Archives of Acoustics

Traditionally I invite you to acquaint with preliminary program and some abstracts of lectures submitted to presentation in 38th Winter School on Vibroacoustical Hazards Suppressions. This national School, organized by Upper Silesian Division of the Polish Acoustical Society and Institute of Physics at Silesian University of Technology, at this year is planned at the first week of March 2010. This conference is organized in different places of Silesian Beskidy Mountains, but this year it is organized in Szczyrk.

The conference is the forum for all environmental vibroacoustics fields. Particularly it concern to traffic noise, industry noise, vibroacoustics of machines, room acoustics, noise protection and similar problems. During the School the theoretical works, experimental, measuring, technical, applied and normative ones are presented.

The School lectures, and other conference materials, will be published in the "Materials of the XXXVIII Winter School on Vibroacoustical Hazards Suppressions" (in Polish) edited by Dr. Roman Bukowski and Dr. Mieczys?aw Roczniak (chairman of the conference). This publication is intend to participants of the School and for many libraries in Poland.

I have a great pleasure to inform the "AA" Readers that the 39th Winter School on Wave and Quantum Acoustics, organized by Upper Silesian Division of the Polish Acoustical Society and Institute of Physics at Silesian University of Technology, is planned at the top of March 2010 in beautiful scenery of Silesian Beskidy Mountains. Many times it was organized in Wisła, Skoczów, Szczyrk, and Korbielów, and this year it will be organized again in Szczyrk.

As always, the School has been a place where achievements of various sections of physical acoustics (especially molecular acoustics, quantum acoustics, acousto-optics, magnetoacoustics, acoustoelectronics, photoacoustics, acoustics of solids etc.) are being exchanged. Moreover, some similar and related topics, for example optoelectronics and thermal wave methods, will be presented too.

As at previous years the School will be divided on three different, but complementary, parts - Winter Workshops (WW). Chronologically it will be: 6th WW on Acoustoelectronics (chairman Prof. Marian Urbanczyk, Silesian University of Technology, Gliwice), 6th WW on Molecular Acoustics, Relaxation and Calorimetric Methods (chairwoman Dr. Marzena Dzida, Silesian University of Technology, Katowice) and 15th WW on Photoacoustics and Thermal Waves Methods (chairman Prof. Jerzy Bodzenta, Silesian University of Technology, Gliwice). Moreover, this year we propose take participation in associated conference - the 4th conference on Integrated Optics - Sensors, Sensing Structures and Methods (chairman Prof. Tadeusz Pustelny, Silesian University of Technology, Gliwice).

The following work presents the idea of constructing a digitally controlled active piezoceramic transducer matrix for ultrasonic projection imaging of biological media in a similar way as in case of roentgenography (RTG). Multielement ultrasonic probes in the form of flat matrices of elementary piezoceramic transducers require attaching a large number of electrodes in order to activate the individual transducers. This paper presents the idea of minimising the number of transducer connections in an active row-column matrix system. This idea was verified by designing a model of a matrix consisting of 16 ultrasonic transducers with electrode attachments optimised by means of electronic switches in rows and columns and miniature transistor switches in the nodes of the matrix allowing to activate selected transducers. The results of measurements and simulations of parameters of the designed matrix show that it is suitable to be used in projection imaging of biological media as a sending probe. In to use the matrix as a universal sending or receiving probe, it was suggested to add further switches that would eliminate the undesired effect of crosstalks in case of switches used for toggling the transducers in the nodes of the matrix.

This article presents the results of experimental studies of simultaneous transmission of ultrasonic waves and laser signals in optical fibers by the use of both the optical single mode and multimode fiber couplers. This work was aimed, among other things, at the study of the way the acoustic energy affects a laser beam. The light wave was guided into one of the coupler's arms. The optical power applied to one input of the coupler is separated into two coupler outputs according to the rate determined by the coupling coefficient. Only an ultrasonic wave generated by a sandwich type transducer is applied to the other arm of the coupler. In this experiment, as in case of the light wave, the acoustic power is separated into both the outputs. One can observe the interaction of both the waves on the two outputs - a modulation of the light wave by means of the ultrasonic wave is possible. The output signal was detected using a PIN diode and an optical power meter (OPM). Temporary courses were observed on an oscilloscope screen. The simultaneous transmission of ultrasounds and optical radiation in optical fibers can be used in the construction of medical equipment.

The following paper presents an idea of minimising the number of connections of individual piezoelectric transducers in a row-column multielement passive matrix system used for imaging of biological media structure by means of ultrasonic projection. It allows to achieve significant directivity with acceptable input impedance decrease. This concept was verified by designing a model of a passive ultrasonic matrix consisting of 16 elementary piezoceramic transducers, with electrode attachments optimised by means of electronic switches in rows and columns. Distributions of acoustic field generated by the constructed matrix model in water and results of the calculations conformed well.

In this paper, numerical results of modeling of acoustic waves propagation are presented. For calculation of the acoustic fluctuations, a solution of the full non-linear Euler equation is used. The Euler equations are solved with the use of a numerical scheme of third-order accuracy in space and time. The paper shows a validation process of the described method. This method is suitable also for an aerodynamic noise assessment on the basis of unsteady mean flow field data obtained from a CFD calculations. In such case this method is called a hybrid CFD/CAA method. The proposed method is numerically decoupled with CFD solution, therefore the information about the mean unsteady flow field can be obtained using an arbitrary CFD method (solver). The accuracy of the acoustic field assessment depends on the quality of the CFD solutions. This decomposition reduces considerably the computational cost in comparison with direct noise calculations.

The presented Euler acoustic postprocessor (EAP) has been used for modeling of the acoustic waves propagation in a cavity and in the flow field around a cylinder and an aerodynamic profile.

Shape optimization on mufflers within a limited space volume is essential for industry, where the equipment layout is occasionally tight and the available space for a muffler is limited for maintenance and operation purposes. To proficiently enhance the acoustical performance within a constrained space, the selection of an appropriate acoustical mechanism and optimizer becomes crucial. A multi-chamber side muffler hybridized with reverse-flow ducts which can visibly increase the acoustical performance is rarely addressed; therefore, the main purpose of this paper is to numerically analyze and maximize the acoustical performance of this muffler within a limited space.

In this paper, the four-pole system matrix for evaluating the acoustic performance - sound transmission loss (STL) - is derived by using a decoupled numerical method. Moreover, a simulated annealing (SA) algorithm, a robust scheme in searching for the global optimum by imitating the softening process of metal, has been used during the optimization process. Before dealing with a broadband noise, the STL's maximization with respect to a one-tone noise is introduced for the reliability check on the SA method. Moreover, the accuracy check of the mathematical models with respect to various acoustical elements is performed.

The optimal result in eliminating broadband noise reveals that the multi-chamber muffler with reverse-flow perforated ducts is excellent for noise reduction. Consequently, the approach used for the optimal design of the noise elimination proposed in this study is easy and effective.

The aim of this paper is to present a way of ranking the nonlinearities of electrodynamic loudspeakers. For this purpose, we have constructed a nonlinear analytic model which takes into account the variations of the small signal parameters. The determination of these variations is based on a very precise measurement of the electrical impedance of the electrodynamic loudspeaker. First, we present the experimental method to identify the variations of these parameters, then we propose to study theoretically the importance of these nonlinearities according to the input level or the input frequency. We show that the parameter which creates most of the distortions is not always the same and depends mainly on both the input level and the input frequency. Such results can be very useful for optimization of electrodynamic loudspeakers.

Bragg scattering of waves propagating in a periodically disturbed substrate is widely applied in optics and micro-acoustic systems. Here, it is studied for Rayleigh waves propagating on a periodically grooved elastic substrate. Practically applied groove depth in the Bragg grating reflectors does not exceed a few percent of the Rayleigh wavelength. Here, the analysis is carried out for periodic grooves of larger depth by applying the elastic plate model for the groove walls. The computed results show that the surface wave existence and reflection depends strongly on both the groove depth and period, and that there are limited domains of both for practical applications, primarily in comb transducers of surface waves.

The aim of this paper is to describe a non-invasive method of examination of the local pulse wave velocity. The measurements were carried out in the model of the artery immersed in a water tank. Two synchronized ultrasonic apparatus VED with the ultrasonic radio frequency echoes acquisition system were used for evaluation of the arterial elasticity. The zero-crossing method was used for determination of the diameter changes of the artery model. The transit time between the waveforms of instant artery diameter was measured at two points of the artery model, separated by the distance of 5 cm. The transit time was determined using the criteria of similarity of the first derivatives of the raising slopes of the curves describing instant vessel's diameter changes. The pulse wave velocity obtained by the proposed two-point method was compared with the results obtained by the one-point method based on the modified Bramwell-Hill relation.