An ultrasonic transducer for controlling an elevation aperture utilizes the electric field-induced polarization properties of relaxor ferroelectric materials. The Curie temperature of the material is typically close to room temperature, so that the application of a bias voltage provides piezoelectric...http://www.google.com/patents/US5396143?utm_source=gb-gplus-sharePatent US5396143 - Elevation aperture control of an ultrasonic transducer
