ULTRASONIC BEAM FOCUSING IN FERROELECTRIC CERAMICS BY APPLICATION OF A NONUNIFORM ELECTRIC-FIELD

A new solution to the problem of controllable focussing of ultrasonic beams is given. It results from the fact that the application of a non -uniform electric field, of a special configuration, in ferroelectric ceramics causes a quadratic change of the velocity in the cross-sectio n of an ultrasonic beam. A new type of a controllable device for acous tic beam focussing - an electroacoustic lens - has been made. The desi gns of lenses have been calculated on the basis of the quadratic elect roacoustic effect and the results are presented of the first experimen tal observation of the phenomenon of ultrasonic beam focussing in non- uniform electric fields of special configurations. The dependence has been established of the focal length on the lens length and the apertu re, as well as on the control voltage value and the electroacoustic pa rameters of the material. The lens was made of ferroelectric ceramics lead-zirconate-niobate, (PbZn1/3NbO3)-based, and had a focal length of 15 cm at a control voltage of 5 kV.