Ultrasonic transducer for radiating and=or receiving ultrasonic waves in gaseous medium

摘要

The transducer has a piezoelectric ceramic disc (3) polarised in the thickness direction. The disc (3) has an electrode surface on each main surface. The disc (3) also has a cylindrical quarter wavelength adaptor (32) on one of the main surfaces whose normal is in the main radiation direction. The adaptor (32) provides acoustic impedance between the piezoceramic disc (3) and the surrounding gaseous medium. The adaptor (32) is made of a central, cylindrical part (33), to provide a wide radiation characteristic. The cylindrical part (33) is surrounded by an annular outer part (34) which is lower than the cylindrical part (33). The height of the cylindrical part (33) is a quarter of the wavelength in the material of the adaptor and is matched to the radial basic resonance of the ceramic disc (3). The radius of the cylindrical part is determined for the width of the radiation characteristic and is considerably smaller than the diameter of the ceramic disc (3).