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The U.S. Court of Appeals for the Federal Circuit’s holding in Festo Corp. v. Shoketsu Kinzoku Kogyou Kabushiki Co. Ltd., 234 F.3d 558 (Fed. Cir. 2000), severely limited the application of the doctrine of equivalents — a vehicle for finding that a product infringes a patent — by holding that the doctrine is not available if the subject patent’s claims have be amended for reasons of patentability. Practitioners might be able to circumvent these restrictions by properly drafting and prosecuting means-plus-function claims pursuant to 35 U.S.C. �112(6). DOCTRINE OF EQUIVALENTS If an accused product avoids literal infringement of a patent’s claims, that product still may be found to infringe under the judicially created doctrine of equivalents. See Warner-Jenkinson Co. v. Hilton Davis Chem. Co., 520 U.S. 17, 21 (1997). Courts may find equivalents if the differences between a patent’s claims and the accused product are insubstantial — that is, if the accused product and the claimed invention perform substantially the same function in substantially the same way to obtain the same result. Graver Tank & Mfg. Co. v. Linde Air Products Co., 339 U.S. 605, 608 (1950). A concept called prosecution history estoppel limits what may be considered equivalent. Prosecution history estoppel applies when a patentee amends a patent application during prosecution for a reason related to patentability, or when the patentee was unable to establish a reason for an amendment that was unrelated to patentability. THE ‘FESTO’ HOLDING In Festo, the Federal Circuit raised and answered several questions intended to resolve issues relating to precisely when and how prosecution history estoppel applies to limit the application of the doctrine of equivalents. Festo, 243 F.3d at 562. The court’s most significant holding for the purpose of this article is the following: If an amendment of a claim element creates prosecution history estoppel, there is no range of equivalents available for the amended claim element, and application of the doctrine of equivalents is completely barred. Id.at 569. Put another way, if a claim has been amended for reasons of patentability, the claim can be infringed only literally. The Festodecision left many wondering whether there is anything left of the doctrine of equivalents. If narrowly amending claims for any reason related to the statutory requirements for obtaining a patent will give rise to prosecution history estoppel, when will any amendment not trigger Festo? The answer may be in 35 U.S.C. � 112(6). SECTION 112(6): ‘AND EQUIVALENTS THEREOF’ Enacted to statutorily overrule Halliburton Oil Well Cementing Co. v. Walker, 329 U.S. 1 (1946), in which the U.S. Supreme Court held a claim that was drafted in functional language to be invalid, �112 (6) permits the use of purely functional language in claims, but restricts the scope of such claims to the structure disclosed in the specification, “and equivalents thereof.” A means-plus-function element contemplated by �112(6) would recite a function the invention will perform rather than the specific structure or materials the invention will use to perform that function. The courts must construe such an element “to cover the corresponding structure, material, or acts described in the specification and equivalents thereof.” Id.The term “means” in a means-plus-function limitation refers to the corresponding structure or structures disclosed in the specification. Chiuminatta Concrete Concepts Inc. v. Cardinal Industries Inc., 145 F.3d 1303, 1308 (Fed. Cir. 1998). Thus, �112(6) permits the courts to find a range of structural equivalents not specifically disclosed in a patent’s specifications. There is no “magic language” that will allow a patent holder to invoke � 112(6). The Federal Circuit has stated that the use of the word “means” triggers a presumption that the inventor used the term advisedly to invoke the statutory mandates for means-plus-function clauses. York Products Inc. v. Central Tractor Farm & Family Center, 99 F.3d 1568, 1574 (Fed. Cir. 1996). However, in the next breath, the Federal Circuit stated that the “mere incantation” of the word “means” in a clause reciting primarily structure cannot invoke �112(6). Id.Thus, a court can ignore the “means” language if the claim is not properly drafted to recite function. In the patent infringement context, “[to] determine whether a claim limitation is met literally, where expressed as a means for performing a stated function, the court must compare the accused structure with the disclosed structure, and must find equivalent structure as well as identity of claimed function for that structure.” Pennwalt Corp. v. Durand-Wayland Inc., 833 F.2d 931, 934 (Fed.Cir.1987) (in banc) (emphasis in original). Infringement of a claim under � 112(6) is properly a matter of literal infringement, without resort to the doctrine of equivalents. Once a court identifies the structure that corresponds to the recited means, it determines equivalents under �112(6) by considering whether the differences between the structure in the accused device and that disclosed in the specification are insubstantial. See Valmont Indus. Inc. v. Reinke Mfg. Co., 983 F.2d 1039, 1043 (Fed.Cir.1993). WHERE THEY INTERSECT Equivalents analysis under �112(6) and the doctrine of equivalents are not coextensive, as �112(6) requires identical, not equivalent, function, and, as the Federal Circuit has stated often, the analyses have different origins and purposes. Nevertheless, the Federal Circuit has stated that the tests for each are closely related. Chiuminatta, 145 F.3d at 1310. A lack of equivalent structure to a means-plus-function element therefore may preclude a finding of equivalence under the doctrine of equivalents. Id. However, the Federal Circuit also has stated that even after a finding of no structural equivalents, the doctrine of equivalents may be valid to protect a patentee claiming an invention in means-plus-function language from a technological advance not contemplated by the specification. In such a case, the technological advance may be so insubstantially different that it should be an infringement. Id. The Federal Circuit has further broken down any barriers between the doctrine of equivalents and means-plus-function elements by approving “a reduced version” of the well-known tripartite test for the doctrine of equivalents to been applied to �112(6). Caterpillar Inc. v. Deere & Co., 224 F.3d 1374,1379 (Fed. Cir. 2000). Even though the doctrine of equivalents and �112(6) originally sprung from “different origins and purposes,” it now could be argued that except in the case of some unknown technological advance, the only difference between the test for determining equivalence under the doctrine of equivalents and �112(6) is the “function” factor of the test: To find infringement under �112(6), the function must be identical; under the doctrine of equivalents, the function must be substantially similar. A POST-’FESTO’ WORLD Now that the Federal Circuit is treating the doctrine of equivalents and means-plus-function claims under arguably identical tests, how will prosecution affect means-plus-function claims in the post- Festoworld? The prosecution history of a patent still affects the interpretation of a means-plus-function claim. Positions taken before the PTO may bar an inconsistent position on claim construction under �112(6). Arguments made in support of patentability may affect the range of equivalents under �112(6). See Cybor Corp. v. FAS Techs. Inc., 138 F.3d 1448, 1457 (Fed. Cir.1998) (en banc). Prior to the Festodecision, the Federal Circuit held that just as prosecution history estoppel may act to estop an equivalence argument under the doctrine of equivalents, positions taken before the PTO may bar an inconsistent position on claim construction under �112 � 6. Alpex, 102 F.3d at 1221. This has always been the case in the literal infringement context and is true of any literal claim interpretation, not just interpretation of means-plus-function claims. With the Federal Circuit effectively merging the analysis of the doctrine of equivalents and the analysis of means-plus-function claims, the critical question becomes, will the Festorule of “no range of equivalents” apply to means-plus-function claims if the function is narrowed by amendment for reasons related to patentability? In other words, because the doctrine of equivalents and � 112(6) “equivalents thereof” are being equated, can a court take away structural equivalents granted by the Patent Act? The answer should be no. First, the majority decision in Festoindicated that the law concerning structural equivalents was not affected by the decision, and that a claim element recited in means-plus-function language literally encompasses the corresponding structure and its equivalents. Festo, 234 F.3d at 589. Moreover, a means-plus-function claim is, by statute, inherently broader than the embodiment disclosed in the patent. Of course, the patent must provide structural support for the function claimed. But one way to avoid the “no range of equivalents” rule created in Festomay be to draft claims using means-plus-function language, and provide several structural examples in the specification. Limiting the range of equivalents for means-plus-function claims creates other tensions. The PTO gives claims their broadest reasonable interpretation consistent with the written description. Claims must be interpreted the same way for determining infringement. A means-plus-function claim should be interpreted broadly so that the range of permissible equivalents is not foreclosed by an amendment that does not limit the claim to the structure recited in the specification. During a patent’s prosecution, a means-plus-function claim may be amended in terms of function to overcome a prior art rejection, but the specification may remain unchanged. The courts still should permit the patentee a range of equivalents that perform the function of the structures shown in the specification. The only thing to which the court should not entitle a patentee is a structure that is equivalent to what the prior art reference that led to the amendment showed. Gregory J. Lavorgna is a partner in the Philadelphia office of Drinker Biddle & Reath LLP. E-mail: [email protected]. Michael F. Snyder is an associate in that office. E-mail: [email protected].

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