Federal Circuit Addresses Whether an Equivalent is Forseeable

Festo Corporation v. Shoketsu Kinzoku Kogyo Kabuskhiki Co., Ltd., [05-1492] (July 5, 2007) [DYK, Michel, Newman] The Federal Circuit affirmed the district courts determination that the alleged equivalent was foreseeable at the time of the amendment.
SIGNIFICANCE: The Federal Circuit held that foreseeability (for prosecution history estoppel purposes) does not require the application to be aware that a particular equivalent would satisfy the insubstantial differences test or the function/way/result test.
BRIEF: At issue was whether whether a aluminum sleeve was a forseeable alternative to Festo Corporation's claimed magnetizable sleeve such that prosecution history estoppel applies. During prosecution, the applicant added the limitation "magnetizable sleeve" while the accused structure was an aluminum (non-magnetizable) sleeve. The amendment did not create a complete bar to the doctrine of equivalents, and the doctrine of equivalents would apply if (1) the equivalent was unforeseeable at the time of the application; (2) the rationale for the amendment bore no more than a tangential relationship to the equivalent; or (3) some other reason suggests that the patentee could not reasonably be expected to have described the insubstantial substitute in question. Festo argued that it was not foreseeable at the time that aluminum could perform the same function. It was agreed that the use of an aluminum sleeve for magnetic shielding was not know at the time.
The Federal Circuit said that unforeseeable meant unforeseeable at the time of the amendment. Later-developed technology or technology was not know in the pertinent prior art usually is not foreseeable. The Supreme Court tied foreseeability to whether the application would have been expected to know of, and thus properly claim, the proposed equivalent at the time of the amendment. Conversely, when the equivalent is know in the pertinent art at the time of the amendment, it is foreseeable. Festo argued that it was not known that an aluminum sleeve would perform the same function, in the same way, to achieve the same result under the function way result test. The Federal Circuit rejected the function/way/result or insubstantial differences tests for foreseeability, and said that an alternative is foreseeable if it is disclosed in the pertinent field of the invention. The Federal Circuit declined to determine in what other circumstances an equivalent might be foreseeable.
The Federal Circuit commented that Festo was trying to include as an equivalent that which is a separate invention -- which the Court said was beyond giving the patentee the scope of its invention. Furthermore, the Federal Circuit observed that in Wilson Sporting Goods, the Federal Circuit held that where an alleged equivalent is patentable, the finding of equivalence, while not foreclosed, is considerable more difficult to make out.