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Doctrine of Equivalents Applied to Means-Plus-Function Limitations: There Is No 'Equivalent of an Equivalent'

By Steven F. Meyer
May 26, 2005

A means-plus-function limitation recites a function to be performed rather than definite structure or materials for performing that function. Chiuminatta Concrete Concepts, Inc. v. Cardinal Indus., Inc., 145 F.3d 1303, 1307 (Fed. Cir. 1998). Such a limitation is more narrow than a counterpart written in structural format. Lighting World, Inc. v. Birchwood Lighting, Inc., 382 F.3d 1354, 1361-62 (Fed. Cir. 2004). Nevertheless, patent drafters still commonly use means-plus-function limitations in computer-related patent claims for convenience sake.

The ramifications of using means-plus-function format include: 1) any equivalent structure in the accused device that was developed after the issuance of the patent cannot literally infringe under '112, ' 6; and 2) the doctrine of equivalents cannot be applied to an accused structure using pre-existing technology developed before the patent issuance. In short, the Patent Statute will not produce an “equivalent of an equivalent” by applying both '112, ' 6 and the doctrine of equivalents to the structure covered by a means-plus-function limitation.

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