The doctrine of equivalents was developed to protect patentees/inventors from copiers who rob the patentees of the full scope of protection by making insubstantial substitutes to avoid literal infringement of the patent.1 Despite an absence of literal infringement of express terms of a patent claim, the infringement can still be proven if an element of an accused product or service and a claimed element of patented invention are found to be legally equivalent under the doctrine of equivalents.2 Stated differently, a patent owner can assert rights that go beyond the scope of a literal claim if the product performs an equivalent function. However when applied too broadly, the doctrine increases uncertainty to the scope of patent claims and interferes with the public-notice function of the statutory claiming requirements.3 It is this balance of the rights of the public versus the right of the patent owner that the court struggles to maintain in applying the doctrine of equivalence.4
Patents grant an inventor the right to exclude others from producing or using the inventor’s discovery or invention for a limited period of time.5 U.S. patent laws were enacted by Congress under its Constitutional grant of authority to protect the discoveries of inventors.6 The main body of law concerning patents is found in Title 35 of the United States Code.7 In order to be patented an invention must be novel, useful, and not of an obvious nature.8
The Federal agency charged with administering patent laws is the Patent and Trademark Office.9 The filing of a patent application and correspondence with the US Patent and Trademark Office (PTO) to obtain a patent is commonly referred to as patent prosecution.10 Patent prosecution begins with the drafting and filing of a patent application. Claims are formal written descriptions of a patent that define the scope of the invention and mark the boundaries of intangible property rights attached to the invention.11
Patent infringement is enforcement of the intangible property right of an inventor granted by a patent.12 Patent infringement cases arise under federal patent law over which the federal courts have exclusive jurisdiction.13
In a patent infringement action, the judge must first construe the claims.14 Claims should express exactly what the inventor of the patented invention created in clear and unambiguous language. However, [t]he very nature of words would make a clear and unambiguous claim a rare occurrence.15 Claim construction is a process of reviewing the words in patent claims to define a scope of the patent in patent infringement lawsuits.16 Claim construction is a question of law.17
A patent owner can prove infringement by establishing literal infringement. Literal infringement is found if the accused product or service literally falls within the language of a claim.18 In other words, every element of a claim must be found in the accused product or service for literal infringement.19 Literal infringement is usually avoided if any recited element in a claim does not appear in the accused product or service.
If literal infringement is absent, the patent owner can establish infringement under the doctrine of equivalents. Determination of literal or equivalent infringement is a question of fact.20 The doctrine of equivalents is an equitable doctrine that may apply when the product or service in question has a structure or performs a function that is an equivalent of an element recited in the claim.21 Therefore, if the doctrine of equivalents is applied in determining whether an infringement of a patent has occurred, it is not necessary that the infringement absolutely fall within the literal wording of the claim.22 Thus, the doctrine of equivalents is about expanding the scope of the property right of a patentee. It slightly expands the scope beyond the literal meaning of the claims.
The doctrine of equivalents is often confused with means-plus-function limitation because both concern the notion of equivalent.23 Equivalent means the same thing under both the means-plus-function limitation and the doctrine of equivalents: an "insignificant difference" that adds nothing of importance.24 Even though the means-plus-function and the doctrine of equivalents seem very similar, there are significant differences between the two inquiries. Under the means-plus-function limitation, a patentee may choose to use a means expression rather than specifically describing the structures of his invention, but the scope of the Ameans@ for performing the stated function must be limited to the structure he specifically disclosed in the specification, and equivalents thereof.25 The limitation is generally known as the means-plus-function or step-plus-function limitation.26
Equivalence analysis under the means-plus-function limitation is essentially the application of the doctrine of equivalence in a limited role.27 The means-plus-function analysis uses the same function-way-result test of the doctrine of equivalents, but the means-plus-function literal infringement stresses functional identity, not equivalency.28 Thus, the means-plus-function equivalence is narrower than the doctrine of equivalents.29 In addition, there is a temporal distinction between the statutory and common law equivalence inquiries.30 The literal meaning of a claim fixes upon issuance, and, as such, equivalence analysis under the means-plus-function only can concern technology in existence at the time of issuance.31 However, under the doctrine of equivalents, equivalency is determined at the time of infringement, and thus an accused technology developed after the issuance of the patent may be found equivalent.32
The doctrine of equivalents can be traced back to the 1853 Supreme Court case of Winans v. Denmead,33 which was ratified in the 1950 Supreme Court decision of Graver Tank Mfg. Co. v. Linde Air Products Co.34 Under Graver Tank, the main formulation of the doctrine is that an infringement of a patent can be found without finding literal infringement if the allegedly infringing device or process "performs substantially the same function in substantially the same way to achieve the same result as the patented invention."35 In other words, there is equivalence if the difference between the claim element and the accused product or service counterpart is insubstantial.
The courts have developed rules to guide application of the doctrine of equivalents. The first of four is the all elements rule. The "all limitations" or "all elements" rule was articulated by the Supreme Court in 1997 in Warner-Jenkinson v. Hilton Davis:
[E]ach element contained in a patent claim is deemed material to defining the scope of the patented invention, and thus the doctrine of equivalents must be applied to individual elements of the claim, not to the invention as a whole. It is important to ensure that the application of the doctrine, even as to an individual element, is not allowed such broad play as to effectively eliminate that element in its entirety. So long as the doctrine of equivalents does not encroach beyond the limits just described, or beyond related limits to be discussed . . . we are confident that the doctrine will not vitiate the central functions of the patent claims themselves.36
The all elements rule requires that all of the elements of a patent claim must be present in an accused product or service, though it need be present only equivalently, to support a finding of patent infringement.37 According to this rule, the doctrine of equivalents may not be used to supply limitations that are wholly missing from an accused product or service.38 Because the all elements rule protects the materiality of each claim limitation, it is also often described as a rule against vitiating a limitation.39
Another legal limitation on the doctrine of equivalents is the doctrine of public dedication. In Maxwell v. J. Baker, Inc., the court held that where a patent application discloses unclaimed subject matter, that subject matter must be deemed to have been dedicated to the public.40 Under the public dedication doctrine, when the patentee discloses a range of possible equivalents in the patent’s specification but declines to claim some of them, the patentee is deemed to have dedicated the unclaimed equivalents to the public.41 Application of the doctrine of equivalents to recapture subject matter deliberately left unclaimed is "contrary to our system of patent examination, in which a patent is granted following careful examination of that which an applicant claims as her invention."42
The existence of prior art also limits the application of the doctrine of equivalents to extend a patentee’s protection beyond literal claims.
The doctrine of equivalents exists to prevent a fraud on a patent, not to give a patentee something which he could not lawfully have obtained from the PTO had he tried. Thus, since prior art always limits what an inventor could have claimed, it limits the range of permissible equivalents of a claim.43
The scope of equivalents cannot be taken in a vacuum, free from the prior art.44 When a question of equivalency is under study, it is also necessary to know if the patent is a pioneer in a whole new field or if the patent shows only a narrow improvement of a subject that is well known.45 Typically, pioneer patents will be given a broader range of protection than an improvement patent under the doctrine of equivalents.46
Claims construction may not be done such that prior art is embraced, if it is, the construction is probably improper.47 Likewise, the asserted range of equivalents cannot extend to cover prior art.48 Stated differently, the range of equivalents cannot include any element so similar to the prior art that the claim would not have been patentable if it had been drafted as such. If the minimum scope necessary to support infringement would encompass the prior art, there is no infringement.49
Finally, the prosecution history estoppel also limits the application of the doctrine of equivalents. Whether a patent owner is entitled to equivalence under the doctrine of equivalents depends on what occurred during prosecution of the patent.50 Many patents are not issued with the claims originally filed. If an examiner rejects the claims as unpatentable over the prior art or some other reason, and the claims are amended to read more narrowly to avoid the prior art, the patentee is barred from asserting the claims in the broader sense.51 Since the patentee gave up the broader construction to obtain allowance of the claims, the patentee is not permitted to assert that the broader construction is the equivalent of the claim which was finally allowed.52 This is known as prosecution history estoppel.53
In Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., the Supreme Court found that making any narrowing amendment relating to claim patentability creates a presumption that all equivalents are surrendered.54 The presumption is rebutted by establishing the equivalents in question to be unforeseeable at the time of the application, or that at the time of the amendment, one skilled in the art could not reasonably be expected to have drafted a claim that would have literally encompassed the alleged equivalent.55 The patent owner may also attempt to rebut the presumption by establishing that the rationale underlying the amendment bears no more than a "tangential relation" to the equivalent in question.56
The courts have strived to balance two countervailing principles: ensuring the notice function of a patent and maintaining the full-breadth protecting of a patent.57 In efforts to balance these interests, the Court developed the doctrine of equivalents and rules to guide its application. The doctrine of equivalents removes the unfairness that could result from an overemphasis on the literal language of patent claims, and thereby afford patentees protection accorded to the patent. On the other hand, the guiding rules limit application of the doctrine of equivalents; so it would not take on "a life of its own, unbounded by the patent claim" to provide a patentee protection that he is not entitled to within the scope of his patent and eliminate the important function of patent; clear public notice of patentee’s scope of exclusive right.58
1 Festo Corp. v. Shoketsu Kinzo Kogyo Kabushiki Co., 535 U.S. 722, 731 (2002).
2 Warner-Jenkinson Co. v. Hilton-Davis Chemical Co., 520 U.S. 17, 21 (1997).
3 Freedman Seating Company v. American Seating Company, 420 F.3d 1350, 1358 (Fed. Cir. 2005).
4 See Warner-Jenkinson, 520 U.S. at 28-29.
5 Joseph S. Cianfrani, An Economic Analysis of the Doctrine of Equivalents, 1 Va. J.L. & Tech. 1, 4 (Spring 1997).
7 See 35 U.S.C. (2006).
8 See 35 U.S.C. ‘’ 101-103 (2006).
9 See 35 U.S.C. ‘ 1-26 (2006).
10 See Id.
11 Joshua D. Sarnoff, Abolishing The Doctrine of Equivalents and Claiming The Future After Festo, 19 Berkeley Tech. L.J. 1157, 1161 (2004). (what’s marking the boundaries)
12 See Id.
13 28 U.S.C. ‘ 1338 (2006).
14 Freeman Seating, 420 F.3d at 1356.
15 Autogiro Co. of Am. v. United States, 384 F.2d 391, 396 (Ct. Cl. 1967).
16 Sarnoff, supra note 11, at 1161.
17 Id. at 1357.
18 John M. Benassi, Proving Infringement With Emphasis On The Festo Cases And The Doctrine Of Equivalency, 804 PLI/Pat 219, 222 (204).
20 Freeman Seating, 420 F.3d at 1357.
23 35 U.S.C 112 ‘6 (2006). An element in a claim for a combination may be expressed as a means or step for performing a specified function without the recital of structure, material, or acts in support thereof, and such claim shall be construed to cover the corresponding structure, material, or acts described in the specification and equivalents thereof.
24 See Warner-Jenkinson, 520 U.S. at 28-29.
25 John N. Kandara, Application of the Doctrine of Equivalents to Means Plus Function Claims: WMS Gaming Inc. v. International Game Tech, 50 Duke L.J. 887, 894-97 (2000).
27 See, e.g., Warner-Jenkinson, 520 U.S. at 40.
28 See Odetics Inc. v. Storage Technology Corp., 185 F.3d 1259, 1267 (Fed. Cir. 1999).
30 See Al-Site Corp. v. VSI Int=l, Inc., 174 F.3d 1308, 1320 (Fed. Cir. 1999).
31 See Chiuminatta Concrete Sys., Inc. v. Cardinal Indus., Inc., 145 F.3d 1303, 1310-11 (Fed. Cir. 1998).
32 Warner-Jenkinson, 520 U.S. at 37.
33 56 U.S. 330 (1853).
34 339 U.S. 605 (1950).
35 Ethicon Edo-Surgery Inc. v. U.S. Surgical Corp., 149 F.3d 1309, 1315 (Fed. Cir. 1998).
36 Id. at 29-30.
38 See SciMed Life Systems, Inc. v. Advanced Cardiovascular Systems, Inc., 242 F.3d 1337, 1347 (Fed. Cir. 2001).
39 David J.F. Gross & Shawn T. Gordon, Claim Construction, Patent Infringement, and the Growing Importance of the Claim Vitiation Defense, 841 PLI/Pat 45, 75 (2005).
40 86 F.3d. 1098, 1108 (Fed.Cir. 1996).
41 Johnson & Johnston Assocs. v. R.E. Serv. Co., 285 F.3d 1046, 1054 (Fed. Cir. 2002).
42 Maxwell, 86 F.3d. at 1107.
43 Wilson Sporting Goods Co. v. David Geoffrey & Associates, 904 F.2d 677, 684 (Fed. Cir. 1990).
45 See Benjamin C. Hsing, Proof of Equivalence after Festo, 725 PLI/at 115, 127 (2002).
47 Wilson Sporting Goods Co., 904 F.2d at 684.
50 Warner-Jenkinson, 520 U.S. at 30-32.
51 Festo, 535 U.S. at 733-35.
54 Id. at 740-41.
55 Id. at 725.
57 Kandara, supra note 25, at 892.
58 Warner-Jenkinson, 520 U.S.at 29.
Sun Y. Pae, Northern Illinois University College of Law