Abstract: The sensor device for detecting the presence or absence of a liquid (2) at predetermined level (N) in a tank (1) comprises a transmitter transducer (51; 51'; 61), a receiver transducer (52, 52', 62), and electronic means (100) for processing the signals applied to the transmission transducer and delivered by the receiver transducer. In the vicinity of the predetermined level (N) of the tank (1), the device includes a detection plate (50; 50', 60) having at least one face (58) which comes into contact with the liquid (2) when the liquid reaches that level. The detection plate carries the transmitter transducer which is disposed for locally generating Lamb waves in the plate, and the plate also carries the receiver transducer which is disposed for detecting the presence or the absence of Lamb waves transmitted along the plate.

Abstract: The resonator (10) includes a monocrystal (11) of a nonpiezoelectric matel with low attenuation of elastic bulk waves, such as corundum, means of supporting the monocrystal fastened to the monocrystal at points corresponding to the vibration nodes, thermal means (40) for directly causing a proper excitation of the monocrystal (11) and optical means (50) for detecting the periodic motion of the resonator without contact. Application in particular in oscillator construction.