Downloaded from orbit.dtu.dk on: Oct 05, 2021 Acoustofluidics: Theory and simulation of streaming and radiation forces at ultrasound resonances in microfluidic devices Bruus, Henrik Published in: Acoustical Society of America. Journal Publication date: 2009 Document Version Publisher's PDF, also known as Version of record Link back to DTU Orbit Citation (APA): Bruus, H. (2009). Acoustofluidics: Theory and simulation of streaming and radiation forces at ultrasound resonances in microfluidic devices. Acoustical Society of America. Journal, 125(4), 2592-2592. General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. Users may download and print one copy of any publication from the public portal for the purpose of private study or research. You may not further distribute the material or use it for any profit-making activity or commercial gain You may freely distribute the URL identifying the publication in the public portal If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. TUESDAY MORNING, 19 MAY 2009 GRAND BALLROOM II, 8:00 A.M. TO 12:00 NOON Session 2aAAa Architectural Acoustics: Multiple Channel Systems in Room Acoustics Ning Xiang, Cochair Architecture, Rensselaer Polytechnic Inst., Troy, NY 12180 Boaz Rafaely, Cochair Electrical and Computer Engineering Dept., Ben Gurion Univ., Beer Sheva, Israel Chair’s Introduction—8:00 Invited Papers 2a TUE. AM 8:05 2aAAa1. A multi-channel audio system based on the theory of integral equations. Filippo M. Fazi and Philip A. Nelson ͑Inst. of Sound and Vib. Res., Univ. of Southampton, Highfield, S0171BJ, Southampton, U.K., [email protected]͒ The basics of a multi-channel audio system, which attempts the reproduction of a desired sound field, are presented. The system’s hardware consists of a three-dimensional array of loudspeakers, and can be used in combination with a specially designed microphone array. The mathematical fundamentals on which this technique is grounded consist of the formulation of the problems as an integral equation. The loudspeaker signals are determined from the knowledge of the target sound field on the boundary of a given control volume. The solution to this inverse problem is computed performing a singular value decomposition of the integral operator involved. For some simple array geometries it is possible to calculate an analytical solution to the problem. A regularization method is applied, as required by the ill-posed nature of the inverse problem under consideration. Some insight into the physical meaning of the ill- posedness is given and some analogies to near-field acoustic holography are suggested. The effectiveness of the method proposed has been verified experimentally and some of the experimental results are presented. Finally, it is shown how this technique has been suc- cessfully applied to the design of a multi-channel auralization system for room acoustics. 8:25 2aAAa2. Representation of the musical instruments directivity using dodecahedron loudspeakers. Gottfried Behler and Martin Pollow ͑Inst. of Tech. Acoust., RWTH Aachen Univ., 52056 Aachen, Germany, [email protected]͒ Room-acoustical measurements in general are performed with omnidirectional sound sources. With respect to auralization, such an impulse response may not be ideal since it does not represent the situation playing an instrument in the room. To achieve the directivity of a real source ͑such as an instrument or human voice͒ with a technical sound source ͑a loudspeaker͒ requires either to copy the body and the surface velocity distribution of that particular source or to reproduce the directional pattern of the radiation using a multiple source configuration like a dodecahedron loudspeaker array with independent excitation of each transducer. The advantage of the latter method is obvious since one single source is able to provide different directivities by changing the excitation profile. To maintain the appropriate excitation of each individual transducer, different approaches can be made. The method described here uses spherical har- monics decomposition of the target radiation pattern and a subsequent calculation of the frequency dependent excitation coefficients for each transducer. The advantage of this method is a flexible and fast calculation delivering filters that can be used either for real time convolution or off-line processing of the measuring signals. To measure the instruments directivity an array with 32 microphones is used. 8:45 2aAAa3. Considering modal aliasing in the implementation of an acoustic echo canceller in the wave domain. Martin Schneider and Walter Kellermann ͑Multimedia Commun.s and Signal Processing, Univ. Erlangen-Nuremberg, Cauerrstr 7, 91058 Erlangen, Ger- many, schneider,[email protected]͒ Traditional multichannel acoustic echo cancellation applied to wave field synthesis systems is computationally extremely expensive due to the large number of channels to be identified. By using wave domain adaptive filtering ͑WDAF͒ one is able to choose an ap- proximation which neglects the interaction ͑exchange of energy͒ between different modes. This reduces the number of necessary adap- tive filter coefficients drastically. Furthermore, it allows to use computationally relatively inexpensive single-channel filter adaptation algorithms. Then, however, modal aliasing due to the limited resolution of the used microphone array becomes a significant problem since it constitutes an interaction between different modes with respect to the microphone signals. The effects of modal aliasing on the adaptation behavior of a WDAF-based echo cancellation system are analyzed and a modified wave domain representation of the syn- thesized wave field is proposed which reflects the limited resolution of the microphone array. 2543 J. Acoust. Soc. Am., Vol. 125, No. 4, Pt. 2, April 2009 157th Meeting: Acoustical Society of America 2543 Downloaded 29 Jun 2010 to 192.38.67.112. Redistribution subject to ASA license or copyright; see http://asadl.org/journals/doc/ASALIB-home/info/terms.jsp 9:05 2aAAa4. Spherical harmonic beamforming for room acoustic analysis. Gary W. Elko and Jens Meyer ͑mh acoustics LLC, 25A Summit Ave., Summit, NJ 07901͒ We describe the potential of using a spherical beamforming microphone array to investigate the spatial correlation of sound fields in rooms. We are building spherical microphone arrays consisting of many acoustic pressure sensors mounted appropriately on the surface of a rigid sphere. Our associated spherical eigenbeamformer decomposes the sound-field into spatially orthonormal spherical harmonics up to third-order. We refer to the signals from the eigenbeamformer as eigenbeams. All eigenbeams have phase centers at the physical center of the array. Due to the orthonormal property of the eigenbeamformer, a diffuse field ideally results in zero correlation between the eigenbeams. Therefore, by measuring the cross-correlation between the eigenbeam signals, one can investigate the prox- imity to the isotropy ͑or “diffuseness”͒ of the sound-field. Simultaneously, the underlying eigen-beam patterns can be steered without effecting the orthonormality property. How the cross-correlation function changes with general orientation of the eigenbeams is another potential measure for sound field diffuseness in rooms. We will show some real room measurements demonstrating the potential use- fulness of this approach. 9:25 2aAAa5. Imaging room acoustics with the audio camera. Adam O’Donovan, Ramani Duraiswami, Nail A. Gumerov, and Dmitry N. Zotkin ͑Perceptual Interfaces and Reality Lab., Dept. of Comput. Sci. Univ. of Maryland, College Park, MD 20742͒ Using a spherical microphone array and real time signal processing using a graphical processing unit ͑GPU͒, an audio camera has been developed. This device provides images of the intensity of the sound field arriving at a point from a specified direction to the spherical array. Real-time performance is achieved via use of GPUs. The intensity can be displayed integrated over the whole frequency band of the array, or in false color, with different frequency bands mapped to different color bands. The resulting audio camera may be combined with video cameras to achieve multimodal scene capture and analysis. A theory of registration of audio camera images with video camera images is developed, and joint analysis of audio and video images performed. An interesting application of the audio camera is the imaging of concert hall acoustics. The individual reflections that constitute the impulse response measured at a particular seat may be imaged, and their spatial origin determined. Other applications of the audio camera to people tracking, noise suppression, and camera pointing are also presented. ͓Work partially supported by NVIDIA and the VA.͔ 9:45 2aAAa6. Proposed method to measure the diffusion coefficient. Peter D’Antonio ͑651-C Commerce Dr., Upper Marlboro, MD 20774, [email protected]͒ A method to measure the uniform diffusion coefficient has been published as an AES Information Document ͓AES-4id-2001, JAES, Vol. 9, pp. 148–165 ͑March 2001͔͒. The method utilizes 37 fixed pressure zone microphones separated by 5 degrees located ona1m semicircle and a loudspeaker located ona2mconcentric semicircle.