Clarity of Language for Doctrine of Equivalents

The district court notably characterized the testimony as «word salad,» emphasizing its failure to provide the requisite detailed, element-by-element analysis of the patent claims.

While acknowledging that expert witnesses need not mirror exact claim language, the appeals court emphasized that testimony must methodically address each claim element and articulate a clear rationale for how the accused product meets the «function-way-result» test for equivalence.

The court explicitly rejected arguments for relaxed evidentiary standards in cases involving simpler technologies. Instead, it maintained that rigorous standards for doctrine of equivalents evidence must apply uniformly across all cases, regardless of technological complexity.

Though one judge partially dissented, suggesting the majority’s approach might impose overly strict requirements for expert testimony, the court defended its position as consistent with established precedent. This precedent has consistently mandated specific, claim-focused testimony to support equivalency arguments.

This decision underscores that success in doctrine of equivalents cases depends on meticulously crafted language in both expert testimony and legal arguments. The challenge of maintaining such precision becomes even more significant when patent applications require translation for multiple jurisdictions.