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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-section of an ultrasonic beam. A new type of a controllable device for acoustic beam focussing—an electroacoustic lens—has been made. The designs of lenses have been calculated on the basis of the quadratic electroacoustic effect and the results are presented of the first experimental 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 aperture, as well as on the control voltage value and the electroacoustic parameters of the material. The lens was made of ferroelectric ceramics lead-zirconate-niobate, (PbZn 1 3 NbO3)-based, and had a focal length of 15 cm at a control voltage of 5 kV. |
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