bluuebunny/crossref_metadata_2025 huggingface dataset:
Rapid Embedded Programming in the Mathworks Environment
Authors: Burns and Daniel , Sugar Thomas G.
Published: January 2003

New, commercially available, automatic, code-generation tools are used in teaching and lab exercises to progress from controller design, to simulation, and finally to implementation on mechanical hardware. An embedded computing system consists of a dedicated, digital, electronic-processor that controls a system that interacts with the environment. Case studies highlighting a force-feedback joystick and motor servo control with encoder feedback are presented to illustrate laboratory exercises that teach mechanical engineering students hardware-in-the-loop control system design. Using these software tools, design iterations and multiple controllers are quickly simulated and downloaded to the actual hardware.
Shape Control of Flexural Vibrations of Circular Plates by Shaped Piezoelectric Actuation
Authors: Nader Manfred , Gattringer Hubert , Krommer Michael , Irschik Hans
Published: January 2003

Vibrations of smart elastic plates with integrated piezoelectric actuators are considered. Piezoelastic layers are used to generate a distributed actuation of the plate. A spatial shape function of the piezoelastic actuators is sought such that flexural vibrations induced by external forces can be completely nullified. An analytic solution of this problem is worked out for the case of clamped circular plates with a spatially constant force loading. The Kirchhoff theory of thin plates is used to derive this analytic solution. Our result is successfully validated by means of coupled 3-dimensional finite-element computations.
A Nonlinear Well-Drillstring Interaction Model
Authors: Melakhessou Hayat , Berlioz Alain , Ferraris Guy
Published: January 2003

This article is devoted to the study of the local contact between the drillstring and the well during drilling operations. The study focuses on the Bottom-Hole-Assembly (BHA), which is subjected to compression. The work is motivated by the need to understand the complex behavior of such a system, in order to improve control over their constructive and destructive potentials. The contact zone is first determined using a global finite-element model obtained from a specific computer program. Contact, which is assumed to be located somewhere on the drill-collar or on stabilizers, is prejudicial and leads to premature abrasive wear of the drillstring, reduction of the Rate Of Penetration (ROP) of the tool into the rock and reduction of the Mean Time Between Failure (MTBF). The proposed mathematical model is expressed in terms of four independent degrees of freedom which are radial displacement, rotation of the section considered, bending along the tangential direction and torsion of the string. They include the effects of bending and torsion, the whirling motion of the drillstring as well as friction phenomena occurring between the drillstring and the well. The tangential effect is modeled by using Coulomb’s law of friction. The nonlinear equations of movement are derived using Lagrange equations and are solved numerically to obtain the response. Specific attention is paid to the study of friction and a consistent contact model capable of taking into account the rolling of the drillstring, both with and without slip, is included in the model. This paper also presents a parametric study on the influence of the initial position of the string and the friction coefficient of the contact on the dynamic behavior of the structure. The model is validated by an experimental set-up equipped with two opto-electronic devices.
Structural Vibration Suppression Using the Piezoelectric Sensors and Actuators
Authors: Lee Y. Y. , Yao J.
Published: January 2003

An experimental study for the active vibration control of structures subject to external excitations using piezoelectric sensors and actuators is presented. A simply supported plate and a curved panel are used as the controlled structures in two experiments, respectively. The Independent Modal Space Control (IMSC) approach is employed for the controller design. In order to increase the adaptability, the time-domain modal identification technique is incorporated into the controller to real-time update the system parameters. The adaptive effectiveness of the time-domain modal identification technique is tested by fixing an additional mass on the simply supported plate to change its structural properties. The vibration suppression performances of the controller are 5.7 dB and 10.8 dB for the simply-supported plate with/without the mass subject to a chirp sine excitation, respectively. For the experiment of the curved panel subject to a sinusoidal excitation, the vibration attenuation of the control scheme is 5.0 dB even the control circuit is subject to some noise generated by electrical and magnetic interferences.
Characterizing Slop in Mechanical Assemblies Via Differential Geometry
Authors: Hennessey Michael P. , Shakiban Chehrzad , Shvartsman Mikhail M.
Published: January 2003

Slop (or backlash) in mechanical assemblies is often present and is usually undesirable from both craftsmanship and performance points of view. It is our belief that this phenomenon is not that well understood and that current methods of assessment are based largely on only qualitative, common-sense approaches. The focus of this paper is on developing an analytical theory for accurately characterizing slop, and on presenting an illustrative example. As one might expect, in principle, with a better understanding of slop, CAD (computer-aided-design) software package designers can create more refined software tools, mechanical engineers can design better products, and manufacturing engineers can be prepared to measure and improve craftsmanship levels. The underlying theory is based on combining concepts from differential geometry, including envelopes, constrained piecewise-smooth sweeps, and sweep vector fields (SVFs), along with basic configuration space (C-space) methods. In essence, the volumetric (or areal) error, which is generated as the movable part in an assembly is swept throughout its complete constrained volume (or area), may be viewed as a quantitative manifestation of craftsmanship errors. A 2-dimensional (2D) idealization of a common assembly that often suffers from poor craftsmanship due to slop, i.e., a doorknob assembly with exaggerated slop, is analyzed. The swept area is calculated using both traditional and SVF methods with the aid of Mathematica™. High quality Mathematica™ visualization of interesting sweeps along the bounding edges of the nonlinear slop constraint region, including generation of all of the envelope curves, is done. Finally, this work attempts to serve as a paradigm for characterizing slop based on engineering criteria.
Definition and Review of Virtual Prototyping
Authors: Wang G. Gary
Published: January 2003

Virtual Prototyping (VP) technique has been interpreted in many different ways, which causes confusion and misunderstanding among researchers and practitioners. Based on a review of the current related research and application, this paper proposes a definition of VP as well as components of a virtual prototype. VP is then compared with and distinguished from virtual reality (VR), virtual environment (VE), and virtual manufacturing (VM) techniques. Given the proposed definition and review of VP, future VP related research topics are suggested.
Axial Wave Propagation in Infinitely Long Periodic Curved Panels
Authors: Pany C. , Parthan S.
Published: January 2003

Propagation of waves along the axis of the cylindrically curved panels of infinite length, supported at regular intervals is considered in this paper to determine their natural frequencies in bending vibration. Two approximate methods of analysis are presented. In the first, bending deflections in the form of beam functions and sinusoidal modes are used to obtain the propagation constant curves. In the second method high precision triangular finite elements is used combined with a wave approach to determine the natural frequencies. It is shown that by this approach the order of the resulting matrices in the FEM is considerably reduced leading to a significant decrease in computational effect. Curves of propagation constant versus natural frequencies have been obtained for axial wave propagation of a multi supported curved panel of infinite length. From these curves, frequencies of a finite multi supported curved panel of k segments may be obtained by simply reading off the frequencies corresponding to jπ/kj=1,2…k. Bounding frequencies and bounding modes of the multi supported curved panels have been identified. It reveals that the bounding modes are similar to periodic flat panel case. Wherever possible the numerical results have been compared with those obtained independently from finite element analysis and/or results available in the literature.
Reduction of Noise Inside a Cavity by Piezoelectric Actuators
Authors: Hagiwara I. , Wang D. W. , Shi Q. Z. , Rao R. S.
Published: January 2003

A new analytical model is developed for the reduction of noise inside a cavity using distributed piezoelectric actuators. A modal coupling method is used to establish the governing equations of motion of the fully coupled acoustics-structure-piezoelectric patch system. Two performance functions relating “global” and “local” optimal control of sound pressure levels (SPL) respectively are applied to obtain the control laws. The discussions on associated control mechanism show that both the mechanisms of modal amplitude suppression and modal rearrangement may sometimes coexist in the implementation of optimal noise control.
Using Response Surface Approximations to Cover Holes in the Design Space: Conceptual Design of a Missile
Authors: Scho¨nning M. Alexandra , Nayfeh Jamal F. , Zarda P. Richard
Published: January 2003

The objective of this paper is to demonstrate an innovative and practical technique in which multidisciplinary optimization can be carried out while there exist points in the design space for which a response cannot be evaluated. It will also be demonstrated how design of experiment and response surface approximations are used to eliminate other complications associated with optimization of large-scaled designs. A multidisciplinary highly coupled air-to-air sparrow like missile design problem will be introduced to demonstrate the practical side of design optimization. The intention here is to provide practical engineering recommendations to others attempting to optimize industrial type design problems.
Time-resolved investigation of the surface chemical modification of poly(ethylene naphthalate) by nitrogen plasma treatment
Authors: Grace J. M. , Zhuang H. K. , Gerenser L. J. , Freeman D. R.
Published: January 2003

A low rf nitrogen plasma source was used to treat poly(ethylene-2, 6-naphthalate) web material. Nitrogen uptake, the N 1s centroid, the N 1s peak width, rearrangement of the ester (from the O 1s spectrum), and oxygen level were measured using x-ray photoelectron spectroscopy as a function of treatment time at several treatment conditions. The observed changes in surface chemistry with treatment time are roughly consistent with a dose response having a linear regime at low doses and a saturation regime at high doses (where dose is power/width/web speed). Hence, to a first approximation, the flux densities (to the web) of relevant species scale with power. As the dose increases, the distribution of nitrogen groups formed broadens and shifts toward higher N 1s binding energy, suggesting that a larger fraction of the nitrogen-containing species are amines at low doses and amides at higher doses. The breadth of the distribution of nitrogen-containing species appears to be strongly correlated with the amount of nitrogen incorporated in the PEN surface. A surface sites model was applied to the measured nitrogen uptake as a function of treatment time. Phenomenological nitrogen incorporation and loss terms were determined in the context of this model. Both terms increase with treatment power and treatment pressure. The ratio, however, varies to a much smaller degree as a function of process conditions, with high powers and pressures giving the highest ratio. Further elucidation of the incorporation and loss processes should be possible with plasma diagnostic data related to species concentrations.
Surface analysis by secondary-ion mass spectroscopy during etching with gas-cluster ion beam
Authors: Fenner D. B. , Shao Y.
Published: January 2003

Primary ions from a gas-cluster ion beam (GCIB) are used to investigate metal and silicon surfaces by mass spectroscopy of the secondary ions, as well as to study the nature of cluster-ion interactions with surfaces. The GCIB consists of condensed nanodroplets of either argon, oxygen, or nitrogen gas from which the singly charged cluster ions are generated. The effects of beam acceleration (∼10–25 kV) and flux (ion current density ∼50–500 nA/cm2) are reported. Secondary-ion analysis is done with a quadrupole mass spectrometer in an ultrahigh vacuum chamber. Argon GCIB incident upon metal surfaces of Al, Au, Cu, Ta, and NiFe all result in strong emission of small metal-cluster ions, metal-argon excimers and various other compound ions. Argon GCIB incident upon Al films and Si wafer surfaces generate strong fluxes of small cluster ions (i.e., Aln+ and Sin+ for n=2–10) which decay in emission intensity (with increasing n) approximately by a power law with exponent ∼2.8 and ∼1.0, respectively. Oxygen GCIB upon Al and Si generate strong fluxes of AlnOm+ and SinOm+ compound ions, respectively, with n=1–5 and m⩾n. Nitrogen GCIB upon Al and Si generate fluxes of nitride compounds. The beam conditions utilized are similar to those known to significantly reduce fine-scale surface roughness (i.e., ion smoothen) and concurrently etch at a rate of ∼1 nm/min. Native oxide films on Al, Cu, Ta, and NiFe metals are depth profiled under various GCIB conditions, thus characterizing mechanisms of cluster–ion interaction with metals. The native surface of a Ta film is investigated in some detail. The TaO+ and C+ ion emissions show a two-part decay and growth, respectively, with accumulating argon-GCIB fluence. These are well fit with exponential functions and the characteristic rates are found to depend linearly on GCIB flux and acceleration. The oxidized surfaces exhibit a minimum threshold in acceleration of ∼7 kV which corresponds to only ∼3 eV per incident argon atom. After the surface oxide is removed by the GCIB, no threshold is observed. The native oxides and Fe/Ni, ratio are depth profiled for a permalloy (NiFe) film showing resolution of the thin oxide layer differentiated from the somewhat thicker metal layer that is enriched with Fe.
Temperature dependence in time-of-flight ion scattering spectra of LiTaO3 (0001̄) and surface charge compensation of pyroelectric changes
Authors: Fang Z. L. , Lui K. M. , Lau W. M. , Makarenko B. , Rabalais J. W.
Published: January 2003

We used time-of-flight scattering and recoiling spectrometry to study the surface of a LiTaO3 (0001̄) single crystal as a function of temperature (22–200 °C). We found that the variations in surface voltage induced by pyroelectric changes of spontaneous polarization could be quantitatively estimated by computing the effects of surface voltage on the ion optics and scattering events, and measuring scattering and recoiling spectral peak shifts. Generally, when LiTaO3 (0001̄) in a steady state at room temperature was probed, its negative spontaneous polarization charge was compensated by an equivalent amount of positive surface charge and the surface voltage was virtually zero. Raising the sample temperature reduced the spontaneous polarization and indeed a rising positive surface voltage was recorded, which shows that the positive surface charge could not be drained out from the insulating surface instantaneously. However, above 160 °C, the surface voltage returned to around zero, which indicates the presence of a thermally induced surface charge compensation mechanism on LiTaO3 (0001̄) above 160 °C. Cooling the sample both closed this surface charge compensation channel and increased the negative spontaneous polarization charge. A rising negative surface voltage, which is a proper pyroelectric response, was experimentally recorded. However, the spectral changes in the cooling cycle were rather complex. First, peak shifts did not follow the theoretical pyroelectric changes, and second, unexpected additional peaks were observed. These spectral behaviors are attributed to the presence of enhanced ion induced electron and negative ion emission as additional surface charge compensation mechanisms which modified the pyroelectric changes of surface voltage on LiTaO3 (0001̄). In addition, these surface properties were found to be sensitive to surface treatments such as sputtering and proton exchange.
Application of a sawtooth surface to accelerator beam chambers with low electron emission rate
Authors: Suetsugu Y. , Tsuchiya M. , Nishidono T. , Kato N. , Satoh N. , Endo S. , Yokoyama T.
Published: January 2003

One of the latest problems in positron or proton accelerators is a single-beam instability due to an electron cloud around the beam. The instability, for an example, causes a beam size blow up of the positron beam and deteriorates the performance of the electron-positron collider. the seed of the electron cloud is the electrons emitted from the surface of the beam chamber, which consists of electrons due to the synchrotron radiation (photoelectrons) and sometimes those multiplied by the multipactoring. Suppressing the electron emission from the surface is, therefore, an essential way to cure the instability. Here a rough surface with a sawtooth structure (sawtooth surface) is proposed to reduce the electron emission from the surface of the beam chamber. A new rolling-tap method is developed for this study to make the sawtooth surface in a circular beam chamber with a length of several meters. The first experiment using a test chamber at a photon beam line of the KEK Photon Factory verifies its validity. The photoelectron emission from the sawtooth surface reduces by one order of magnitude compared to the usual smooth surface. In the second experiment under a bunched positron beam in the KEK B-Factory, however, the electron emission is comparable to that of a smooth surface and the behavior is quite different from the previous one. The reason is that the beam field excites the multipactoring of electrons and the decrease of the photoelectron emission by the sawtooth surface is wiped out. The sawtooth surface will be effective to reduce the electron emission under the situation with external magnetic fields or without strong beam fields where the electron multipactoring hardly occurs.
Effect of gas pressure on reactive pulsed laser ablation of a silicon target
Authors: Inada Mitsuru , Umezu Ikurou , Sugimura Akira
Published: January 2003

Hydrogenated silicon and silicon nitride films are synthesized by reactive pulsed laser ablation of a silicon target in hydrogen or nitrogen gas. A correlation between gas pressure and morphology or bonding configuration of deposits was investigated. With increasing gas pressure, the surface morphology abruptly changed from film to an assembly of nanoparticles at 30 Pa in hydrogen and 20 Pa in nitrogen gas. The content of Si–H and Si–N bonds in the deposits was maximized at 50 and 5 Pa in hydrogen and nitrogen gas, respectively. The influence of gas type on nanoparticle formation and reaction between silicon and ambient gas are discussed.
Gas-efficient deposition of device-quality hydrogenated amorphous silicon using low gas flows and power modulated radio-frequency discharges
Authors: Biebericher A. C. W. , van der Weg W. F. , Rath J. K. , Akdim M. R. , Goedheer W. J.
Published: January 2003

Hydrogenated amorphous silicon samples have been deposited by plasma-enhanced chemical-vapor deposition, using a square-wave amplitude-modulated radio-frequency excitation. In this article it will be shown that a combination of amplitude modulation and low gas flows improves the gas-utilization efficiency by a considerable amount. Using a conventional 50 MHz SiH4/H2 plasma with gas flows of 30 sccm, both for SiH4 and H2 at a pressure of 20 Pa, the gas-utilization efficiency is about 8%. It increases up to 50%, by modulating the amplitude of the radio-frequency excitation signal and reducing both gas flows to 10 sccm, keeping the pressure constant. In this case, the deposition rate amounted to 0.55 nm/s. The combination of amplitude modulation and gas flow reduction gives rise to sufficient ion bombardment and hydrogen dilution at low flows. Device-quality optoelectronic properties are obtained under these conditions. The refractive index at 2 eV is about 4.25 and the microstructure parameter has a value around 0.02. The electrical properties were also appropriate for solar cell application. The photo-to-dark-conductivity ratio varied between 105 and 107. The material exhibited a low defect density which is in the order of 1015–1016 cm−3. The Urbach energy amounted to 52 meV on the average.
Nondestructive evaluation of alternative substrate quality using glancing-incidence x-ray diffraction and Raman spectroscopy
Authors: Haugan H. J. , Cain A. M. , Haas T. W. , Eyink K. G. , Eiting C. J. , Tomich D. H. , Grazulis L. , Busbee J. D.
Published: January 2003

Alternate substrate technology holds promise for the growth of high-quality lattice-mismatched epitaxial films. Unfortunately, the technology has been plagued by difficulties in reproducibility of results. Some of this problem resides in a lack of characterization of the thin, twist bonded layer used as the template for subsequent epitaxial growth. In this work, grazing-incidence diffraction (GID) and micro-Raman spectroscopy were used to characterize the alternative substrate prior to growth. The 14- and 50-nm-thin GaAs layers were bonded to (100) GaAs substrates and, subsequently, exposed by standard thinning and etching techniques. The crystalline quality of the thin bonded substrates was studied by GID. The full widths at half maximum (FWHM) of the 004 peaks were used to monitor the optimum bonding condition. The measured FWHM varied from 29 to 601 arc s with smooth surfaces exhibiting the lowest values. The effects of bond pressures on template layers were studied for a series of 50 nm alternative substrates prepared using pressures ranging from 75 to 25 psi with a constant bonding temperature of 450 °C. All transferred template layers prepared within this pressure range showed poor quality (FWHM ranged from 324 to 601 arc s) when compared to bulk GaAs of 15 arc s. Micro-Raman measurements were also carried out on these samples. A transverse optical (TO) phonon line is seen and the intensity ratios of the TO to longitudinal optical phonon were much higher than that of GaAs substrate, confirming that the bonding process is causing damage to the thin template layer.
Environmentally benign etching process of amorphous silicon and tungsten using species evaporated from polytetrafluoroethylene and fluorinated ethylene propylene
Authors: Fujita Kazushi , Hori Masaru , Goto Toshio , Ito Masafumi
Published: January 2003

Environmentally benign etching process of amorphous silicon (a-Si) and tungsten (W) by using a plasma process with an evaporation of solid materials system has been developed for replacing a conventional plasma process using green house gases, such as SF6 gas and perfluorocompound gases causing global warming. The evaporation system was designed to generate fluorocarbon species from solid materials by a CO2 laser irradiation. An electron cyclotron resonance (ECR) plasma using O2 accompanied with injection of species evaporated from solid materials has been applied to a-Si and W etching for cleaning process in chemical vapor deposition chamber. Fluorinated ethylene propylene (FEP) and polytetrafluoroethylene (PTFE) are selected as the solid material and the etching characteristics between FEP and PTFE have been compared. Furthermore, the etching of a-Si and W films has been performed in the divergent magnetic field ECR downstream plasma [electron density (ne); ∼1010 cm−3, electron temperature (Te); 1.5–2.8 eV] and a planar ECR plasma [ne; ∼1010 cm−3, Te; 3.4–4.4 eV] using O2 gas with FEP evaporation. As a result, high etching rates of a-Si and W films of above 100 nm/min were successfully obtained at a substrate temperature of 400 °C in the planar ECR plasma of higher electron temperature. CFx (x=1–3) radical densities and F atom density in plasmas were measured by an infrared diode laser absorption spectroscopy and an actinometric optical emission spectroscopy, respectively. On the basis of these measurements of species, the etching mechanisms of a-Si and W films are discussed.
Ion enhanced deposition by dual titanium and acetylene plasma immersion ion implantation
Authors: Zeng Z. M. , Tian X. B. , Chu P. K.
Published: January 2003

Plasma immersion ion implantation and deposition (PIII–D) offers a non-line-of-sight fabrication method for various types of thin films on steels to improve the surface properties. In this work, titanium films were first deposited on 9Cr18 (AISI440) stainless bearing steel by metal plasma immersion ion implantation and deposition (MePIII–D) using a titanium vacuum arc plasma source. Afterwards, carbon implantation and carbon film deposition were performed by acetylene (C2H2) plasma immersion ion implantation. Multiple-layered structures with superior properties were produced by conducting Ti MePIII–D + C2H2 PIII successively. The composition and structure of the films were investigated employing Auger electron spectroscopy and Raman spectroscopy. It is shown that the mixing for Ti and C atoms is much better when the target bias is higher during Ti MePIII–D. A top diamond-like carbon layer and a titanium oxycarbide layer are formed on the 9Cr18 steel surface. The wear test results indicate that this dual PIII–D method can significantly enhance the wear properties and decrease the surface friction coefficient of 9Cr18 steel.
Kinetic energy influences on the growth mode of metal overlayers on dendrimer mediated substrates
Authors: Curry M. , Arrington D. , Street S. C. , Xu F. T. , Barnard J. A.
Published: January 2003

Evidence is presented here for kinetic energy influences on the growth mode and chemical interactions of Cr, Co, and Cu deposited by sputtering and evaporative methods on self-assembled monolayers of amine-terminated poly(amidoamine) (PAMAM) dendrimers on SiOx. X-ray photoelectron spectroscopy (XPS) measurements show that metal nitrides are formed upon deposition of the more reactive metals and the extent of reaction increases with increasing kinetic energy of the deposited species. A peak observed at 398.5 eV in the N 1s spectrum following Cu deposition apparently indicates bond breaking in the internal amido branches of the dendrimer structure but not formation of the metal nitride. Atomic force microscopy (AFM) reveals obvious changes in the surface topography due to the dendrimer adlayer, particularly for the less reactive Cu.
Observation of copper atoms behavior in a vacuum arc discharge using laser spectroscopy
Authors: Sung Y. M. , Hayashi Y. , Okraku-Yirenkyi Y. , Otsubo M. , Honda C. , Sakoda T.
Published: January 2003

In order to investigate the most important parameters influencing the breaking characteristic of a vacuum circuit breaker (VCB), the behavior of copper (Cu) particles emitted from electrodes designed as an imitation of a vacuum valve of the VCB was observed. The temporal-spatial intensity distributions due to Cu particles in an excited state or a neutral state were measured using the laser induced fluorescence (LIF) technique and a charge coupled device camera attached with a special filter. The diffusion velocity of a Cu atom was also investigated by evaluating a Doppler shift of the LIF signal. The results showed that most Cu particles were emitted from the anode and were in an excited state or an ionized state during an arc discharge. Also, Cu particles were distributed between electrodes even after the discharge chocked, and its diffusion velocity in the direction of the cathode from the anode was about 2.6 km/s.
Photoinduced second-harmonic generation in the indium tin oxide crystalline films
Authors: Ebothé J. , Kityk I. V. , Hichou A. El , El Idrissi B. , Addou M. , Krasowski J.
Published: January 2003

The nanosized thin layers (about 1–2 nm) between the indium tin oxide crystalline films and glass substrates were studied using photoinduced optical and second-order nonlinear optical [second-harmonic generation (SHG)] effects. Photoinduced changes of the effective energy gap were found for the first time in the In2O3 films doped by different amount of Sn deposited on the glass substrates. The photoinduced second-order susceptibilities show a good correlation with the behavior of the fundamental absorption edge. The maximal SHG response of the photoinduced signal was observed for a pump-probe delay times equal to about 26 ps. The experimental measurements indicate that the observed effects are stimulated by two factors: the first factor is related to the interface potential gradients on the border glass interface. The second factor is a consequence of the additional polarization due to insertion different amount of Sn atoms. The observed phenomenon may be proposed as a sensitive tool for investigations of thin semiconducting-glass interface layers.
Application of Padé via Lanczos approximations for efficient multifrequency solution of Helmholtz problems
Authors: Wagner Marcus M. , Pinsky Peter M. , Malhotra Manish
Published: January 2003

This paper addresses the efficient solution of acoustic problems in which the primary interest is obtaining the solution only on restricted portions of the domain but over a wide range of frequencies. The exterior acoustics boundary value problem is approximated using the finite element method in combination with the Dirichlet-to-Neumann (DtN) map. The restriction domain problem is formally posed in transfer function form based on the finite element solution. In order to obtain the solution over a range of frequencies, a matrix-valued Padé approximation of the transfer function is employed, using a two-sided block Lanczos algorithm. This approach provides a stable and efficient representation of the Padé approximation. In order to apply the algorithm, it is necessary to reformulate the transfer function due to the frequency dependency in the nonreflecting boundary condition. This is illustrated for the case of the DtN boundary condition, but there is no restriction on the approach which can also be applied to other radiation boundary conditions. Numerical tests confirm that the approach offers significant computational speed-up.
Active stereo sound localization
Authors: Reid Greg L. , Milios Evangelos
Published: January 2003

Estimating the direction of arrival of sound in three-dimensional space is typically performed by generalized time-delay processing on a set of signals from a fixed array of omnidirectional microphones. This requires specialized multichannel A/D hardware, and careful arrangement of the microphones into an array. This work is motivated by the desire to instead only use standard two-channel audio A/D hardware and portable equipment. To estimate direction of arrival of persistent sound, the position of the microphones is made variable by mounting them on one or more computer-controlled pan-and-tilt units. In this paper, we describe the signal processing and control algorithm of a device with two omnidirectional microphones on a fixed baseline and two rotational degrees of freedom. Experimental results with real data are reported with both impulsive and speech sounds in an untreated, normally reverberant indoor environment.
Investigation of phase coupling phenomena in sustained portion of musical instruments sound
Authors: Dubnov Shlomo , Rodet Xavier
Published: January 2003

This work investigates aperiodicities that occur in the sustained portion of a sound of musical instrument played by a human player, due to synchronous versus asynchronous deviations of the partial phases. By using an additive sinusoidal analysis, phases of individual partials are precisely extracted and their correlation statistics and coupling effects are analyzed. It is shown that various musical instruments exhibit different phase coupling characteristics. The effect of phase coupling is compared to analysis by means of higher order statistics and it is shown that both methods are closely mathematically related. Following a detailed analysis of phase coupling for various musical instruments it is suggested that phase coupling is an important characteristic of a sustained portion of sound of individual musical instruments, and possibly even of instrumental families. Interesting differences in phase deviations where found for the flute, trumpet and cello. For the cello, the effect of vibrato is examined by comparing the analysis of a closed string sound played with a natural vibrato to analysis of an open string sound that contains no vibrato. Following, a possible model for phase deviations in the cello is presented and a simulation of phase fluctuations for this model is performed.
Acoustic near-field characteristics of a conical, premixed flame
Authors: Lee Doh-Hyoung , Lieuwen Tim C.
Published: January 2003

The occurrence of self-excited pressure oscillations routinely plagues the development of combustion systems. These oscillations are often driven by interactions between the flame and acoustic perturbations. This study was performed to characterize the structure of the acoustic field in the near field of the flame and the manner in which it is influenced by oscillation frequency, combustor geometry, flame length and temperature ratio. The results of these calculations indicate that the acoustic velocity has primarily one- and two-dimensional features near the flame tip and base, respectively. The magnitude of the radial velocity components increases with temperature ratio across the flame, while their axial extent increases with frequency. However, the acoustic pressure has primarily one-dimensional characteristics. They also show that the acoustic field structure exhibits only moderate dependencies upon area expansion and flame temperature ratio for values typical of practical systems. Finally, they show that the local characteristics of the acoustic field, as well as the overall plane-wave reflection coefficient, exhibit a decreasing dependence upon the flame length as the area expansion ratio increases.
Broadband sound propagation in shallow water and geoacoustic inversion
Authors: Knobles D. P. , Koch R. A. , Thompson L. A. , Focke K. C. , Eisman P. E.
Published: January 2003

Part of an experiment to test a measurement package in a shallow water region in the Gulf of Mexico was designed to gather broadband acoustic data suitable for inversion to estimate seabed geoacoustic parameters. Continuous wave tow acoustic signals at multiple frequencies and broadband impulsive source signals were recorded on a horizontal line array in a high-noise environment. Simulated annealing with a normal mode forward propagation model is utilized to invert for a geoacoustic representation of the seabed. Several inversions are made from different data samples of two light bulb implosions, the measured sound speed profiles at the HLA and at the positions of the light bulb deployments, and for two different cost functions. The different cost functions, measured sound speed profiles, and measured time series result in different inverted geoacoustic profiles from which transmission loss is generated for comparison with measurements. On the basis of physical consistency and from the comparison of the transmission loss and time series, a best estimate geoacoustic profile is selected and compared to those obtained from previously reported inversions. Uncertainties in the sound speed profile are shown to affect the uncertainties of the estimated seabed parameters.
The reflection of bounded inhomogeneous waves on a liquid/solid interface
Authors: Vanaverbeke S. , Windels F. , Leroy O.
Published: January 2003

Fourier analysis and normal mode theory are used to describe the reflection of bounded inhomogeneous waves on a liquid/solid interface. Nonspecular reflection phenomena in the Rayleigh angle are studied in detail. In this way, an explanation is given for the Rayleigh dip phenomenon for positive inhomogeneity factors and the related result of a reflection coefficient larger than unity when the sign of the inhomogeneity factor is reversed. In the limit of large beamwidths, the reflection coefficient predicted by the infinite plane inhomogeneous wave theory is obtained. These results are entirely consistent with the experimental work published by Deschamps [J. Acoust. Soc. Am. 96, 2841–2848 (1994)]. The energy efficiency of Rayleigh wave excitation is investigated as well. It is shown that for large beamwidths, the energy efficiency for bounded inhomogeneous waves is considerably higher in comparison with Gaussian and square-profiled beams.
The role of envelope beat cues in the detection and discrimination of second-order amplitude modulation (L)
Authors: Füllgrabe Christian , Lorenzi Christian
Published: January 2003

The present study extends previous work from Lorenzi et al. [J. Acoust. Soc. Am. 110, 2470–2478 (2001)] by investigating the respective contribution of two temporal cues (fast modulation sideband and slow envelope beat cues) to the detection and discrimination of “second-order” sinusoidal amplitude modulation (SAM). Second-order SAM detection and rate discrimination abilities were measured at low beat rates (fm′⩽128 Hz) with a “carrier” modulation rate fixed at a high value (fm=256 Hz). The second-order SAM data were compared with first-order SAM detection and rate discrimination thresholds measured in similar conditions at rates fm between 1 and 256 Hz. The results showed that (1) through 64 Hz, first- and second-order SAM detection thresholds increased similarly when stimulus duration decreased from 2 s to 250 ms, whereas first-order SAM detection thresholds remained unaffected by changes in duration when fm⩾128 Hz, and (2) through 32 Hz, first- and second-order SAM rate discrimination thresholds were similar and substantially lower than first-order SAM rate discrimination thresholds measured at fm⩾128 Hz. These data demonstrate that the perception of second-order SAM is mainly based on the slow envelope beat cues. They also suggest a substantial contribution of the slow envelope beat cues appearing at the output of modulation filters tuned to or near fm to the perception of second-order SAM.
Spectral models of additive and modulation noise in speech and phonatory excitation signals
Authors: Schoentgen Jean
Published: January 2003

The article presents spectral models of additive and modulation noise in speech. The purpose is to learn about the causes of noise in the spectra of normal and disordered voices and to gauge whether the spectral properties of the perturbations of the phonatory excitation signal can be inferred from the spectral properties of the speech signal. The approach to modeling consists of deducing the Fourier series of the perturbed speech, assuming that the Fourier series of the noise and of the clean monocycle-periodic excitation are known. The models explain published data, take into account the effects of supraglottal tremor, demonstrate the modulation distortion owing to vocal tract filtering, establish conditions under which noise cues of different speech signals may be compared, and predict the impossibility of inferring the spectral properties of the frequency modulating noise from the spectral properties of the frequency modulation noise (e.g., phonatory jitter and frequency tremor). The general conclusion is that only phonatory frequency modulation noise is spectrally relevant. Other types of noise in speech are either epiphenomenal, or their spectral effects are masked by the spectral effects of frequency modulation noise.
Ear-canal acoustic admittance and reflectance effects in human neonates. I. Predictions of otoacoustic emission and auditory brainstem responses
Authors: Keefe Douglas H. , Zhao Fei , Neely Stephen T. , Gorga Michael P. , Vohr Betty R.
Published: January 2003

This report describes the extent to which ear-canal acoustic admittance and energy reflectance (YR) in human neonates (1) predict otoacoustic emission (OAE) levels and auditory brainstem response (ABR) latencies, and (2) classify OAE and ABR responses as present or absent. Analyses are reported on a subset of ears in which hearing screening measurements were obtained previously [Norton et al., Ear. Hear. 21, 348–356 (2000a)]. Tests on 1405 ears included YR, distortion-product OAEs, transient-evoked OAEs, and ABR. Principal components analysis reduced the 33 YR variables to 5–7 factors. OAE levels decreased and ABR latencies increased with increasing high-frequency energy reflectance. Up to 28% of the variance in OAE levels and 12% of the variance in ABR wave-V latencies were explained by these factors. Thus, the YR response indirectly encodes information on inter-ear variations in forward and reverse middle-ear transmission. The YR factors classify OAEs with an area under the relative operating characteristic (ROC) curve as high as 0.79, suggesting that middle-ear dysfunction is partly responsible for the inability to record OAEs in some ears. The YR factors classified ABR responses less well, with ROC areas of 0.64 for predicting wave-V latency and 0.56 for predicting Fsp.
Ear-canal acoustic admittance and reflectance measurements in human neonates. II. Predictions of middle-ear dysfunction and sensorineural hearing loss
Authors: Keefe Douglas H. , Gorga Michael P. , Neely Stephen T. , Zhao Fei , Vohr Betty R.
Published: January 2003

This report describes relationships between middle-ear measurements of acoustic admittance and energy reflectance (YR) and measurements of hearing status using visual reinforcement audiometry in a neonatal hearing-screening population. Analyses were performed on 2638 ears in which combined measurements were obtained [Norton et al., Ear Hear. 21, 348–356 (2000)]. The measurements included distortion-product otoacoustic emissions (DPOAE), transient evoked otoacoustic emissions (TEOAE), and auditory brainstem responses (ABR). Models to predict hearing status using DPOAEs, TEOAEs, or ABRs were each improved by the addition of the YR factors as interactions, in which factors were calculated using factor loadings from Keefe et al. [J. Acoust. Soc. Am. 113, 389–406 (2003)]. This result suggests that information on middle-ear status improves the ability to predict hearing status. The YR factors were used to construct a middle-ear dysfunction test on 1027 normal-hearing ears in which DPOAE and TEOAE responses were either both present or both absent, the latter condition being viewed as indicative of middle-ear dysfunction. The middle-ear dysfunction test classified these ears with a nonparametric area (A) under the relative operating characteristic curve of A=0.86, and classified normal-hearing ears that failed two-stage hearing-screening tests with areas A=0.84 for DPOAE/ABR, and A=0.81 for TEOAE/ABR tests. The middle-ear dysfunction test adequately generalized to a new sample population (A=0.82).
The synergy between speech production and perception
Authors: Ru Powen , Chi Taishih , Shamma Shihab
Published: January 2003

Speech intelligibility is known to be relatively unaffected by certain deformations of the acoustic spectrum. These include translations, stretching or contracting dilations, and shearing of the spectrum (represented along the logarithmic frequency axis). It is argued here that such robustness reflects a synergy between vocal production and auditory perception. Thus, on the one hand, it is shown that these spectral distortions are produced by common and unavoidable variations among different speakers pertaining to the length, cross-sectional profile, and losses of their vocal tracts. On the other hand, it is argued that these spectral changes leave the auditory cortical representation of the spectrum largely unchanged except for translations along one of its representational axes. These assertions are supported by analyses of production and perception models. On the production side, a simplified sinusoidal model of the vocal tract is developed which analytically relates a few “articulatory” parameters, such as the extent and location of the vocal tract constriction, to the spectral peaks of the acoustic spectra synthesized from it. The model is evaluated by comparing the identification of synthesized sustained vowels to labeled natural vowels extracted from the TIMIT corpus. On the perception side a “multiscale” model of sound processing is utilized to elucidate the effects of the deformations on the representation of the acoustic spectrum in the primary auditory cortex. Finally, the implications of these results for the perception of generally identifiable classes of sound sources beyond the specific case of speech and the vocal tract are discussed.
A passive means for cancellation of structurally radiated tones
Authors: Zapfe Jeffrey A. , Ungar Eric E.
Published: January 2003

The concept of cancellation of constant-frequency sound radiated from a vibrating surface by means of an attached mechanical oscillator is discussed. It is observed that the mass of a mechanical oscillator whose spring is attached to the vibrating surface will vibrate at comparatively large amplitudes and out of phase with that surface, provided that the surface vibrates at a frequency that is slightly higher than the oscillator’s natural frequency. From this observation it is concluded that an oscillator’s mass with a relatively small surface area can produce a volume velocity that is equal and opposite to that of the vibrating surface, resulting in cancellation of the sound radiated from the surface. Practical considerations in the design of such an oscillator are discussed, and the canceling performance from oscillators consisting of edge-supported circular disks is analyzed. An experimental canceling oscillator consisting of an edge-supported disk is described, and measurements made with this disk attached to a piston are shown to be in good agreement with analytical predictions. A tonal noise reduction exceeding 20 dB was demonstrated experimentally.
Effect of outer hair cell piezoelectricity on high-frequency receptor potentials
Authors: Spector Alexander A. , Brownell William E. , Popel Aleksander S.
Published: January 2003

The low-pass voltage response of outer hair cells predicted by conventional equivalent circuit analysis would preclude the active force production at high frequencies. We have found that the band pass characteristics can be improved by introducing the piezoelectric properties of the cell wall. In contrast to the conventional analysis, the receptor potential does not tend to zero and at any frequency is greater than a limiting value. In addition, the phase shift between the transduction current and receptor potential tends to zero. The piezoelectric properties cause an additional, strain-dependent, displacement current in the cell wall. The wall strain is estimated on the basis of a model of the cell deformation in the organ of Corti. The limiting value of the receptor potential depends on the ratio of a parameter determined by the piezoelectric coefficients and the strain to the membrane capacitance. In short cells, we have found that for the low-frequency value of about 2–3 mV and the strain level of 0.1% the receptor potential can reach 0.4 mV throughout the whole frequency range. In long cells, we have found that the effect of the piezoelectric properties is much weaker. These results are consistent with major features of the cochlear amplifier.