There are provided an ultrasonic transducer that performs transmission and/or reception of an ultrasonic wave and a propagation medium portion that forms a propagation path of the ultrasonic wave. A density ρ1 and an acoustic velocity C1 of the propagation medium portion and a density ρ2 and a sound...http://www.google.se/patents/US20050139013?utm_source=gb-gplus-sharePatent US20050139013 - Ultrasonic sensor
