Accused Dome Equivalent to Recited "Plate" After Amendment Which Was Tangential to Contested Element

In a rare decision involving Doctrine of Equivalence for an amended claim term, the Federal Circuit in Primos, Inc. v. Hunter's Specialties, Inc., et al. (June 14, 2006; 05-1001,-1376) agreed with the district court that prosecution history estoppel did not preclude the application of the doctrine of equivalents to the term "plate" in claim 2 of U.S. Patent No. 5,415,578 for a "Game Call Apparatus" shown below:

Claim 2 of the ’578 patent reads as follows:

A game call apparatus to be completely inserted inside a person’s mouth for calling game, comprising:

a frame;

a membrane (22) of material stretched over the frame;

a flexible and moldable peripheral edge extending outwardly from the frame; and

a plate (15) having a length, the plate extending generally upward from the frame and over a portion of the membrane, the plate being differentially spaced above the portion of the membrane at various locations along the length of the plate.

According to Circuit Judge Lourie, the term "plate" in was amended in two ways: (1) by requiring that it have a "length" and (2) by adding the limitation that the plate be "differentially spaced" above the membrane.

The district court correctly recognized that the addition of the term "length" did not narrow the scope of the claim because every physical object has a length. The district court also determined that adding the limitation that the plate be "differentially spaced" above the membrane did narrow the scope of the claim, and the court assumed that the reason for the amendment was a substantial one relating to patentability. We agree with the district court, however, that the territory surrendered by the "differentially spaced" amendment comprises plates that are not differentially spaced above the membrane. That conclusion is consistent with the prosecution history. The patentee added the "differentially spaced" limitation to distinguish the diaphragm mouth call from a prior art device that consisted of a shelf-like structure positioned on top of the membrane without any spacing. The accused device, however, includes a dome that is spaced above the membrane. Because the accused device’s dome includes the spacing, the amendment was merely tangential to the contested element in the accused device, and thus prosecution history estoppel does not apply to prevent the application of the doctrine of equivalents.

Hunter’s Specialties also argues that the court should not have allowed the application of the doctrine of equivalents because, by doing so, the claim limitation "plate" in claim 2 of the ’578 patent was vitiated. According to Hunter’s Specialties, the court’s construction of the term "plate" requires a specific structure "of relatively uniform thickness and flatness which may also have some moderate curvature to it. Hunter’s Specialties asserts that allowing a "dome" to be
considered an equivalent to a "plate" would eliminate that limitation from the
claim. Primos responds that the "all limitations rule" is not applicable to the
circumstances in this case. According to Primos, the term "plate" does not
convey a definitive, geometric shape or structure, and thus that claim
limitation was not vitiated. Primos asserts that the district court properly
allowed the jury to consider whether a "dome" was equivalent to a "plate" and
that in doing so, no claim limitation was eliminated.

We agree with Primos that the application of the doctrine of equivalents was not improper in this case. Under the doctrine of equivalents, "a product or process that does not literally infringe upon [sic] the express terms of a patent claim may nonetheless be found to infringe if there is ‘equivalence’ between the elements of the accused product or process and the claimed elements [sic] of the patented invention." Warner-Jenkinson Co., Inc. v. Hilton Davis Chem. Co., 520 U.S. 17, 21 (1997) (citation omitted). The "all limitations rule" restricts the doctrine of equivalents by preventing its application when doing so would vitiate a claim limitation. Warner-Jenkinson, 520 U.S. at 29 (stating that the doctrine of equivalents cannot be applied broadly so as to "effectively eliminate that [claim] element in its entirety"); Lockheed Martin Corp., 324 F.3d at 1321 ("[I]f a court determines that a finding of infringement under the doctrine of equivalents ‘would entirely vitiate a particular claim element,’ then the court should rule that there is no infringement under the doctrine of equivalents." (citation omitted)).

On appeal, Hunter's Specialties argues that we should reverse the jury’s finding of equivalence because the substitution of the accused dome for the claimed "plate" would vitiate the "plate" limitation and thereby violate the all limitations rule. As the district court recognized, Hunter’s Specialties is essentially contending that there can be no equivalent to the claimed "plate." Our precedent has recognized that "[t]here is no set formula for determining whether a finding of equivalence would vitiate a claim limitation, and thereby violate the all limitations rule. Rather, courts must consider the totality of the circumstances of each case and determine whether the alleged equivalent can be fairly characterized as an insubstantial change from the claimed subject matter without rendering the pertinent limitation meaningless." Freedman Seating Co. v. Am. Seating Co., 420 F.3d 1350, 1359 (Fed. Cir. 2005) (citations omitted). Thus, because Primos’s theory of equivalence (i.e., that a dome is equivalent to the claimed "plate") does not "effectively eliminate . . . [the ‘plate’ limitation] in its entirety," it does not violate the all limitations rule. Noting that Hunter’s Specialties has not challenged whether the jury’s finding is supported by substantial evidence, we affirm the jury’s finding that the accused dome is equivalent to the claimed "plate."