Judge Sleet recently reversed a jury’s finding of infringement under the doctrine of equivalents, holding that prosecution history estoppel precluded a finding of infringement. Energy Transp. Grp., Inc. v. Sonic Innovations, Inc., C.A. No. 05-422-GMS (D. Del. June 7, 2011). The patent at issue pertained to “a host controller for programmable ditigal hearing aid system.” Id. at 23. The court agreed with the accused infringer that “[t]he prosecution history shows that the patentee amended the patent application and introduced new claims that are similar to broader claims previously rejected[,]” and stated that the “newly added limitation that narrows the claim” created “a rebuttable presumption of surrender[.]” Id. at 24. Although the patentee claimed that “the limitation in question was not added to overcome prior art[,]” Judge Sleet found that this “argument is not persuasive and is irrelevant as a matter of law.” Id. at 24-25. The patentee attempted to use “this prior art argument in an attempt to rebut the presumption of estoppel based on a ‘tangential relation[,]'” but the court stated that the tangential relation exception to prosecution history estoppel is irrelevant “‘unless it is ‘clear’ that the rationale underlying the amendment is only peripheral to the alleged equivalent[.]'” Id. at 25 (citations omitted). Thus, Judge Sleet held that the jury’s verdict that the asserted claims “are infringed under the doctrine of equivalents cannot stand.” Id. at 26.