This article is written by Palak Poddar. It is an attempt to highlight the complex topic of the doctrine of equivalents as a type of patent infringement. This article further discusses in detail about the examples of the doctrine of equivalents, the advantages, the applicability, the limitations of this and provisions relating to this doctrine along with landmark case laws relating to this concept. 

It has been published by Rachit Garg.

Introduction 

Inventions have the power to reshape the world around us, right? Vehicles for traveling, telephones for communication, television for entertainment, the light bulb for electricity, the internet for communication of computer networks, and many more are examples of life-changing inventions. These inventions not only changed the lives around us but also revolutionized the specific industry for which it has been made. Also, what names come to your mind when you think of these inventions? It’s the name of the inventor, right? The person who has invested sleepless nights and overcomes multiple hurdles for his passion to contribute to society. What if someone tried to steal their invention and uses their own name instead? Well for that we have Intellectual Property Rights (IPR) in place! These rights safeguard inventors’ interests and prevent infringers from taking credit. 

Though laws, rules, regulations, and legal provisions can be complex to understand at first, knowing about the same can be beneficial for you. It can help you to understand the rights of patent owners and how they protect their inventions. As they are contributing to society, society makes sure that this hard work pays off and is rewarded. Government agencies have taken necessary steps to recognize these inventions and made laws, rules, and regulations that protect inventors in case of infringement of their rights. Over time the laws relating to intellectual property have been transforming. It has undergone multiple changes to come up with the shape it is now. The Courts have seen multiple challenges while dealing with cases related to patent law infringement. To provide clarity on the subject matter, it has also laid down some doctrines and principles that need to be followed while tackling any matter related to invention. One such important doctrine is the “doctrine of equivalent”. In this article, we will be understanding this doctrine in detail and also undergo many other relevant topics related to this doctrine. 

What is patent infringement? 

The US patent law gives the inventors the authority to make, use, sell, and import their inventions and also prohibits others from doing so. Section 35 USC 271 deals with the provision related to the infringement of patents. It specifically mentions what actions are considered as infringement of a patent and what are the remedies available to the patent holder in case of patent infringement. When someone makes, uses, sells, or offers to sell any patent invention without the permission of the patent owner or inventor within the United States it is considered to be a patent infringement. If someone tries to import the invention into the United States without the permission of the actual owner, it will also be considered patent infringement. However, patent infringement will only be considered if the term of the patent invention is valid and enforceable. 

Meaning of the term “Whoever” used in the provision

The term “whoever” used in the entire provision has been defined particularly. It says that the meaning of the term will include individuals or entities, states, instrumentalities of states, its officers or employees, or other instrumentalities acting in an official capacity. The provision mentions that it includes both governmental as well as non-governmental entities. The provision clearly says that states, their instrumentalities, employees, and their officers will be held responsible under this provision in the same manner as private entities and individuals. 

Actions considered infringement 

Section 35 USC 271 states that whoever directly infringes any patent invention by making, using, selling, or offering to sell without the authority of its patent owner particularly in the United States will be liable and said to be the “infringer” as given under Clause (b) of Section 35 USC 271. The same provision also talks about indirect infringement, wherein someone knowingly sells or imports a specific component designed for patent infringement only and not for any other purpose that will also be held liable as a contributory infringer. 

If someone without permission of the patent owner supplies a portion or an element of a patent invention in such a way that it promotes the combination of this invention outside the United States which results in patent infringement and that person will be considered an infringer. Along with that, when someone supplies a component of a patent invention that was specifically made after having particular knowledge about the fact that the combination of these will be outside the US and which subsequently infringes the patent application, he will also be considered an infringer. 

Remedies available for the patent holder 

The patent owner can claim relief and take legal action in the following cases-

• If someone generates revenue from acts that constitute contributory infringement that too without permission. 
• If someone licenses or authorizes someone to perform acts that constitutes a contributory infringement that is done without consent. 

The patent owner has the liberty to either enforce his right against the infringer or contributory infringer or choose not to use any right or license obtained from patent protection. 

Term of patent 

Patent rights in the US are granted for a limited duration of time as given under Section 35 USC 154. These terms of patents are granted based on the type of patent they are. Generally, there are three types of patents:- plant patent, design patent, and utility patent. Utility patents are patents granted for new inventions, improved and useful processes, machines, articles of manufacture, and the composition of matter from which is made. A design patent is granted for new, original, unique, and ornamental designs on any article of manufacture. The last one, a plant patent is granted for invention or discovery related to the asexual reproductive system or in a new variety of plants. 

The term of utility and plant patent is valid up to 20 years from the date of filing of the patent application. However, in the case of a design patent, the term of a patent is 15 years, from the date of grant of the patent application. Their terms can be extended based on certain conditions and approval of USPTO. 

Type of patent infringement 

US patent law categorizes the types of patent infringement mainly into two main categories based on the infringer’s actions. These categories are direct and indirect patent infringement. These types further specify various ways in which someone violates the rights of the patent owner. Let’s understand each one of them: 

Direct infringement 

Direct infringement is a straightforward form of patent infringement wherein an activity is done by the infringer which falls within the scope of a valid and enforceable patent claim. This infringement occurs when an individual or entity makes, sells, uses, imports, or offers to sell a patent invention without permission. This is the most common type of Infringement. In direct infringement, the infringer’s product performs the same function and should contain the same component in the unauthorized version of the patent. The product or process should match the same description as provided in the patent invention of the actual owner. Now direct infringement can be done in two ways:- literal infringement or infringement by the doctrine of equivalent which can also be termed as non-literal infringement. 

Literal infringement 

Literal infringement is considered when someone’s process or product matches the exact description and element of the claimed invention of an already existing patent invention. To establish literal infringement the owner has to prove that the accused invention is identical or equivalent to the elements involved in his claimed invention. In the case of literal infringement, there is a clear, direct, and unambiguous overlap between the claimed invention and the accused’s invention features of the product or processes. It must contain every single essential element of at least one claimed invention with one-to-one correspondence. In this, the product and process match the exact description, therefore, it leaves no room for other interpretation or ambiguity. 

Example: Suppose there is a pharmaceutical company with the name “ABC Pharma Ltd”. It has invented a drug that helps to cure diseases like Tuberculosis. The drug has been made by the combination of several chemical substances and other synthetic compounds. Now there is another company with the name “Zen Pharma Ltd, that started manufacturing the same drug, using similar chemical substances and materials that ABC Pharma used, this will be an example of literal infringement. 

Non-literal infringement (Doctrine of equivalent)

Non-literal infringement which is also known as infringement under the doctrine of equivalents is a legal principle that has been given for infringement of patent matters in the United States. It is applicable to the situation where an accused product or process of an invention does not literally match the product or process of the claimed invention. 

In infringement under the doctrine of equivalence, the product or process of an invention does not really match or is identical to the claimed invention, but they still perform the same functions that give the same result as the claimed patent invention. Even though the language of the description of the claimed patent invention is not identical to the accused invention, the court will still consider it a patent infringement as the end result is exactly the same in this. 

Example: Let’s take a similar example of the above pharmaceutical case wherein Zen Pharma Ltd used the same process that resulted in making a drug composition exactly identical to the claimed invention by ABC Pharma Ltd. Now earlier the process was the same, which resulted in patent infringement. Now, in the infringement under the doctrine of equivalents, the process is different. Zen Pharma is making drugs with slightly different combinations of chemical substances and compositions than ABC Pharma but the drug performs the same function which is curing tuberculosis, it operates in the same way while reacting with the body and producing the same result i.e., effectively curing the disease. This will be considered an infringement under the doctrine of equivalent. 

Indirect infringement 

Indirect infringement is another type of patent infringement in which an individual or an entity does not directly perform the act of patent infringement but encourages or induces others for doing such infringement. This is also known as secondary infringement or infringement with secondary liability. Unlike direct infringement, in this infringement, the person does not himself perform copying each and every element of the claim but it contributes to the third party in performing the same activity of infringement. 

This is a legal protection given under the patent law of the United States for cases beyond direct infringement and for the people who promote such activities of patent infringement. This safeguards the invention of the patent as it is held by parties involved in the inducement of infringement and make them liable for such actions. Indirect infringement can be done in three ways:- Infringement by inducement, contributory infringement, and vicarious infringement. 

Infringement by inducement 

A person who actively induces a patent infringement is considered an infringer and will be held liable as given under provision 35 USC 271 (b). Cases of infringement by inducement happen when any person encourages another person to perform direct infringement of a patent invention. This encouragement will lead to secondary liability on that person, and thus, he will be held liable for indirect infringement of patent invention. To prove that there is infringement by inducement two things are necessary to establish:-

• Accused knowledge of the patent invention 
• His action in promoting infringement of that invention 

Contributory infringement 

Contributory infringement is another type of indirect infringement and a form of secondary liability arising out of direct infringement. It is explicitly mentioned under section 35 USC 271 C. In the contributory infringement, the person will be held liable for an infringement even though he himself did not perform such activity of infringement. The accused in this type of infringement has supplied such components, material, or apparatus that is specifically designed or made to use in a patent invention. The accused make such a contribution knowingly that it is going to infringe the patent invention. To constitute a contributory infringement there must be three elements that should be present: 

• A direct act of infringement by another party,
• A specific component with no other use, 
• knowledge, and intent of the act. 

In this type, a person is responsible for actively facilitating patent infringement by supplying key components of infringement activity. 

Vicarious infringement 

Vicarious infringement is the third category of indirect patent infringement or secondary liability arising out of direct infringement. Vicarious liability holds parties responsible for patent infringement of actions that are under their control or direction. The person will be held accountable for the patent infringement, if he directly controls the actions of the person actually infringing it. The person should be getting benefit from the activity or he must have some interest in doing that activity. To constitute vicarious infringement there must be three elements:- 

• The ability to control or direct;
• direct infringement by another person; and 
• benefits from infringing activities. 

What is the doctrine of equivalents?

The doctrine of equivalents is a legal principle used to determine the extent of patent protection for the patent owner beyond the literal language of the claimed patent. This principle is applied to matters where each and every element of a patent invention is not exactly identical to infringing product or process. The main aim of this principle is to give protection to the patent owners from infringers wherein they steal the invention smartly. They make small changes to avoid infringement, but that invention gives a similar result to that of the claimed invention. This is another form of direct infringement. Unlike literal infringement, in this type of infringement, the accused invention does not match word by word description of the claimed patent invention, but it matches the end result. With the minor changes in it, the functionality remains the same for both the accused invention and claimed invention. 

The first and foremost question that is been checked while determining any case of the doctrine of equivalence is whether the accused product or process of the invention contains the element that is similar to the design of the claimed patent invention. The case has been explained in detail in the later part of this article. 

This doctrine was laid down by the United States Supreme Court through a landmark judicial ruling in the case of Graver Tank & Manufacturing Co. v. Linde Air Products Co. (1950). The Court in the case recognized the doctrine for the first time. After the case came into existence, the court made it clear that the patent owners will get more protection, in the case where after doing minor changes the infringer’s patent invention is performing the same function and giving the same result. It established the relationship of the doctrine of equivalents with patent infringement

Section 2186 of the Manual of Patent Examination Procedure (MPEP) provides the relationship of the doctrine of equivalents with patent infringement matters. It provides the primary question that arises while dealing with any patent infringement matter under the doctrine of equivalents “Whether the accused product or process contains elements that are identical or equivalent to each element as claimed in the patent invention?”  

Meaning of the word “equivalent” 

The term “equivalent” in the doctrine of equivalents refers to the product or process that is not identical to the claimed patent invention but is similar in such a way that it performs the same function, in the same way and achieves the same result. The term equivalent in this doctrine is used to define something that is similar or can be comparable to something else but it’s not exactly the same. 

For example, let’s see two toy cars that look different, but they function similarly and their results are also similar, these two toy cars will be considered equivalent. As per US patent laws, a valid patent holder can challenge a patent invention that is equivalent to it. To be considered equivalent, as per the doctrine of equivalent, the accused product or process of the patent invention must be practically and functionally interchangeable.  This means that while there must be some differences, these differences are not enough to materially affect the function and result of the patent invention. 

The patent law of the United States defines the word equivalent as anything that is comparable in these below-mentioned things but which is not identical to it:

1. Content
2. Substance
3. Material
4. Denomination 
5. Number 
6. Quality, etc. 

Examples of the doctrine of equivalents

Let’s understand the doctrine of equivalents with some examples:-

Zipper v. Velcro 

Suppose there is a company named Samsa Textile Ltd. that has started manufacturing a different set of clothes that uses zippers in those clothes to keep their clothes close and secure them for a while. They obtained the patent for their unique creation with the motive to secure clothes. Then there is another company named Auza Foster Inc. that started selling clothes with not traditional zippers in it, but with “velcro” in it. Now you cannot say that Auza Foster has literally infringed the patent because the material they used is different. But still, there is a patent infringement. Why? Because they use the same function which is securing clothes here in the same way which is fastening fabric together. And it achieves the same result which is securing clothes and keeping them closed. 

Pencil v. Pen 

Let’s take another example of two companies. One is BCJ Suppliers Inc. and the other is MPJ Stationary Co. BCJ. The first company holds a patent for manufacturing a unique lead advancement mechanism pencil that advances its lead with a twist. The other company MPJ started manufacturing a pen with the same mechanism that extended the writing tip with a twist. Now BCJ can easily sue MPJ for infringement of a patent under the doctrine of equivalents as the patented invention is performing the same function that is to advance the writing tip by twisting. Through this, they both are substantially obtaining the same result which is an extension of the writing utensil. 

Light Bulb v. LED Bulb 

Take another example of ABC Light House Co. which has obtained a patent for a traditional light bulb with a filament design in it. Now another company with the name Genz Light Solution has started manufacturing LED bulbs. They are prepared with different lighting technology as compared to the ABC Light House. Now technically there is no literal infringement as the technology has changed, but still, this can be considered as infringement under the doctrine of equivalents. Here, both of them are performing the same function which is providing light here, in the same way, which is converting electricity into light obtaining the same result which is lightning a space. 

Stairs v. Ladder 

Suppose a  company named Neshti Ladder Inc., has patented its foldable ladder with a specific locking mechanism. There is another company with the name “Pelto Home Improvement Co.” that started making stairs with a slightly different locking mechanism but has the same functionality. Now, Neshti Ladder can sue the company for infringement as their stairs uses the same function which is securing stairs, in the same way by providing a locking mechanism to obtain the same result which is for the purpose of providing access to higher areas.

Evolution of doctrine of equivalents 

The early foundation of patent 

In the early stage of the United States patent law, there was no concept of “patent claims” at all. To determine the case of infringement, the US Supreme Court simply compared the accused’s infringenment product with the original patent description. It came into focus when the Patent Act, 1870 was categorically highlighting the significance of patent claims. 

Central Claiming 

At that time, since there was no concept of a patent claim another approach was running which was known as “central claiming”. In center claiming, the claim was capturing the central part of the invention or core invention. Sometimes this claim also included language that made reference to the patent specification. 

Peripheral claiming 

After that, the Court gradually shifted to another concept, namely, “peripheral claiming”. The Court, adopted this claim after the case of Graham v. John Deere Co. (1966). In peripheral claiming the inventor and patent office work together to draft the language of claim that specifies the patent boundaries. This has been done through several negotiations, office actions, and with amendments to it between the patent office and the inventor. The patent office mainly takes care of two things:

• The claim should not include any prior art 
• The patent holder is not claiming something which they are not actually allowed to claim as per law. 

Peripheral claiming makes it easy to give notice to the public. However, the language of this claim was far more critical than the prevalent claim. The whole burden of proof, in this case, lies upon the patent attorney who is drafting the claim. Therefore, it is crucial for them to draft the claim in clear and accurate language that does not overreach any other patent invention. Under this system, the doctrine of equivalent helps to protect the drafter to avoid making any mistakes in the patent claim which can substantially restrict the scope of patent invention.

Beginning of the modern foundation of doctrine 

The doctrine has been established by the US Supreme Court in the case of Graver Tank & Manufacturing Co. v. Linde Air Products Inc.(1950). The primary case wherein the “triple identity test” or “Function-way-result test” has been given. So, there has been an evolution of the claim system in the US. The court in the Graver Tank case also establishes three elements which are function, way, and result. Along with this, in the case, the Court established the foundation of patent infringement matters which gives protection in cases beyond the literal language of the patent claim. 

After almost 50 years the Court finds the need to revisit the matter of the doctrine of equivalents in the case of Warner Jenkinson Co. v. David Hilton Chemical Co. (1997). In the peripheral claiming system the claim was emphasized as a whole. After the case, the primary objective was to determine each element of the claim. The Court changed the way the doctrine of equivalent works. Now, it is not considering the whole infringement device rather it is focusing on each individual part of the claim. To prove infringement under this doctrine the patent owner needs to prove that the accused product or process of patent invention matches each element or part of the claim. This is how the doctrine of equivalents is applicable now. 

It is also important to understand that the triple identity test can also be used to establish the similarity between the claimed parts. However, it is not the only way. It is at the court’s discretion to determine the measure of equivalence and how the measure is to be determined in a particular case. 

Applicability of the doctrine of equivalents 

The applicability of the doctrine of equivalents is extended beyond the literal language of the claim of patent invention. It gives protection for the cases beyond literal infringement which protects an inventor’s rights and encourages innovation in the market. This doctrine holds key principles and functions that are applicable to this doctrine. The Supreme Court has given the Function-way-result test which is also known as the “triple identity” test. This test is to determine whether the patent infringement has been done under the doctrine of equivalent. Let’s check this in more detail.  

Function-Way-Result Test (FWR Test)  

Function-way-result Test (FWR Test) is a fundamental principle that is applicable to the doctrine of equivalent. This test is also known as the “Triple Identity Test”. This test is a three-step test, in which three things are evaluated while considering the term “equivalence”. This test includes checking how the accused product or invention is different from the claimed patent invention in terms of its functioning, the way to achieve that function and its final result. If all the elements of the Function-Way-Result test met certain criteria then the accused invention is said “equivalence” under the doctrine of equivalent. 

Function 

The first thing that the FWR Test checks is the function of the element in both the claimed invention and the accused product or process. Here function refers to what the element does in the product or process and what purpose it serves in the overall invention. 

For example, if the invention is a scissor which is a cutting substance, the element would be the specific component that provides the cutting action. If the accused patent invention performs the same function as that of the claimed invention, then the first component in the FWR test is completed and there may be an infringement. 

The way 

The second test in the FWR Test is the “way” test in which the element’s way of doing that particular function is examined. Both the accused product or process of invention and claimed patent invention has been examined in this process. This test looks at the aspect of the method and process used by the element in achieving that function. It includes different sets of mechanisms, processes, and structures to achieve a specific goal in both inventions. To complete this test both the claimed invention and the accused invention have to function in the same way. 

Results 

The third and last test in the FWR test is the “result” test wherein the Court evaluates the results produced by the element of both inventions, claimed invention, and accused invention. Results simply mean the overall effect or outcome of the element after performing a specific function in a specific way. It is the end goal for which all the hard work has been done. If this end result is the same in both the claimed invention and accused invention then this test is passed and there may be chances of patent infringement of the invention. 

Advantages of the doctrine of equivalents 

The doctrine of equivalents is a useful legal principle that protects the rights of patent owners or inventors. It has several advantages from maintaining a balance between the inventor’s right to encouraging innovation. Other than this, there can be various advantages of this principle. Let’s understand each one of them in detail. 

Promote innovation 

The primary advantage of this doctrine is that it promotes innovation. As this doctrine gives protection beyond the literal language, it allows inventors to focus on their innovative concept rather than focusing on a specific description of the claim. Along with this, the doctrine gives protection to existing inventions by preventing others from making substantial changes to avoid infringement. This step could encourage innovations as the inventor knows that their invention is safe. 

Fair competition in the marketplace

This principle helps competitors to bring out their own unique innovation rather than replicating someone else’s invention with some minor changes in it. It encourages genuine competitors in the market which has their own product or process of invention. Due to this, the competition in the marketplace will be healthy and free from any unfair trade. If the competition in the marketplace is fair it prevents someone from getting unfair benefits without putting in the same level of effort and creativity. 

Protection against the non-literal language of a claim

Earlier there was no patent protection granted in cases that extended beyond the literal language of the claim. Since this doctrine came into place, it is now easy to get the protection for cases wherein the inventor has minutely made the changes but actually copied the invention. It was necessary to get protection for inventions that are functionally similar but not literally similar. It is a smart move played by the accused which should not be encouraged at all.

Encourage technological process

Nowadays, there has been a rapid shift in the technology domain. In this digital era it is important that we get this type of doctrine in place to protect innovation. It does not allow the accused to take advantage of technology and get credit for something that he has not done. It prevents them from taking advantage of technological loopholes to steal the invention and get benefits from it. 

Case-specific legal analysis

This doctrine gives multiple tests, principles, and rules that are applicable on a case to case basis. These tests, principles, and rules are thoroughly examined as per the specific circumstances of the case as well as the technological nuance involved in it. This gives more specific and appropriate results rather than relying solely on the rigid interpretation of the doctrine. This prevents the rigid applicability of the doctrine and ensures a fair determination of each patent infringement matter.  

Making prima facie case of equivalence (MPEP 2183)

Making a prima facie case of equivalence under Section 2183 of the Manual of Patent Examination Procedure refers to the process by which the patent owner has to prove that the accused product or process is equivalent to his patent invention. To prove this, the inventor or the patent owner has to present evidence or argument in his favor. It is an essential step in evaluating patent infringement litigation matters. The patent owner needs to prove that the infringement is not a literal infringement but is based on the substantial similarity between the two inventions. 

As per this Section, any examiner who finds a prior art element that:

• Performs the same function that is specified in the claim; 
• Is not excluded by any explicit definition as provided in the specification for an equivalent; and
• Is the equivalent of means plus function limitation in the claim

Then, the examiner needs to explain why the prior art element is considered equivalent while examining the process during the office action. This simply means that the examiner needs to show how the prior art element performs the same function as specified in the claim even if it does not have the exact same structure. The examiner needs to provide a clear rational explanation of how the prior art element is relevant to the current patent application as also referred to in the Re Bond Case (1990).   

Below is a detailed explanation of the essential elements required for making a case of equivalence: 

Performs the same function as specified in the claim 

To fulfill this requirement, the prior art element (which is any existing product or technology) needs to perform the same function or accomplish the same purpose as what is described in the patent claim. In other words, when the prior art or claimed invention is operated it should be given a similar effect or result in both of them. 

Is not excluded by explicit definition in the patent specification 

The patent specification contains a detailed description of the patent invention along with its different versions and variations. It also includes specific definitions along with their limitations. To satisfy this condition, the patent specification must not exclude prior art elements from its description. If a description of a patent specification has explicitly mentioned that they are not covering some particular element, then those will not be considered equivalents for infringement. 

Is an equivalent of means plus function limitation in the claim

This condition is applicable only on means plus function patent claims. A “means plus function claim” is a form of a patent claim in which the claim of an element is defined by its function rather than its specific structure or material. To be considered an equivalent under the doctrine of equivalent, the element of the prior art and means plus function should perform substantially in the same way even if it has a different structure of design. 

Factors supporting the conclusion that prior art is equivalent to a patent claim are: 

• Function-Way-Result test

The first factor is the function, way, and result test, in which the inventor has to provide a detailed comparison of how the prior art element performs the same function, using the same way. It also achieves the same result as that of the corresponding element disclosed in the patent specification. As held in the case of Kemco Sales Inc. v. Control Papers Co. (2000), the United States Court of Appeal, Federal Circuit held that the accused device and claimed device invention are not substantially the same. Here, the difference is based on the fact that one company provides a device for sticking internal surfaces which is used to seal the inner surface of the envelope pocket. Whereas, the other company was involved in making devices used as a sticking substance to flap attached to the outer surface of the pocket. Though, both the patent inventions are close enough, they perform the same function but the way of doing it is different in both devices. The results and outcomes of both inventions are also different. 

• Obviousness to a person of ordinary skill 

The other factor that determines whether a particular prior art element is equivalent to the other is its obviousness to the person of ordinary skill in the art. To fulfill this condition the person who has the ordinary skill in the relevant field should recognize that the element of the prior art can be used interchangeably with the corresponding element described in the patent specification. In other words, we can say that someone who has knowledge in the relevant field can see the prior art element as a substitute for the claimed element. The United States Court of Appeal, Federal Circuit has briefly described this factor in the case of Caterpillar Inc. v. Deere & Co. (2000), and Data Line Corp. v. Micro Technologies Inc. (1987). 

• Insubstantial differences 

The third factor is the insubstantial difference factor wherein it is required to show that the prior art element and corresponding element disclosed in the patent specification have only minor changes. These slight differences are not enough to change the overall function and operation of the invention. The United States Court of Appeal, Federal Circuit has addressed this factor in detail in the matter of IMS Technology Inc. v. Hass Automation Inc. (2000), and Valmont Industries, Inc. v. Reinke MFG Co. (1993). The emphasis of both cases is on establishing the difference between prior art elements and the element of a particular claimed invention should be minimal. 

Also, in the case of Caterpillar Inc. v. Deere & Co. (2000), the Federal Circuit also clarified that while dealing with the matter related to the means plus function claim, the overall structure that performs the claimed function is important. Individual components of the structure are not the key focus for equivalence. Additionally, while determining matters related to equivalence, any potential benefit of a structure that is not directly related to the claimed function should not be taken into consideration. The main consideration is whether the prior art element or element of the claimed invention is essentially performing and functioning in the same way and it is not affected by minute differences between the components. 

If the examiner finds that the prior art element is meeting with any one factor for the equivalence mentioned above it will be concluded that the element is equivalent to the claimed patent invention. The examiner should consider that the claimed limitation is met by the prior art element. Additionally, the examiner should also establish why it is obvious for someone with ordinary skills to use the structure, material, and acts described by the applicant instead of those in the prior art. 

Burden of proof 

The burden of proof then shifts to the applicant to show that the element of prior art invention is not equivalent to the structure, material, or acts disclosed in the application as also highlighted in Re Brown Case (1972). Further analysis of the equivalent should not be done by the examiner until the examiner presented his argument on how the element of the prior art is not different from his own invention. The reason should be given by the applicant with proper justifications, as also specified in Re Mulder Case (1983). 

Examiner to consider obviousness in the case of non-equivalence 

Even if the applicant has shown that the prior art element is not at all equivalent to the material, structure, or act as described in the application, the examiner still needs to check whether the claimed means-plus-function would have been obvious for the person skilled in the art of that subject matter. They should do a detailed analysis on this as also prescribed under Section 35 USC 103. Though non-equivalence prevents the prior art element from anticipating means plus function limitation in the claim, it does not stop it from making the claim obvious. If the exact scope of equivalence can be drawn uncertain, Section 35 USC 102 and 35 USC 103  rejection can be applicable if other claim limitations as anticipated by the prior art. Although, to reject a claim it is best to rely on prior art reference but there is also an alternative to it. It can also be rejected even when prior art shows elements that are different from each other, specific structure, material, or acts from what is described in the specification and yet performs the same functions specified in the claim. 

Limitations of the doctrine of equivalents 

This doctrine is protecting the interest of the patent owners but there are also some limitations imposed on the applicability of the doctrine. This limitation has been given to protect this doctrine from being misused and also to promote fair competition in the marketplace. Through these tests and principles, the court has placed limitations on the doctrine.  Let’s understand each rule and principle in detail and how it affects the application of this doctrine. 

Insubstantial difference test 

The insubstantial difference test is the legal principle used while evaluating the matter of patent infringement with the doctrine of equivalents. It refers to the minor or slight difference that the accused made in his product or a process of the patent invention to avoid infringement claims of the actual patent owner. Their differences are so small that it has no effect on the overall performance and the result of the invention. It prevents infringers from making minor changes to avoid liability arising out of infringement. 

This test is generally preferred for both mechanical and chemical patent infringement matters. However, in the case of Mylan Institutional LLC v. Aurobindo Pharma Ltd. (2017) United States Court of Appeal for Federal Circuit (CAFC) clarifies that the “Insubstantial Difference Test” should be preferred in case of chemical matters. This consideration of finding the substantial difference between the inventions can lead to innovation and fair competition in the marketplace. 

Prosecution history estoppel 

This is another legal principle of patent law related to the doctrine of equivalent. prosecution history estoppel limits the scope of patent holders’ rights based on the statement made during the patent application process which can also be considered as prosecution history. It prevents patent holders from later asserting any claim or making amendments during the prosecution of the patent application, especially to secure the grant of a patent. 

Section 2103 of the Manual of Patent Examining Procedure (MPEP) provides that during the procedure of the patent application, the inventor or the applicant has to interact with the patent examiner. This interaction can be for various purposes such as filing an application, explaining the scope of the invention, and justifying the objections raised by the examiner in order to avoid any rejection. This estoppel ensures that inventors don’t claim more rights than what they have originally asked for. Once the patent has been granted they can’t claim new things. They have to stick to the choice of whatever they have made in the first place. 

Prosecution history estoppel occurs in two circumstances 

Claim amendment-based estoppel  

Whenever any inventor or applicant makes any patent invention claim they have to prove that the invention is different from the prior art. Due to this, they need to make amendments to the claim. This claim can narrow the scope of a patent claim as it is now too specific. It excludes the subject matter that could be covered otherwise if it hasn’t been amended. 

Arguments-based estoppel 

During the patent application examination process, the inventor or applicant has presented many arguments in front of the patent officer and to USPTO to justify the claim. The arguments can be presented for various purposes. For instance, the arguments can be presented to justify the claim as novel or non-obvious, how it’s different from the prior art, the replies to the objection, and many others. Now, whether these arguments are oral or written this defines the scope of the claim invention and restricts the interpretation of the same. 

Disclosure dedication rule 

Whenever any patent invention application is filed, the inventor or the applicant has to describe the invention in detail including the different versions and variations of it. This description goes live in front of the general public and then it becomes “patent specification”. Now, there are certain versions and variations of the patent invention that the inventor talks about in public. However, these versions and variations are not included in the patent description when filed with the USPTO. These versions and variations will be considered as “dedicated to the public”. This simply means that the inventor knowingly chooses not to protect this specific version and variation of the invention. The “disclosure dedication rule” says that the inventor later cannot come back claiming those variations and versions under the doctrine of equivalent. Though the doctrine protects equivalent inventions, it prohibits inventors from claiming those specific aspects of the invention that they choose not to be patented. 

How the disclosure dedication rule works

Public disclosure 

This includes the disclosure of a description related to the patent invention as a part of the patent record which is publicly accessible. The description has a detailed amount of information about the patent invention including its variation, embodiments, alternative configurations, and various other elements. 

Unclaimed element 

The inventor has chosen what he wants to be patented in the description he disclosed. Everything apart from that or any other variety will not come under his right as patent specification. He has the absolute right to whatever elements he claimed but apart from that he has no right to the elements he avoids or chooses not to get protected under his name. 

The doctrine of equivalent 

Even though the doctrine of equivalent grants protection for the patent owners whose invention has been infringed beyond the literal words claimed in the patent description. This rule restricts the patent owner to claim the element that has not earlier been protected under the patent specification.

Vitation rule  

Vitation rule or doctrine of vitiation is another defense to the doctrine of equivalent this defense can be taken in cases when two elements of the patent claim are different or completely opposite to each other. The vitiation rule prevents the doctrine of equivalent from being used to make a claim term meaningless. It makes sure that the equivalency is not forced between the elements that are contradictory to each other. The vitiation rule comes into the picture only when it is clearly examined that no jury can find the two elements equivalent to each other due to their extreme difference. 

When the vitiation rule applies there’s no need for a judge to pass the matter to the jury. They can simply take the decision as there is no equivalence that is evident. In cases when the elements look different but they function in the same way, the vitiation rule will not be considered nor will it apply in those matters. It will be applicable only in cases of extreme difference where there is no possibility of equivalency. 

If for any reason the judge is not able to decide, in that particular case, the matter has been passed to the jury to decide and make further comments. This rule is most common these days. This is because in this case, the court passes the burden of proof on the patent holder. He needs to establish that the accused product or process is similar to his under the doctrine of equivalents. 

All-element rule 

This is another limitation placed on the applicability of the doctrine of equivalents. As per this rule, it is important that each element in the product or process of both patent inventions should be equivalent individually. This rule gives importance to each element present in the tests or principles applicable to the doctrine. For example, let’s consider a hypothetical invention of a mechanical device. The patent invention consists of three components A, B, and C. In the patent claim, all three elements A, B, and C should be present. Now, as per this rule, if the accused patent invention produces a similar device with components A, B, and C then the all-element rule is satisfied and there will be an infringement. If the accused invention device has components A, B, and X then the all-element rule is not satisfied.   

Factors determining All-Element rule

Individual element analysis 

Each element of the patent invention is carefully observed. The rule says that if any individual’s patent claims found elements similar to the accused product or process infringement will happen. To establish infringement it is important that all the elements specified in the patent claim explicitly and under the doctrine of equivalents have to be present in the accused patent invention. 

Substantial similarity  

This rule accepts that the doctrine of equivalent allows for minor changes in the accused product as long as the difference between them is insubstantial. Though, the difference between the patent claim and the accused product or process should be minor. It should not change the overall function, operation, and result of the patent invention. 

Landmark Cases on the Doctrine of Equivalents in US Patent Law

Graver Tank & Manufacturing Co. v. Linde Air Products Inc (1950) 

A  brief overview of the case 

In this landmark case of 1950, the US Supreme Court established the doctrine of equivalents under the US patent law. This was the first case when the doctrine was given by the Court. After this case, the people can claim their patent invention even if there was a substantial difference between the claimed invention and the accused invention. 

Facts of the case

In this case, Graver Tank Manufacturing Co. holds a patent for a method of gas adsorption using active carbon. Adsorption of gas is a process wherein a solid is produced with van der Waals molecular forces. To simplify this, the process includes passing mixtures of gases through activated carbons that adsorb gases and spread them effectively. This process was also included in the specification of the patent application while submitting it to the patent office. Now there’s another company with the name ‘Linde Air Products Inc.’ that is also involved in manufacturing and selling a product that has a gas adsorption formula in it. However, they used a slightly different method of doing it. They used a different chemical called molecular sieves rather than using activated carbon in the procedure. However, the chemical processes were different in both cases. 

Issues involved in the case 

The primary issue involved in this case was whether the use of molecular sieves could be considered a different material or process from patent activated carbon method, and can there be a patent infringement under the doctrine of equivalents. 

Rule of law applied 

The Court introduced and established the doctrine of equivalents in the case. This further helps in preventing others from making insubstantial changes in the invention to avoid patent infringement. This doctrine further broadens the scope of patent claims which is extended beyond the literal language of the patent claim. 

Judgment or final conclusion 

After careful examination of the case, the federal Court observed that in both methods the gas has been separated from the mixture which results in the same functional outcode. Even though the material and process of both the companies are different, the Court found that the patent invention of Linde Air Product Inc. is equivalent to Graver Tank Manufacturing Co. under the doctrine of equivalent. The Court further established this doctrine of equivalents. After this prominent case, the patent owners have the right to claim their right on their patent invention, even if it is not literally infringed. The Court held that the claimed patent invention has infringed another patent invention when there is an insubstantial difference between both inventions’ products or processes. 

Warner-Jenkinson Co. v. Hilton Davis Chemical Co.(1997)

A brief overview of the case 

The leading case of Warner Jenkinson Co. v. Hilton Davis Chemical Co. (1997) focuses on the interpretation and applicability of the doctrine of equivalents. The question, in this case, revolves around the perspective of whether the accused has infringed patent invention under the doctrine of equivalents or not. 

Facts of the case

The facts of the case were like this: There was a company with the name Warner Jenkinson. The company has obtained a patent related to a method of detecting specific chemical compounds in a solution. For this effective method, a particular type of reagent is used to achieve chemical detection. Now another company with the name Hilton Davis Chemicals also has a product that can detect similar chemical compounds in a solution. However, Warner Jenkinson’s found out that this company was not using the exact same reagent from their patent invention but they were using a slightly similar one. Though the function, way, and outcome of Hilton’s product were the same, which is detecting chemical compounds in a specific solution. Warner Jenkinson’s company filed a case against the accused company alleging infringement of patent invention under the doctrine of equivalents.   

Issues involved in the case 

1. The main issue in the case was whether Helton’s David Chemical Co. has a product that actually infringes or is equivalent to the patent invention claimed by Warner Jenkinson’s company. Though the company uses a different reagent to achieve the same function. 
2. The second issue was whether the difference between the reagents of the two companies are substantial enough to justify the claim for equivalence under the doctrine of equivalents.

Rule of Law applied

The Federal Circuit introduced and applied the “triple identity” test to determine the equivalence under this case. The test is followed by thorough research on three things that are:- function, way, and result test. It checks whether the product is substantially using the same function, in the same way to achieve the same result. 

Judgment and final conclusion 

The United State Court of Appeal, Federal Circuit after observations held that the Hilton Davis Chemical Co. does not infringe the claimed patent invention under the doctrine of equivalents. It further clarifies that while the product has a similar function and outcome to claimed patent invention, it has a different way of doing that function. As here the company has different reagents which is substantially not enough to prove the equivalence. This judgment further clarifies the importance of each element in the “triple identity” test. Each element will be evaluated separately to determine the equivalence under the doctrine of equivalent. 

Cortland Line Co., Inc v. Orvis Co. Inc. (2000)

A  brief overview of the case 

This case provides a detailed interpretation of the applicability and scope of the doctrine of equivalents under United States patent law. This case further provided clarity on how the doctrine works and when to apply it. 

Facts of the case

The facts of this case revolve around two companies, wherein Cortland Line Co. was involved in making fishing lines with certain unique characters. It is a long threaded material that is used with fishing rods to catch fish. The company has already obtained a patent for fishing line technology. Now there is another company with the name Orvis Co. which started manufacturing and selling similar types of fishing line products. Cortland Line Co. filed a case against another company for infringement of its patent invention under the doctrine of equivalents. 

Issues involved in the case 

1. The main issue involved in this case is whether the product of Orvis Co. infringes the patent invention of Cortland Line Co. even if there were substantial differences between both inventions.
2. Is the difference between both the inventions substantial enough to avoid the infringement under the doctrine of equivalent? 

Rule of law applied 

The Court applied the pre-existing doctrine of equivalent to resolve the matter. Along with the doctrine the Supreme Court also checked its limitations and saw whether the accused product performed the same function, in the same way, and achieved the same result as that of the patent claim. 

Judgment or final conclusion 

The Supreme Court after careful observation gave a judgment that Orvis Co. Inc has infringed the patent invention of Cortland Line Co. as the difference is not substantial enough. The Orvis Co’s product is performing the same function, in the same way, and achieves the same result. The difference is very minor and it is not enough to prove the case of non-infringement. The Court also evaluated this case with an “insubstantial difference test”. It found out that the difference is insubstantial to the person having ordinary skill in the art. The Court further clarifies that the minor variation, structure, or function will fall under the doctrine of equivalents if it fundamentally changes the essence of the invention.   

Johnson and Johnson Association Inc. v. R.E. Service Co. Inc. (2002)

A  brief overview of the case 

The famous case of the Johnson and Jonson Association v. R.E. Service Co. Inc. (2002) revolves around the disputed matter that involved the usage of aluminum and steel substances while making circuit boards. The case came into existence when the company filed a lawsuit against R.E. Service Co. for violation of their patent right because they were using similar substrates without permission. The Federal Circuit in this matter has discussed the concepts related to patent infringement, the doctrine of equivalents, and the scope of the doctrine of equivalents. 

Facts of the case

The company Johnson and Johnson was involved in the manufacturing and production of printed circuit boards. The boards are constructed using thin layers of conductive copper foil that are pressed together and given heat with a non-constructive resin bonding for the layers. Mainly, human workers play the role of manually handling the copper sheet during the layering process. The invention is to prevent the damage to the final sheet by attaching the aluminum sheet to the copper foils. This allows the humans to handle the board safely during the assembling process. Another company R.E. Service Co. Inc. is manufacturing a similar kind of substrate by using the same process but with steel in it. The company further argued that Johnson’s Co. uses aluminum substrate and not steel substrate therefore there is no infringement in the case and both things are not equivalent to each other. 

Issues involved in the case

The main issue in this matter revolves around the applicability of the doctrine of equivalent and also does the doctrine also covers the subject matter which is disclosed in the patent specification but not explicitly claimed by the patent owner. 

Rule of law applied 

The rule of law applied here is related to the doctrine of equivalent that includes details on the language of the patent specification. The disclosure dedication rule was carefully examined in the matter and says that there is no access to subject matter which is disclosed but not explicitly claimed. 

Judgment and final conclusion 

The US Court in this case held that the patent owner cannot get the benefit to use the subject matter which is disclosed in the patent specification but not explicitly claimed by them. The requirement for claims in the patent application is a crucial step of the patent process as it clearly defines the invention and provides the basis for accessing infringement. When a patent owner discloses their patent invention they have chosen what they need to protect it. The patent owner will not get the claim over a certain subject matter that he does not claim. Once the claim is written in the application, it is disclosed to the general public and is accessible to them. Therefore, it will not get patent protection. In the present case, the specification of the patent invention mentioned other metals like steel or other nickel alloys, but the claim was specifically confined to aluminum only. The court emphasized that the patent owner cannot narrow the claim and later use the doctrine of equivalents to cover the matter which he has disclosed but not claimed. 

The court has also given an alternative remedy in case someone fails to make a claim on a part of the invention which they forget to claim earlier. It says that the patent owner can file a  reissue application within two years of the original patent grant. In the application, the patent holder can broaden the scope of original claims by including the unclaimed subject matter to it. The patent holder can also file a separate application to claim the disclosed subject matter which is also done by the company Johnson and Johnson in this case. 

Festo Corp. v. Shoketzu Kinzoku Kogyo Kabushiki Co. (2002) 

A  brief overview of the case 

This case mainly revolved around the rule of prosecution history estoppel under the doctrine of equivalent. The case specifically elaborated on the scope of protection granted under the doctrine of equivalents. Also, an emphasis is given related to the effects of amendments that are made during the patent application process in the claim of patent infringement. 

Facts of the case

The company Festo Corporation holds a patent invention for its innovative pneumatic piston of cylindrical design that is used in the automation industry. During the application of the patent claim, the company made some amendments to the patent application. They made some changes to get the approval of the patent application from the patent office. However, these amendments narrowed down the scope of patent invention claims by adding specific limitations to them. Now there was another company with the name ‘Shoketzu Kinzoku Kogyo Kabushiki’. They produce a similar pneumatic piston with a cylindrical design that was claimed in the patent invention of Festo Corporation. The company Festo corporation has argued that there is an infringement of their design patent under the doctrine of equivalents claiming that there is an insubstantial and minor difference. 

Issues involved in the case 

The main issue involved in this case is the interpretation of the rule of prosecution history estoppel. The question before the Court was whether the amendment made by Festo Corp. during the patent application process limits the scope of protection to only amended claims or if the doctrine of equivalents will still be applicable in this case scenario. 

Rule of law applied 

In this case, the rule of prosecution history estoppel is applied. Any person can amend their patent claim and make modifications to it in order to get approval and avoid rejection of the patent application. This rule states that when any person who has already made any patent claim gets approval from the USPTO. They cannot say that the changes also cover something that they were not initially in the claim. These were part of the invention that they gave up on. This rule narrows the scope of patent protection under the doctrine of equivalents.

Judgment and final conclusion 

The US Supreme Court gave a complex judgment that covers various aspects related to patent infringement. The court has restricted the scope of the doctrine of equivalents with prosecution history estoppel. The Court also emphasized factors on which arguments are to be done and factors that are important to consider. These factors include unforeseeable development, slight changes made for the reason of unrelated patentability, and unforeseeable equivalents at the time of management. Clarification has been given in this case for the relationship between the prosecution history estoppel and doctrine of equivalent. The case provides guidelines to determine when and how the doctrine will be applied in a particular case even if the amendments have been made during the patent application process. This clarity further helps to prevent misuse of the doctrine and further extends the patent coverage beyond the literal meaning. 

Eli Lilly and Co. v. Hospira Inc. (2019)

A brief overview of the case

This case is the most recent case in which the United States Court of Appeals, Federal Circuit has discussed the doctrine of equivalents along with its applicability in modern times. The case is a detailed analysis of the application of this doctrine in the matter related to the pharmaceutical industry. 

Facts of the case 

The company Eli Lily is involved in making a certain type of chemotherapy drug that is used to treat certain types of non-small cell lung cancer and mesothelioma (a type of cancer that covers the outer surface of a body organ). The drug is made using disodium salt and a combination of other active ingredients named Alimta. This drug contains an element called pemetrexed disodium. Now there’s another company named Hospira Inc. that has taken approval from the United States Food and Drug Administration (FDA) to market a generic version of this drug Alimta. However, this company’s drug contains pemetrexed di tromethamine which is a salt of pemetrexed. Eli Lily has approached the court to file the matter against the other company for infringement of patent under the doctrine of equivalents. 

Issues involved in the case 

The primary issue involved in this case is whether the Eli Lily Co. during the process of patent obtaining a patent owner gave up their right to dissolved salt, which is a different type of salt used by the accused company Hospira Inc. The case solved the question of whether the usage of both salts will be considered equivalent to each other under the doctrine of equivalence. 

Rule of law applied 

Both the prosecution history estoppel and the disclosure dedication rule were applied by the court for determining the case under the doctrine of equivalent. The court has carefully examined the statements and amendments made during the patent application process by Eli Lilly Co. which comes under prosecution history estoppel. Also, the court checked the disclosure and description of patent specification language to determine all things the company wants to claim its right to, and what the company is giving up which comes under the Disclosure dedication rule. 

Judgment and final conclusion 

The United States Federal Circuit ruled in favor of Eli Lilly Co. and held that the generic version of Alimta manufactured by Hospira Inc. is equivalent under the doctrine of equivalent. The composition of salt pemetrexed di tromethamine is considered similar to salt pemetrexed disodium. The court first performed function, way, and result tests to determine the different forms achieve the same function which gives chemotherapeutic effect in substantially the same way as through administration and it achieves the same result. The case was analyzed through the prosecution history estoppel and disclosure dedication rule which gives the inference that Eli Lily has primarily intention to protect the kind of salt and include it in their patent invention. Thus, even the generic form of salt will be protected by way of the doctrine of equivalents. 

Conclusion

Statistics reveals that in recent times cases related to patent infringement under the doctrine of equivalents have rapidly increased. Especially, in industries related to technology, electronics, and pharmaceuticals. This is the most important reason for awareness about this topic. It is important to understand the topic in-depth, and one must be aware of how important it can be in order to deal with patent infringement matters that are beyond the literal scope of a patent claim. Along with that, “triple identity test” is also an important aspect of this doctrine that needs to be checked while observing matters related to this. It consists of function, way, and result test that is essential to be evaluated. These elements can be examined individually also at the same time together also. If all three element criteria have been satisfied the infringement has been confirmed.  

Though this doctrine promotes various innovations and inventions, it also has some limitations that protect this doctrine from being misused. These limitations such as insubstantial difference, prosecution history estoppel have their criteria to be examined that have already been clarified by the Court through various judgments. The concept of the doctrine of equivalent has also evolved with time. The Court has been given detailed clarification on the topic through various landmark judgments like Warner Jenkinson Co. v. Hilton David Chemical Co. The doctrine creates a gap between innovation and protection yet it is a little complex to understand. As in the era where every company has so much to offer to their customer it is important that every element and every word of their product or service should be protected. 

It is also important to understand that the grant of a patent is a quid-pro-quo (give and take). It has a beginning and end date as well. A patent owner is free to enjoy his rights once granted by the patent office. Once the disclosure has been made to the world, they can enjoy the monopoly over their invention. However, the right is just for a limited period of time. The term of the patent expires and after expiration, it falls under the public domain. When any patent invention falls under the public domain it is free for the public to use, and nobody can claim his rights on it. Therefore, if the doctrine of equivalent was not there, it could not only be unfair on the part of the patent holder but it could also stop the patent inventor to disclose their invention to the world. Due to this, no inventor can now find an alternative or substitute to this. 

Frequently Asked Questions (FAQs)

What is the doctrine of equivalents in US patent law? 

The doctrine of equivalents under US patent law is the legal principle that provides protection to the patent owner in cases where the infringement is beyond the literal word of the patent invention. As per this principle, the person will be liable for infringement of a patent invention if they make minor changes to their invention in order to avoid infringement. To establish that there is an infringement the person needs to prove that his invention is performing in substantially the same way, using the same function, and giving the same result. 

What is an example of the doctrine of equivalent?

The best example of the doctrine of equivalent is a company named X involved in manufacturing and selling a special toaster that has a pop-up spring mechanism in it. Now there is another company with name Y that started manufacturing and selling similar toasters but with a slight difference in the mechanism which is a counterweight system here. This company is said to be infringing the patent invention of company X as it is using the same function, in the same manner, and achieving the same result. 

How does the doctrine of equivalent work?

The doctrine of equivalents in US patent law works on tests and factors involved while determining whether any invention is equivalent to a patent claim or not. The test includes a “triple identity test” or “function-way-result test” in which the infringement will be accepted if the accused patent invention is performing the same function, in the same way, and substantially obtain the same result. If these conditions of each element are met, infringement will be confirmed under the doctrine of equivalents. 

What is the difference between literal infringement and infringement under the doctrine of equivalent? 

Under the US patent law, there are two kinds of infringement, one is literal infringement and the other one is infringement under the doctrine of equivalent. Literal infringement is when the accused invention is exactly the same as the description written in the patent claim. To establish this infringement the language between the patent claim and the accused patent or process should match. In the doctrine of equivalent the protection is given for a case that is beyond literal infringement. The protection is given for cases beyond the literal language of patent claims.  

What are the limitations of the doctrine of equivalent?

The doctrine of equivalents has some limitations that affect the applicability and scope of this doctrine. This is to protect this doctrine from being misused. Such limitations are prosecution history estoppel, disclosure dedication rule, all element rule, and Insubstantial difference test. These limitations have their own way of interpretation and application of the cases and patent infringement matters. It is examined by keeping into check certain factors such as specific circumstances, language of claim, and purpose of patent protection. 

What are some famous cases related to the doctrine of equivalent?

The court has given various judgments to elaborate on the applicability and interpretation of the doctrine. The doctrine was established in the case of Graver Tank & Manufacturing Co. v. Linde Air Products Co. (1950). The other important cases are Warner Jenkinson Co. v. Hilton Davis Chemical Co. (1997), Festo Corp v. Shoketzu Kinzoku Kogyo Kabushiki Co. (2002), Cortland Line Co., Inc v. Orvis Co. Inc. (2000), Elli Lilly Co. v. Hospira Inc. (2019) and Johnson & Johnson Association v. R.E. Service Co. (2002). 

What is prosecution history estoppel in the doctrine of equivalent? 

Prosecution history estoppel is a limitation placed on the application of the doctrine of equivalent. This rule simply means whenever any patent owner has made specific changes to their patent claim in order to get the approval and avoid rejection they have made their choice. They cannot later claim for elements that they have not included at the time of amendment of the patent claim. It will denote that they deliberately choose not to protect that part or that form of the patent invention. 

Is the doctrine of equivalent applicable to all types of patents? 

Yes, the doctrine of equivalents is applicable to all types of patent invention. However, the application of this doctrine can vary depending on various factors such as the type and nature of the invention. There are three types of patents on which this doctrine is applicable. They are utility patents, plant patents, and design patents. The specific application of this doctrine is also based on the claimed element that the person is choosing. 

References 

• https://www.law.cornell.edu/wex/doctrine_of_equivalent 
• https://www.galliumlaw.com/evolution-of-the-doctrine-of-equivalents-through-case-law
• https://www.oblon.com/publications/narrow-claiming-and-the-scope-of-equivalents
• https://www.uspto.gov/web/offices/pac/mpep/s2186.html 
• https://www.uspto.gov/web/offices/pac/mpep/s2186.html#:~:text=The%20doctrine%20of%20equivalents%20arises,under%20the%20doctrine%20of%20equivalents. 
• https://docs.manupatra.in/newsline/articles/Upload/5FEA310F-B604-483E-993B-46E346604C57.pdf 
• https://heinonline.org/HOL/Page?public=true&handle=hein.journals/jpatos70&div=80&start_page=511&collection=sccjournals&set_as_cursor=3&men_tab=srchresults 

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