https://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&p=1&u=/netahtml/PTO/srchnum.html&r=1&f=G&l=50&d=PALL&s1=9884895.PN.

https://patents.justia.com/patent/6372224

https://patents.google.com/patent/US7279327B2/en