This morning brings another Federal Circuit decision on the Festo case … this time, a panel opinion affirming the trial judge’s conclusion that the purported equivalent in the case (a nonmagnetizable sleeve) was foreseeable at the time of the narrowing claim amendment and thus cannot be recaptured as an infringement by means of the doctrine of equivalents.

Festo had argued on remand “that it was not foreseeable at the time of the amendments that the equivalents could perform the same function as the Festo device.”  Slip op. at 10.  Specifically, “[b]ased on the patent specification, Festo argued that a purpose of the sleeve was to shield against magnetic field leakage; while aluminum was well known [as a sleeve material], its utility to provide magnetic field shielding was unknown and that its use for that purpose was unforeseeable at the time of the amendment.”  Id.  Put another way, “Festo contends that the [alleged] equivalent must be foreseeable under the function/way/result test at the time of the amendment” before the patentee can be charged with having surrendered it with a narrowing amendment.  Slip op. at 15.
In a lengthy opinion, and over Judge Newman’s dissent, Judge Dyk (writing for himself and Chief Judge Michel) rejects Festo’s theory about how to analyze foreseeability for purposes of salvaging an infringement theory from fatal prosecution history estoppel.  The court states the foreseeability standard as follows:

“Rather, we find that an alternative is foreseeable if it is disclosed in the pertinent prior art in the field of the invention.  In other words, an alternative is foreseeable if it is known in the field of the invention as reflected in the claim scope before amendment.”  Slip op. at 16.

“[W]e conclude that, contrary to Festo’s argument, the foreseeability requirement does not require the knowledge that the equivalent would satisfy the function/way/result test or the insubstantial differences test.” Slip op. at 18.

“An equivalent is foreseeable if one skilled in the art would have known that the alternative existed in the field of art as defined by the original claim scope, even if the suitability of the alternative for the particular purposes defined by the amended claim scope were unknown.” Slip op. at 21.