Ed Carstensen and the recognition of nonlinear acoustics in biomedical ultrasound

Nonlinear acoustics in biomedical ultrasound was not well recognized, nor utilized in the era leading up to the 1980s. The discipline was experiencing rapid growth and experimentation, but without consideration of nonlinear effects, even though they were significant. Ed Carstensen was one of the first to become suspicious of the “linear assumption,” mostly in his own experiments. In 1979, he contacted me and asked for help in making the community aware of nonlinear acoustics at biomedical frequencies and intensities. The two of us, with the help of David Blackstock and Ed’s graduate students, W.K. Law and N.D. McKay, set out to produce a pair of tutorial manuscripts, to call the community’s attention to acoustic nonlinearity. These were published in the Journal of Ultrasound in Medicine and Biology, Vol. 6, p 345-357, and 359-368 (1980). The first was a description of pertinent nonlinear acoustic theory, as then used, and the second was an experimental demonstration of nonlinear effects, easily recognizable in the laboratory. The present paper recounts the situation at the time (37 years ago) which experienced a turning point, once nonlinear acoustics was recognized. Existing perplexities were resolved and new paths of research and development were identified. Some discussion of here-to-fore unappreciated individuals and history in nonlinear acoustics is also presented. [Work supported by Applied Research Laboratories, The University of Texas at Austin.]