Basic Patent Infringement Analysis

Anyone who makes, uses, sells, or offers for sale in the United States, or imports into the United States, an infringing product or process may be held liable for patent infringement. However, liability for patent infringement is not limited to only those who commit acts of direct infringement. The statute also provides that whoever actively induces infringement of a patent may be held liable as an infringer. In addition, contributory infringers may be held liable for selling a component of a patented device constituting a material part of the invention and not a staple article or commodity of commerce suitable for substantial non-infringing use.
Patents are enforceable only by courts of the country that issued them.

In the U.S., patent infringers may be held liable for up to three times their profits or a reasonable royalty in connection with any willfully infringing activity. Courts may also award attorney fees and issue orders ("injunctions") stopping the allegedly infringing activities while a lawsuit proceeds and/or thereafter. Design patents (with a "D" preceding the number) are enforceable for fourteen years from the date they are issued, while utility patents are enforceable for up to twenty years from their earliest filing date as long as periodic "maintenance fees" are paid to the government.

It is the claims of a patent that define the protected subject matter. For design patents, the drawings themselves serve as the claims and the test for infringement is simply whether, in the eye of an ordinary observer, giving such attention as a purchaser usually gives, the accused and patented designs are substantially the same. The resemblance must be such as to deceive the observer, inducing them to purchase one supposing it to be the other. This test is often supplemented with the so-called "point of novelty" test that requires the infringing design to include the particular features that distinguished the design over the prior art.

For utility patents, the claims are sequentially numbered sentences at the end of the patent. So-called "dependent claims" in utility patents refer back to an independent claim in the same application and are construed to include all the limitations of the earlier, intervening claims. For utility patents, the claims generally begin with a preamble ending in a transitional phrase such as "comprising", "consisting essentially of" or "consisting of" which is then followed by a list of features that define the scope of protection provided by the patent. The transitional term "comprising", is synonymous with "including," "containing," or "characterized by," and does not exclude additional, unrecited elements or method steps. The transitional phrase "consisting of," on the other hand, excludes any element, step, or ingredient not specified in the claim. The transitional phrase "consisting essentially of" falls somewhere between "comprising" and "consisting of," and limits the scope of a claim to the specified materials or steps and those that do not materially affect the basic and novel characteristics of the invention.

Literal infringement requires that the accused product or process include each and every element of the claim following the transitional phrase. Consequently, if one or more of the structural or functional limitations of the claim is not satisfied, then the requirements for literal infringement are not met. In general, terminology in a utility patent claim is given its ordinary meaning unless the inventor has expressly or implicitly used the term in a manner that is inconsistent with its ordinary meaning in either the specification or the file history. Extrinsic evidence, such as technical treatises, dictionaries, and expert testimony, may be used to construe the claims only if intrinsic evidence, such as the specification, file history, and prior art, do not resolve any ambiguity in the meaning of a term.

However, even if a utility or design patent claim does not literally "read on" an accused product or process, it may still be infringed under the Doctrine of Equivalents if the differences between the accused product or process and the claims are insubstantial. In this regard, courts have considered evidence of known interchangeability, copying, and designing around the element recited in the claim for determining whether the corresponding feature in the accused device is substantially different from the claimed structure.

In the special case where an element in a utility patent claim is expressed as a means or a step for performing a specified function, the element will be construed to cover the corresponding structure, materials, or acts described in the specification, and equivalents thereof as long as the alleged "means/step-plus-function" claim element must not recite a definite structure, material, or act which supports the function recited in the claim. For literal infringement of means-plus-function claims, the accused device must perform the identical function specified in the claim element by virtue of a corresponding structure that is disclosed in the patent specification for performing that function, or an equivalent of that corresponding structure. A structure disclosed in the specification is deemed to be a "corresponding structure" only if the specification clearly links or associates that structure to the function recited in the claim.

The standard for determining whether such literal equivalence exists in a means-plus-function limitation is whether the differences between the pertinent structures disclosed in the specification and the structure of the accused device are insubstantial. An insubstantial change is one that adds nothing of significance to the structure, materials or acts disclosed in the specification. For mechanical inventions, courts have also considered whether the elements of the accused device performs substantially the same function in substantially the same way in order to achieve substantially the same result as the means plus function limitation in the claim.