1. C. Benvenuti, US Patent 6,468,043 (October 22, 2002).
2. N. Najafi, S. Massoud-Ansari, S. Tadigadapa, Y. Zhang, US Patent 6,499,354 (December 31, 2002).
3. D.R. Sparks, US Patent 6,923,625 (August 2, 2005).
4. K. Chuntonov, EP 1 600 232 (November 30, 2005).
5. P. della Porta, C. Boffito, L. Toia, US Patent Appl. 20,040,101,686 (May 27, 2004).