40khz air ultrasonic ceramictransducers enclosed prowave 400er18s a 40khz oslash18mm enclosed transducer receiver that may be hermetically sealed and is suitable for outdoor use as well as for use in dusty and contaminated indoor environments the receiver is matched to an equivalent transmitter and has its peak sensitivity at the resonant frequency of the transmitter the back of the housing is completely sealed with resin protecting it from exposure to the environment suitable applica