bluuebunny/crossref_metadata_2025 huggingface dataset:
Finite difference time domain numerical simulation of ultrasonic propagation in coated contrast agents
Authors: Belfor Galaz , Haiat Guillaume , Nicolas Taulier , Wladimir Urbach
Published: May 2008

Acoustic wave propagation in solutions of ultrasound contrast agents (UCA) designed for in situ drug delivery remains unclear due to the complex interaction between ultrasound and the coated particles (mode conversion, scattering, multiple reflections). To address this problem, two-dimensional Finite Difference Time Domain numerical simulations of ultrasound transmission and reflection were performed in solutions of an aqueous suspension of spheres made of fluid surrounded by a polymeric capsule. Simulations were made for particle concentrations equivalent ranging from 2 to 87 mg/ml. For each concentration 15 aqueous solutions with randomly located particles were considered. The speed of sound c, the attenuation coefficient and the integrated backscattered coefficient were computed from the transmitted and backscattered signals. The values of c decrease from 1498 m/s to 1432 m/s when the concentration increases, in good agreement with an effective medium model. The attenuation coefficient at 5 MHz is an increasing function of the concentration, from 0.05 to 1.2 dB/cm. The integrated backscattered coefficient increases with the concentration for low concentration values but decreases for high concentration (with a maximum value for a concentration of about 50 mg/ml). Our numerical simulations successfully mimic experimental results of ultrasound propagation in solutions of UCA.
New theoretical models for lipid-shelled ultrasound contrast agents
Authors: Doinikov Alexander A.
Published: May 2008

Analysis of existing theoretical models for lipid-coated contrast agents is presented. A general theoretical approach to the development of zero-thickness encapsulation models, allowing the testing of different rheological laws for encapsulation, is proposed. Based on available experimental data, analysis of the rheological behavior of encapsulating lipid shells is made. The problems of the existing models, such as the dependence of shell parameters on the initial bubble radius and the "compression-only" behavior, are discussed. Physical explanations for the observed effects and new theoretical models for their simulation are offered. In particular, it is shown that the inclusion of nonlinear shell viscosity allows one to model the "compression-only" behavior. It is also very important to select an appropriate rheological law describing the dependence of the shell viscosity on the shear rate. A correct choice reduces considerably the spread of the experimentally estimated values of the shell parameters and makes them look more ordered. Whereas with an inappropriate rheological law, the experimental data may look rather chaotic.
Simultaneous measurement of pressure and temperature in a focused ultrasound field with a fiber optic hydrophone
Authors: Canney Michael S. , Bailey Michael R. , Khokhlova Vera A. , Sapozhnikov Oleg A. , Crum Lawrence A.
Published: May 2008

The characterization of high intensity focused ultrasound (HIFU) fields is important for both clinical treatment planning as well as for regulation of HIFU medical devices. In previous work, we have used a 100-μm fiber optic probe hydrophone (FOPH) to measure pressure waveforms from a 2-MHz HIFU source with 42-mm aperture and 44-mm focal length. The formation of shock waves with peak positive pressure of up to 80-MPa were measured and modeled in transparent tissue-mimicking gel phantoms and boiling was achieved in milliseconds [Canney MS, et al., J. Acoust. Soc. Am., 120:3110 (2006)]. In this work, the FOPH was also used to measure temperature changes in tissue phantoms from HIFU at peak focal intensities of 5000-20,000 W/cm2. Temperature measurements were obtained by first low-pass filtering the voltage signal measured from the FOPH to remove the acoustic part of the measurement. Then, calibration of voltage to temperature was performed using results from a separate calibration experiment. Experimental measurements were compared with numerical modeling using a KZK-type model for acoustic propagation coupled with a heat transfer model. In summary, temperatures of 100°C were measured at the HIFU focus in milliseconds, in agreement with modeling [Work supported by NIH DK43881, NSBRI SMS00402, and RFBR.]
Visualization of transducer fields using a two-dimensional acousto-optic sensor
Authors: Pergantis Charles , Sandhu Jaswinder , Popek Witold
Published: May 2008

In this paper we will report on the use of a novel two-dimensional acousto-optic (2D AO) sensor as a simple, fast and cost-effective method of mapping transducer fields, which could be useful for quality control and quality assurance (QC/QA) of diagnostic and therapeutic transducers. This capability could be particularly useful for monitoring power output of therapeutic transducers prior to administering ultrasound based thermo-therapy treatment. It may also provide a quick tool for determining beam position and other transducer field characteristics such as propagation angle, beam diameter, divergence, and cross-sectional uniformity. Current standard transducer field mapping practices requires point-by-point scanning over a ball reflector or a hydrophone to map the transducer field. This approach is tedious, requiring hours of scanning time to generate the full cross-sectional and axial field distributions. The 2D AO system could overcome some of the drawbacks of current conventional scanning methodologies.
Uncertainty Evaluation of Effective Radiation Area of Ultrasound Transducers: Preliminary Results of Inmetro's Laboratory of Ultrasound
Authors: Alvarenga Andre V. , Costa-Felix Rodrigo
Published: May 2008

According to the "Guide to the Expression of Uncertainty of Measurement" (GUM), on calculation of the uncertainty of a given measurement it is necessary to take into account two types of uncertainty: Type A and Type B. Type A uncertainty is obtained from the statistical analysis of a series of observations, while Type B comes from sources that can not be evaluated considering statistical analysis, but can be obtained from previous measurements, knowledge on the behaviour of the measuring equipment, manufacturer's specifications, and data from certificates or handbooks. Herein, the Effective Radiation Area (ERA) of ultrasound transducers has been estimated at Inmetro's Laboratory of Ultrasound using an acoustic pressure field mapping system. ERA calculation protocol developed was based on Standard IEC 61689. Besides, the Type A uncertainty was estimated from 4 repetitions of the full procedure for the determination of ERA, and Type B one was estimated from the mathematical model for ERA calculation, obtained based on IEC 61689 and the GUM. Initial tests using US transducer of 1.0 MHz and 2.25 MHz indicated an expanded uncertainty inferior to 7.0%. This preliminary result encourages further research and development in order to increases frequency range to be assessed.
High intensity ultrasound activation of coagulation factors
Authors: Mitchell Stuart B. , Juaire Noemie C. , Wang Yak-Nam
Published: May 2008

Although it has been demonstrated that High Intensity Focused Ultrasound (HIFU) can induce vascular cauterization, acoustic hemostasis technology has not been successful in making the transition from proof-of-concept to clinical settings. One reason for this lack of acceptance is the limited understanding of the fundamental mechanisms involved in ultrasound-vessel and ultrasound-blood interactions. The aim of this research was to investigate the hematological and biochemical mechanisms which are influenced by HIFU induced coagulation. HIFU was used to induce coagulation in an in vitro hematological flow system and in animal models. The flow circuit and in vivo arteries were instrumented with flow probes and thermocouples in the treatment region. Physiological parameters were recorded throughout the in vivo experiments. Blood samples were drawn for analysis prior to, during, and immediately following each HIFU treatment. Clotting time, complete blood count, and biochemical analysis were performed immediately and citrated samples were immediately centrifuged and frozen for future analysis. Results indicate that HIFU can change local and systemic levels of thombin/anti-thrombin complex (TAT) and tissue plasminogen activator (tPA), as well as induce changes in activated clotting time (ACT). These results indicate that HIFU can induce coagulation via the coagulation cascades (TAT) and that normal hematological response to thrombus formation is unaffected.
The effect of high intensity focussed ultrasound (HIFU) on pH responsive PEGylated micelles
Authors: Smith Moira J. , Eccleston Mark E. , Slater Nigel K.
Published: May 2008

The effect of HIFU on pH responsive PEGylated micelles was investigated. Micelles can be used as drug carrier vehicles reducing unwanted drug toxicity. HIFU is able to release drugs from the circulating micelles, as well as improving intracellular uptake of both micelle-encapsulated and free drugs non-invasively. Large molecules generally enter cells by endocytosis. Endosomes gradually become acidic and fuse with enzyme containing lysosomes degrading the endosomal contents and preventing them from reaching their intracellular target. Using pH responsive polymers enables endosomes to be distrupted, releasing their contents into the cytoplasm before degradation occurs. Addition of poly(ethylene glycol), referred to as PEGylation, prolongs circulatory half-life and reduces degradation within the bloodstream. HIFU did enable release of encapsulated molecules from the modified micelles, and the micelles were taken up by H69 human carcinoma cells in vitro. Further work will investigate optimization of the micelles to maximize encapsulated drug release. The combined approach of using both pH responsive PEGylated micelles and HIFU to deliver drugs would provide more accurate targeting of therapies allowing higher therapeutic doses to be administered, reduce unwanted side effects and give patients a higher quality of life.
Liver fibrosis identification by spectral slope of the backscattering curve
Authors: Meziri Mahmoud , Pereira Wagner C. , Tiah Naceur , Remita Naamane , Boudjema Bouzid , Laugier Pascal
Published: May 2008

Ultrasonic tissue characterization is primarily based on radio-frequency (RF) signals. Different studies have demonstrated that the RF signals are closely linked to tissue structures. The processing of these signals using spectral methods has shown the possibility of deriving quantitative parameters (attenuation and backscattered coefficients) and also of providing a means to estimate the elementary properties of tissue (scatterer size, concentration, periodicity) by evaluating spectral parameters (slope, intercept etc). We have estimated the spectral slope of the average backscattering curve to test its potential in the discrimination of fibrosis stages (F0, F1, F2, F3, and F4, METAVIR scale) from 20 in-vitro human liver samples, insonified at 20 MHz. The slope estimations were (dB/MHz): 0.95,0.24 (F0), 1.15,0.43 (F1), 1.20,0.26 (F3) and 1.07,0.33 (F4). The Kolmogorov-Smirnov test (p>0.05) indicated that the slope alone cannot discriminate all fibrosis groups (as well as the other mentioned parameters). When associated to integrated backscattered coefficient, discriminant analysis has correctly classified 80% of liver samples (p<0.0000). The misclassification resulted from some F0 samples grouped as F4 or vice-versa, which agrees with our previous results that suggested some parameter overlapping for normal and cirrhotic hepatic tissue. Nevertheless, combination of these parameters can help the diagnosis of liver fibrosis.
Sensitivity study of the acoustic nonlinearity parameter for measuring temperatures during High Intensity Focused Ultrasound treatment
Authors: Van Dongen Koen W. , Verweij Martin D.
Published: May 2008

The aim of High Intensity Focused Ultrasound (HIFU) is to locally increase the temperature in a body. For an adequate application of the treatment it is important to measure non-invasively the temperature profiles in the heated region. Most efficiently, this is done with the same modality as being used for heating. Consequently, the preferred measuring method should rely on the temperature dependence of an acoustic medium parameter. The goal of this study is to determine which parameter is most sensitive to temperature changes. To find the most suitable parameter, the temperature dependence of the speed of sound (SOS), the density of mass and the acoustic nonlinearity parameter B/A are compared for water. The temperature dependence of the SOS and the mass density are obtained by interpolating values found in literature. Since measured values of the B/A parameter are only known for a few coarsely distributed temperature values, it has been synthesised from a two-dimensional function describing the SOS versus temperature and pressure. It turns out that the B/A parameter is far more sensitive for temperature changes than the other parameters. Comparison with measured B/A values confirms the idea that nonlinear acoustics is a favourite candidate to measure temperature profiles.
The scattering of sound by a moving sphere in a stratified liquid
Authors: Bach Jason , Ku David , Declercq Nico F.
Published: May 2008

The interaction of sound with a sphere and the Doppler shift caused by scatterers in motion are well described in the literature. A numerical study is performed on the interaction of sound with a moving sphere and with multiple moving spheres. The study shows how the reflected sound fields are influenced by the relative motion and relative position of the spheres. The aim of the research is to discover efficient acoustic methods to detect and characterize moving spheres at different levels of complexity determined by the number of spheres, their relative velocities and the velocity of the surrounding liquid. At a first stage the interaction of sound with a single sphere in a stratified fluid flow is investigated. The research is performed in the framework of the use of ultrasound for biomedical applications.
Two coupling media method for ultrasonic velocity measurement in biological tissues
Authors: Mathieu Jérôme , Leydier Audrey
Published: May 2008

Measuring the ultrasonic velocity in soft materials, especially in biological tissues, is never easy. One of the main problems is that the thickness of the sample in test is badly defined. From time-of-flight measurement method uncertainties in the thickness induce important uncertainties in experimental results. This causes that the ultrasonic velocity is often a poor criteria whereas it could be a good one. This paper brings a new method to measure the ultrasonic velocity in soft materials without knowing the sample thickness The main idea of this method is to use two different coupling media for making two relative time-of-flight measurements. The comparison of these two measurements gives the ultrasonic velocity in the sample in test. Furthermore, this comparison can give the local sample thickness of the sample. The uncertainty calculi show up that the effect on the thickness uncertainties is drastically reduced by using this new ultrasound method. This method is validated on reference samples, in silicon. Before concluding, some experimental results obtained with mouse skin samples are presented.
Carotid Inter-adventitial Distance based Vascular Age and Heart Disease Risk Estimation from B mode Ultrasound
Authors: Joseph Jayaraj , Kumar Kishore , Jayashankar V
Published: May 2008

A method to estimate the risk of heart disease in a person, based on diagnostic ultrasound is proposed here. The "vascular age" obtained from carotid ultrasound is very commonly used as a measure of cardiac health. Existing methods of vascular age estimation make use of the Carotid Intima Media Thickness (CIMT) measurements to arrive at an estimate of the vascular age. Recent work has demonstrated that the carotid inter adventitial distance (CAD) has a direct relation with the risk of coronary heart disease in persons. It has also been demonstrated that CAD correlates better to a number of risk factors accounting for heart disease than the CIMT. Hence, we propose a method to estimate vascular age based on CAD. B mode images of the carotid artery are analyzed to find out the carotid inter adventitial distance. The vascular age is estimated from carotid diameter using a statistical model developed based on the Atherosclerosis Risk In Communities Limited access database. This vascular age is then used to modify standard risk assessment procedures like the Framingham risk equation to give a better estimate of coronary heart disease risk. A comparison of the method with the CIMT based method is also performed.
Applying Genetic Algorithms to Optimise Breast Ultrasound Images Segmentation Procedure Based on Morphological Operators
Authors: Alvarenga Andre V. , Pereira Wagner C. , Infantosi Antonio F. , Azevedo Carolina M.
Published: May 2008

Ultrasound (US) image segmentation is a complex problem due its textural nature. To address this difficulty, different segmentation procedures have been described to support radiologists in recognising abnormal US-image areas. This work proposes a procedure, based on Genetic Algorithms (GA) and Morphological Operators (MO), to segment breast tumours on ultrasound images. Each chromosome represents a complete image processing sequence, composed of MOs and structuring elements (SE). The GA generates 500 chromosomes of 93 genes, where the three first genes summed indicate the number of performed operations, the following 45 genes represent the operations' sequence, and the last 45, the SE-disk diameter (in pixel). The best segmentation sequence (best chromosome) is selected using an objective function, based on the weighted sum of the number of false-positive and false-negative pixels. The gold standards are the tumour contours depicted by an experienced radiologist. Twenty images are used to train the GA procedure, and the best chromosome tested with 40 different images. The performance of the procedure is assessed using the overlap ratio among the obtained segmentation and the gold standard. All tested images present an area overlap ratio superior to 70%. This initial result encourages us to go further by increasing the number of images.
Measuring physiological properties of lymphoedemous tissues by ultrasound: theoretical foundations
Authors: Barbone Paul E. , Leiderman Ricardo , Bamber Jeff , Berry Gearoid , Oberai Assad A. , Zhang Yixiao
Published: May 2008

Roughly one in four breast cancer survivors report some degree of arm oedema. Lymphoedema is a build-up of excess lymph fluids in the tissues. Persistent lymphoedema leads to pain, diminished limb function, increased risk of infection, soft tissue fibrosis, and severe cases can be grossly disfiguring. From a mechanics perspective, the lymphoedemous tissue may be thought of as a two phase composite, consisting of both fluid and solid phases. Here we discuss the use of composites mixture theory to model the mechanics of lymphoedemous tissues. By treating the tissue as a fluid-solid composite, rules-of-mixtures may be used to estimate the effective moduli in terms of the properties of the individual components and their respective volume fractions in these two states. The mechanical properties of the tissue may be measured in vivo using a generalization of the methods of ultrasound elasticity imaging. We discuss how the measured ''effective stiffness" depends upon whether the tissue is drained or undrained, and how ultrasound may be used to measure these properties. Thus we explore the possibility of evaluating volume fractions and component properties of the individual tissue phases from ultrasound elasticity imaging.
Multilayered non-invasive temperature estimation from backscattered ultrasound
Authors: Teixeira Cesar A. , Graça Ruano Maria , Ruano António , Pereira Wagner C.
Published: May 2008

A major drawback on the application of thermal therapies is the lack of reliable knowledge about temperature in the region under treatment. The most attractive approach is non-invasive temperature estimation (NITE) strategies and, among them, techniques based on backscattered ultrasound (BSU) are a convenient choice for its portability and simplicity. Using BSU some methods have been proposed for temperature estimation basically for homogeneous media, and simple operating situations. More complex scenarios can be explored by non-linear approaches. In this work, a methodology based on neural networks is presented for temperature estimation in a multilayer phantom. A three-layer gel-based phantom was heated at eight intensities, between 0.30 and 2.0 W/cm2 (at 1MHz) for 15 minutes. Temperature and BSU signals were acquired from five spatial-points at each 10 seconds. Temporal echo-shifts, induced by temperature change, were computed from the BSU signals, and used as model's input information. Neural models were developed to estimate temperature at four intensities. Then models were validated in data including all the intensities. The best model presents a maximum absolute error of 0.43 °C for untrained situations. To the best of our knowledge this is the first NITE approach in multilayered media.
Overcoming Scaling Problems in Miniaturized Silicon Microphones
Authors: Lee Sung B. , Schafer David E. , Loeppert Peter V.
Published: May 2008

In 2008 it is projected that global demand for mobile devices will reach 1.2 billion units. Compared to electronic gadgets from 2002 when 430 million cell phones were sold world wide, these devices are smaller, have more features, and will generally be priced lower. In order to keep up with designers and manufacturers who relentlessly pursue efficient use of space at lower cost, it is required that component manufacturers pursue the same goal. For a microphone manufacturer like Knowles, this led to the introduction of world's first commercialized surface-mountable microphone, the SiSonic™ microphone, in 2002. MEMS technology is used to manufacture the complex miniaturized components used in SiSonic™ microphone. Straightforward miniaturization of microphone diaphragms made of silicon, a common material in MEMS technology, instead of traditional diaphragm materials leads to poor performing microphones. To take advantage of MEMS technology without sacrificing microphone performance we developed the free plate technology. In this presentation we discuss the use of free plate technology to overcome difficulties related to miniaturization in MEMS.
Silicon microphones: a commercial success? and what comes next
Authors: Thompson Stephen C.
Published: May 2008

The first silicon microphone commercial product was introduced to the market in late 2005. As of early 2008 the cumulative production is well over a half billion units and the production rates continue to rise. To date the acoustical performance of these microphones is only as good as that of the of the lowest priced miniature electret microphones. Yet acoustical systems manufacturers often prefer silicon microphones because they are compatible with automated insertion and wave soldering assembly methods. Silicon microphones are also more environmentally stable in sensitivity than are electrets which may be important in matched microphone applications. Current research activities are investigating methods to reduce the internal noise improve matching tolerances, and further reduce manufacturing costs. This paper will review the current state of silicon microphones in commercial manufacture, and will survey some of the areas of current research in an attempt to suggest some possible directions of future market development.
Optimization of miniaturized silicon microphones using a two-wafer approach
Authors: Miao Jianmin , Tan Chee Wee , Wang Zhihong
Published: May 2008

A two-wafer concept is proposed for the fabrication of silicon microphones with emphasis on deep reactive ion etching and wafer bonding techniques. For miniaturized sensor structures with an air gap of 1-2 microns, the viscous damping effect dominates the dissipation mechanism, which can have an adverse influence on the microphone performance, namely frequency response characteristic and mechanical-thermal noise. Therefore, an optimum microphone performance has its origin in a well-designed backplate structure. A silicon backplate with carefully placed acoustic slots and holes is attached to a silicon nitride/metal-based diaphragm. An impediment to achieve high sensitivity is the residual stress that is presented in the diaphragms. Besides the process optimization of less stress silicon nitride layer and the introduction of corrugated diaphragm, an investigation is carried out to determine the effects of sputtering parameters of Cr/Au metal electrode film (thickness, sputtering process pressure and process power) on the residual stress of silicon nitride/metal diaphragm. Details of modeling, fabrication and experimental results will be presented.
Piezoelectric Cantilevers for Low-Noise Silicon Microphones
Authors: Littrell Robert , Grosh Karl
Published: May 2008

Microphones fabricated using microelectromechanical systems (MEMS) technology are one of the fastest growing applications of MEMS. Capacitive sensing has been the dominant detection principle used in MEMS microphones. Piezoelectric sensing, however, offers advantages including simpler accompanying circuitry and the possibility for simpler fabrication. Piezoelectric microphones have been limited primarily by a high noise floor, typically at least an order of magnitude higher than, otherwise similar, capacitive microphones. We present a low noise piezoelectric cantilever microphone to overcome the main limitation of previously constructed piezoelectric microphones. Aluminum Nitride (AlN) has been selected as the piezoelectric material because its piezoelectric coupling coefficient, in combination with its electric permittivity, and its piezoelectric loss coefficient enable low-noise devices. Through both mechanical and electrical optimization, models indicate that by combining several short, thin cantilevers made exclusively of Molybdenum and AlN, microphones with a die size of 1mm x 1mm, 10 kHz bandwidth, 2mV/Pa sensitivity, and noise floor below 40 dBA can be constructed using a simple 4 mask process. Analytical and numerical models and experimental results will be presented.
A low-noise biomimetic differential microphone
Authors: Miles Ronald N. , Su Quang T. , Cui Weili , Jones Stephen A. , Degertekin F. Levent , Bicen Baris , Garcia Caesar , Hall Neal A.
Published: May 2008

A miniature differential microphone is described that has a noise floor that is substantially lower than that of existing devices of comparable size. The sensitivity of a differential microphone suffers as the distance between the two pressure sensing locations decreases, resulting in an increase in the input sound pressure-referred noise floor. In the microphone described here, the two sources of microphone internal noise, the diaphragm thermal noise and the electronic noise, are minimized by a combination of novel diaphragm design and the use of low-noise optical sensing. The differential microphone diaphragm measures 1 mm by 2 mm and is fabricated out of polycrystalline silicon. The diaphragm design is based on the coupled ears of the fly Ormia ochracea. The sound pressure input-referred noise floor of this miniature differential microphone has been measured to be less than 36 dBA.
On determination of microphone response and other parameters by a hybrid experimental and numerical method
Authors: Barrera-Figueroa Salvador , Jacobsen Finn , Rasmussen Knud
Published: May 2008

Typically, numerical calculations of the pressure, free-field and random-incidence response of a condenser microphone are carried out on the basis of an assumed displacement distribution of the diaphragm of the microphone; the conventional assumption is that the displacement follows a Bessel function. This assumption is probably valid at frequencies below the resonance frequency. However, at higher frequencies the movement of the membrane is heavily coupled with the damping of the air film between membrane and back plate, and with resonances in the back chamber of the microphone. A solution to this problem is to measure the velocity distribution of the membrane by means of a non-contact method, such as laser vibrometry. The measured velocity distributions can be used together with a numerical formulation such as the Boundary Element Method for estimating the microphone response and other parameters such as the acoustic centres. In this work, a hybrid method is presented. The velocity distributions of condenser Laboratory Standard microphones were measured using a laser vibrometer. This measured velocity distribution was used for estimating the microphone responses and parameters. The agreement with experimental data is good. This method can be used as an alternative for validating the parameters of the microphones determined by classical calibration techniques.
Diffraction based optical MEMS microphones and accelerometers with active electrostatic force feedback
Authors: Bicen Baris , Garcia Caesar , Hall Neal A. , Okandan Murat , Cui Weili , Su Quang T. , Miles Ronald N. , Degertekin Levent
Published: May 2008

Diffraction-based optical displacement detection method and its use in low noise micromachined microphones have been shown earlier. [Hall et al., J. Acoust. Soc. Am. 118, 3000-3009 (2005), Garcia et al., J. Acoust. Soc. Am. 121, 3155 (2007)]. In these devices, the integrated electrostatic port of the sensor is uncoupled from the integrated optical sensing. This structure enables one to use this port for sensitivity tuning, self characterization, and active control to adjust the device dynamics. Given that the displacement noise of integrated optical sensor is below the thermal-mechanical noise of the mechanical structure, one can implement force feedback methods such as active Q-control, or adjust device stiffness without adding substantial noise to the system. We implemented micromachined optical microphones and accelerometers with integrated optoelectronics integrated in a 1.5mm3 volume. We present experimental results on force feedback Q-control of low noise omnidirectional, and biomimetic directional optical microphones, as well as adjusting the stiffness of accelerometers to improve their frequency response. [Work supported by NIH Grant 5R01DC005762-03 and the Catalyst Foundation.]
Advanced Processing of Microphone Array Data for Engineering Applications
Authors: Guidati Sandro
Published: May 2008

Microphone arrays are tools for the localisation and quantification of sound sources. The use of the technology is strongly related to the progresses in computer technology. For a long time the application was limited to military or scientific use. The focus of the systems designed for industrial applications lies on fast setup and basic evaluation (e.g. delay-and-sum beamforming). The resulting boundaries are mainly a limited dynamic range and the limitation to free field environments. Although a wide range of algorithms for advanced evaluation has been developed, only few of them are integrated in industrial systems. This is mainly due to the fact that these algorithms require considerably longer computation time, expert knowledge and the integration of additional hardware. This paper presents techniques for almost real-time processing of microphone array data including multiband beamforming, coherence/incoherence filtering and the integration of measured source characteristics for the application in strongly reverberant environments. By combining the signals of multiple cameras it is possible to detect the distance between the array and a three dimensional source distribution increasing the accuracy of the localisation and quantification.
Differential microphone array for speech recognition
Authors: Martin Philippe , Lissek Hervé , Dines John
Published: May 2008

Speech recognition applications embedded on a PDA are already available on the market. The usual hardware for this kind of system is a single microphone mounted on the PDA, giving good results within quiet environments. Though, the recognition rate falls drastically as the signal to noise ratio decreases. Arrays of microphones are then particularly interesting, allowing the discrimination of useful sounds sources within parasitic ones, thanks to an improved directivity pattern. In speech recognition applications on PDA, a trade-off is to be found on an array small enough to guarantee the ergonomics of the whole system, while operating on a bandwidth covering the frequency range of human voice, from 300 Hz up to 6 kHz and low distortion ratio. Differential arrays are well adapted to fulfill these specifications, since they are known to be robust and allow small dimensions for a high directivity index. The performances could be improved by the addition of adaptive post-filtering and noise reduction algorithms. This work describes the design and the implementation of a recording device dedicated to speech recognition applications on PDA, based on overlapping differential arrays. The assessment of its performances in a noisy environment is carried out and show the system efficiencies.
Time-Shift Sensor Noise Suppression Algorithm
Authors: De Cheveigne Alain
Published: May 2008

We propose a new method to remove sensor noise from multichannel data recordings. Each channel is projected on the span of the time-shifted neighboring channels, and replaced by its projection. Noise specific to any sensor is attenuated, whereas any signal component that loads more than one sensor is preserved. The inclusion of a range of time shifts allows the method to compensate for any delay or convolutional mismatch in the signal paths between sensors. The method is expected to be of use for microphone arrays to reduce sensor-specific noise, e.g. thermal noise, wind noise, or overloading. The new method extends a previous method for sensor noise suppression in physiological recordings (EEG, MEG), that performed the same operation without the delays.
Acoustic Computerized Tomography for Temperature Distribution Measurement in Rectangular Space
Authors: Minamide Ayumu , Wakatsuki Naoto , Mizutani Koichi
Published: May 2008

In this research, we propose an improved algorithm of Acoustic Computerized Tomography to measure temperature distribution in rectangular space. Temperature distribution measurement is used in various fields, such as, air-conditioning control in offices, temperature control in greenhouse. If acoustic transducers are fixed, they are ordinarily arranged at equal intervals on a circle. However, it is difficult to take circular arrangements of transducers in the rectangular spaces. Thus, we devise to arrange the transducers on a rectangle. Therefore, a problem is occurs that projection data could not be obtained at equal angular intervals. To solve this problem, we propose non-uniform angular interval Back-Projection to weight the projection data with respect to its angular intervals. We confirm usefulness of the proposed method by numerical simulations. In the simulations, 24-acoustic transducers are arranged at equal intervals on a rectangle whose aspect ratio is two. By using the proposed method, the shape approaches to the given temperature distribution, and RMS error of the reconstructed distribution to the given distribution decreases about 25 % compared to the error of conventional CT.
Two-input two-output speech enhancement with binaural spatial information using a soft decision mask filter
Authors: Hongo Satoshi , Sasaki Ai , Sakamoto Shuichi , Li Junfeng , Suzuki Yôiti
Published: May 2008

A two-input two-output speech enhancement method that preserves binaural spatial information in the output is effective for realizing a comfortable auditory communication system. Such a system benefits from the noise reduction capability provided by the signal processing technology, in addition to the binaural processing of the human auditory system. We investigated a two-input two-output speech enhancement method that calculates soft decision mask filters to attenuate a noisy time-frequency bin. The soft decision mask filter is estimated for each direction of arrival (DOA) based on a target noise ratio calculated using an adaptive filter that cancels the target signal. Results of computer simulations show that the proposed method has superior capabilities for maintaining spatial information in the two-output signals and for segregating the target signal in arbitrary azimuth and elevation DOA.
Finite element and boundary element modeling of multimodal arrays
Authors: Bernard Julien
Published: May 2008

Modern active sonar arrays exhibit the following characteristics: low operating frequency, large number of transducers, small transducer spacing compared to wavelength, and in some cases, multimodal transducers. This results in strong, complex acoustic interaction phenomena which can involve both a large number of array elements and multiple transducer modes. To predict the performance of such arrays, this paper presents a modeling approach which is both accurate and computationally economical. First, the generic equivalent circuit for an array of multimodal transducers is described. The field of application of such a model, the definition of the parameters, and the characteristics which can be calculated from it are provided. Second, the computation of the equivalent circuit parameters is performed using commercial finite element and boundary element codes. Specifically, a method is described to compute the mechanical, electrical, self and mutual radiation parameters of the various transducer modes. Finally, the methodology is applied to a 12 element volumetric array of flextensional transducers, with both λ/2 and λ/4 spacings.
The design of a wideband and widebeam piston transducer in a finite closed circular baffle
Authors: Sahin Zekeriyya , Koymen Hayrettin
Published: May 2008

The design of a high power piezoelectric underwater transducer operating at frequency range 45kHz-85kHz with acoustic power capability in excess of 150W is described. The transducer consists of two back-to-back elements. Each element is formed by stacked PZT-4 ceramic rings, a matching and a steel backing layer, and placed in a finite rigid circular baffle. We investigate the dependence of bandwidth and beamwidth to the combination of piston and baffle radii, a and b, respectively. With a ka of 2.45 (k:wave number) and b/a ratio of 2, the transducer resonates at 65kHz with 70% bandwidth and has a beamwidth of 60° at each half space. We show that when two transducers are placed at right angles spatially and driven in parallel, we can obtain an omnidirectional beam pattern horizontally in the lower frequency band. The beam pattern exhibits two dips in each quadrant at the higher end of the frequency band, which are within 7 dB. We also investigated power handling capability of the transducer from thermal point of view using finite element analysis. The input impedance measurements agree well with the numerical results within the pass band.
Acoustic radiation of wind instruments resonators
Authors: Mallaroni Bastien , Mattei Pierre-Olivier , Herzog Philippe
Published: May 2008

Optimization of the acoustic radiation of wind instruments resonators may be based on the study of finite length circular ducts radiating in unbounded medium, as this is a model realistic enough, but which allows advanced analytics developments. Our approach is based on the calculation of resonance frequencies of such a simplified wind instrument. These are the complex frequency singularities of the operator describing the global resonator/external fluid system. A Newton's method is used to search for the singularities of the multimodal Green's function of the duct. This is obtained by the product of impedance matrices which relate pressure and velocity between two abscissae inside the duct. A variable coupling factor is introduced with external acoustic radiation, described by a multimodal radiation impedance based on the Zorumski formulation. Examples of variation of the resonance frequencies with this coupling factor will be given. Surprisingly, regular variations of the coupling lead to non regular evolution of the resonances. Physical interpretation of this behaviour will be discussed.
Longitudinal voice source and acoustic analysis of English girl cathedral choristers
Authors: Howard David M.
Published: May 2008

Since 1998, the authors have been recording girl choristers who sing at Wells Cathedral in England to enable a longitudinal quantitative exploration of voice development for girls aged between 8 and 16 who are involved in professional choral singing on a daily basis. The recordings are made of their acoustic output and the output from an electrolaryngograph for a series of vocal tasks including speaking and singing. Changes have been observed on a longitudinal basis for larynx closed quotient (the percentage of each cycle for which the vocal folds remain closed), long-term average spectra as well as in the overall spectral coverage in terms of frequency and dynamic ranges. Evidence of observations will be presented and their implications will be discussed with reference to source-filter interaction as appropriate.
Phonetograms of laryngeal source parameters for different vowels and laryngeal mechanisms
Authors: Lamesch Sylvain , Doval Boris , Castellengo Michèle
Published: May 2008

This paper explores how the laryngeal source is adjusted by the singer when the sung vowel changes. As the source parameter adjustments may depend on intensity and pitch, comparisons are done through phonetograms computed for each vowel. Distinction is made in the phonetograms between the two main laryngeal mechanisms (M1 and M2). Male and female subjects were recorded producing crescendos and decrescendos from C3 to C5 on /a/, /i/ and /o/ in order to obtain a reduced phonetogram for each vowel and each laryngeal mechanism. Sound, electroglottographic signals and vertical larynx position (VLP) were recorded. Investigations were done on the open quotient and the VLP. The results show a smaller vocal dynamic on /i/ (and in a smaller extent on /o/) in each laryngeal mechanism, and differences on the intensity low limit of the highest part of the M1-phonetogram. Clear tendencies about the larynx position were measured. They are similar for both laryngeal mechanisms, but differ among singers. The Oq seems to be lower on /i/ than on /a/ and /o/ for M1 productions.
Resonance strategies and glottal behaviour in the two main laryngeal mechanisms for professional operatic singers
Authors: Henrich Nathalie , Smith John , Wolfe Joe
Published: May 2008

In lyrical singing, two principal laryngeal mechanisms are used to produce all the notes across the singer's tessitura. Laryngeal mechanisms M1 and M2 are characterised by a greater and lesser vibrating mass respectively. Different timbres between the two are at least partly explained by their different glottal behaviours. However, different adjustments of the vocal-tract resonances, which can also contribute to different timbres, may also be involved, but have been neglected. We studied seven professional operatic singers, who produced sustained vowels at the same pitch using both laryngeal mechanisms. Vocal-tract resonances were directly measured during phonation, by broadband acoustic excitation at the mouth. Glottal behaviour and laryngeal movement were measured indirectly with an electroglottograph. As expected, we measured lower values of open quotient and higher sound pressure levels in M1 than in M2. In most cases, the first two vocal-tract resonances were characterised by lower frequencies in M2 than in M1. In the singer's formant region, similar resonance-frequency values were found for both laryngeal mechanisms. The effect on the sound spectrum of an open-quotient increase together with a first-formant decrease may be modelled by source-filter theory. The theoretical and measured amplitudes of the first two harmonics will be compared.
Chest, head and whistle registers in an untrained female singer analyzed by videokymography, strobolaryngoscopy and sound spectrography
Authors: Svec Jan G. , Sundberg Johan , Hertegard Stellan
Published: May 2008

There has been a lack of objective data on the singing voice registers, particularly on the so called "whistle" register, occurring in the top part of the female pitch range, which is accessible only to some singers. This study offers unique strobolaryngoscopic and high-speed (7812.5 images/s) videokymographic data on the vocal fold behavior of an untrained female singer capable of producing three distinct voice qualities, i.e., the chest, head and whistle registers. The sound was documented spectrographically. The transition from chest to head register, accompanied by pitch jumps, occurred around tones B4-C#5 (500-550 Hz) and was found to be associated with a slight decrease in arytenoids adduction, resulting in decrease of the closed quotient. The register shifts from head to whistle, also accompanied by pitch jumps, occurred around tones E5-B5 (670-1000 Hz) without any noticeable changes in arytenoids adduction. Some evidence was found for the vocal tract influence on this transition. The mechanism of the vocal fold vibration in whistle register was found principally similar to that at lower registers: vibrations along the whole glottal length and vertical phase differences (indicated by sharp lateral peaks in videokymography) were seen on the vocal folds up to the highest tone G6 (1590 Hz).
Doppler effect in aeroacoustics
Authors: Varnier Jean
Published: May 2008

Doppler effect in aeroacoustics The prediction of acoustic fallout caused at the ground level by aircraft in flight or by launchers at take-off sets the problem of the distortion of the emitted sound spectrum by the Doppler effect. Former studies applied to this problem use a geometrical formalism based on simplifying hypotheses such as homogeneous atmosphere, rectilinear trajectory and constant velocity of the sound source. Other studies consider the supersonic case using a model of spherical waves inside the Mach cone. These approaches are in fact not well adapted to the real cases, and the literature does not give many practical examples concerning this topic. In this study, we propose a new time approach of the Doppler effect that allows to avoid the complexity of the geometrical models and to take into account real atmosphere, curvilinear trajectories or accelerations of moving sound sources. This model allows to easily calculate the frequency shift and the change of acoustic level of the signal recorded at a given hearing point, in both cases of subsonic and supersonic sound sources. We present a first validation of this method applied to signals recorded in Kourou during the atmospheric phase of Flight 521 of Ariane 5.