Ahrens, U.U.AhrensLangen, A.A.LangenVasiliadis, N.N.Vasiliadis2022-03-082022-03-081993https://publica.fraunhofer.de/handle/publica/302834The description refers to an ultrasonic sensor having at least one ultrasonic sensor which excites a control unit at a specific ultrasonic frequency, and which irradiates an ultrasonic wave field which is shaped and guided by a downstream channel having sound-proof limiting walls, and an ultrasonic receiver. The sensor according to the invention is characterized by the fact that, adjacent to the transmitter, the downstream channel has a first cavity whose dimensions are approximately equal to the dimensions of the transmitter in a perpendicular direction to the propagation directions of the sound, and which is limited by a diaphragm whose diameter is smaller or at most equal to the ultrasonic wavelength, and, adjacent to the diaphragm, said channel having a second cavity having a sound exit opening in the direction of propagation which forms the sound lobe.de608670patent1989-3916632