Showing papers in "Archives of Acoustics in 2009"

Synthetic Transmit Aperture in Ultrasound Imaging

Abstract: The paper describes the use of synthetic transmit aperture (STA) imaging in medical ultrasound. The synthetic aperture (SA) imaging is a novel approach to today's commercial systems. In these systems the image is acquired sequentially one image line at a time that puts a strict limit on the frame rate and the possibility of acquiring a sufficient amount of data for high image quality. This limitation can be lifted by employing SA imaging where the data are acquired simultaneously from all directions over a number of emissions, and the full image can be reconstructed from those data. Due to the complete data set, it is possible to have full transmitting and receiving focusing at the entire image region to improve the contrast dynamic and spatial resolution. The paper describes the STA imaging with a single element transmitting and all elements receiving apertures. In experiments, 32-element linear transducer array with 0.48 mm inter-element spacing and a burst pulse of 100ns duration were used. The single element transmission aperture was used to generate a spherical wave covering the full image region. The 2D ultrasound images of wire phantom are presented to demonstrate the benefits of SA imaging.

Computer modelling of coupled spaces: variations of eigenmodes frequency dueto a change in coupling area

Abstract: Acoustically coupled spaces have recently been drawing more and more attention in the architectural acoustics community, thus a determination of shapes and frequencies of eigenmodes in these room systems from computer-based models has become increasingly significant. In this investigation, an eigenvalue problem was solved numerically for a simple room system consisting of two connected rectangular spaces. In a numerical procedure, the forced oscillator method with a finite difference algorithm was applied. In order to determine the influence of irregularity of system shape on eigenmodes frequency, a modal behaviour in the coupled spaces was studied for several sizes of coupling area. Calculation results have shown that with the exception of a fundamental mode, the changes in resonant frequencies were relatively small. However, an increase in a system irregularity led to a coincidence of frequencies of neighbouring modes and variations in a sequence of modes on a frequency axis, which both contributed to a degeneration of eigenmodes.

Nonconscious Control of Voice Intensity During Vocalization

Abstract: There are two separate visual systems in the human brain. Evidence from studies on both the humans and other primates has shown that there is a distinction between vision for perception and vision for action, which is reflected in the organization of the visual pathways in the cerebral cortex of primates. In recent years, researchers have attempted to find a similar dissociation between action and perception in human audition. The hypothesis tested in this paper is that the voice intensity is tracked and controlled by an auditory motor system. The results of this control are used for nonconciously correct the vocal production. To observe the dissociation between perception and motor control, a subliminal experimental situation was created, in which values below the perceptual threshold (values which were not processed through normal channels or apparatus of perception) were used. The hypothesis was that a subliminal modification of an auditory voice feedback would cause an appropriate correction as a response, even if this change was not actually perceived. Assuming that the auditory system functions in the same way as the visual one and processes the information vital for motor reactions in real time, a reaction that would compensate such a modification should be expected.

Structure and Ultrasonic Properties of Vanadium Tellurite Glasses ContainingCopper Oxide

Abstract: The elastic properties of vanadium tellurite glasses, 65TeO2-(35-x)V2O5-xCuO, with different compositions of Copper (x=7.5 to 17.5mol% in steps of 2.5mol%) have been studied at room temperature (300K). The ultrasonic velocity measurements have been made, using a transducer having resonating frequency of 4MHz (both longitudinal and shear). The density, molar volume, and ultrasonic velocities show interesting features, which are used to explore the structural changes in the network. Elastic moduli, Poisson ratio, crosslink density, Microhardnes, and Debye temperature of the glasses have been determined using the experimental data. The composition dependence of the elastic properties explores useful information about the physical properties of the vanadium tellurite glasses doped with Copper. Quantitative analysis has been carried out in order to obtain more information about the structure of the glass under the study, based on bond compression model and the Makishima [ampersand] Mackenzie model. The observed results through ultrasonic non-destructive evaluation, investigate the structural changes and mechanical properties of the glass.

Motor Nonlinearities in Electrodynamic Loudspeakers: Modelling and Measurement

Abstract: This paper studies the motor nonlinearities of a classical electrodynamic loudspeaker. Measurements show the dependence of the voice-coil inductance with its position and with the driving current as well as the force factor dependence on the coil position. They allow the tuning of the parameters of a model proposed for these dependences. Time and frequency analysis of the model help in the explanation of both the harmonic and intermodulation distortions observed in classical loudspeakers.

The Domain of Pitch in Music

Abstract: The aim of this paper is to discuss some of the physical and psycho-physiological mechanisms that contribute to transformation of the unidimensional sensation pitch into the important medium where most significant elements of music-communication code could develop. It is argued that pitch in music should not be regarded as a simple, unidimensional sensation, but it should be seen as a complex auditory system (PITCH DOMAIN) of four sensations, two in the subdomain of PITCH VALUE (natural pitch and categorized pitch or a system of pitch classes) and two in the subdomain PITCH DISTANCE (natural pitch distance and a system of musical intervals). In such a multidimensional structure pitch is particularly suited to overcoming the limitations of memory. Another part of analysis concerns the role of short-term memory (STM) and long-term memory (LTM) operating in relation with various forms of pitch. In particular, an important role of STM for natural pitch is emphasized, in maintaining the stability and coherence of any musical performance. In the remaining parts of this paper the analysis concerns specific forms of the auditory memory that contribute to the sensation of pitch distance, and problems of psychological scaling of pitch.

Triangular Bezier patches in modelling smooth boundary surface in exteriorHelmholtz problems solved by the PIES

Abstract: The paper proposes the use of triangular parametric Bezier patches as a new and effective way to generate three-dimensional boundaries in acoustics problems. The boundary geometry composed of triangular Bezier patches has been directly linked to the parametric integral equation system (PIES) to numerical solving exterior Helmholtz problems. A primary advantage of the proposed approach is to avoid the necessity of conventional domain or boundary discretization. The obtained numerical solutions compared with literature exacts results are characterized by high accuracy and convergence.

Sound power radiated from rectangular plates

Abstract: An equation for calculating the sound power radiated from a rectangular plate with arbitrary boundary conditions is derived, in which the sound power radiated from the plate is represented in terms of the normal velocity distribution on the plate and a coupling matrix. The velocity distribution on the plate is expressed in terms of the modal amplitudes and normal modes. The coupling matrix for arbitrary boundary conditions is developed mathematically using the Rayleigh integral. Finally, an approach to compute the radiation efficiency for modes of vibration is presented and the radiation efficiency of the first four most efficient vibration modes for six different boundary conditions is presented.

Bistatic sonars: sea trials, laboratory experiments and future surveys

Abstract: Bistatic sonars use separate transmitter and receiver(s), optimising the information received from seabed/target(s) scattering. Laboratory experiments are ideal to understand scattering processes and to optimise data collection strategies. They can be full-scale or scaled down. In the latter case, the influence on bistatic scattering processes needs to be carefully weighed, to validate the transition to full-scale experiments. This is particularly relevant as sea trials are expensive, difficult to conduct, and generally impossible to repeat. This article presents the results from: (1) scaled experiments on bare seabed and targets, performed at Bath and other places; (2) full-scale experiments in the GESMA submarine pens during the EC-SITAR project and (3) sea trials from similar experiments in Italy and Sweden. These results are put into the wider context of other international efforts. These three approaches (scaled and full-scale experiments plus sea trials) can be used in synergy. This has important implications for future experiments, the design of surveys and instruments, and analyses of past/future acoustic datasets.

Temperature Fields Induced by Low Power Focused Ultrasound in Soft Tissues During Gene Therapy. Numerical Predictions and Experimental Results

Abstract: The aim of this work is twofold. Firstly, to verify a theoretical model which is capable of predicting temperature fields appearing in soft tissues during their ultrasound treatment. Secondly, to analyze some aspects of the dynamics of Heat Shock Response induced by the heating process in the context of therapeutic treatment. The theoretical investigations and quantitive analysis of temperature increments at any field point versus time of heating process, depending on the heat source power, spatial distribution and duration as well as on the tissue thermal properties, has been carried out by Finite Element Method (FEM). The validation of the numerical model has been performed by comparison of the calculation results with the experimental data obtained by measuring in vitro of the 3D temperature increments induced in samples of the turkey and veal liver by the circular focused transducer with the diameter of 15mm, focal length of 25mm and resonance frequency of 2MHz. Various ultrasonic regimes were considered. They were controlled by adjusting ultrasound power and exposure time. The heat shock proteins (HSP) and misfolded proteins (MFP) levels during the proposed cyclic sonification are presented.

Modelling and Vibration Control of Planar Systems by the Use of PiezoelectricActuators

Abstract: n recent years, a great deal of work has been done on the development of control methodologies for structural and acoustic applications by using piezoelectric actuators. This paper presents the derivation of the models for planar structures with surface-mounted piezoelectric actuators. In the first approach, a parametric system identification procedure is employed to establish a mathematical model of the considered system, on the basis of the data collected from the measurements. The second approach consist in modelling of the fluid-acoustic-structural dynamics in the form of the partial differential equations, derived from physical principles such as forces and moments balance. Assuming axially symmetrical vibrations, on the basis of the models derived, the control algorithm has been developed for the circular plate to which centrally placed PZT actuators were bonded. The results of performed simulations are included and discussed.

Insertion Loss of Spiral Ducts - Measurements and Computations

Abstract: This work presents measured and computed characteristics of insertion loss (IL) of spiral ducts. Numerical and experimental models of spiral ducts have been investigated. For the numerical modeling, a three dimensional model computed by the use of a finite element method in a COMSOL Multiphysics computer application has been used. For the experimental modeling, there has been made a spiral duct model by using a three dimensional rapid prototyping technique. An acoustic system with a round silencer has been ivestigated, and the spiral duct has been inserted at the inlet. IL is considered in this paper as the difference between the sound pressure level (SPL) [dB] probed at only one outlet point of the acoustic system without and with an acoustical filter (spiral duct), respectively. The results of measured and computed IL of spiral ducts presented in this paper confirm the fact that this newly discovered technical solution for attenuating sound in ducted systems has an applicable potential. There are visible small discrepancies between the measurements and computations. The results can differ due to the non ideal dimensions of the experimental model and the non ideal inlet and outlet surroundings of the experimental acoustic system. However, the IL characteristics of the computed model is almost wholly covered by the IL characteristics of the measured model.

Analysis of Dome Home Hall theatre acoustic field

Abstract: The modelling of compartment in simulation software enables determination of acoustic parameters' distributions in a virtual compartment. The elementary question is how much the simulations reflect the actual state in a room. Analysing the acoustics of dome-shaped compartments, i.e. for instance various basilicas, a conclusion can be drawn that the acoustics of these objects is very good. Therefore the authors decided to analyse the influence of a dome shape on acoustic parameters of the compartment.

Formant frequency estimations of whispered speech in Chinese

Abstract: Formant frequencies are important cues for characterizing whispered speech. However, it is difficult to exactly estimate its formant by the conventional linear prediction coding algorithm. The main reason is that the formant bandwidth of a whisper is wider than that of voiced speech. This brings up the pole interaction problem that then leads to the result that one or more real roots are regarded as spurious and deleted from the original LP polynomial. To reduce the degradation of pole interactions, an improved root-finding formant estimation algorithm has been proposed. In this algorithm, the whisper formant bandwidth is modified to make the spectral energy of the remained formant polynomial equal to that of the original LP polynomial. Experimental results with six Chinese whispered monophthong phonemes show that the formant frequencies obtained by the proposed algorithm produce a more reliable formant spectrum than the one that does not consider the pole interaction effect.

Use of Quantitative Ultrasound to Measure Acoustic Properties of HumanSkin

Abstract: The scattering of ultrasonic waves depends on the size, shape, acoustical properties and concentration of scatterers in the tissue. The spectrum of the ultrasonic backscatter can be used to characterize non-invasively the structural and mechanical properties of tissue. We intend to apply the custom-designed high-frequency ultrasonic scanner for the skin and cutaneous lesions characterization by evaluating their attenuating and scattering properties. In this pilot study, we have explored the possibility of extracting the human skin backscattering coefficient (BC) from the ultrasonic B-scans obtained in vivo at 20-30MHz. The measured BC values of normal skin (dermis) agree well with the published data. We have found also that the spatial resolution of the BC determination using our scanner is sufficient (aprox. 1mm2) to characterize small skin lesions and assess their penetration depth.

Spatial Resolution of Attenuation Imaging

Abstract: The attenuating properties of biological tissue are of great importance in ultrasonic examination even though its anatomical variability limits diagnostics effectiveness. We are currently developing a technique for parametric imaging of attenuation and we intend to apply it for in vivo characterization of tissue. The diagnostic usefulness of the proposed technique crucially depends on the precision of the attenuation estimate and the resolution of the parametric image. These two parameters are highly correlated, since the resolution is reduced whenever averaging is used to minimize the errors introduced by the random character of the backscatter. Here we report on the results of numerical processing of both, simulated and recorded from a tissue-mimicking phantom echoes. We have analyzed the parameters of the estimation technique and examined their influence on the precision of the attenuation estimate and on the parametric image resolution. The optimal selection of attenuation image parameters depending on its intended diagnostic use, was also considered.

Non-parametric methods of estimation of type A uncertainty of theenvironmental noise hazard indices

Abstract: A control of environmental noise hazards requires estimation of uncertainty of noise indices LDEN, LN. Assessment of the type A standard uncertainty in measurement results - expressed as the standard deviation of the mean, calculated the most often at the assumption of a normal distribution - is significant for the process. Such assumption - in relation to the noise measurement results - is of a relatively low likelihood. Thus, there is a need of looking for non-standard procedures of the standard deviation estimation of the mean of results, without any information of belonging to a certain class of distribution. The aim of the hereby paper is an indication of the possibility of using non-parametric estimators of a density function in the calculation process of the type A standard uncertainty of environmental noise hazard indices. An attention was directed towards kernel estimators. The origin of their application, advantages and the method of constructing was described on the basis of a continuous monitoring of a traffic noise recorded on one of the main arteries of Krakow in 2004 and 2005. Usefulness of three forms of estimators, it means: kernel, unbiased and of maximum likelihood, was analysed. Keywords:acoustic monitoring of environment, analysis of the results, type A standard uncertainty in measurements, kernel estimator.

Determination of Transport and Thermal Properties of Silicon Samples by thePhase-Lag and Sf/Sr Methods

Abstract: The paper presents results of photoacoustic studies of thermal and transport properties of silicon samples. It shows for the first time the influence of plasma waves on the Sf/Sr and phase-lag frequency photoacoustic characteristics and describes a procedure leading to the determination of both thermal diffusivity and the life time or the diffusion length of excess carriers from those characteristics.

Verification of two methods of railway noise propagation

Abstract: The noise maps of agglomerations comprise those of road traffic-, tram-, aircraft-, industrial- and railway noise. EU recommends the use of a few selected calculation methods for the estimation of noise: for road traffic noise - NMPB-Routes-96, for aircraft noise - ECAC.CEAC Doc 29, for industrial noise - ISO 9613-2 and for railway noise - Reken en Meetvoorschrijft Railverkeerslawaai 1996 (for tram noise - there is no specific computation method). However, the Member States can use their own computations methods provided that these methods have been positively verified. The results of the calculations using their own method and interim method must be compatible. In this paper, two methods of railway noise propagation are compared: the first one recommended by EU and the second one developed at the Adam Mickiewicz University in Poznan. The results obtained by the two methods are similar.

Study of the Effect of the Orchestra Pit on the Acoustics of the Kraków OperaHall

Abstract: The orchestra pit acoustics are mostly assessed by musicians and directors of musical performances using the sense of hearing, i.e. in a subjective manner. This paper proposes a method for an objective assessment using such parameters as Support (ST) and Sound Strength (G), which are obtained by measurements. ST defines the quality of how orchestral musicians hear one another in the orchestra pit, whereas G determines the impression of loudness at selected points of the auditorium. To determine the value of these parameters, acoustic measurements were performed in the orchestra pit and the auditorium of the Krakow Opera Hall. A numerical model was also developed, which was employed for multivariant computer simulations using the CATT-acoustic software. The purpose of the paper is to present a methodology for objective assessment of the orchestra pit acoustics.

Calculation models for acoustic analysis of sacral objects

Abstract: Application of the technique of singular value decomposition (SVD) for analysis of acoustic properties of sacral objects has been presented in the paper. Previous researches by means of the SVD technique were related to the simplified calculation model basing on a three-index observation matrix. The next stage of researches presented in the paper is an attempt of decomposition of the observation matrix containing five partial indices of the index acoustic assessment of sacral objects. The matrices obtained through the SVD decomposition have been used for calculation of weights of partial indices applied for the global assessment of acoustic quality of the sanctuaries. The comparison of acoustic assessments of the sanctuaries by the global indices containing traditional weights and the weights obtained by means of the SVD technique has been performed.

Response of a plate to PZT actuators

Abstract: In this paper, the response of a plate with arbitrary boundary conditions to PZT actuators is derived. It is assumed that the plate and the actuators are rectangular and the edges of the PZT actuators are parallel to the respective edges of the plate. The response of the plate is decomposed into normal modes. The modal amplitude of the normal mode is represented in terms of the shape function of the actuator and the normal mode. The shape function of the actuator is given as a~singularity function. The normal modes for the boundary conditions with which we are concerned are calculated based on theoretical analyses of Magrab. The results of this paper are useful in designing an active noise control system in which the PZT actuators are used as the control sources.

Weakly nonlinear dynamics of short acoustic waves in exponentially stratifiedgas

Abstract: The types of linear motion over an ideal gas affected by gravity are specified approximately in the case of large characteristic wave number of perturbation k: k[ampersand]gt;[ampersand]gt; 1/H, where H is the scale of density and pressure decrease of the background gas, the so-called height of the uniform gas. The corresponding approximate operators projecting the overall vector of perturbations into specific types are derived, along with equations governing sound in a weakly nonlinear flow. The validity of approximate formulae are verified for the concrete examples of initial waveforms. The numerical analysis reveals a good agreement of these approximate expressions with the exact ones obtained previously by the author. The analysis applies to the weakly nonlinear flow as well, with the small Mach numbers (M[ampersand]lt;[ampersand]lt;1). The links inside modes are redetermined by including terms of order M2 and M2/kH.

Self-Tuning Control with Regularized RLS Algorithm for Vibration Cancellationof a Circular Plate

Abstract: The self-tuning control assumes that the vibrating system is unknown and the controller procedure has the ability to identify the process and to update the necessary control law. Such an algorithm provides the relevant regulator parameters according to the obtained parametric object model. The algorithm can be described as a combination of the following two procedures: the online identification and the computation of the controller parameters. Nearly all of the identification procedures are related to the Least Squares (LS) estimate of a model output. Classified as an ill-posed problem, it implies that the obtained solution is potentially very sensitive to the data perturbations. In order to avoid such problems, the regularized version of the RLS method has been considered in this paper. By solving the linear system of equations with a non-singular Sylvester matrix, the formulas for the unknown coefficients of the considered PID-type controller structure have been obtained. The results of the tests and simulations for the circular plate vibration cancellation have been also included.

Statistical Characteristics of the Damped Vibrations of a String Excited byStochastic Forces

Abstract: Our theoretical study aims at finding some statistic parameters characterizing the damped vibrations of a string excited by stochastic impulses. We derive the dependence of these parameters on the parameters of the string as well as on the stochastic distributions of the impulse magnitude, and on the place of the action. We also carry out a numerical simulation verifying the derived mathematical model and interpret the differences between the results obtained in simulation and the mathematical calculations. This study is the fourth stage of a research aimed at designing a probe that facilitates the process of measuring of the parameters, determining the quality of a technological process.

Numerical Simulation for the Bell Directivity Patterns Determination

Abstract: The analysis of various sound sources is performed on the basis of their directivity patterns. The literature does not contain any information about directivity patterns of bells that are instruments broadly applied to sacral purposes or to create a certain sound space from the aesthetic point of view. The paper presents the methodology of determining the bell directivity patterns by an example of the Russian bell. This example was applied because exact values of geometrical parameters and measuring data of the bell were available. The model was created by means of FEA (finite element analysis). It included a coupling between the bell and its surrounding acoustic medium. During the modal analysis, the first three natural frequencies of the bell were calculated, and then, using the harmonic analysis, the directivity patterns were determined for the frequencies. Afterwards, the transient response of the system in selected measuring points was determined. The obtained results are important for bell-founders and architects because thanks to the knowledge of directivity patterns, the constructions supporting the bells can be designed in a better way and the sound propagation can be determined more precisely. The presented method of auralisation of the bell sound makes the cooperation between the designer and the receiver fairly convenient.

Feedforward vs. Feedback Fixed-Parameter H2 Control of Non-StationaryNoise

Abstract: Stationary random noise can be modelled as a wide-sense stationary white noise filtered by a minimum phase filter. Such filter can be used to design an optimal control filter minimising variance of the signal being the effect of the noise and the secondary sound interference. However, in many environments the noise is subject to change. For instance, some of the noisy devices are switched on and off, speed of some rotors or fans changes, etc. As a result contribution of different frequency components may significantly vary in time. Solving the optimisation problem to update control filter is rather avoided in on-line systems. In adaptive approach there are problems with convergence or some unpleasant transient acoustic effects. In this paper, the fixed-parameter approach to control is appreciated. Dominating frequency components/bands can usually be distinguished for the acoustic environment. Then, the idea of generalised disturbance defined by a frequency window of different type can be applied. If a reference signal, correlated with the disturbance to be reduced is available in advance, a feedforward structure can be applied, and otherwise, a feedback structure is used. Spectral and inner-outer factorisations are employed in order to cope with non-minimum phase character of the acousto-electric plant. Efficiency of the proposed approach for both control structures is verified based on the data obtained from an active personal headset. The generalised disturbance based control systems are confronted with the classical Wiener control systems designed for the given disturbance.

Simulated annealing optimization on multi-chamber mufflers hybridized withperforated plug-inlet under space constraints

Abstract: optimizing the acoustical performance of mufflers within a compact volume is necessary. To depress the acoustical performance, a multi-chamber muffler hybridized with perforated plug-inlet tubes which may dramatically increase the acoustical performance, is then adopted and optimized under space constraint. In this paper, both the numerical decoupling technique and simulated annealing (SA) algorithm for solving the coupled acoustical problem of perforated plug-inlet tubes and optimizing the muffler shape are used. To appreciate the acoustical ability of the new mufflers, traditional multi-chamber mufflers with extended inlet tubes have been assessed. Furthermore, noise reductions in broadband and pure tones noise are also introduced. But before the SA operation can be carried out, the accuracy of the mathematical model has to be checked by experimental data. Results reveal that the maximal STL is precisely located at the desired target tone. In addition, the acoustical performance of mufflers conjugated with perforated plug-inlet tubes is superior to that hybridized with extended inlet tubes. Moreover, the more chambers the mufflers have, the higher acoustical performance they will reach. Consequently, we demonstrate a successful SA application to the muffler design.

Experimental Study of Simultanoeus Transmission of a Light Wave and anUltrasonic Wave in an Optical Fiber with the Use of a Mach-ZehnderInterferometer

Abstract: The possibility of acoustic wave propagation in optical waveguides creates new prospects for the simultaneous use of a light wave and an ultrasonic wave in, for instance, medicine for cutting biological tissues with a surgical ultrasonic laser knife A Mach-Zehnder optical waveguide interferometer was used in the experimental studies of simultaneous transmission of those two wave types If ultrasonic vibrations are delivered to one of the interferometer arms, a light modulation effect is produced This paper presents measurement results for different methods of delivering ultrasonic waves to the optical fiber, ie using radial vibrations of a piezoelectric disk or longitudinal vibrations generated by a sandwich ultrasonic transducer with a velocity transformer

Transmission of ultrasonic waves in optical fibers with the use of sandwich type transducer

Abstract: Optical fibers are commonly used to transmit laser beams. The possibility of acoustic wave propagation in optical waveguides creates new prospects for simultaneous transmission of laser beams and ultrasonic waves. This combined technology could be useful in e.g. surgical treatment. A comparative analysis of both systems shows that combining the advantages of ultrasounds and laser light in one device, makes it possible to compensate for the faults of each of the technologies and to improve the effectiveness of surgical operations. The article presents the results of experimental studies of transmission of ultrasonic wave in optical fibers using a sandwich-type ultrasonic power transducer. It also presents amplitude characteristics of an ultrasonic signal propagated in an optical fiber. The effect of the length of the fiber on the achieved output signal amplitudes was studied. The relation of the output signal of a capacitive sensor to the power applied to the sandwich-type transducer was presented. The reflected power during ultrasonic wave propagation in an optical fiber was also measured. The measurements of the ultrasonic wave transmission were performed for single-mode and multi-mode step-index optical fibers.