bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantifying viscoelasticity of boundary sensitive tissues using mechanical wave dispersion ultrasound vibrometry
Authors: Nenadic Ivan , Urban Matthew , Pislaru Cristina , Bernal Miguel , Greenleaf James
Published: September 2012

The cardiovascular diseases such as atherosclerosis, coronary artery disease, hypertension and diastolic dysfunction have been associated with arterial stiffening and decreased ventricular compliance. Noninvasive techniques capable of quantifying elasticity and viscosity of cardiovascular tissues could facilitate early diagnosis and improve treatment. Here, we present a technique that uses focused ultrasound radiation force to excite mechanical waves in the tissue of interest and pulse echo to track the tissue deformation. Analysis of tissue deformation as a function of time using Fourier transforms allows calculation of the phase wave velocity dispersion (change of velocity as a function of frequency) of various modes of deformation. Continuum mechanics equations governing the motion of a viscoelastic plate and a tube are used to model the myocardial wall and arteries, respectively. Dispersion equations are derived for the two geometries and fit to the measured velocity dispersion to estimate tissue elasticity and viscosity. ECG-gated in vivo measurements of porcine myocardial and arterial elasticity and viscosity through a heart cycle are reported. The results show that both elasticity and viscosity increase during systole and decrease during diastole in the myocardium and arteries, consistent with underlying physiology.
An energy functional approach for inverse characterization of material properties in elastodynamics
Authors: Aquino Wilkins , Diaz Manuel , Urban Matthew
Published: September 2012

We present an inverse problem methodology based on the Error in Constitutive Equations (ECE) approach for the identification of material properties in the context of frequency-domain elastodynamics. In the ECE approach, we define a cost functional based on an energy norm that connects a set of kinematically admissible displacements and a set of dynamically admissible stresses. The set of kinematically admissible displacements is composed of fields that satisfy essential boundary conditions and possess sufficient regularity (i.e. smoothness). The set of dynamically admissible stresses is composed of fields that satisfy conservation of linear momentum and natural (i.e. traction) boundary conditions. The inverse problem is solved by finding material properties along with admissible displacement and stress fields such that the ECE functional is minimized. Experimental data is introduced in the formulation as a quadratic penalty term added to the ECE functional. The talk will focus on the reconstruction of elastic and viscoelastic properties in heterogeneous materials in the context of frequency-domain dynamics. Our findings indicate that ECE methods provide faster and more accurate results than conventional least-squares minimization. We will show numerical and experimental results that demonstrate the salient features of the method.
Quantitative ultrasound imaging for assessing and monitoring therapy
Authors: Ghoshal Goutam , Kemmerer Jeremy P. , Karunakaran Chandra , Oelze Michale L.
Published: September 2012

Conventional ultrasound, which is routinely used for diagnostic imaging applications, is mainly qualitative. However, novel quantitative ultrasound (QUS) imaging modes are being adapted to quantify tissue properties for diagnosing disease, classifying tissues and monitoring and assessing therapy. Ultrasound is a propagating wave that interacts with a medium as a function of the spatially-dependent mechanical properties of the medium. By analyzing the backscattered wave, various properties of the propagating media can be quantified. QUS techniques based on parameterizing spectral features and envelope statistics of the backscattered signal were used to monitor and assess therapy from high intensity focused ultrasound (HIFU) treatment. QUS parameters were obtained by fitting theoretical models to backscatter coefficients (BSCs) that are estimated from backscattered radiofrequency signals. Additional parameters were estimated by fitting the homodyned K distribution to the statistics of the envelope of the backscattered signal. These parameters can be related to tissue properties and microstructure, such as the shape, size and organization of microstructure. Experimental results will be presented to demonstrate the applicability of QUS imaging to monitor and assess HIFU treatments on mouse mammary tumors.
Shear wave generation using hybrid beamforming methods
Authors: Nabavizadeh Alireza , Greenleaf James F. , Fatemi Mostafa , Urban Matthew W.
Published: September 2012

Elasticity imaging is a medical imaging modality that measures tissue elasticity to aid in diagnosis of certain diseases. Shear wave-based methods have been developed to perform elasticity measurements in soft tissue. Hybrid beamforming applies both the conventional spherical and axicon focusing to produce a beam for generating a shear wave with increased depth-of-field so that measurements can be made with a plane-like shear wave. We present our aperture design and beam optimization performed using Field II simulations. We varied the number of elements devoted to spherical and axicon focusing as well as the opening angle used for axicon focusing. We tested hybrid beamforming in three elastic phantoms and an excised kidney. We evaluated the shear wave speed measurements accuracy in the phantoms as well as the depth-of-field for each hybrid beam. We compared our results with those from using beams generated using spherical and axicon focusing. Our results show that hybrid beamforming is capable of producing a long narrow beam that performs well when among the 128 elements of transducer, 48 elements are allocated to each axicon portion and 32 elements for spherical aperture while the angle of the axicon aperture is set less than 20.
On the compressional-shear coefficient of nonlinear elasticity in soft isotropic solids
Authors: Guzina Bojan , Dontsov Egor , Urban Matthew , Kinnick Randall , Fatemi Mostafa
Published: September 2012

Acoustoelasticity is a technique that allows quantification of the elastic nonlinearity coefficients (the so-called third-order moduli) of a material by measuring the variation of the sound speed in different directions (and/or polarizations) versus the applied uniaxial static stress. When dealing with nominally isotropic solids, the variation of the shear wave speed in two orthogonal directions with the applied stress permits the computation of two out of three independent nonlinearity coefficients. To generate the shear wave in an experimental setting, the acoustic radiation force pulse was applied to uniaxially deformed phantoms with strains of up to 30%. The results demonstrate that the compressional-shear coefficient C, which governs the variation of the (linear) shear modulus with hydrostatic pressure was found to vary substantially from one phantom to another, with the highest value observed in an agarose-based phantom. The importance of this nonlinearity parameter resides in the fact that the magnitude of the acoustic radiation force (ARF) in soft solids is proportional to C-1. For consistency, the values of C obtained from the acoustoelasticity experiment are compared to those deduced from the shear wave amplitude via its relationship to the magnitude of the ARF used to generate the shear wave.
Elastography and tactile imaging for mechanical characterization of superficial muscles
Authors: Turo Diego , Otto Paul , Egorov Vladimir , Sarvazyan Armen , Gerber Lynn H. , Sikdar Siddhartha
Published: September 2012

Quantification of the mechanical properties of muscle is of significant clinical interest. Local changes in the mechanical properties of muscle are often associated with clinical symptoms. In particular, myofascial trigger points (MTrPs) are a very common, yet poorly understood and overlooked, cause of nonarticular musculoskeletal pain. MTrPs are localized, stiff, hyperirritable tender nodules, palpated in taut bands of skeletal muscle. Objective validated measures of the mechanical properties of MTrPs could potentially be a clinical outcome measure. We are investigating ultrasound shear wave elastography and tactile imaging as complementary objective methods to assess the mechanical properties of MTrPs. In an ongoing clinical study, we recruited 50 subjects (27 healthy controls and 23 with symptomatic chronic neck pain and active MTrPs). The upper trapezius muscles in these subjects were imaged using shear wave elastography using an external vibration source with varying frequency in the range [50–200] Hz to measure shear wave speed and dispersion in tissue, and tactile imaging using an array of pressure sensors allowing 3D reconstruction of mechanical structure of tissue. Preliminary analysis demonstrates that symptomatic muscle tissue in subjects with neck pain is mechanically more heterogeneous and stiffer compared to normal muscle in control subjects (p < 0.05).
Sound-power flow
Authors: Hickling Robert J.
Published: September 2012

To understand sound-intensity measurement, it should be realized that sound intensity is sound-power flow per unit area in the direction of sound propagation. Sound intensity can be measured in fluids such as air or water. Generally measurements cannot be made inside a solid. However there may be ways of measuring sound intensity in a solid, if the solid is transparent. Also sound intensity can be computed in a solid and then measured in a surrounding fluid to collate with the calculated results. In general the measurement of sound-intensity is relatively new. It can be measured either as a vector in three or two dimensions or as a single vector component. These features are discussed, together with some examples of sound-intensity measurement. An important use of a single component of sound intensity is the measurement of the sound power of a noise source. Another use is locating the primary sources of noise in operating machinery. The full sound-intensity vector can determine the direction of a noise source. Two vectors can determine the location of the source in space.
Complex technique of sound intensity measurements and properties of the basic sound fields
Authors: Tichy Jiri , Elko Gary W.
Published: September 2012

An overview of sensors and signal processing for the measurement of sound intensity and other energy related quantities such as reactive intensity, potential and kinetic energy is summarized. Many examples of energy propagation, vortices formation, radiationn from sources, sound interference and other acoustic phenomena are presented and analyzed.
Wide band pressure and velocity (p-v) tympanometry with calibrated sound intensity micro-probes
Authors: Stanzial Domenico , Sacchi Giorgio
Published: September 2012

Wide band p-v tympanometry can be defined as the measurement of the acoustic immittance of the ear, possibly in normal air pressure condition of the ear canal, and in the full audio frequency range. The most important innovation pioneered by the p-v tympanometry regards the introduction of a different principle of measurement based on the direct acquisition of, both, pressure and velocity (p-v) signals at the ear canal entrance. The measurement can be done by using a pre-calibrated couple of dedicated micro-sensors: an ordinary microphone and an acoustic velocimetric micro-device. This invited speech will report about wide band measurements of ear immittance functions carried out by means of a modified tympanometric probe hosting a pre-calibrated sound intensity micro-probe, and their comparison, with data obtained by standard 226 Hz tympanometry.
A comprehensive examination of the acoustic vector fields scattered by cylindrical bodies
Authors: Barton Robert J. , Moss Geoffrey R. , Smith Kevin B.
Published: September 2012

In this study, the properties of the scattered acoustic vector fields generated by infinite-length and finite-length rigid and elastic cylinders are investigated. Analytical solutions are derived from general acoustic pressure scattering models, and analyzed for wave numbers in the resonance region. The separable active and reactive components of the acoustic intensity are used to investigate the structural features of the scattered field components. Numerical results are presented for the near field and transition regions. A finite element model is developed for both rigid and elastic cylindrical bodies. The finite cylinder model and analysis is then extended to include interactions with an elastic half space. The vector properties of the time-independent complex intensity components and their relations to field energy density quantities are summarized.
Investigating measurement of acoustic intensity for rocket sound field characterization
Authors: Gee Kent L. , Blotter Jonathan D. , Sommerfeldt Scott D. , Thomas Derek C. , Bostwick Kenneth S. , Christensen Benjamin Y.
Published: September 2012

An effort to characterize the aeroacoustic source regions and noise environment around launch vehicles has resulted in study of the hardware and processing methods used to calculate acoustic intensity. Because of the extremely harsh measurement environment and other source region characteristics, these investigations have included selection, calibration, and arrangement of microphones and examination of the required pressure and particle velocity estimates. The results of analytical, laboratory, and field experiments are described as a summary of lessons learned during the on-going effort.
A comparison of directional robustness for endfire versus Blumlein microphone arrays used in hearing aids
Authors: Burns Thomas
Published: September 2012

An endfire microphone array uses two omnidirectional microphones in a delay-and-sum configuration. A Blumlein array mixes one omnidirectional and one (bi)directional mic. Each can be engineered to provide any 1st order directional pattern. The three critical factors for providing good directionality include the relative sensitivity and phase between the microphones in addition to the placement of the hearing instrument on the user’s head. In this context, a directional system is robust if its factors can operate over a wide range of levels without degrading the directional performance. In this study, each array was engineered to have the same aperture spacing and tuned to the same freefield polar pattern; this tuning provided the nominal operating levels. Both arrays were placed in-situ on a measurement manikin and 614 impulse responses were acquired in ten degree resolution on all four microphones for different in-situ positions. The data for each array were combined as described above, and the aforementioned factors were varied around the nominal range of levels in a simple central composite design of experiments. The results of the in-situ directional response show improved robustness for a Blumlein mix.
Doubly steered array of modal transducers
Authors: Butler John L. , Butler Alexander L. , Ciufo Michael J.
Published: September 2012

Line or planar arrays steered to end fire generally require quarter wavelength spaced transducer elements with 90 degree sequential phase shifting to attain a unidirectional beam in an end fire direction. Half wave length element separation with 180 degree sequential phase shifts yield end fire but in both directions and at a reduced level. Part of this lower level bipolar directionality is due to the fixed broadside directionality of the transducer elements. However, use of reduced-size, leveraged-circular, acoustical-modal transducer elements, which allow incremental steering, provide a means for substantial end fire steering without the need for quarter wavelength spaced elements. In this case the elements, as well as the array, can be steered in the same direction attaining full-strength, unidirectional end fire steering at half wavelength array spacing. We present the physics of the leveraged-circular, acoustic-modal, transducers and their operation in the monopole, dipole and quadrupole modes along with their implementation and application in doubly steered arrays.
Underwater vector intensity measurements in the ocean and laboratory
Authors: Dall'Osto David R. , Dahl Peter H.
Published: September 2012

Underwater measurements of the acoustic intensity vector field can be provided by either spatially separated hydrophones or by a sensor measuring a property of particle motion, such as particle acceleration. These measurements are used to formulate the vector intensity as the product of pressure and particle velocity. The magnitude of the vector intensity is not necessarily equal to the plane-wave intensity (the mean square pressure divided by the density and sound-speed of the medium) which is often used to define pressure measurements in terms of intensity. In regions of strong destructive interference, the magnitude of the vector intensity may be greater than the plane-wave intensity. Measurements of an impulsive source on a vertical line array of pressure sensors spanning a shallow sea (60 m) off the coast of South Korea are presented to demonstrate properties of the complex intensity vector field in an ocean waveguide. Here, the vertical complex intensity is formulated by finite-difference methods. These vertical intensity observations in the ocean waveguide have implications on properties of the complete vector field. A laboratory experiment using a tri-axial particle acceleration sensor is presented to provide a connection between measurement of elliptical particle motion and complex intensity.
Effect of boundary diffusers in a reverberation chamber: A preliminary investigation
Authors: Adelgren Jacob R. , Bradley David T. , Mueller-Trapet Markus , Vorlaender Michael
Published: September 2012

In this project, the sound field behavior in a 1:5 scale reverberation chamber has been measured and analyzed. Both hanging diffusers and boundary diffusers have been applied in an effort to increase the chamber’s sound field diffusivity, which has been characterized based on the guidelines set forth in several American and international standards, including ASTM C423, ASTM E90, and ISO 354. Objective data from measured impulse responses for several configurations of the diffusers will be presented. These data will be compared to those from the empty chamber and to the criteria from the standards. The relative effectiveness of hanging diffusers vs. boundary diffusers will be discussed.
Source tracking and scatter localization in a reverberant environment
Authors: Williamson Laura M. , Risetter Justin D. , Pierfelice Michael A. , Dowling David R.
Published: September 2012

Matched field processing (MFP) has been shown to be effective for remote sound source localization when the receiving array clearly records direct-path sound from a stationary source. Unfortunately, in imperfectly characterized confined environments, source motion, echoes, and reverberation commonly degrade localization performance. This poster presentation describes three acoustic technology development efforts focused on using matched-field processing, with and without the first reflections, (i) to track a moving source, (ii) to improve localization results by adjusting the receiving array geometry, and (iii) to determine the conditions under which a discrete scatterer may be localized. Experiments were conducted in a 1.0-meter-deep and 1.07-meter-diameter cylindrical water tank using a single sound projector, a receiving array of 16 hydrophones, and a linear actuator capable of moving the source at a speed of 0.5 m/s. Measured localization performance is reported for impulsive (100 micro-second) and longer duration signals having center frequencies from 30 kHz to near 100 kHz. As expected, source and scatterer localization accuracy is found to be limited by reverberation. The eventual application of this research is localizing sub-visual cavitation bubbles and other hydroacoustic sound sources in hydrodynamic test facilities. [Work supported by NAVSEA through the Naval Engineering Education Center.]
Auditory change detection with common and uncommon sounds
Authors: Heberle Amanda L. , DeLong Caroline M.
Published: September 2012

Change deafness, the inability to detect a change in an auditory scene, is similar to change blindness, the inability to detect a change in a visual scene. In this experiment, participants were asked to detect changes in auditory scenes (one, three, or five sounds). The sounds were either common sounds (e.g. alarm clock) or uncommon sounds (e.g. science fiction laser). Only one sound was modified in pitch or loudness for half of the trials. Participants were not always able to detect changes in a sound sequence (M = 67.1%) even though they could almost perfectly discriminate between the ten sounds (M = 99.2%). Participants performed best with a scene size of one (M = 82.6%) and worse with a scene size of five (M = 63.8%). Participants performed significantly better with common sounds (M = 74.7%) vs. uncommon sounds (M = 69.1%). Participants were significantly better at detecting a pitch change (M = 80.8%) than a loudness change (M = 53.5%). These results are consistent with the idea of change deafness. We remember the gist of an auditory scene but we don’t detect changes in every sound.
Techniques for measuring ultrasonic tissue properties of cells
Authors: Daniels Aislinn R. , Mahajan Aditya D. , Rodriguez Yim J. , Herd Maria-Teresa
Published: September 2012

Measuring ultrasonic characteristics of cells outside the cellular matrix is of interest. Analyzing these properties at the cellular level may identify qualities specific to a cell type, possibly leading towards cell identification and disease diagnosis without invasive techniques such as biopsy. The purpose of this research is to develop a reliable method of examining cellular characteristics using quantitative ultrasound. Measurements were made using single element transducers at frequencies of 5-50 MHz in a controlled water-tank environment. Speed of sound and attenuation were measured using through transmissions with unfocused transducers, and backscatter was measured using pulse/echo transmissions with focused transducers. To test our experimental techniques we measured high-frequency properties of a tissue mimicking phantom and compared the results to the current standards. As our experiment required testing at a smaller scale than previous tests of these methods, we also created small holding tubes with smaller phantoms of the same material to compare the larger sample measurements. These miniature phantoms show a remarkable consistency in the data obtained when compared to a large phantom, which verifies the applicability of the methods on a small scale.
Designing and building transducers for use in a molecular acoustics experiment
Authors: Hicks Ashley J. , Slaton William V.
Published: September 2012

This work describes the design, construction, and testing of two capacitance transducers for use in a larger project investigating the molecular absorption of sound in certain gases. The transducers are based on designs presented in the literature, modified to work optimally in our system which consists of 4-inch diameter steel pipe. The experiments will be conducted at atmospheric pressure, eliminating design constraints involved when using high pressure gas. However, work done by Bass & Shields shows that to work in these experiments at atmospheric pressure, transducers must have a frequency range of 1 kHz - 100 kHz. [J. Acoust. Soc. Am. Vol 62, p. 346-353, 1977] The basic concept of our transducer depends upon creating a parallel plate capacitor from metal that is flexible enough to move when a sound wave hits it. Our design utilizes 0.051 mm thickness alumninized Mylar film tensioned with a brass retaining ring over a brass backing plate with both secured to a Delrin plastic base for its electrically insulating properties. We will report on the transducer’s frequency response characteristics and initial testing in a send/receive configuration in a sound absorption experiment.
The role of vowel inherent spectral change in the intelligibility of English vowels spoken by English-, Chinese-, and Korean-native speakers
Authors: Tchen Stephanie , Jin Su-Hyun , Liu Chang
Published: September 2012

This study is designed to investigate the relationship between Vowel Inherent Spectral Change (VISC) and vowel intelligibility of native and non-native speakers of English. VISC refers to the relatively slow varying changes in formant frequencies associated with each vowel category (Neary and Assman, 1986). Such spectral change has been known to be a major factor in the perception of both the phonetic and phonemic English vowels. In the previous research projects conducted in our lab, we recorded 12 English vowels in /hVd/ format spoken by English native (EN), Chinese native (CN) and Korean native (KN) speakers and examined vowel intelligibility. Overall, vowel intelligibility was significantly higher for native talkers than for non-native talkers. Within non-native speaker groups, CN had slightly higher intelligibility than KN speakers. In this study, we are going to analyze an acoustic feature of the vowels, VISC, spoken by these native and non-native speakers. It is hypothesized that the acoustic differences of vowels spoken by different groups of speakers can account for the variances in vowel intelligibility.
Floor vibration response to Irish dancing
Authors: Smith Valerie K. , Korman Murray S.
Published: September 2012

Using Irish step dance impulses of actual techniques, one could use various vibration sensors (B&K microphone and I/O SM11 geophone) to perform a time frequency analysis of the transient response of a supported portable wooden dance floor resulting from forced transient vibration. The steps included (1) a “tap” (the wooden tap on the toe of the shoe hitting the floor), (2) a “stamp” (a combination of the wooden toe and plastic heel hitting the floor simultaneously) and (3) a “shuffle” (a brushing of the wooden tap on the toe once forwards and once backwards against the dance floor). Experiments were performed using laminated veneer lumber (plywood) supported by four small rubber mounts near the edges. Floors were (a) 1 m square (d = 3/4 inch thick), (b) 0.5 m square (d = 1 inch), (c) 1m by 0.5m (d = 1 inch) and (d) 0.5 m diam (d = 1 inch). FFT analysis of a transient is compared with the geophone/microphone frequency response (same location) using a swept sine loudspeaker excitation. In (b) the lowest frequencies were 110 and 470 Hz for a “tap” at the center. Performance is enhanced. Green’s function analysis is presented. [Ji, and Ellis, The Structural Engineer 3rd ser. 72 (1994), p 37- 44.]
Monitoring the pressure impact of a runner's footstep on the inner sole of the shoe
Authors: Blackburn Jacqueline A. , Korman Murray S.
Published: September 2012

The research goals are to learn about the biomechanics of human footsteps and apply the knowledge to the understanding of the subsequent wave energy that is transferred into the ground or track surface. Phase (1) research is focused on learning about the time development of the footstep pressure that a runner’s foot is transferring to the innersole of an athletic shoe, along with accelerometer information. A Tekscan FlexiForce Model A401 force sensor (25.4 mm sensing diameter and 0.208 mm thick) coated with a polyester substrate was chosen due to its versatile force range if biased and placed in an operational amplifier feedback loop. The response time is <5 microseconds. Two force sensors will be placed on the upper side of a removable innersole to measure force near the ball and heel of the foot. Phase (2) is to use a Digi Intl XBee 802.15.4 Development Kit to communicate (using a wireless link) the transducer voltage responses. The transmitting module is strapped to the runner’s ankle. A receiving module receives data streams and connects to a USB computer interface. Phase (3) converts the data streams to measurements of pressure vs. time. Preliminary experiments and a data analysis will be presented.
Acoustic properties of flight approved materials
Authors: Mann Justin , Sisson Matthew , Slaton William
Published: September 2012

The purpose of this project is to analyze the acoustic impedance and absorption properties of various flight approved materials currently and potentially used by NASA in its work with the International Space Station. These materials, consisting of Bisco, Acoustifoam, and other metallic foams, in addition to Durette, Kevlar, and other manufactured felts, will be used in an experimental procedure utilizing an impedance tube. This procedure uses two microphones at fixed positions from a material under test. An audio source, at the opposite end of the testing material, drives sound through the impedance tube and sweeps through a range of distinct frequencies. As the sound propagates down the tube, the two microphones measure the superposition of the driven, incident sound wave and the sound wave reflected off the test material. When used in conjunction with processing software packages, these microphone responses can be recorded and evaluated to produce complex impedance quantities as functions of frequency. By using these results as a means to measure sound absorption coefficients of specific materials, these tested, flight approved materials may be specifically arranged and utilized to both maximize efficiency and minimize excess noise. These possible applications will not only provide scientific data but also potentially affect astronauts on current and future missions for NASA.
Guitar pickups—Where next?
Authors: French Mark , Huston Davin
Published: September 2012

Electromagnetic guitar pickups have been in wide use for more than 50 years. Not only are the basic operational principles unmodified, some of the most popular pickups are exact copies of 50 year old designs. This situation begs the obvious question of where pickup design is headed and where there are opportunities for improvements. There are only a few underlying physical phenomena that can be harnessed to sense string motion. However, it would seem that there is plenty of room for innovative applications of familiar physical principles. This paper discusses current trends in pickup designs, suggests direction for further development and describes an effort to update the design of inductive pickups.
The harmonica as a blues instrument: Part I
Authors: Ramsey Gordon
Published: September 2012

This is part one of two presentations on the same project. The modern harmonica, or harp, has been around since the early 19th century. It is typically used in blues, country, rock and roll and folk music. These musical genres are somewhat similar in structure and form, and often borrow ideas from each other. The harmonica is appropriate as a backup to the main vocal melody and instruments due to its rich harmonic structure and subdued intensity. The ability to apply vibrato and gradual slurs make it a perfect instrument to get the “bluesy” idea across. Our harp research group has investigated the physical properties of harmonica structure to illustrate how different structures lead to varied sounds, each of which is appropriate to a particular style of music.
The harmonica as a blues instrument: Part II
Authors: Wiseman Joseph , Banaszak Chris , Ramsey Gordon
Published: September 2012

This is part two of two presentations on the same project. The modern harmonica, or harp, has been around since the early 19th century. It is typically used in blues, country, rock and roll and folk music. These musical genres are somewhat similar in structure and form, and often borrow ideas from each other. The harmonica is appropriate as a backup to the main vocal melody and instruments due to its rich harmonic structure and subdued intensity. The ability to apply vibrato and gradual slurs make it a perfect instrument to get the “bluesy” idea across. Our harp research group has investigated the physical properties of harmonica structure to illustrate how different structures lead to varied sounds, each of which is appropriate to a particular style of music.
Full-scale rocket motor acoustic tests and comparisons with models: Updates and comparisons with SP-8072
Authors: James Michael M. , Salton Alexandria R. , Gee Kent L.
Published: September 2012

Development of the next-generation space flight vehicles has prompted a renewed focus on rocket sound source characterization and near-field propagation modeling. Measurements taken during a static horizontal firing of Alliant Techsystems Orion 50S XLG are compared to the predicted levels produced from NASA’s SP-8072 Distributed Source Methods (DSM-1 and DSM-2). Two modifications to the SP 8072 prediction model are considered in regards to the source directivity and the source power spectral distribution. All models considered provide a good first-order approximation given an appropriate total acoustic sound power. However, a more physical model is needed to adequately map out the critical near-field region as well as the far-field propagation. A new intensity-based measurement system and corresponding procedures are currently being developed for determining this near field energy flow and for achieving source characterization capabilities beyond traditional pressure measurements. These advances are believed to be a step toward improved measurements and modeling of the rocket plume.
Frequency-based spatial correlation assessments of the Ares I subscale acoustic model test firings
Authors: Kenny Robert J. , Houston Janice
Published: September 2012

The Marshall Space Flight Center has performed a series of test firings to simulate and understand the acoustic enviroments generated for the Ares I liftoff profiles. Part of the instrumentation package had special sensor groups to assess the acoustic field spatial correlation features for the various test configurations. The spatial correlation characteristics were evaluated for all of the test firings, inclusive of understanding the diffuse to propagating wave amplitude ratios, the acoustic wave decays, and the incident angle of propagating waves across the sensor groups. These parameters were evaluated across the measured frequency spectra and the associated uncertainties for each parameter were estimated.
Scale model tests for acoustic prediction and reduction of epsilon launch vehicle at lift-off
Authors: Tsutsumi Seiji , Ishii Tatsuya , Ui Kyoichi , Tokudome Sinichiro , Wada Kei
Published: September 2012

Test campaign using 1/42-scale model is conducted to predict acoustic level of the Epsilon launch vehicle at lift-off. Analogy between sub-scale and full-scale tests is investigated to obtain the same feature of the acoustics. Methodology to correct the measured data obtained in the sub-scale test for predicting the full-scale environment is also clarified in this study. The acoustic results around the practical shape of the launch-pad are successfully obtained. The parametric studies are conducted to reduce noise level in the test campaign with the help of the numerical simulation, and the effect for noise reduction is observed up to 5dB in 1/1-octaveband SPL.
Analysis of noise from reusable solid rocket motor firings
Authors: Gee Kent L. , Kenny R. Jeremy , Jerome Trevor W. , Neilsen Tracianne B. , Hobbs Christopher M. , James Michael M.
Published: September 2012

As part of investigations into the design of next-generation launch vehicles, near and far-field data were collected during horizontal static firings of reusable solid rocket motors. In addition to spectral analysis at individual microphone locations, the spatial variation of overall and one-third octave band pressure levels at sideline and polar arc arrays is considered. Analysis of the probability density functions reveals positively skewed pressure waveforms, but extreme skewness in the first-order estimate of the time derivative because of the presence of significant acoustic shocks.
Dynamic stabilization of the Rayleigh-Bénard instability in a cubic cavity
Authors: Carbo Randy M. , Smith Robert W. , Poese Matthew E. , Swaminathan Anand
Published: September 2012

The dynamic stability of the Rayleigh-Bénard instability with vertical vibration in a cubic container is computationally modeled. Two periodic parametric drives are considered (sinusoidal and rectangular), as well as two thermal boundary conditions on the sidewalls (insulating and conducting). The linearized equations are solved using a spectral Galerkin method and Floquet analysis. Floquet analysis recovers both the synchronous and the subharmonic regions of instability. The conditions necessary for dynamic stability are reported for Rayleigh numbers from critical to 107 and for Prandtl numbers in the range of 0.1-7.0, and the approach produces maps over a wide range of Rayleigh number and vibration parameters for stability. The linear model is compared to data set available in the literature [G. W. Swift and S. Backhaus J. Acoust. Soc. Am. 126, 2273 (2009)] where the performance of system simulating an inverted pulse tube cryocooler is measured. The relevant instability for this case is the synchronous instability. Over this limited data set, the model appears to bound the empirically observed conditions for stability, but in some cases the model would seem to predict significantly higher required periodic acceleration amplitudes that appear to have been observed by Swift. Comparison with another data set is on-going. [Research supported by the Office of Naval Research and ARL Exploratory and Foundational Research Program.]
Thermoacoustic device for nuclear fuel monitoring and heat transfer enhancement
Authors: Ali Randall A. , Garrett Steven L. , Smith James A. , Kotter Dale K.
Published: September 2012

The Fukushima Dai’ichi nuclear disaster of 2011 exposed the need for self-powered sensors that could transmit the status of the fuel rods within the reactor and in spent fuel ponds that was not dependent upon availability of external electrical power for either sensing or telemetry. One possible solution is the use of a thermoacoustic standing wave engine, incorporated within a fuel rod, which is heated by the nuclear fuel. The engine’s resonance frequency is correlated to the fuel rod temperature and will be transmitted by sound radiation through the reactor's or storage pond’s surrounding water. In addition to acting as a passive temperature sensor, the thermoacoustic device will serve to enhance heat transfer from the fuel to the surrounding heat transfer fluid. When activated, the acoustically-driven streaming flow of the gas within the fuel rod will circulate gas away from the nuclear fuel and convectively enhance heat transfer to the surrounding coolant. We will present results for a thermoacoustic resonator built into a Nitonic® 60 (stainless steel) fuel rod that can be substituted for conventional fuel rods in the Idaho National Laboratory’s Advanced Test Reactor. This laboratory version is heated electrically. [Work supported by the U.S. Department of Energy.]
Addition of a series spring to a lumped element model of a novel thermoacoustic refrigerator
Authors: Mitchell Eric C. , Garrett Steven L. , Smith Robert W. M. , Poese Matthew E. , Keolian Robert M.
Published: September 2012

A lumped element model is introduced for an “in-line” traveling-wave thermoacoustic refrigerator, based on a recent patent by Backhaus and Keolian [US Pat. No. 7,908,856 (22 Mar 2011)]. This model couples three electro-mechanical motors to the acoustical domain using a flexure sealed piston. Results of this lumped-element model were found to be in good agreement with a DELTAEC model. Since large displacements result in flexure fatigue, the addition of a series spring between the motor and piston was evaluated to reduce flexure seal displacement while matching the optimum load impedance. The assignment of the correct dynamic mass of the series spring when both the motor and flexure ends of the spring are moving has not been addressed previously in the literature. To determine the two effective masses required at each end of the spring, the spring is discretized into a large number of elements and is converted into a simplified circuit model to assign values to lumped-element components. These values depend upon an initial knowledge of both end velocity magnitudes and phases. This enables an iterative solution for the effective spring masses since velocities need to be known for effective masses to be determined and vice versa. [Work supported by the Applied Research Laboratory and the U.S. Department of Energy.]
Complex intensity in circular ducts containing an obstruction
Authors: Kirby Ray , Prisutova Jevgenija , Duan Wenbo , Horoshenkov Kirill
Published: September 2012

Sound intensity may be defined as a complex quantity in which the real part of the intensity is related to the magnitude of the local mean energy flow, and the imaginary part to the local oscillatory transport of energy. By treating intensity as a complex quantity it is possible to visualise energy flow in a different way and this has the potential to aid in the interpretation of, say, sound fields scattered by objects. Accordingly, the sound field scattered by an object placed in a semi-infinite circular duct is examined here. Experimental measurements of complex intensity are obtained in three (orthogonal) directions using a Microflown intensity probe, and measurements are compared to predictions obtained using a finite element based theoretical model. Comparisons between prediction and measurement are undertaken for both plane wave and multi-modal sound fields and here it is noted that when at least one higher order mode propagates it becomes more difficult to obtain good agreement between prediction and experiment for the complex intensity.
Modeling interferometric sensor response to the photoacoustic effect in layered systems
Authors: Marcus Logan , Raspet Richard , Aranchuk Vyacheslav
Published: September 2012

Chemical elements and molecules have characteristic absorption spectra that can be used for identification and detection. The photoacoustic effect has previously been used to perform spectroscopic measurements. We describe a modified photoacoustic spectroscopy method to accomplish standoff detection of thin layers of materials using an interferometric sensor. The interferometric sensor measures changes to the optical path length of an interrogation beam incident on a surface. We have developed a detailed model of the physical processes that result when a system comprised of a thin layer on a larger substrate is excited by the absorption of a modulated Gaussian laser beam. The modulated excitation beam generates heating in the sample which leads to surface motion, modulation of the temperature profile in the adjacent air, and an acoustic wave which all contribute to the signal. The model allows for the calculation of the measured signal of the interferometric sensor using the physical properties of the sample and the excitation beam. The presented model and experimental work are all applied to an idealized system comprised of a thin layer of gold on a low absorptivity borosilicate substrate to validate the computation. Future work will extend to a variety of layers and substrates.
Infrasound scattering by the Lamb dipole vortex
Authors: Naugolnykh Konstantin
Published: September 2012

The infrasound scattering by the Lamb dipole is considered in the present paper in Born approximation and using the asymptotic presentation for the Green function of the scattered field. The Lamb dipole consists of two vortexes rotating in the opposite direction what induces the specific features of process of scattering infrasound by this object. They probably accompanied the infrasound generation by high-intensity atmospheric events such as cyclones.
Acoustic streaming in channel bifurcated by an elastic partition
Authors: Sunny Megha , Nabat Taoufik , Thompson Charles
Published: September 2012

Fluid motion in a narrow channel partitioned along its long axis by a flexible membrane is examined. The enclosed fluid is excited by the time harmonic displacement in the channel cross-section. The acoustic streaming that ensues and its impact of microfluidic transport is of particular interest in this work. A three-dimensional regularized Stokeslet based analysis is presented for fluid motion in the low streaming Reynolds number regime. The effect of frequency modulation on fluid motion is examined.
Acoustic scattering from dual frequency incident fields
Authors: Nguon Chrisna , Denis Max , Chandra Kavitha , Thompson Charles
Published: September 2012

The pressure field produced by the spatial interaction of two high frequency incident beams in a three-dimensional scattering object is investigated. Of particular interest is the radiated pressure produced in response to the difference-frequency component generated from the non-linear interaction between the beams and the scattering medium. The influence of high acoustic contrast and resonant scattering is considered in the analysis. This work presents a computational study of the scattered pressure that results from the Reynolds stress in a fluid scatterer. Using Padé approximants, it is shown that the stress tensor can be computed using a uniform expansion in the contrast gauge for the scattered pressure. This allows one to investigate scattering volumes characterized by high compressibility contrast.
Infants' ability to separate superimposed vowels
Authors: Werner Lynne , Lau Bonnie , Flad Ashley
Published: September 2012

Three- and seven-month-old infants were tested using an observer-based procedure in three tasks to assess sound source segregation and selective attention. The stimuli were tokens of the vowels /a/ and /i/, spoken by two male talkers, 519 ms in duration, presented at 70 dB SPL. Success was defined as achieving 80% correct in fewer than 40 test trials. In the first task, infants heard one vowel spoken by one talker repeated at 1319 ms intervals. They learned to respond when the talker changed on one repetition of the vowel. In the second task, the tokens of the two talkers producing the same vowel were superimposed. Infants heard combined tokens repeatedly and learned to respond when the vowel produced by one talker changed. In the third task, either talker could produce the changed vowel. Infants learned to respond when one talker, but not the other, produced the changed vowel. Nearly all infants succeeded in the first two tasks. Nearly all 7-month-olds, but few 3-month-olds succeeded at the third task. These results suggest that the ability to selectively attend to one of two easily discriminable voices matures after the ability to segregate those voices. [Work supported by R01DC00396 and P30DC04661.]
Off-frequency masking effects on intensity discrimination
Authors: Patra Harisadhan , Seeman Scott , Burkland Adam , Motzko Joseph , Lolley Erin
Published: September 2012

Intensity discrimination, where a listener detects an intensity increment in an equal duration sinusoid or pedestal, is often used as a measure of intensity resolution. Intensity discrimination may be considered as tone-in-tone masking, where the pedestal is the masker and the increment is the signal. Despite the similarity between intensity discrimination and tone-in-noise masking, research suggests that a high-pass noise outside the critical band centered on the signal frequency adversely affects listeners’ intensity-discrimination thresholds. The present study examines the limits of off-frequency masking effects on intensity discrimination in five normal-hearing young adults. Detection thresholds for a 50-ms increment, added to a 50-ms-long 1000-Hz pedestal in phase, were obtained in quiet and notched-noise (NN) conditions. The pedestal and noise levels were 60 dB SPL. NN stimuli were generated by filtering telegraph noise. The low-frequency cutoffs of the NN-notches were 188, 250, 375, 500, and 750 Hz while the high-frequency cutoffs were 1500, 2000, 3000, 4000, and 6000 Hz. The detection thresholds were poorer in NN conditions than in quiet, even when cutoff frequencies were more than one octave away from the signal frequency. Effects of off-frequency maskers on the psychometric functions are discussed. [Supported by BU research and scholarship grant.]