Infringement: Doctrine of Equivalents


A patent confers exclusive rights to a patentee to prevent others from making, using, importing, offering to sale, or selling any subject matter falling within the scope of the patent claims.

The rights conferred by a patent are constrained by the jurisdiction i.e. if a patent is granted in the USA then the patentee has the right to enforce the patent in the USA only.

In this study, we are discussing some important key terminologies associated with infringement along with the basic understanding of infringement under the Doctrine of Equivalents.

When A Patent Is Said To Be Infringed?

As per 35 US Code 271(a): A patent is said to be infringed in the United States if anyone sells, offers to sell, makes or use any patented invention without authority, or imports any patented invention into the United States during the term of the patentee.

To prove infringement, the plaintiff has to show up to the satisfaction of the court using  evidence that the accused product comprises each element (or an equivalent) of the patented invention.

What Are The Types Of Infringement?

The infringement majorly divided into two types i.e. Direct Infringement and Indirect Infringement.


Direct Infringement can be further divided into two categories.

Literal Infringement 35 USC 271(a)

Infringement under the Doctrine of equivalents35 USC 112(f)

Indirect Infringement can also be further divided into two categories.

Inducement Infringement 35 USC 271(b)

contributory Infringement35 USC 271(c)

Patent Infringement inquiry

The court analyzes the infringed patent in two stages:

> Literal Infringement.

> Infringement under the Doctrine of Equivalent.


What Is Literal Infringement?

When an infringer replicates a patented invention exactly as it is being claimed, in such a case the infringement is considered to be the literal infringement.

Let’s understand the literal infringement with the following example:

Technology being Claimed: “A conductive plastic composition: Teflon;”

Accused Product: “A conductive plastic composition made of a mixture of polyester and Teflon”

Teflon  <=> a mixture of polyester and Teflon

As we can see, all the components of the claimed invention are present in the infringing product. In such a case, when the features of the accused/alleged product(s) are within the literal meaning or language of the patented claims, then the infringement is said to be Literal Infringement.

What Is Infringement Under Doctrine Of Equivalents (DOE)?

Infringement under the Doctrine of Equivalents (DOE) is a way for a patentee to file an infringement suit even though the claimed invention is not present in the accused product. DOE as a term is not mentioned in the US Patent Act of 1952 however, at one solitary place i.e. 35 USC 112, the Patents Act quotes

“The claim which discloses the functions of a component instead of the system, process, or composition, such claim shall be understood from the described specifications”.

And the above statement of the Patent Act is used as the base for proving infringement under the Doctrine of Equivalents.

Let’s Understand the DOE via a case study “Graver Tank& Manufacturing Co. v/s Linde Air Products Co. (1950)”

Technology being claimed: “Flux to be used in an electric welding process wherein the claimed flux composition is a combination of “alkaline earth metal silicate (i.e., silicates of calcium and magnesium) and calcium fluoride”.

Accused Product: The flux composition which is a combination of “non-alkaline earth metals (i.e., silicates of calcium and manganese) and calcium fluoride”.

Alkaline earth metal <=> Non-alkaline earth metals

Calcium fluoride <=> Calcium fluoride

As we can see, that the accused product does not contain all the elements of the claimed invention i.e. the claimed invention uses alkaline earth metals whereas the accused product makes use of non-alkaline earth metals. In such a case, under the doctrine of equivalents, the accused device, process, or composition doing the same function for obtaining the same result as the patented device, process, or composition can be protected.

How to identify Infringement under the Doctrine of Equivalents?

The court laid out two tests for applying the Doctrine of Equivalents:

> Triple Identity Test.

> Substantially Difference Test


Limitations of Doctrine of Equivalents (DOE)

The Doctrine of Equivalents has the following limitations in its applications:

1.    All – Elements Rule/ All-limitation Rule: The  Doctrine of Equivalents is applicable on an “element-by-element” basis i.e., when all the claim limitation(s) are identified in the accused product(s). Under this rule, the DOE is not applicable to the patented invention as a whole and not to the overall accused product(s).

2.    Obviousness: Under this rule, the invention shall not be known to the person ordinary skilled in the field of this invention.

3.    File History or Prosecution History Estoppel: Under this rule, during the prosecution of the patent, the dropped subject matter cannot be claimed by the patentee. Thus, the claims must be interpreted from their rejections, cancellations or amendments.

4.    Dedication Rule: Under this rule, the Doctrine of Equivalents cannot be applied for unclaimed subject matter.

5.    Means-Plus-Functions Claims: Under this rule, infringement is barred under the Doctrine of Equivalents if the equivalent element is known before the grant of the patent.

Some Cases Where DOE Couldn’t Be Applied To Establish Infringement

Since, the doctrine of equivalents varies from case to case, below given are the details of some prominent cases where the doctrine of equivalents couldn’t be applied to establish infringement due to the limitations imposed on DOE.

Case 1.SciMed Life Systems, Inc. v. Advanced Cardiovascular Systems (2001)

Technology being claimed by SciMed Life Systems was using lumen catheters whereas the accused product was making use of dual-lumen catheters (side-by-side catheters).

The district court ruled that the SciMed patents do not disclose about using the dual-lumen catheters instead the patents criticize the use of dual-lumen catheters in the prior art.

The court’s decision that Advanced Cardiovascular Systems had not infringed upon the SciMed patents came on the basis that “though the claim is broad enough to cover all types of catheters the patent, at no point in the specification, discusses the use of dual-lumen catheters. The preferred embodiment of the inventions discusses the use of co-axial lumen catheters which cannot be considered as equivalent to the dual-lumen catheters, the reason being that the specification of the patent limits the scope of the claims to co-axial lumen catheters.

Thereby, If the patentee limits the scope of the claims in the specification by making clear that the invention does not include a specific feature, that feature is deemed to be outside the scope of the claims and infringement under the doctrine of equivalents cannot be established.

Case 2.Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki (2002)

The technology is claimed by Festo Corp. in one of the patents was”a piston-driven device that uses one-way sealing rings and that its outer sleeve would be made of a magnetizable material” whereas the defendant’s product was also a similar device avoiding the limitation of one-way sealing ring i.e. the Shoketsu’s product has two-way sealing rings.

The plaintiff argued that the defendant’s product was adequately similar to the patented invention and infringement under the doctrine of equivalents can be established.

But the catch here was that during the prosecution of the patent, the plaintiff narrowed down the claims to comply with the Patent Office’s requirements by dropping the part of the claim covering the technology pertaining to two-way sealing rings.

According to the limitations of the Doctrine of Equivalents “during the prosecution of the patent, the dropped subject matter cannot be claimed by the patentee”.


We have studied different types of infringement and come to know about infringement under DOE and how it is different from literal infringement. Also, we have gone through some case-studies in which DOE couldn’t be applied to establish infringement.

Authored By: Anshita Garg, Senior Research Associate, Operations Team