Bijeenkomst NAG: Grensoverschrijdende akoestiek, 23 november 2011

Beatrixgebouw Jaarbeurs Utrecht
Dagvoorzitters: prof. Jan Wouters prof. dr. ir. Bert Roozen

Aanmeldingen

Leden van het NAG melden zich aan via het aanmeldingsformulier dat zij hebben ontvangen. Niet-leden zijn eveneens welkom op deze lezingendag. De kosten voor deelname en lunch voor niet-leden bedragen € 70,00, te voldoen ter plaatse. Bij betaling van dit bedrag hebben deelnemers recht op vrijstelling van het 1e jaar contributie van het NAG bij aanmelding als lid. Studerende niet-leden kunnen gratis deelnemen aan de lezingendag en betalen uitsluitend, voor zover van toepassing, € 15,00 voor de lunch, te voldoen ter plaatse.

Programma

09.30 – 10.00 Ontvangst en koffie/thee

10.00 – 10.40 Microbubble acoustics for diagnostic ultrasound imaging and therapy Michel Versluis, Physics of Fluids Group, University of Twente

Medical ultrasound imaging is greatly enhanced by the use of ultrasound contrast microbubbles which act as a blood pool agent. We study the interaction of the bubbles with ultrasound to improve diagnostic imaging protocols. The typical ultrasound contrast agent is composed of a suspension of microbubbles (radius 1-5 micrometer) which are coated with a phospholipid, albumin or polymer shell to prevent the bubble from quickly dissolving in the blood. We characterize the nonlinear acoustic bubble behavior near resonance by changing the frequency whilst monitoring the dynamic response of single bubbles, obtaining their resonance curves. From pressure scans we then deduce the viscoelastic properties of the shell material at MHz driving frequencies, which allows us to develop new and improved diagnostic imaging protocols. Activated bubbles close to cells can also induce cell membrane poration, or sonoporation, allowing local drug and gene delivery. We study the interaction of bubbles with cell membranes, pore formation and uptake of model drugs. We also try to clarify the fundamental physical mechanisms underlying the drug delivery potential of liquid perfluorocarbon cavitation nanodroplets for tumor imaging and therapy.

10.40 – 11.00 Koffie/theepauze

11.00 – 11.50 De Vlammentafel. (Design and demonstration of a 2 dimensional Rubens-tube) Wessel Westerveld, Wexel, geluids'-kunstenaar Ysbrand Wijnant, Dept. of Applied Mechanics, University of Twente

De stichting SART (Stichting ARTwekkelo) is opgericht in 2007 met de doelstelling beeldende kunst te stimuleren en te faciliteren. In het project 'SART & Science' worden samenwerkingsverbanden tot stand gebracht tussen kunstenaars en wetenschappers, die leiden tot uitwisseling van kennis, inzichten en visies en tot de vervaardiging van concrete kunstinstallaties. In het kader van dit project is een samenwerking tot stand gekomen tussen de auteurs van dit stuk: Wessel Westerveld (de kunstenaar) en Ysbrand Wijnant (de wetenschapper). Deze samenwerking heeft geresulteerd in een tweedimensionale versie van de zogenaamde 'Rubens tube'.

Een 'Rubens tube,' zoals beschreven door Rubens en Krigar-Menzel in 1905, is een lange buis voorzien van een rij kleine gaatjes waardoor brandbaar gas naar buiten stroomt. De buis is aan één zijde gesloten en de andere zijde is verbonden met een luidspreker. De ontsteking van het brandbare gas resulteert in een rij vlammetjes. Een, door de luidspreker opgewekte, akoestisch staande golf in de buis verandert de (locale) hoogte van de vlammen en visualiseert daarmee het eendimensionaal golfpatroon in de buis. Door dit spectaculaire resultaat wordt de 'Rubens tube' in het onderwijs veel gebruikt als demonstratie model en onderzoeksproject.

In tegenstelling tot de eendimensionale golfpatronen in een buis, ontstaan in een platte doos, tot de zogenaamde cut-on frequentie, tweedimensionale golfpatronen. Zoals in de Rubens buis zouden deze twee dimensionale patronen wellicht ook zichtbaar kunnen worden gemaakt met behulp van kleine vlammen. Deze veronderstelling heeft geleid tot het idee van een tweedimensionale 'Rubens tube', waarbij de vlammen die ontstaan op een geperforeerde plaat reageren op het geluidsveld in de platte doos. Achteraf bleek, uit een literatuurstudie, een dergelijke configuratie reeds bekend te zijn; de doos wordt een vlammentafel genoemd.

In deze presentatie zal worden ingegaan op fysica achter de waargenomen hoogte modulatie in de Rubens buis, de fysica achter en de realisatie van de tweedimensionale versie, waarbij specifiek zal worden ingegaan op de vloeistofstructuur interactie (hetgeen, in tegenstelling tot de 'Rubens tube,' voor de vlammentafel een grote rol blijkt te spelen). Tevens zal de vlammentafel worden gedemonstreerd.

11.50 – 12.30 Actively listening to microcracks: Nonlinear ultrasonics for non-destructive testing of solids. Koen Van Den Abeele, K.U.Leuven Campus Kortrijk, Belgium

The development of non-destructive testing (NDT) techniques is ever-evolving and needs continuous further upgrading because of (a) the increasing demand to more sensitive and more reliable detection, (b) the need for earlier detection of defects and (c) the emergence of new industrial materials and composites. In recent years, research in nonlinear elastic wave spectroscopy (NEWS) has lead to a class of innovative non-destructive inspection techniques that provide an extreme sensitivity in diagnosing and localizing incipient damage in the form of microcracks or delaminations, adhesive bond weakening, thermal and chemical damage, etc… which is superior to what can be obtained with traditional technologies. Among other features, NEWS techniques use the fact that microcracks and delaminations additionally scream at higher tones and/or subharmonic tones of the frequency at which they are excited. By active listening to microcracks and analyzing the resulting nonlinear features in the ultrasonic signals, the sensitivity of ultrasonic NDT techniques can be improved considerably.

12.30 – 13.40 Lunchpauze

13.40 – 14.20 Acoustic levitation: application to contactless handling in micro-assembly Pierre Lambert, BEAMS Dept., Université Libre de Bruxelles

Apart from contact micromanipulation, there exists a large variety of levitation techniques among which standing wave levitation will be proposed as a way to handle (sub-)millimetric components. This paper will compare analytical formulas to calculate the order of magnitude of the levitation force. It will then describe digital simulation and experimental levitation set up. Stable levitation of various components (cardboard, steel washer, ball, ceramic capacity, water droplet) was shown along 5 degrees of freedom: the only degree of freedom that could not be mastered was the rotation about the symmetry axis of the acoustic field. More importantly, the present work will show the modification of the orientation of the radial force component in presence of an object disturbing the acoustic field. This property can be used as a new feeding strategy since it means that levitating components are spontaneously pushed towards grippers in an acoustic plane standing wave.

14.20 – 15.10 Micro-Thermoacoustic energy generation Kees de Blok en Douglas Wilcox Aster Thermoakoestische Systemen, Veessen Bosch Thermotechnology/Nefit B.V., Apeldoorn

Thermoacoustic (TA) energy conversion is an emerging generic cross-cutting energy conversion technology that can be applied in a vast number of applications, requiring heating, cooling, or power generation.

Thermoacoustic energy conversion uses the compression, expansion and displacement of the gas in an acoustic wave to force the gas to undergo a thermodynamic (Stirling) cycle. That way thermoacoustic energy conversion can convert heat to acoustic power (engine) and to use acoustic power to pump heat to high or low temperature levels (heat pump). Acoustic power can also be converted with high efficiency to electricity and vice versa.

Thermoacoustic systems use an environmentally friendly working medium (e.g. helium) in a Stirling-like cycle, and contain no moving parts in the cycle itself. These properties will enable new applications which are not feasible today for technical or economic reasons. Although the dynamics and working principles of TA systems are quite complex and involve many disciplines such as acoustics, thermodynamics, fluid dynamics, heat transfer, structural mechanics, and electrical machines, the practical implementation is relatively simple. This offers great advantages with respect to the economic feasibility of this technology. The presentation will address emerging applications as well as the basic principles. A simple “singing tube” thermoacoustic engine that converts heat into sound will also be presented. The engine consists of only three parts: a stack that consists of a plug of porous ceramic, an electrical heater attached to one end of the plug and a Pyrex test tube. Electrical current passes through the heating element and imposes a temperature gradient across the stack. The Pyrex tube acts as a miniature organ pipe and sets up a standing acoustic wave. Despite its simplicity, this engine is capable of producing a sound level of 85 dB.

15.10 – 15.30 Koffie/theepauze

15.30 – 16.10 Binaural acoustical and electrical stimulation in severely hearing impaired Anneke Lenssen, Tom Francart and Jan Wouters ExpORL KU Leuven

Relaxed implantation criteria resulting from the success of cochlear implants (CI’s) over the years as a treatment for severe hearing impairment lead to more and more CI users who still have residual hearing in the non-implanted ear. The combination of a CI and a hearing aid is often called bimodal stimulation. Although the fitting of a hearing aid (HA) in the ear contralateral to the CI can lead to binaural benefits and improves speech understanding in quiet, bimodal listeners still perform poor in sound localization and speech understanding in noisy surroundings. In localization of sound sources binaural cues such as the interaural time difference (ITD) and interaural level difference (ILD) play an important role. The ability to perceive binaural cues is also strongly related to understanding a target speaker in a noisy environment. Binaural cues are not optimally present in the sound transmitted to the auditory system mainly due to independent fitting of the devices, lack of synchronization between the devices and several processing steps in the CI speech processing. Current research focuses on the development of binaural processing strategies to improve the transmission and perception of binaural cues in bimodal stimulation. Latest results show benefit from synchronized temporal envelope modulations in the electrical signal on the perception of ITD in vowel stimuli with bimodal stimulation.

16.10 – 17.00 Borrel

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