Non-uniformly poled Gaussian and Bessel function transducers

A technique has been developed to polarize piezoelectric ceramic elements with spatially nonuniform electric fields. Used as ultrasonic transducers, these piezoelectric elements then produce nonuniform sound-field profiles corresponding to the spatially nonuniform polarization strength poled into the element. Gaussian transducers and Bessel function transducers have been built using this technique. The Bessel function transducer, of particular interest in achieving diffractionless beams was made to produce an ultrasonic beam profile approximating that of the Bessel function J₀(r ) both in amplitude and in phase out to the third zero. The beam profiles of these nonuniformly poled transducers were mapped out in a water-immersion tank with a point probe and compared with beam profiles calculated with a Gauss-Hermite model excellent agreement was obtained. Such transducers containing prescribed field profiles can be electroded and mounted in the same manner as conventional piston transducers