Abstract: In a detection device of the presence of frost and/or measuring the thickness of the frost by ultrasound, a probe with a piezoelectric ultrasonic transducer generates an ultra-sonic acoustic emission wave and detects ultrasonic acoustic echo waves reflected by the frost. An actuating device for the probe is arranged to provide to the transducer electrical energizing signals. The probe comprises: a frost detector placed in front of the transducer and constituted of a material having an acoustic impedance between 30.times.10.sup.5 and 44.times.10.sup.5 kg m.sup.-2 s.sup.-1. This detector has a surface designed to be exposed to the surrounding atmosphere to be covered with frost. An acoustic delay device is adapted to ensure acoustic coupling and adaptation between the transducer and the detector and to separate in time the ultrasonic emission add reflected waves. A body of heat insulating material covers the assembly of the detector, the transducer and the acoustic delay device.

Abstract: An ultrasonic probe for measuring liquids at high temperature and under high pressure. The ultrasonic probe comprises a leak-tight protective sleeve which has an end face closed by a thin metallic wall. The protective sleeve contained internal elements which are in particular a transducing piezoelectric plate and a damping cylinder. The piezoelectric element has one face which is in mechanical and electrical contact with the internal face of the thin sleeve wall and the other face which is supported on a damping cylinder. The thin sleeve wall of the sleeve end face is constituted by a metallic layer obtained by cathodic sputtering.