The Doctrine of Equivalents (DOE) is a judicially created rule in U.S. patent law that allows a patentee to assert infringement even if an accused product or process does not literally infringe the claims of a patent. The doctrine ensures that competitors cannot make trivial modifications to avoid infringement while still appropriating the invention’s benefits. However, the DOE is not unlimited. There are significant limitations to its application, as discussed below.

The Doctrine of Equivalents Covers Insubstantial Differences

At its core, the DOE addresses cases where an accused product or process does not fall within the literal scope of a patent claim but differs only insubstantially from the claimed invention.

One common test to assess whether an element of the accused device is an insubstantial difference compared to the claim limitation is through the Function-Way-Result (FWR) test, which asks:

1. Does the element of the accused product or process perform substantially the same function as the claim limitation?
2. Does it do so in substantially the same way?
3. Does it achieve substantially the same result?

Another important rule under DOE is the All-Elements Rule, which ensures that the DOE is applied to each individual element rather than the invention as a whole. This prevents the patentee from effectively rewriting the claims to ignore or omit individual limitations.

Restrictions on the Doctrine of Equivalents

1. Claim Amendments (Prosecution History Estoppel)
   In Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., the Supreme Court explained that:
   

   “A narrowing amendment made to satisfy any requirement of the Patent Act may give rise to an estoppel.” (Festo, 535 U.S. 722, 2002).

   If a patentee narrows a claim during prosecution to secure a patent, they are estopped from later expanding the claim’s scope under the DOE.  You cannot give up scope during examination and take it back during litigation.  That would be unfair.

   Facts and Application in Festo:
   In Festo, the patentee amended claims related to a magnetically coupled rodless cylinder system to overcome a rejection for lack of novelty. The amendment added specific limitations about the composition of the sealing material to avoid prior art. The accused infringer used a different material for the seal, which did not literally infringe the claims. The court held that the narrowing amendment barred the patentee from arguing DOE to cover the alternative material.

2. Narrowing Arguments (Argument-Based Estoppel)
   In Southwall Technologies, Inc. v. Cardinal IG Co., the Federal Circuit stated:
   

   “Clear assertions made during prosecution in support of patentability… may create an estoppel.” (Southwall, 54 F.3d 1570, 1995).

   If a patentee argues that the claim must include a specific feature to distinguish prior art, they cannot later claim that the DOE applies to an accused product that lacks that feature.

   Facts and Application in Southwall:
   Southwall had a patent for a coated glass product with specific layers for thermal insulation. During prosecution, Southwall distinguished its invention from prior art by emphasizing a unique chemical composition in one layer. The accused product used a different composition. The court ruled that Southwall could not invoke DOE because its statements during prosecution precluded claiming equivalents to the distinguished feature.

3. Disparaging the Prior Art
   In SciMed Life Systems, Inc. v. Advanced Cardiovascular Systems, Inc., the Federal Circuit ruled:
   

   “Having specifically identified, criticized, and disclaimed the [prior art] configuration, SciMed cannot now invoke the doctrine of equivalents to embrace a structure that was specifically excluded from the claims.” (SciMed, 242 F.3d 1337, 2001).

   If a patentee criticizes a feature in the prior art to distinguish their invention, they cannot later claim that the criticized feature is equivalent to their claimed invention.

   Facts and Application in SciMed:
   SciMed’s patent covered a dual-lumen catheter design and explicitly criticized coaxial lumens (a different configuration) as inefficient. The accused infringer used a coaxial lumen design. The court held that SciMed could not argue DOE to cover coaxial lumens because the patent had expressly disclaimed them as undesirable.

4. Disclosed but Not Claimed (Disclosure-Dedication Doctrine)
   In Johnson & Johnston Associates Inc. v. R.E. Service Co., the Federal Circuit stated:
   

   “When a patent drafter discloses but declines to claim subject matter, this action dedicates that unclaimed subject matter to the public.” (Johnson & Johnston, 285 F.3d 1046, 2002).

   If a patentee discloses options in the specification but does not claim them, they cannot later argue that those options are equivalents under DOE.

   Facts and Application in Johnson & Johnston:
   The patentee disclosed multiple materials, including aluminum, for use in a substrate but only claimed steel. The accused infringer used aluminum in their product. The court held that aluminum was dedicated to the public because it was disclosed but not claimed, and DOE could not be used to cover it.

5. Prior Art Constraint
   In Wilson Sporting Goods Co. v. David Geoffrey & Associates, the Federal Circuit explained:
   

   “A patentee should not be able to obtain, under the doctrine of equivalents, coverage which he could not lawfully have obtained from the PTO by literal claims.” (Wilson Sporting Goods, 904 F.2d 677, 1990).

   The DOE cannot extend a patent’s scope to cover what is already disclosed in prior art.

   Facts and Application in Wilson Sporting Goods:
   The patentee claimed a type of golf ball dimple pattern. The accused infringer’s dimple pattern was similar but fell within the scope of prior art that the patentee had not been able to claim. The court held that DOE could not be used to cover the accused product, as doing so would improperly extend the claim scope into the prior art.

How Understanding DOE Can Help You

Understanding the DOE and its limitations provides critical insight into two key areas of patent practice:

1. Evaluating Potential Infringement:
   By learning how DOE applies, you can better assess whether a product or process might infringe a patent even if it does not literally fall within the claim language. This can help in avoiding inadvertent infringement or assessing potential liability.
2. Drafting and Responding to Office Actions:
   When drafting patent claims or responding to an office action, you are not just making changes to overcome rejections. You must carefully consider how the words will be construed in litigation:
   • Are the claims broad enough to cover variations under literal infringement?
   • Will a narrowing amendment to secure patentability give up DOE for a particular feature?
     Strategic drafting ensures that claims provide sufficient coverage without unnecessarily surrendering equivalents. Similarly, in responding to office actions, being mindful of how amendments might limit future assertions under DOE is crucial to protecting the patent’s value.

Understanding these nuances can significantly improve decision-making during prosecution and enforcement of patents, leading to a stronger patent.

Understanding the Doctrine of Equivalents is key to protecting your innovation. Whether you’re drafting claims, responding to office actions, or assessing infringement risks, every word matters. Contact us today at (949) 433-0900 or schedule a consultation to ensure your patent strategy is strong, enforceable, and tailored to safeguard your rights. Let’s work together to protect what you’ve created!