1. Amtower, P.K., 2007, U.S. Pat., 0,251,615
2. Dixon, S.J., Tunick, B.R. and Brown, E.D., 2006, U.S. Pat., 0,272,754
3. Hugus, G.D. and Sheridan, E.W., 2010, U.S. Pat., 0,251,694
4. Chan, M.L. and Turner, A.D., 2003, U.S. Pat., 0,047,260
5. Dehm, H.C., 1977, U.S. Pat., 4,038,115