According to an aspect, there is provided a structure for a thin-film bulk acoustic resonator. The structure comprises a substrate (101) comprising a cavity (104) having at least one slanted flat surface (103) facing away from the cavity and a piezoelectric bulk material layer (102) deposited on said at least one slanted flat surface.

An optical monitoring system serves to monitor surroundings, having a monitoring apparatus, the visual or scanning field of which is captured by a lens, and a protection panel (112) which protects the lens from precipitation and covers at least the visual or scanning field of the monitoring apparatus. In order to avoid the signal quality of the monitoring apparatus being impaired by precipitation on the protection panel, it is proposed that the protection panel (12; 112; 218; 318) is acoustically coupled to at least one ultrasonic transducer (10). The optical monitoring system can be included into the control system of a vehicle for autonomous driving, wherein, overall, it is possible to obtain increased safety of the control system.

An ultrasonic transducer having a transducer element, a housing, a coupling element with a front and a back, wherein the back of the coupling element is acoustically coupled to the top of the transducer element in order to couple the ultrasonic waves generated by the transducer element out to the environment in a transmit mode or in order to pass the ultrasonic waves received from the environment by the coupling element on to the transducer element in a receive mode. The transducer element and the coupling element are arranged in the housing. A first electrode is connected to a contact area formed on the bottom of the transducer element. The transducer element is arranged in a shielding device made of a metallically conductive material, and the opening of the shielding device is covered by a metallic, conductive screen so that the shielding device and the screen form a Faraday cage.