in a thermoacoustically effective position relative to the acoustic field. A toroidal prime mover poses some interesting questions. A toroidal prime mover has the cold end connected to the hot end via a duct that does not impose any obvious dominating boundary conditions that would force a node or antinode at any particular point. Indeed, if the stack and heat exchangers were not there and the toroid had a uniform cross section, a standing wave would have no preferential orientation. In this work, a toroidal thermoacoustic prime mover has been built and an experimental study is presented. A model based on acoustic propagation in infinite periodic waveguides is proposed to simulate the experimental results. [Work supported by the Office of Naval Research.]

Ultrasonic apparatus for clot dissolution and plaque ablation includes a radiator for coupling ultrasonic waves into plaque and a piezoelectric crystal, connected with said radiator, for the intravascular generation of ultrasonic waves; said ultrasonic waves being propagated along a longitudinal axis of said piezoelectric crystal and having an inertial node position within said piezoelectric crystal. The piezoelectric crystal is constructed in order to prevent significant power loss caused by a shifting of the inertial node of the generated ultrasonic waves to a position exterior to said piezoelectric crystal due to loading of the radiator caused by the coupling of ultrasonic waves into the clot or plaque.