AC.3. International Commission for Acoustics

Report of C7 to the 1999 General Assembly for 1996-99

Officers 1997-1999:

Chairman: T. Kihlman Sweden,
Vice-Chairman: G. Rasmussen, Denmark
Secretary: A. Alippi, Italy

Members:

P. Bury, Slovak Republ.
L.A. Crum, USA
G.A. Daigle, Canada
A. Krokstad, Norway
L.M. Lyamshev, Russia
G.J. Quentin, France
G.M. Sessler, Germany
A. Sliwinski, Poland
H. Tachibana, Japan
R. Zhang, China

WebSite: http://gold.sao.nrc.ca/ims/ica/

Recent activities of the commission:

The International Commission for Acoustics held their 16th International Congress on Acoustics jointly with the 135th meeting of the Acoustical Society of America (ASA) in Seattle, Washington, USA, 20-26 June, 1998.

This Congress was a very successful one, and because it was held jointly with a meeting of the ASA, it took on a special character of its own. In particular, we had over 50 countries represented and approximately 2060 registered participants, as well as nearly 200 accompanying persons who participated in many of the social events. Our technical program for the meeting listed approximately 1500 papers that were presented in approximately 15 simultaneous sessions during the 5 day meeting. Nearly 40% of the participants were from outside the US. A special feature of the meeting was 16 plenary lectures that covered most of the topical areas of acoustics

The Proceedings of the conference was published in both print and electronic format. These proceedings contained 1488 2-page regular papers and 16 6-page plenary papers. A fully-searchable CD ROM of the proceedings was provided to each of the participants.

An important event of the Congress was the General Assembly. The Acoustics Commission has reorganized as an Affiliate Commission of the IUPAP so that it can more fully represent the Acoustical Societies of the World. In preparation for this Congress, all major national and regional acoustics organizations were invited to apply for membership in the Commission and send delegates to the First General Assembly to be held at the Congress venue. We were pleased that 70 representatives from over 30 acoustics organizations attended the congress and passed the new By-Laws of the Commission. In addition, a Governing Board was elected; for the purposes of communication, the officers of the new board are as follows:

President LAWRENCE A. CRUM Applied Physics Laboratory 1013 NL 40th St. University of Washington Seattle, Washington 98105-6698 USA tel: +1 206 685 8622 fax: +1 206 685 8621 e-mail: lac@apl.washington.edu Treasurer: VOLKER MELLERT Physics Department - Acoustics, University of Oldenburg D - 26111 Oldenburg Germany Tel: +49 441 798 3572 Fax: +49 441 798 3698 e-mail: volker@aku.physik.uni-oldenburg.de_

Secretary-General: GILLES DAIGLE Institute for Microstructural Sciences National Research Council Ottawa K1A 0R6 CANADA tel: +1 (613) 993 6188 fax: +1 (613) 952 3670 e-mail: gilles.daigle@nrc.ca_ Past-President: TOR KIHLMAN Chalmers University of Technology Department of Applied Acoustics S-412 96 Goteborg SWEDEN tel: +46 31 772 22 01 fax: +46 31 772 22 12 e-mail: tk@ta.chalmers.se

A special effort was made to attract scientists from as broad a base as possible, especially from less-developed countries. Accordingly, we used funds supplied by both the IUPAP and the IUTAM, as well as donations from local industries to fund registration scholarships and travel stipends for approximately 50 individuals. Also, we arranged for low cost housing at the University of Washington (board and room) and in some special cases we even housed participants with families in the Seattle area

There was another important aspect of this conference. One of our goals for this meeting was to generate a sufficient budgetary surplus so that we in the International Commission on Acoustics could sponsor small, specialty meetings, particularly in less developed countries. By this sponsorship, we hope that we can make the exciting new developments in acoustics available to as many engineers and scientists as possible. We are pleased to report that the Acoustical Society of America, which assumed financial responsibility for the meeting, realized a large enough surplus so that they could provide the ICA with an allocation of US$25,000. We anticipate that these funds will serve an important role in advancing the state of knowledge of acoustics through out the world.

New developments in the field of acoustics

Sonoluminescence:

When an acoustic wave of moderate pressure amplitude is propagated through an aqueous liquid, light emissions can be observed. This conversion of mechanical energy into electromagnetic energy represents an energy amplification per molecule of over eleven orders of magnitude! Recently, it has been discovered that a single, stable gas bubble, acoustically levitated in a liquid, can emit optical emissions each cycle for an unlimited period of time. Presumably, the oscillations of the bubble cause the gas in the interior to be heated to incandescent temperatures during the compression portion of the cycle. Furthermore, some recent evidence indicates that the lifetime of the optical pulse can be on the order of or less than 50 picoseconds, and that the temperature in the interior of the bubble can exceed 100,000 K. Since conventional explanations expect the bubble to remained compressed and the temperatures elevated in the interior of the bubble for times on the order of tens of nanoseconds, it is likely that some rather unusual physics is occurring. There have even been some recent suggestions that sonoluminescence may be due to quantum vacuum radiation. The best guess, however, is that a shock wave is created in the gas which is then elevated to high temperatures by inertial confinement. If shock waves are the mechanism for SL emission, then optimization of the process could lead to extraordinary physics, including nuclear fusion. (L. A. Crum)

Ocean Acoustic Time-Reversal Mirror:

A time-reversal-mirror (TRM), also referred to as a phase conjugate array, has been implemented in two experiments conducted in the Mediterranean Sea in April of 1996 and 1997. The experiments were carried out jointly by the Marine Physical Laboratory of the Scripps Institution of Oceanography and the NATO SACLANT Undersea Research Center. A TRM focuses acoustics energy to a predetermined spot specified by a probe source, regardless of the time invariant complexity of the medium. Previously, megahertz TRM experiments had been conducted in an ultrasonics laboratory {University of Paris) over ranges of less than one meter. The ocean experiments utilized a vertical source-receiver array (SRA) spanning 77 m of a 125 m water column with 23 sources and receivers and a single source/receiver transponder (SRT) co-located in range with another vertical receive array (VRA) of 46 elements spanning 90 m of a 145 m water column located from 6.3 km to 30 Km from the SRA. The TRM demonstration consisted of transmitting a 50 ms pulse with center frequency of 445 Hz from the SRT to the SRA, digitizing the received signal and retransmitting the time reversed signals from all the sources of the SRA. The retransmitted signal was then received at the VRA. An assortment of runs were made to examine the structure of the focal point region and the temporal stability of the process. The process was extremely robust and stable out to 30 Km. This research may lead to new concepts in acoustic ocean imaging, sonar and communications. (W. Kuperman)

Recent Developments in Psychological & Physiological Acoustics:

High interest continues in otoacoustic emmissions (OAEs), which are low-level sounds generated by the inner ear, either spontaneously or from external stimulation. They are measured using sensitive microphones placed in the external ear canal, and appear to reflect normal, nonlinear processes in the cochlea. Their potential as a screening tool for quickly and accurately identifying hearing loss is being assessed in a clinical trial with 7,000 newborns in the U.S. Exciting recent work on gender and hormonal influences on OAEs may reveal more general processes of brain differentiation during development. In behavioral research with human listeners, work with head-related transfer functions (HRTFs) is bringing realistic virtual auditory environments closer to reality. An HRTF is the frequency response (filter characteristic) between a sound source in space and the ear, shaped in large part by the pinna, and thus unique to each individual. Although sound reproduction is improved using average HRTFs, people prefer sounds processed with their own HRTF. The first home audio equipment using this technology recently became available. Other hot topics in psychological acoustics include the inter-related areas of auditory scene analysis, sound-source segregation and auditory selective attention. Considerable progress, including computational models, reflect progress in our understanding of the perplexing question of how listeners parse complex incoming sound fields from multiple sources into relevant and irrelevant auditory signals. (D. Neff)

High Intensity Focused Ultrasound:

For years acoustic researchers have concentrated on demonstrating that low acoustic intensities used in diagnostic ultrasound produce no or minimal bioeffects, therefore making ultrasound imaging safe. The tide is turning. Therapeutic ultrasound researchers intentionally turn up the intensity to produce BENEFICIAL bioeffects. We have shown that High Intensity Focused Ultrasound (HIFU) can stop bleeding from injured solid organs and major blood vessels in about a minute, "acoustic hemostasis". The therapeutic intensities are about 4 orders of magnitude larger than those of the diagnostic ultrasound, i.e. 10,000 W/cm2 vs. 0.1 W/cm2. At these intensities, two major effects are caused by ultrasound. Thermal effect raises the temperature to above 60 °C, causing coagulative necrosis of cells and tissues. While this thermal effect is shared by several other energy modalities including laser, electrical current, and simple hot irons, ultrasound has the distinct advantage that it can produce the thermal effect deep within a tissue, where hemorrhaging may be occurring in a patient with internal bleeding. This effective mechanism has been responsible for the success of HIFU in "deep volume cauterization" of solid organs, around an injury site. Mechanical effect, which is unique to ultrasound, is just beginning to be explored. Bulk streaming due to ultrasound radiation pressure can push blood out of the way, perhaps back into a bleeding vessel, for better visualization of the operating field as well as enhanced energy deposition in the injury site. Also, tissue emulsification as a result of the large pressure oscillations can provide a seal for solid organ wounds, or a plug for vascular lacerations. Such tissue homogenates contain a large concentration of tissue factors that may accelerate coagulation and hemostasis by orders of magnitude. HIFU may provide hemostasis methods for both surgical and extracorporeal applications. The surgical applications may include pre-cauterizing volumes of tissues that are planned to be removed by surgery, "bloodless resection", as well as providing a general tool of hemostasis. The extracorporeal applications may include arrest of bleeding in trauma patients at the scene of an injury, or during transport to the hospital. Such methods would reduce bleeding and improve the outcome of subsequent trauma surgery, where HIFU methods may come to the rescue again. Acoustic hemostasis may provide an effective, limb- and life-saving method in the near future. (S. Vaezy)

L.A. Crum