Patent Prosecution Disclaimers

Patent Prosecution Disclaimers



Background: Prosecution Disclaimers

When an applicant makes statements to the patent office while prosecuting a patent, these statements (referred to as part of the "prosecution history") can affect the scope of patent protection.

Under the doctrine of "prosecution history estoppel," an amendment of a claim limitation may restrict that limitation to its literal scope and prevent it from covering devices or methods using an equivalent to the limitation. Arguments made during prosecution of a patent can also be used to limit the ability of a patent claim to cover equivalents. Prosecution history estoppel is discussed in more detail in our May 30, 2002 and January 3, 2002 IP Law Alerts.

Under another doctrine referred to as "prosecution disclaimer," the prosecution history can be used to limit the literal scope of patent claims. Recently, in Omega Engineering, Inc. v. Raytek Corp., the Federal Circuit analyzed statements made by the applicant to determine whether those statements limited the structures and methods covered by the claim. As the court emphasized, a disclaimer must be clear and unambiguous to limit the claim scope.

The Omega Patents

The three patents owned by the plaintiff, Omega Engineering, related to infrared thermometers, or radiometers. These thermometers operate by remotely detecting the amount of infrared radiation emitted by an object, thereby measuring the object's temperature. A lens focuses the infrared radiation in the device, to define a field-of-view, or "energy zone," as with a telescope or camera. Omega's patents concerned a sighting device used to "strike the periphery of the energy zone for visibly outlining said energy zone."

In order to overcome a rejection by the patent examiner based on prior art that illuminated an entire surface, Omega argued that its invention used "at least one laser beam that is able to outline the energy zone on the surface to be measured, rather than illuminate the entire zone. The clear advantage offered by such a device is that it only directs energy at the edge of the energy zone to be measured to outline same and, as such, has virtually no effect on the temperature to be taken."

The Scope of the Disclaimer

Omega brought an infringement action against the defendants, whose products used laser beams that outlined the energy zone and directed some light into the interior of the energy zone. The District Court, relying on Omega's arguments, construed the claims to exclude devices in which any of the laser light struck inside the energy zone. Accordingly, the District Court granted summary judgment of noninfringement against Omega.

The Federal Circuit disagreed. It concluded that "Omega did not clearly and unmistakably disavow a device that directs light into the interior of the energy zone. Stated otherwise, the patentee did not deliberately and unambiguously define its invention as a device whose laser beams would remain outside of the energy zone," but rather as a device whose laser beams would have "virtually no effect on the temperature measurement to be taken."

Although the Federal Circuit found an unequivocal disclaimer, that disclaimer narrowed the ordinary meaning of the claim term only as is "congruent with the scope of the surrender." In determining that the disclaimer was limited to devices that had no appreciable effect on the temperature measurement, the court looked to the statements themselves and the prior art that was being distinguished. Due to conflicting testimony, a factual issue remained as to whether the defendants' devices infringed the claims as limited by the disclaimer


In Omega, the Federal Circuit emphasized that courts are to indulge in "a heavy presumption that claim terms carry their full and customary meaning ... unless the patentee unequivocally imparted a novel meaning to those terms or expressly relinquished claim scope during prosecution." To limit claim coverage, disclaimers must be "clear and unmistakable."

The Omega case provides a reminder that patent applicants must be careful in how they word arguments during prosecution. These arguments can limit both the literal scope of a claim and the range of equivalents under the doctrine of equivalents. Even where it is necessary to explain what the invention covers (or does not cover), applicants should limit the arguments as much as possible to avoid giving up any more coverage than is necessary.

Joshua Migliazzo
[email protected]

Donald Steinberg
[email protected]