Format: 

[1]F. Lastname, "Title of patent," U.S. Patent Number, Month Day, Year. Available: URL or Database Name, Accessed on: Month Day, Year.

[2]F. Lastname, "Title of patent," U.S. Patent Number, Month Day, Year.

Examples: 

[1]W. A. McMillan, L. a. Christel, D. A. Borkholder, S. J. Young, "Apparatus for analysis of a nucleic acid amplification reaction," U.S. Patent 6942971 B2, Sep. 13, 2005. Available: https://www.google.com/patents/US6942971, Accessed Dec. 12, 2017.

Notes: 

If there are multiple dates associated with your patent, use the issue date as the date of publication (see p.37, "Patents: Note"). Persistent URLs to patents may be difficult to locate; Google Patents is usually the best source for these. Consider including an access date for online materials at the end of your citation (see p. 39, "Reports and Handbooks: Examples," 2).

Questions? Contact an RIT Librarian at libraryhelp@rit.edu

Source:
IEEE - Patents (p. 37); Patents (p. 40)