Patent Infringement under the Doctrine of Equivalents in the Federal Circuit

When a device performs substantially the same function, in substantially the same way, to obtain substantial the same result as a patented device, the patent is infringed under the doctrine of equivalents. This doctrine developed to prevent minor and unsubstantial changes in a device from being used to avoid liability for patent infringement. The Court of Appeals for the Federal Circuit has addressed the major issues involving the doctrine of equivalents, and these decisions, as well as others, are examined. Specifically, the relationship between the doctrine of equivalents and the statutory equivalents of §112(6) of the Patent Act of 1952 is analyzed. Additionally, the “element by element” approach and “invention as a whole” test for the doctrine of equivalents are contrasted, and the Pennwalt decision on which is the proper method is reviewed. Finally, the effect of doctrine of prosecution history estoppel and the reverse doctrine of equivalents on the doctrine of equivalents is considered.