A bearing is mounted within a housing having an acoustic-electric transducer mounted on its outside. A stationary annular outer race has at least one sensor, an electric-acoustic transducer, and an electronic system interconnecting the sensor and the electric-acoustic transducer. The electric-acoustic...http://www.google.com/patents/US5805080?utm_source=gb-gplus-sharePatent US5805080 - Bearing with an electric-acoustic transducer for transmitting information regarding various parameters within the bearing 
