What is Patent Infringement?

The statutory basis for direct patent infringement is in the federal statutes which provides that it is patent infringement for one to make, use, sell or offer to sell any patented invention without authorization (35 USC §271(a)).  One may also be liable for patent infringement by actively inducing or contributing to infringement of another (35 USC §§ 271(b)(c)).

To determine whether someone is infringing a patent, one must look to the patent claims.  The patent claims are the heart of the invention and describe the scope of the patent. 

There is patent infringement if the potentially infringing device or process falls within the language of any claim in the patent, typically described as falling within the “scope of the claim.”  However, before the comparison of the claim to the accused device or process, the scope of the claim must be determined. 

In claim interpretation, words are generally given their ordinary meaning as understood by a person having ordinary skill in the pertinent field.  The patentee is allowed to be his or her own lexicographer. In other words, he or she may use terms in a different manner so long as that meaning is clearly explained in the patent document.  In determining the meaning of a patent claim, one first looks to the intrinsic evidence, that is, the patent document, including the patent claims, the specification, the drawings, and the prosecution history. 

Most of the time the intrinsic evidence will be sufficient to interpret a patent claims and its limitations and resolve any ambiguity.  However, sometimes the court looks to extrinsic evidence, such as dictionary definitions, prior art (previously patented inventions), or expert opinion.

Claim interpretation and determining claim scope is a question of law for the court, not a question for the jury.

Literal Patent Infringement

Once the scope of the claim is determined, each patent claim is compared to the accused device or process.  Literal infringement occurs when every element in the patent claim (each limitation) is found in the accused device or process.

Infringement Under the Doctrine of Equivalents

If there is no literal infringement, inquiry under the Doctrine of Equivalents occurs.  The doctrine of equivalents is a judicially created doctrine which permits a finding of patent infringement if the accused device or process is so similar to the claimed invention that the differences are viewed to be insubstantial. 

There is inherent tension between literal infringement and infringement under the doctrine.  On the one hand, courts do not want to expand the patent rights beyond what was stated in the patent document, especially since the patent claim serves as public notice of the invention.  On the other hand, courts do not want to allow infringers to avoid infringement by making unimportant or insubstantial changes to a claimed invention. 

The inquiry into infringement under the doctrine of equivalents can be complicated and uncertain.  Generally, the inquiry is whether an element of the accused device performs substantially the same function in substantially the same way to obtain the same result as the claimed invention.  (Graver Tank & Mfg. Co. v. Linde Air Products Co., 339 U.S. 605, 85 USPQ 328 (1950)). 

Under the doctrine of equivalents, it is a challenge to determine what range of equivalents would be considered within the scope of the patent claims.  It is a constant balance between the public notice function of patent claims (to inform the public of the scope of the patented invention), and stopping infringers from avoiding patent infringement by making insubstantial changes to the claimed invention. If you believe your invention has been infringed upon, either literally or through the doctrine of equivalents, it might be helpful to employ an experienced intellectual property attorney to help sort out these issues.

About Our Firm

Protecting your intellectual property rights is a complex business. If you suspect that your product might have been infringed, it may be advisable to rely on the expertise of an experienced IP rights lawyer to protect your rights. The Intellectual Property team at the Law Offices of James Scott Farrin is headed by Attorney Tara J. Williams, a patent attorney with more than 20 years of legal experience. The firm also has a unique contingency based Intellectual Property Department for certain infringement matters. The department’s goal is to assist small-business owners, artists and inventors to protect their creative endeavors when they may not otherwise have the resources necessary to do so. Call 1-866-760-4047, for a free, confidential review of your potential claim – or simply complete the contact form on the side of this page.