40khz air ultrasonic ceramictransducers enclosed prowave 400et18s a 2900pf 40khz oslash18mm enclosed transducer transmitter that may be hermetically sealed and is suitable for outdoor use as well as for use in dusty and contaminated indoor environments the transmitter is of the pulse transit type and consists of an aluminium housing with an integral diaphragm the transducer resonating at the the first harmonic the back of the housing is completely sealed with resin protecting it from