Page 50 - Spring 2007

PHYSICAL ACOUSTICS:
THE PHYSICAL ACOUSTICS SUMMER SCHOOL (PASS)
Thomas J. Matula
Applied Physics Laboratory, University of Washington Seattle, Washington 98105
The Physical Acoustics group within the Acoustical Society of America is a very diverse community. The scope of our work extends from infrasound, with fre- quencies as low as 1 mHz, up to high-frequency ultrasound, where frequencies might exceed 50 MHz. Being so diverse, it is difficult to discuss all aspects of physical acoustics in such a short article. Instead, this article will focus on a topic of great pride to our members—the Physical Acoustics Summer School (PASS).
With financial help from the Office of Naval Research (ONR), the biennial Summer School was established in 1992. The objective of the school has been to bring together students and professionals for a week of lectures and informal discus- sions emphasizing various topics of interest to physical acoustics. A high priority is placed on frequent interactions between students and the expert lecturers. To accomplish this goal, PASS is held in remote rustic locations where distractions are minimized, and full week attendance is required for all par- ticipants. The isolation has obvious benefits for the students— as the week progresses, the students become more comfortable and their interactions increase. Another benefit for the students is discussions with other students. This is encouraged in part by having students from different universities room together. The result is new friends and future collaborators. However, the stu- dents are not the sole beneficiaries; without constant distrac- tions and deadlines, the lecturers can also relax and enjoy sci- entific discussions with enthusiastic students and other partici- pants.
The school’s format is divided into formal lectures, infor- mal discussions, and evening social discussions. The lectures are held in a classroom setting. Most days consist of two 3-hour lectures (with short breaks at the end of each hour). Because the lectures are demanding, students are expected to possess a cer- tain amount of background knowledge. Yet, because of the var- ied backgrounds of the students, mathematical rigor is often replaced by physical insight. Normal topics that are taught include nonlinear acoustics, thermoacoustics, medical acoustics, infrasound, solid state acoustics, bubbles, and molec- ular acoustics. Specialized topics are also taught, including res- onant ultrasound spectroscopy, sonoluminescence, outdoor sound propagation, interaction of sound with light, transduc- ers, and acoustic microscopy. An almost complete list of topics is given below in Table 1 along with the names of lecturers who have taught those courses over the years.
During the afternoon and evening breaks some partici- pants play volleyball, while others might lay out in the sun, play pool, or just ‘hang out,’ relaxing and re-charging. The breaks encourage one-on-one interactions between students and lec- turers. Imagine being able to talk casually with an expert, with- out having to face them across a desk in an office with the tele- phone ringing and their e-mail program beeping at them. Discussions can linger, and be continued later in the week. This
format also benefits the lecturers because they have similar time constraints. As with the students, they can bring up a topic, think it over, bring it up again, develop ideas, etc. over the entire week.
Each evening there is a social that brings everyone together to talk about that day’s lectures. The atmosphere is again very casual, with beer and wine available to both lecturers and students over twenty-one. Students are encouraged to ask more questions about the lectures they heard. The lecturers may also go into more detail about a particular topic, or discuss related topics.
Fig. 1. The evening social is relaxed, but scientific discussion is still required
One of the highlights of the summer school is the session on acoustics demonstrations. Demonstrations are used to impart physical intuition into waves and oscillators. For most of the sum- mers, Bob Keolian and others have served as the Masters of Ceremonies for the demos. In one 3-hour session, they might show 15-20 demos, ranging from pendulums (to demonstrate bent tuning curves or parametric oscillations) to phase locking of oscillators, to acoustic motors, to hearing and cochlear waves.
Fig. 2. A “Ruben's Tube” demo uses flames erupting out of holes in a tube to demonstrate waves of various sorts. Daphne Kapolka is running the experiment behind the tube, with Bob Keolian assisting. According to Bob, there is a speaker on one end of the tube sending in sound. The other end of the tube is blocked. Propane enters through a port on the side and there are small holes every inch on the top. The blackboard describes a previous demo on nonlinearities (bent tuning curve) in simple physical systems (a parametric pendulum).
48 Acoustics Today, April 2007