Nonlinear acoustics in E. L. Carstensen’s career

HIFU and harmonic imaging are hallmarks of present day biomedical ultrasound. But it wasn’t always this way. At one time linear theory ruled supreme. Although by the early 1970s nonlinear acoustics had made its way into many areas of acoustics, e.g., physical acoustics, underwater sound, and aeroacoustics, biomedical ultrasound remained a safe haven for small‐signalists. Ed Carstensen changed all that. By the mid‐1970s he realized that linear theory could not account for certain phenomena he observed. At the 1978 Allerton Conference his invited talk entitled ‘‘Nonlinear Aspects of Ultrasonic Absorption’’ may have been the first public disclosure that nonlinear effects are important in biomedical ultrasound. His first archival work appeared as two papers in 1980; Tom Muir was a coauthor for both. During the next decade Ed and a series of colleagues showed that absorption could easily be dominated by nonlinear propagation effects. In turn the increased absorption causes increased heating, an important practical application. Ed’s pioneering work paved the way for many of the well‐known applications today.