Abstract: N elementary transducers are distributed regularly along a line of scanni An ultrasonic frequency receiver is associated with phase lag means. The distribution over n successive elementary transducers of the phases corresponding to focusing at a predetermined distance or several successive distances from the line is stored. That distribution corresponds to several Fresnel zones. Switches first connect a generator to a group of n' transducers corresponding to the central Fresnel zone of said stored distribution and later connect a group of n transducers to the receiver direct and via the phase lag means according to the stored distribution(s). The groups of n' and n elementary transducers are shifted along the line at intervals of time. The phase lag means may consist of inverter means causing a phase angle of .pi..

Abstract: The device for transmitting or receiving ultrasonic waves or pulses to and from well-defined adjustable directions or distances includes a capacitive transducer consisting of a layer of dielectric material tightly packed between two electrodes, one at least of which is formed of an appropriate array of elongated strips of circular or rectilinear shape.