History of the flextensional electroacoustic transducer

The flextensional electroacoustic transducer is resurging as a candidate for high-power, low-frequency active sonar. It has experienced steady investigation and development since the late 1950s and is popular enough now so that it is even advertised in naval and ocean-related publications. Despite this popularity, the history of its invention and development has remained cloudy. The invention is usually credited to William J. Toulis during the late 1950s. However, at least two flextensional designs were invented, developed, and constructed during 1929–1936 by a pioneer in underwater acoustics, Harvey C. Hayes, at the U. S. Naval Research Laboratories in Washington, DC. These flextensionals were intended as aeroacoustic foghorn sources. The Hayes flextensionals then vanished from development during the mid-1930s, and the concept was not revisited (in the U.S.) until the mid-to-late 1950s by Toulis and Frank R. Abbott at the U. S. Naval Electronics Laboratory, San Diego, CA. This paper will review the history of the flextensional transducer beginning with Hayes’ work, review the classes of flextensional transducers, and discuss modern flextensional transducers.