Federal Circuit Limits Equivalents Doctrine

The doctrine of equivalents is often invoked by patentees attempting to broaden the reach of a patent claim to cover that which the claim literally could not cover.  After concluding that the accused product does not infringe the claim literally because it does not contain one or more limitations of that claim, the court or jury may still find that the accused product infringes the claim under the doctrine of equivalents if the difference between the accused device and that limitation is "insubstantial".  Hilton Davis Chem. Co. v. Warner-Jenkinson Co., 520 U.S. 17, 28-29 (1997).  The doctrine prevents an accused infringer from avoiding infringement by changing only minor or insubstantial details of a claimed invention while retaining their essential functionality.  See id.