Page 14 - Spring 2015

Allan D. Pierce: A Celebration of a Career in Acoustics in Commemoration of His Retirement as editor-in-Chief of the Acoustical society of America
til 1973, then at Georgia Tech until 1988, followed by Penn State University until 1993, and finally at Boston Univer- sity, from which he retired in 2012. His MIT days saw him teaching many of the fundamental courses in mechanical engineering. Given his newness to the area, this must have required considerable effort, but it did not deter him from expanding his research activities in acoustics. An extraordi- nary piece of work done with Joe Posey was reported in Na- ture in 1971 (Posey and Pierce, 1971). The article explained how the yield of an explosion could be determined by the ex- amination of simple characteristics of the infrasonic wave- form measured by a microbarograph without knowing the specific parameters of the atmosphere. The Nature article gave a simple formula and a graph showing good agreement between actual and calculated yield. Allan has stated that the US government did not care that the paper gave the yield of weapons in tests done by the USSR, but they were very per- turbed that it provided information about US tests.
Another area of acoustics to which Allan contributed ex- tensively was sonic booms. Most notably, he was the first to explain the N-wave spikes and changes in rise time that of- ten appeared in sonic boom waveforms. He determined that they were due to focusing and defocusing by atmospheric turbulence. He wrote many other articles and reports on the subject, including two references cited by Rogers and Magl- ieri in their article contained in this issue of Acoustics Today.
More recently, Allan Pierce published a number of papers with Bill Carey on the properties of acoustic sediments, es- pecially the frequency dependence of the plane wave attenu- ation coefficient in the low-frequency range (see, e.g., Pierce and Carey, 2010). This parameter is an important factor in shallow-water acoustics because sound propagation always involves strong interaction with the bottom. This is a con- troversial subject. Conventional wisdom says that the plane- wave attenuation coefficient is proportional to frequency. Recent measurements conflict with this assertion. Working backward from the measured data led to identification of the effect as being proportional to the 1.8 power of frequency. Pierce and Carey showed that it should be proportional to the square of frequency, which is close to the measurements, and that the difference is due to the effects of shear in the sediment.
These are only a few of the diverse areas of acoustics in which Allan Pierce has worked. Together with Yves Berthelot, Al- lan was among the first to examine how a laser beam moving
supersonically across the surface of the ocean could gener- ate sound within the ocean (Pierce and Berthelot, 1988). In structural acoustics, Allan worked with Jerry Ginsberg to develop simplified semianalytical tools for modeling the acoustic interaction of a submerged vibrating structure. Such problems are extraordinarily demanding from a computa- tion perspective because small details of the structure can have a profound impact on the acoustic field that is radiated or scattered. This feature led Allan to explore the concept and implications of "fuzzy structure” theory. This is a way of representing, in a statistical manner, the multitude of de- tails in a complicated and poorly understood structure like a submarine. His work on this subject with David Feit and Vic Sparrow greatly influenced the direction of research.
Most recently, Pierce and his student Amadou Thiam have been studying energy harvesting from ocean gravity waves, which resulted in a presentation at a session on Energy Har- vesting at the San Diego ASA meeting in 2011. As if these efforts were not sufficiently prodigious, Allan's published works also contributed to understanding of many other ar- eas of acoustics, including diffraction along the ground and around obstacles. Not even bioacoustics escaped his atten- tion, as evidenced by his paper on how a cicada, despite its small size, can make so much noise (Hughes et al., 2014).
A hint of Allan's ultimate devotion to ASA may be found in an aspect the reader might already have observed. Nearly all of the papers mentioned thus far were published in JASA. Indeed, the overwhelming majority of Allan's work has been published in JASA. Although Allan has enhanced the repu- tation and recognition of JASA in many ways, there is little doubt that one of the most significant is Allan's selection of JASA as the venue for his papers.
Beyond his research, it is not obvious what aspect of acous- tics was most widely impacted by Allan Pierce. It might be education. Probably the greatest influence he has had in this arena is his book Acoustics: An Introduction to Its Physical Principles and Applications (Pierce, 1989) originally pub- lished in 1981.
It is simultaneously a textbook, a monograph, an encyclo- pedia, a literature survey, and a history book. It was the only one that we ever thought to use as a textbook when we taught graduate-level acoustics while we were active at Georgia Tech. We cannot say that most students were happy about our choice because the book’s objective is to raise a student's expertise to a high level. We told our students on
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