M. A. Breazeale
Dehua Huang
Natl. Ctr. for Phys. Acoust., Univ. of Mississippi, University, MS 38677
The Gaussian distribution of an ultrasonic field has attracted attention and interest because of its unique features: analytic mathematical solution for a sound field in a homogeneous medium; no maxima or minima in Fresnel zone; a single beam free of sidelobes in the Fraunhofer region. Heretofore the mathematical attractiveness of the Gaussian function has been used in many physical theories. It has been used in connection with underwater acoustics, interface problems, medical ultrasonics, nondestructive evaluation, acoustical microscopy, nonlinear acoustics, etc. The Gaussian beam not only is an ideal mathematical model, but it is beginning to be physically realizable. Several methods reported to be successful in the megahertz frequency range have failed to produce a Gaussian distribution in the kilohertz range. This paper presents an improved design that is successful for a kilohertz Gaussian transducer. It has worked in the megahertz frequency range also. Gaussian transducers at 375 kHz (4 in. diam) and at 332 kHz (5 in. diam) have been made in our lab. The frequency--transducer size relation has been set by a 30-dB sidelobe suppression criterion. Theoretical design and experimental verification are presented. A 6-in.-diam Gaussian transducer that works at even lower frequency is in progress. [Work supported by ONT.]