1. M.S. Greenwood, Ultrasonic fluid densitometer for process control, US Patent 6,082,180 issued July 4, 2000
2. M.S. Greenwood, Ultrasonic fluid densitometer having liquid/wedge and gas/wedge interfaces, US Patent 6,082,181 issued July 4, 2000
3. M.S. Greenwood, R.V. Harris, Pitch-catch only ultrasonic fluid densitometer, US Patent 5,886,250 issued March 23, 1999
4. M.S. Greenwood, J.C. Lail, Ultrasonic fluid densitometry and densitometer, US Patent 5,708,191 issued January 13, 1998
5. On-line ultrasonic density sensor for process control of liquids and slurries;Greenwood;Ultrasonics,1999