Composite wall, notably motor vehicle windshield, including an ultrasonic device for detecting the presence of foreign bodies on one of its faces

摘要

The panel (8) comprises two plates (20,22) having respective thicknesses (e1,e2), separated by an intermediary layer (24), of thickness (e3). An ultrasonic detector (12) is fitted to the second plate (22) external face (16), to detect any foreign bodies on the first plate (20) external face (18). The detector transducer (26) emits an ultrasonic signal, frequency f and receives reflected signals from the first plate outer face. These reflections represent presence or absence of foreign matter. The intermediate layer houses (40) an element (42) inserted between and in contact with the two outer plates, adjacent to the transducer. The frequency f is related to the plate and element thicknesses (e1,e2,e3), the ultrasound wave propagation speed in the three materials (V1,V2,V3) and three respective constants (K1,K2,K3). The transducer may be piezoelectric (28).