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This paper investigates the performance of active noise control (ANC) systems with two reflecting surfaces that are placed vertically on ground in parallel. It employs the modal expansion method and the boundary element method to calculate the noise reduction of the systems with infinitely large and finite size reflecting surfaces, respectively. Both experimental and simulation results show that the noise reduction of the system can be significantly increased after optimizing the surface separation distance and their locations with the sound sources. It is found that the sound radiation of the primary source can be completely reduced in principle if the surface interval is less than half the wavelength and the source line is perpendicular to the surfaces for infinitely large reflecting surfaces. Even with finite size ones, the noise reduction performance improvement is still significant compared with those without any reflecting surfaces. For example, for an ANC system with a source distance of 0.074 m, experiments achieve an improvement of 8.6 dB at 800 Hz where two 0.2 m × 0.2 m parallel reflecting surfaces are placed with a distance of 0.15 m around the system on ground. The mechanisms for the performance improvement are discussed.

A theoretical approach was recently introduced by Guidetti and Royston [J. Acoust. Soc. Am. 144, 2312–2323 (2018)] for the radially converging elliptic shear wave pattern in transverse isotropic materials subjected to axisymmetric excitation normal to the fiber axis at the outer boundary of the material. This approach is enabled via a transformation to an elliptic coordinate system with isotropic properties. The approach is extended to the case of diverging shear waves radiating from a cylindrical rod that is axially oscillating perpendicular to the axis of isotropy and parallel to the plane of isotropy.A theoretical approach was recently introduced by Guidetti and Royston [J. Acoust. Soc. Am. 144, 2312–2323 (2018)] for the radially converging elliptic shear wave pattern in transverse isotropic materials subjected to axisymmetric excitation normal to the fiber axis at the outer boundary of the material. This approach is enabled via a transformation to an elliptic coordinate system with isotropic properties. The approach is extended to the case of diverging shear waves radiating from a cylindrical rod that is axially oscillating perpendicular to the axis of isotropy and parallel to the plane of isotropy.

Cardioid microphones/hydrophones are highly directional acoustical sensors, which enjoy easy availability via numerous commercial vendors for professional use. Collocating three such cardioids in orthogonal orientation to each other, the resulting triad would be sharply directional yet physically compact, while decoupling the incident signal's time-frequency dimensions from its azimuth-elevation directional dimensions, thereby simplifying signal-processing computations. This paper studies such a cardioid triad's azimuth-elevation direction-of-arrival estimation accuracy, which is characterized here by the hybrid Cramer-Rao bound. This analysis allows the cardioidicity index (α) to be stochastically uncertain, applies to any cardioidic order (k), and is valid for any real-valued incident signal regardless of the signal's time-frequency structure.

High order Lamb waves are investigated for the effects of stress on both symmetrical and anti-symmetrical modes in an aluminum plate for wave propagation and load parallel. Data are compared with those for the case of load and measurement axis perpendicular. It is the S1 mode which exhibits significantly higher sensitivity to stress than other Lamb modes. For aluminum the use of the S1 mode for stress measurement is found to be about six times more sensitive, than bulk waves, for the load-measurement axes parallel case and this compares with about ten times for the case of load-measurement axes perpendicular.

Strain-dependence of ultrasound speed in cancellous bone was determined by applying a range of uniaxial compressive strains in the elasticity region, in a single direction, parallel or perpendicular to the propagating wave. Compressive strain modulated the ultrasound speed significantly. The decrease of ultrasound speed was found to change linearly as a function of strain. The changes of broadband ultrasound attenuation were also determined for the two dilatational waves (parallel or perpendicular to the strain). They do not follow linear relation or constant sign of change with strain for the examined specimens. Considerable possibilities open up for using developments in acoustoelasticity for nondestructive ultrasonic techniques.

A “figure-8” sensor is so labeled because its spatial pattern resembles the character “8” with regard to the sensor's axis. This figure-8 pattern narrows as the sensor's order increases. Using two such figure-8 directional sensors of higher order, oriented perpendicularly to each other—this paper pioneers closed-form signal-processing algorithms to estimate an incident signal's azimuth-elevation bivariate direction-of-arrival. Monte Carlo simulations verify these proposed algorithms' efficacy and statistical closeness to the corresponding Cramer-Rao bounds.

Laboratory measurements of finite-amplitude, wideband elastic pulse propagation in a thin bar of Texas moss sandstone have been reported [Muir et al., JASA 147 (2020)] that utilized pulses generated by impact excitation with a pendulum hammer at one end of the bar. Each pulse is essentially unipolar in strain, with bandwidth of approximately 3 kHz and amplitude between 10 and 130 microstrain. Reduction of the sandstone elastic modulus by up to 17% resulted from propagation of the impact-generated pulse, as calculated from time-of-flight measurements of the pulse as it reflected between the ends of the bar. In the present work, elastic softening is observed locally using a Dynamic Acousto-Elastic Testing (DAET) configuration. During propagation of an impact-generated pulse, changes in the sandstone elastic properties are observed by tracking variations in the arrival time and amplitude of a continuous-wave 1 MHz P-wave signal that propagates perpendicular to the bar axis. Repetitive reflection of the pulse from the stress-free ends of the bar enables separate observation of effects from compressive and tensile strains. Reduction of the elastic modulus of up to 20% is observed, with almost all of the softening occurring during the tensile phase of the impact-generated pulse. a)Deceased.

Computer-controlled digital holographic techniques are developed and used to measure shape and four-dimensional nano-scale displacements of the surface of the tympanic membrane (TM) in cadaveric human ears in response to tonal sounds. The combination of these measurements (shape and sound-induced motions) allows the calculation of the out-of-plane (perpendicular to the surface) and in-plane (tangential) motion components at over 1 000 000 points on the TM surface with a high-degree of accuracy and sensitivity. A general conclusion is that the in-plane motion components are 10–20 dB smaller than the out-of-plane motions. These conditions are most often compromised with higher-frequency sound stimuli where the overall displacements are smaller, or the spatial density of holographic fringes is higher, both of which increase the uncertainty of the measurements. The results are consistent with the TM acting as a Kirchhoff–Love's thin shell dominated by out-of-plane motion with little in-plane motion, at least with stimulus frequencies up to 8 kHz.

Gradient index (GRIN), refractive, and asymmetric transmission devices for elastic waves are designed using a solid with aligned parallel gaps. The gaps are assumed to be thin so that they can be considered as parallel cracks separating elastic plate waveguides. The plates do not interact with one another directly, only at their ends where they connect to the exterior solid. To formulate the transmission and reflection coefficients for SV- and P-waves, an analytical model is established using thin plate theory that couples the waveguide modes with the waves in the exterior body. The GRIN lens is designed by varying the thickness of the plates to achieve different flexural wave speeds. The refractive effect of SV-waves is achieved by designing the slope of the edge of the plate array, and keeping the ratio between plate length and flexural wavelength fixed. The asymmetric transmission of P-waves is achieved by sending an incident P-wave at a critical angle, at which total conversion to SV-wave occurs. An array of parallel gaps perpendicular to the propagation direction of the reflected waves stop the SV-wave but let P-waves travel through. Examples of focusing, steering, and asymmetric transmission devices are discussed.

Redirection of acoustic energy by 90° is shown to be possible in an otherwise acoustically transparent sonic crystal. An unresponsive “deaf” antisymmetric mode is excited by matching Bragg scattering with a quadrupole scatterer resonance. The dynamic effect causes normal unidirectional wave motion to strongly couple to perpendicular motion, analogous to the quasi-static Poisson effect in solids. The Poisson-like effect is demonstrated using the first flexural resonance in cylindrical shells of elastic solids. Simulations for a finite array of acrylic shells that are impedance and index matched to water show dramatic acoustic energy redirection in an otherwise acoustically transparent medium.

Tendons are bands of fibrous connective tissue connecting muscles to bones. They are composed of parallel arrays of collagen fibers closely packed together which makes them highly anisotropic. The anisotropy of the acoustic properties of tendons was investigated at an ultra-fine resolution (< 7 μm) using quantitative acoustic microscopy (QAM). Chicken tendons were fixed (formalin) while loaded longitudinally, then cryosectioned (16-µm) at several orientations (every 15 deg) from parallel (i.e., 0 deg) to perpendicular to the fibers (i.e., 90 deg). Two regions of two sections per angle were scanned using a QAM system operating at a center frequency of 250 MHz yielding a total of 28 QAM datasets which were processed to yield two-dimensional (2D) maps of the bulk modulus, mass density, acoustic impedance, and speed of sound for each scanned region. Acoustic parameters were averaged within each 2D map and mean and standard deviations computed at each angle. Results demonstrated a strong acoustical anisotropy. For instance acoustic impedance increased from 1.68 ± 0.08 to 1.87 ± 0.19 MRayl between 0 and 75 deg. Similarly, the speed of sound increased from 1686 ± 90 to 1958 ± 186 m/s between 0 and 75 deg. These results demonstrate the value of QAM to investigate the anisotropy of tissue microstructure and pave the way for using it to characterize other soft tissues with complex three-dimensional fiber orientations. [Work supported in part by NIH Grants EY023966 and EY028662.]

In this paper, acoustical noise intensity fluctuations recorded by single hydrophones (SHRUs) in the Shallow Water 2006 experiment are studied. The area of experiment (New Jersey Atlantic shelf) is characterized by a remarkable activity of internal waves, in particular, approximately twice per day trains of nonlinear internal waves (NIW) consisting of up to ten separate peaks with the amplitudes about 10–15 m and wave front parallel to the coastal line move toward the beach. During its motion trains of NIW cross positions of five SHRUs, located about 5–8 km to each other along line perpendicular to the coast as well as thermistor’s strings which allow us to estimate the shape and evolution of trains while they are propagating. It is shown that the appearance of irregular wideband sound field (amplitude by up to 20–40 dB greater than noise background) takes place when the train of NIW is passing through the location of the corresponding SHRUs. The nature of these signals is discussed, and the spectrum and specific temporal variations as well as other characteristics are analyzed. [Work was supported by ONRG, NSF, and BSF.] In this paper, acoustical noise intensity fluctuations recorded by single hydrophones (SHRUs) in the Shallow Water 2006 experiment are studied. The area of experiment (New Jersey Atlantic shelf) is characterized by a remarkable activity of internal waves, in particular, approximately twice per day trains of nonlinear internal waves (NIW) consisting of up to ten separate peaks with the amplitudes about 10–15 m and wave front parallel to the coastal line move toward the beach. During its motion trains of NIW cross positions of five SHRUs, located about 5–8 km to each other along line perpendicular to the coast as well as thermistor’s strings which allow us to estimate the shape and evolution of trains while they are propagating. It is shown that the appearance of irregular wideband sound field (amplitude by up to 20–40 dB greater than noise background) takes place when the train of NIW is passing through the location of the corresponding SHRUs. The nature of these signals is discussed, and the spectrum and...

The secondary edge source line integral formulation for diffraction modeling uses edge sources with a 1/r dependency, in addition to a directivity function. At first sight, this might seem to contradict the expected 1/r behavior for the gradient near the edge of a thin screen. An analysis is presented for the special case of perpendicular plane wave incidence onto a thin screen, which shows that the secondary edge source formulation does indeed lead to the expected behavior close to the edge of an ideal wedge.

Fully-sampled two-dimensional (2D) arrays can have two-way focusing of the ultrasound beam in both lateral directions leading to high quality, real-time three-dimensional (3D) imaging. However, fully-sampled 2D arrays with very large element counts (>16 000) are difficult to manufacture due to interconnect density and large element electrical impedance. As an alternative, row-column or crossed electrode arrays have been proposed to simplify transducer fabrication and system integration. These types of arrays consist of two one-dimensional arrays oriented perpendicular to each other. Using conventional delay-and-sum beamforming, each array performs one-way focusing in perpendicular lateral directions which yield higher sidelobe and acoustic clutter levels compared to fully-sampled 2D arrays with two-way focusing. In this paper, the use of spatial matched filters to improve focusing of row-column arrays is investigated. On receive, data from each element are first spatial match filtered in the elevation direction. After summation, the data are filtered again in the azimuth direction. Beam widths comparable to one-way focusing are seen in azimuth and beam widths comparable to two-way focusing are achieved in elevation. 3D beam patterns from computer simulation results using a 7.5 MHz 128 × 128 row-column array are shown with comparison to a fully sampled 2D array.

The movement of a sound image may not coincide with that of the sound source in a room with reflective walls. A listener sitting by a reflective wall perceives the movement of the sound image bending around their head when a sound source approaches the wall straight in the front of them. In order to investigate this perception quantitatively, we measured the trajectory of the sound image perceived by a listener against a sound source moving straight in front of them using a magnetic motion sensor. The sound source was a 1/3-octave band noise with a center frequency of 300, 750, 1500, 3000, or 6000 Hz emanating from a small moving loudspeaker at a sound pressure level of 70 dB. The loudspeaker moved on a rail perpendicular to the wall in front of the listener at a constant linear velocity. The listener tracked the direction of the moving sound image with his fingers by holding a motion sensor with his eyes closed. Results show that the sound image trajectory bent around the listener’s head only when the stimulus contained low frequency components below 1.5 kHz, suggesting that interaural time difference plays an important role in the phenomenon. The movement of a sound image may not coincide with that of the sound source in a room with reflective walls. A listener sitting by a reflective wall perceives the movement of the sound image bending around their head when a sound source approaches the wall straight in the front of them. In order to investigate this perception quantitatively, we measured the trajectory of the sound image perceived by a listener against a sound source moving straight in front of them using a magnetic motion sensor. The sound source was a 1/3-octave band noise with a center frequency of 300, 750, 1500, 3000, or 6000 Hz emanating from a small moving loudspeaker at a sound pressure level of 70 dB. The loudspeaker moved on a rail perpendicular to the wall in front of the listener at a constant linear velocity. The listener tracked the direction of the moving sound image with his fingers by holding a motion sensor with his eyes closed. Results show that the sound image trajectory bent around the listener’s head only when the st...

In this article, the effects of uniaxial compressive loading on the ultrasonic scattering from polycrystalline grains are shown for 10 MHz ultrasound in annealed, 1018 steel. The results show a decreasing value of the stress-dependent backscatter coefficient for normal incident ultrasound when the compression loading is perpendicular to the scattering direction. The change due to scattering is about 2 orders of magnitude greater than changes observed by others using ultrasonic wavespeed measurements. It is anticipated that this research can serve as the basis for many methods associated with nondestructive determination of stress in structural materials.

To design an ultrasonic sensor to measure the attenuation and density of slurry carried by a large steel pipeline (diameter up to 70 cm) is the goal of this research. The pitch-catch attenuation sensor, placed in a small section of the pipeline, contains a send unit with a focused transducer that focuses the ultrasound to a small region of the receive unit on the opposite wall. The focused transducer consists of a section of a sphere (base ∼12 cm) on the outer side of the send unit and a 500 kHz piezoelectric shell of lead zirconate titanate epoxied to it. The Rayleigh surface integral is used to calculate the pressure in steel and in water (slurry). An incremental method to plot the paths of ultrasonic rays shows that the rays focus where expected. Further, there is a region where the parallel rays are perpendicular to the wall of the receive unit. Designs for pipeline diameters of 25 and 71 cm show that the pressure in water at the receive transducer is about 17 times that for a pitch-catch system using 5 cm diameter disk transducers. The enhanced signal increases the sensitivity of the measurements and improves the signal-to-noise ratio.

In the laboratory setup, a borehole traverses a dry sandstone formation, which is subjected to a controlled uniaxial stress in the direction perpendicular to the borehole axis. Measurements are made in a single loading-unloading stress cycle from zero to 10 MPa and then back down to zero stress. The applied stress and the presence of the borehole induce anisotropy in the bulk of the material and stress concentration around the borehole, both azimuthally and radially. Acoustic waves are generated and detected in the water-filled borehole, including compressional and shear headwaves, as well as modes of monopole, dipole, quadrupole, and higher order azimuthal symmetries. The linear and non-linear elastic parameters of the formation material are independently quantified, and utilized in conjunction with elastic theories to predict the characteristics of various borehole waves at zero and finite stress conditions. For example, an analytic theory is developed which is successfully used to estimate the changes of monopole tube mode at low frequency resulted from uniaxial stress, utilizing the measured material third order elasticity parameters. Comparisons between various measurements as well as that between experiments and theories are also presented.

The frequency shift of the acoustic interference striations is caused by the depth variation of the thermocline in shallow water waveguide. Based on the perturbation theory, a relationship between the frequency shift of the interference striations and the contoured sound speed profile is established. In a given frequency band, if the modal horizontal wave number difference acts as a monotonic function of frequency, the frequency shift of interference striations has a direct correlation with the contoured SSP. This relationship is verified by simulation calculation as well as experiment data. It is found that if the propagation direction of sound is parallel to the wave front of internal wave, the frequency shift of the interference striations has a determined relationship with the contoured SSP that passing through the source; while when sound propagates in a direction perpendicular to the internal wave’s wave front, the frequency shift is then associated with the contoured mean SSP in the entire sound pr...

This paper reports a new effect whereby a physiological-level direct-current electrical field (at 1.4 V/cm) can induce time-varying mechanical strain in various types of biological tissues and gel phantoms. This effect cannot be explained by the piezoelectric effect, tissue contraction, temperature changes, and electrorestriction. The induced strain in tissues was analyzed by processing ultrasound echo signals. The sample expanded perpendicularly to the applied electric field. The expansion rate depended on the history of the applied electric field. The speed of sound changed little compared with the expansion. The new effect might be related to electrokinetic effects.

We present recordings made by an Intensity Vector Autonomous Recorder (IVAR) deployed on the seafloor during the Sediment Characterization Experiment (SCE17) conducted on the New England Mud Patch [40°28’ N, 70°35’ W] in March of 2017. IVAR continuously and coherently records four channels of acoustic data, three from a tri-axial accelerometer embedded in a neutrally buoyant sphere and one from an omnidirectional hydrophone positioned 10 cm above the centroid of the sphere 1.2 m above the seafloor. Here we focus on IVAR recordings of a 57 Hz continuous wave tone generated by a low-frequency acoustic source (J-15) that was towed at 30 m depth by the R/V Endeavor along transects roughly parallel and perpendicular to bathymetric contours. Over the entire tow track deep signal fades occur in 1000 m intervals, suspected to be caused interference between two modes trapped by the sediment basement. A signature in the vector data identifies an additional interference structure superimposed on this pattern (a 2 + ...

Pressure waves can travel through coupled media, such as water and land. A field experiment was performed to characterize impulsive signal propagation between these media. Balloon pops underwater provided the in-water source, while sledgehammer blows provided the land-based source. Data were collected using a distributed sensor array that included locations on land and in the water, using a combination of microphones, hydrophones, and geophones. The array extended 75 m from the shore onto land and 75 m into the water perpendicular to the shoreline. Additional sensors were placed 25 m from the nominal shoreline and parallel to the shore. Source locations varied over the area to maximize capture of varying propagation paths. Data are analyzed for travel time, amplitude, and waveform shape. A description of the field experiment and results are presented. [Work funded by U.S. Army ERDC.]

Very large subaqueous sand dunes were discovered on the upper continental slope of the northeastern South China Sea (SCS) in the spring of 2007 during an ONR 322OA-funded field experiment which was designed to study the large transbasin internal solitary waves (ISW) that are generated by tidal forcing in the Luzon Strait. These internal waves and sand dunes are important acoustical features, as it is expected that they will cause significant anomalies in the acoustical field. In the spring of 2014, a broadband source was deployed to transmit 850-1150 Hz LFM signals to receivers on a mooring in the center of the sand dune field. The acoustic transect was oriented perpendicular to the dune crests, ISW fronts and isobaths. Data analysis and extended modeling are presented to quantify the degree to which these features impact the propagation of broadband signals in the 100-2000 Hz band as a function of source depth and frequency.

Sound equalization in closed spaces can be significantly improved by generating propagating waves that are naturally associated with the geometry, as, for example, plane waves in rectangular enclosures. This paper presents a control approach termed effort variation regularization based on this idea. Effort variation equalization involves modifying the conventional cost function in sound equalization, which is based on minimizing least-squares reproduction errors, by adding a term that is proportional to the squared deviations between complex source strengths, calculated independently for the sources at each of the two walls perpendicular to the direction of propagation. Simulation results in a two-dimensional room of irregular shape and in a rectangular room with sources randomly distributed on two opposite walls demonstrate that the proposed technique leads to smaller global reproduction errors and better equalization performance at listening positions outside of the control region compared to effort regularization and compared to a simple technique that involves driving groups of sources identically.

A coupled pair of nonlinear parabolic equations is derived for the two components of the particle motion perpendicular to the axis of a shear wave beam in an isotropic elastic medium. The equations account for both quadratic and cubic nonlinearity. The present paper investigates, analytically and numerically, effects of cubic nonlinearity in shear wave beams for several polarizations: linear, elliptical, circular, and azimuthal. Comparisons are made with effects of quadratic nonlinearity in compressional wave beams.

The objective of this study was to measure the backscatter coefficient of formalin-fixed myocardial tissue as a function of angle of insonification relative to the myocardial fiber direction. Backscatter measurements were performed on eight cylindrical formalin-fixed lamb myocardial specimens and compensated for attenuation and diffraction effects to determine the backscatter coefficient. The backscatter coefficient at 5 MHz was found to be maximum for insonification perpendicular to the predominant myofiber orientation and minimum for parallel insonification, with values of (17+/-14) and (1.2+/-0.7) x 10(-4) cm(-1) sr(-1) (mean+/-standard deviation), respectively.

Many materials (e.g., rubber or biologic tissues) are "nearly" incompressible and often assumed to be incompressible in their constitutive equations. This assumption hinders realistic analyses of wave motion including acoustoelasticity. In this study, this constraint is relaxed and the reflected waves from nearly incompressible, hyper-elastic materials are examined. Specifically, reflection coefficients are considered from the interface of water and uni-axially prestretched rubber. Both forward and inverse problems are experimentally and analytically studied with the incident wave perpendicular to the interface. In the forward problem, the wave reflection coefficient at the interface is evaluated with strain energy functions for nearly incompressible materials in order to compute applied strain. For the general inverse problem, mathematical relations are derived that identify both uni-axial strains and normalized material constants from reflected wave data. The validity of this method of analysis is demonstrated via an experiment with stretched rubber. Results demonstrate that applied strains and normalized material coefficients can be simultaneously determined from the reflected wave data alone if they are collected at several different (but unknown) levels of strain. This study therefore indicates that acoustoelasticity, with an appropriate constitutive formulation, can determine strain and material properties in hyper-elastic, nearly incompressible materials.

Besides radiating sound from the note area being struck, a steelpan radiates from neighboring note areas that vibrate sympathetically, from the areas between notes, and from the skirt [Rossing et al., Phys. Today 49(3), 24-29 (1996)]. Measurements were taken in an anechoic chamber using a four-microphone intensity probe to visualize the acoustic radiation from selected notes on a double second and a low tenor steelpan. Swept sinusoidal excitation was effected using an electromagnet. Sound intensity maps were drawn for the first three harmonics.

Noise barriers are commonly used to protect communities from transportation noise. In the present study, three types of barriers, modeled as half planes, have been tested in the laboratory: a conventional rigid barrier with a straight top edge, a straight top edge barrier covered with sound absorbing material, and a rigid barrier with a jagged top edge. Measurements were taken not just behind the barriers, but around them on a plane perpendicular to their top edge. Measured signals were compared against theoretical predictions contributing to further validation of a theoretical model. The sound absorbing material was found to affect the diffracted field more in the front of the barrier than behind it. The diffracted field in front of a jagged edge barrier, similar to the field behind it, was found to depend on the geometry of the edge in the area where the shortest diffraction path intersects the edge profile. Last, the performance of the three barriers was compared with one another in all areas around the barrier. It was found that the jagged edge barrier provides shielding similar to the sound absorbing barrier but at a fraction of the cost.

An analytical and numerical study on the levitation force induced by pressure radiation in gas squeeze films is investigated. The levitation phenomenon is known to occur when a planar object is placed at close proximity to a vibrating piston. The existing analytical approaches are based on either conventional acoustic radiation, where the fluid is assumed inviscid or on a variant of the Reynolds equation that incorporates viscous effects. Alas, these solutions are often in poor agreement with accurate numerical results and, at best, describe appropriately cases that include a limited range of object weights and vibration frequencies. In this work, two cases are addressed: the flow induced by vibrations perpendicular to a flat surface and that by flexural wave propagation parallel to the surface. For the first case, numerical and second-order analytical perturbation solutions are obtained and compared, proving them to be in good agreement. In addition, a novel, analytical expression for the levitation forc...

Non-reciprocal and refractive devices for elastic waves are designed using a solid with aligned parallel gaps. The gaps are assumed to be thin so that they can be considered as parallel rectangular cracks separating effective thin plates. To formulate the transmission and reflection coefficients for SV- and P-wave, an analytical model is established using thin plate theory with displacement and force continuous at the junction between plate and exterior body. The analytical model compares well with full FEM simulations. The non-reciprocity effect for P-waves is achieved by sending an incident P-wave at a critical angle, at which total conversion to SV-wave happens, with respect to the normal of a free boundary. An array of parallel gaps perpendicular to the propagation direction of the reflected waves stop the SV-wave but let P-wave travel through. Thus, the energy transmission is high from one side to another and is low from the opposite direction. The refractive effect for SV-waves is achieved by choosing the slope of the edge of plate array, and plate members for |T| = 1 at the same frequency with the ratio between plate length and flexural wavelength fixed. Examples of elastic non-reciprocal and wave steering devices will be discussed.

A feasibility study is presented of the use of a thin fiber to detect sound. The fiber is assumed to be supported on each end, with a deflection in response to a sound wave that propagates in the direction perpendicular to its long axis. The driving force on the fiber is the result of viscous forces in the oscillating air, which are well-known to be very important in determining the flow-induced motion of small structures. A simplified analytical model of the fiber's response is presented where it is argued that for fibers that are sufficiently thin, elastic and inertial effects become strongly dominated by viscous forces in the fluid. As a result, the fiber's motion becomes a very close approximation of that of the acoustic flow in its vicinity. Electrodynamic transduction of the fiber's motion provides a means of sensing sound with remarkable accuracy if the fiber diameter is taken to be measurably below one micron.

A linear array with 23 microphones is used to scan a planar section of the sound field radiated into an anechoic environment by a range of brass instruments excited by a sinusoidal sine sweep. The planar section contains the symmetry axis of the bell and covers a rectangular area of 0.9 by 0.6 metres, starting at the plane of the bell and extending away from it along the longest side. The linear microphone array is perpendicular to the symmetry axis and is stepped along the axis. The resulting matrix of signals is processed to separate the linear and non-linear parts of the response; the three-dimensional pressure distribution in the sound field is deduced on the assumption that the field is cylindrically symmetric. This data then allows the visualization and further analysis of the frequency dependence of radiated wave fronts in brass instrument bells. Comparison is drawn between the observations and the predictions of several popular radiation models.

Measurement of acoustic fields is an important aspect of ultrasound research and development. The corresponding data is usually collected by a raster scan using a single point receiver moved by a computer-controlled positioning system. A faster approach could be based on the use of a 1D linear multi-element array with several tens or hundreds of small elements, which is moved in a direction perpendicular to the beam axis. The drawback of such an approach is difficulty in making small, closely-positioned receiving elements that provide sufficient signal-to-noise ratio. The current paper presents an alternative design for a 1D linear array: instead of using small elements, here it is suggested to use narrow but long elements, with a width on the order of a half wavelength or less and a length larger than the extent of the ultrasound beam being studied. The drawback of the proposed long-element arrays is absence of resolution in the direction along the element. This problem is solved by incrementally rotatin...

The oscillation modes of a supersonic circular twin jet and multijet with square configuration where the center-to-center spacing of nozzles was fixed to 1.4 times the nozzle diameter were investigated experimentally. It is found that the twin jet oscillates simultaneously in three different oscillation modes for the pressure ratios of about 4.1. From the acoustical observation, these oscillation modes are identified as one lateral oscillation mode perpendicular to a plane composed of the twin jet axes and two lateral oscillation modes parallel to this plane. For a multijet with a square configuration, only one lateral oscillation mode was observed. In this case, it is observed that when the spacing between two facing sides of the square formed by four jets is stretched, the spacing between the other two sides shrinks and vice versa.

Experiments performed at the USNA Acoustics Lab use turbulent flow to generate nonlinear scattering of mutually perpendicular crossed beams (f1 = 1.9 MHz, f2 = 2.1 MHz, 15 cm focal lengths) at the combination sum frequency component (f+ = 4 MHz). The object is to simulate blood flow through a constriction, and measure the nonlinear scattering downstream with a receiving circular plane array transducer (4 MHz) that rotates azimuthally in the plane of the transmitted beam axes about the intersection. Angular dependent Doppler shift (about f+), spectral broadening, skewness and kurtosis measurements vs. angle help predict the characteristics of the turbulence. The setup involves a 4 cm diameter polyethylene (0.5 mm thick) tube cut in two sections (22 cm upstream (a), 38 cm downstream (b)). The sections are mated with a special block union allowing one to insert individual thin orifice plates of different diameters. The far section ends are open but are connected through opposite side ports on (a) and likewis...

Results of an experiment to measure vertical spatial coherence from acoustic paths interacting once with the sea surface but at perpendicular azimuth angles are presented. The measurements were part of the Shallow Water 2006 program that took place off the coast of New Jersey in August 2006. An acoustic source, frequency range 6-20 kHz, was deployed at depth 40 m, and signals were recorded on a 1.4 m long vertical line array centered at depth 25 m and positioned at range 200 m. The vertical array consisted of four omni-directional hydrophones and vertical coherences were computed between pairs of these hydrophones. Measurements were made over four source-receiver bearing angles separated by 90°, during which sea surface conditions remained stable and characterized by a root-mean-square wave height of 0.17 m and a mixture of swell and wind waves. Vertical coherences show a statistically significant difference depending on source-receiver bearing when the acoustic frequency is less than about 12 kHz, with results tending to fade at higher frequencies. This paper presents field observations and comparisons of these observations with two modeling approaches, one based on bistatic forward scattering and the other on a rough surface parabolic wave equation utilizing synthetic sea surfaces.

The attenuation coefficient and phase velocity of plane sound waves propagating in three perpendicular directions in glass wool were measured in the frequency range 50–10 000 Hz. For glass wool of mass density 14 kg/m3 at the frequency 1000 Hz, the attenuation constant for propagation perpendicular to the glass wool sheets was 75 dB/m, and for propagation parallel with the sheets 57 dB/m. For mass density 30 kg/m3, the corresponding numbers were 140 and 100 dB/m. The measured values were compared with calculated ones taking into account the movements of the fiber skeleton. The calculations need the elastic moduli, which were measured. For density 14 kg/m3 and deformation perpendicular to the glass wool sheets, the static modulus was 2.0 kPa, and for parallel deformation 120 kPa. The corresponding numbers for mass density 30 kg/m3 were 16 and 390 kPa. ©2000 Acoustical Society of America.

Plane wave incidence on a rigid biconic target is considered. A biconic reflector consists of two cones truncated by planes perpendicular to their axes and joined at their smaller flat faces. The cone angles are allowed to be variable, provided their sum is equal to 90 degrees. The backscattering cross section is expressed in terms of a surface integral of the geometrical acoustics field, which results from incident singly and doubly reflected rays. A saddle-point calculation gives a first-order high-frequency approximation in which the backscattering cross section is proportional to the incident wave number and a function of the angle of incidence, cone angles, and inner and outer radii of the truncated cones. This expression is algebraically complex but easy to implement numerically. Results are presented that exercise the parameters of the problem. An interesting result of the solution is that for fixed outer radii there is a nonzero optimum inner radius for backscattering strength. For broadside incidence on 45 degrees cones with equal outer radii, this optimum value is approximately equal to 11% of the outer radius.

An analysis was made of the SH-interfacial wave propagation on an interface between semi-infinite piezoelectric media. In particular, a sufficient condition for the existence of the SH-wave on the metallized rigid contact was derived. It has been shown that on the metallized rigid contact between two completely identical piezocrystals the SH-localized wave always exists, with the exception of at most two orientations of the interface. An investigation was performed of specific features of the sound reflection—transmission at incident angles corresponding to the resonant excitation of the leaky wave originating from the “supersonic” interfacial wave due to misorientation of crystals that constitute the bicrystal. Also, it has been established that in 6 mm crystals an interfacial “supersonic” wave may remain purely localized even when the direction of propagation is not perpendicular to the axis 6 or when the interface is not parallel to this axis.

In contrast to a thin plate having no shear component of deformation, a Timoshenko–Mindlin plate cannot support a concentrated line dipole moment exerted by a pair of equal and opposite line forces acting normal to its lateral surface. In this paper, it is argued that, in order to account for all the connectivity between a rib and the plate, it is necessary to assume a nonzero width footprint for the rib upon the plate. This footprint is idealized by a connection between the rib and plate along two lines parallel to the rib. The problem posed is one dimensional, with plate responses invariant in the direction of the rib; therefore, along each line of contact, the rib exerts upon the plate only a normal force and a tangential (shear) force perpendicular to the rib. These four initially independent forces combine to produce resultant opposing forces acting on the end of the rib which generate velocities of the rib that can be related to those of the plate. The response quantity of interest is the structural power reflected from the rib due to a wave propagating freely in a direction normal to the rib and incident upon it. It is shown that the rib footprint cannot be set equal to zero if the rib’s rotational properties are to have a meaningful influence on the calculated reflected power.

The generation of sound by a piano soundboard is investigated experimentally, through measurements of the sound pressure, p, and the soundboard velocity, vb, produced in response to a force applied at the bridge. Results for the ratio p/vb as a function of frequency, for forces applied perpendicular to the soundboard at different locations (i.e., driving points) on the bridge, are presented. At all locations, p/vb is largest at frequencies of order ∼1 kHz, and falls off below a few hundred Hz and above ∼5 kHz. A few results obtained with the force applied along the string direction (i.e., parallel to the plane of the soundboard) are also described. These results are compared and contrasted with previous experiments, and with theoretical expectations.

A mathematical model is developed for the coupling of two finite plates at an arbitrary angle for the prediction of the dynamic response and power flow at the coupling edge and at any cross section. The coupling at the joint edge considers bending, out-of-plane shear, and in-plane longitudinal (perpendicular to the joint edge) vibration. No constraint is imposed on the in-plane displacement perpendicular to the coupling edge. The exact solution for flexural mode shapes and resonance frequencies of rectangular plates with one edge free and the other edges simply supported is considered. This exact solution satisfies both the displacement and force boundary conditions, consequently it is used in the coupling of plate panels. An approximate relation is derived for prediction of the flexural resonance frequencies of higher-order modes with a reasonable accuracy. An approximate solution is presented for the in-plane response of the same plate panels when excited by in-plane forces perpendicular to the free edge. A simple expression is given for an approximate estimation of the cut-off frequencies for the different in-plane modes. The frequency response of the individual plate panels is presented as receptance functions for both flexural and in-plane vibration which are used in the plate coupling. The vibrational power injected into a plate by out-of-plane concentrated force and moment is computationally investigated. The importance of power input by a small moment excitation in some resonant bands even at low frequencies is highlighted. The spatial distribution of the components of flexural power transmitted by shear and moment across a section of the plate are investigated and the reason for the circulatory patterns of active power flow in plates is illustrated. The power flow characteristics in two plates coupled at an arbitrary angle is examined by a computational example. The effect of the coupling angle on the components of input power and power flow across the coupling edge is investigated. It is shown that the coupling of the two plates is mainly due to moment at frequencies up to the cut-off frequency of the first in-plane mode. Above this frequency, the coupling is due to out-of-plane shear and in-plane vibration with a diminishing participation of the moment in transmitting vibrational power through the coupling edge.

Previous studies on the local active control of noise in free space show that the size of the quiet zone and the total sound power output of the control system are mainly determined by the spatial arrangement of primary sources, secondary sources, and error sensors. When a nearby reflective surface is introduced, the size of the quiet zone and the total power output of the system will be affected. The research presented in this paper examines the influence of the presence of a nearby reflective plane on the control system with different alignments to the reflective surface. It is found that the reflective surface significantly affects the size of the quiet zone and the sound power output of the system, as compared with the same control system in free space. The effect is related to two important parameters of the control system: the heights of the sources and the error sensor above the surface and the distances between the primary and secondary sources and between the secondary source and the error sensor. While the quiet zones created by most arrangements of the control system in half-space are smaller than those for free space, the quiet zones created by the arrangements of the control system perpendicular to the reflective surface may be larger than those for free space.

The acoustic attenuation of acoustic fiber materials is mainly determined by the dynamic resistivity to an oscillating air flow. The dynamic resistance is calculated for a model with geometry close to the geometry of real fibre material. The model constists of parallel cylinders placed randomly. Two case are treated: flow perpendicular to the cylinder axes, and flow parallel to the axes. In each case two new approximate procedures were used. In the first procedure, one solves the equation of flow in a Voronoi cell around the fiber, and averages over the distribution of the Voronoi cells.The second procedure is an extension to oscillating air flow of the Brinkman self-consistent procedure for dc flow. The procedures are valid for volume concentrations of cylinders less than 0.1. The calculations show that for the density of fibers of interest for acoustic fibre materials the simple self-consistent procedure gives the same results as the more complicated procedure based on average over Voronoi cells. Graphs of the dynamic resistivity versus frequency are given for fiber densities and diameters typical for acoustic fiber materials.

This paper deals with the prediction of the dynamic response and vibrational power flow in general three-dimensional coupled beam structures. An arbitrary loading condition is assumed and flexural waves in two perpendicular planes and longitudinal and torsional waves, may be excited simultaneously in each beam. The interaction of different wave types at the coupling boundaries is therefore expected. Suitable for the low- and medium-frequency range, the modal receptance method used here allows the prediction of the detailed structural response and power flow components carried by the different wave types through joint boundaries and at any cross section of the beam structure. The mathematical description of the three-dimensional beam structure and the manipulation of receptance matrices are presented in such a form that the vibration of any complex beam structure may be described systematically and with clear physical interpretations. The prediction of the input and output power for each component beam quantifies the energy dissipation in the beam, which may be taken as a measure of the spatial average response level of the beam. Computational examples of the power flow components at the joint boundaries of the component beams in coupled three-dimensional structures are used to illustrate the significance of the theoretical results.

A new type of wood-based material for guitar back plates as a substitute for Brazilian rosewood was produced based on Japanese cedar logs with a small diameter, of which the utilization is limited despite its availability. The sapwood portion of logs with a diameter of 20 cm was processed to veneers of 2 mm thickness using a rotary lathing machine. The veneers were impregnated with a low-molecular-weight phenolic resin, laminated in parallel, and compressed perpendicular to their plane. When the veneers were treated with a 3% or 5% aqueous solution and compressed to a density of 0.8 without adhesives, the specific dynamic Young’s modulus (E/γ, ratio of stiffness to specific gravity) and tan δ (damping) of the materials became almost the same as those of Brazilian rosewood in the lower-frequency range, not only in the longitudinal direction but also across the longitudinal direction. However, the frequency dependencies of the specific Young’s modulus and tan δ of the materials differed from those of Brazilian rosewood, which may be partially related to the higher values of E/G of laminated compressed wood as a result of the increased density induced by deformation of the cell walls.

A new way of calculating the airflow resistivity of randomly placed parallel cylinders is presented. The calculation is based on Voronoi polygons, and the resistivity is given by the mean spacing between the fibers, their diameters, and the physical properties of air. New explicit formulas for the resistivity are given, which are valid for the cylinder (fiber) concentrations found in acoustic materials. A one-dimensional model consisting of parallel plates with random spacing between the plates is first discussed. Then a two-dimensional model consisting of parallel cylinders randomly spaced is treated for flow parallel and perpendicular to the cylinders. The resistivity formulas are exact for plates and approximate for cylinders.

This study evaluates the effects on electromagnetic midsagittal articulometry (EMA) coils from electrode activation on an electropalatography (EPG) artificial palate, and on EPG contact patterns induced by EMA coils. In order to investigate the first issue, five transducer coils on a fixed magazine were placed equidistantly among themselves and with respect to the three transmitter coils of an EMA helmet. Two palate positions were used, i.e., perpendicular to the magazine (to emulate possible effects on coils placed on the nose, upper incisors, jaw, and lips) and parallel to it (to imitate effects on coils placed on the tongue surface). A thin leaf of aluminum firmly pressed by a mold was used to create contact activation. Data for different degrees of contact activation were subtracted from data obtained with no artificial palate (perpendicular condition) or with an artificial palate with zero ‘‘on’’ electrodes (parallel condition). Only for the most extreme condition, i.e., a high degree of contact activation and a short coil‐to‐artificial palate distance, do the effects slightly exceed the noise level for the EMA equipment. The analysis of the second issue was carried out for coils attached to the tongue tip, the tongue blade, and the tongue dorsum during the production of several consonants. Coil‐to‐lingual contact effects occur mostly near the midline of the artificial palate at different locations, depending on the degree of contact and the location of the consonant.

A theoretical and experimental study of the acoustic response of a submerged stiffened cylindrical shell is presented. The internal rib is modeled as a clamped‐free plate mounted inside the shell perpendicular to the shell surface. The stiffened shell is excited by a normally incident acoustic pressure wave. Wave propagation around the circumference of the shell and associated sound radiation are discussed. From the directivity of the monostatic scattering, the resonances in the scattered sound pressure field can be separated into three different types. A mechanical admittance is used to help identify the different types of resonances excited in the fluid‐loaded stiffened shell. Each type of resonance is shown to be associated with a particular type of interaction between the shell and the rib in terms of the components of the coupling forces: i.e., the normal force, the transverse force, and the coupling moment. For kR ranging from 16 to 35, the normal coupling force is shown to control the symmetric fle...