Transportation Group, Inc. v. William Demant Holding A/S, No. 2011-1487 (Oct. 12, 2012). 1614025.html

Energy Transportation Group (ETG) owns two patents whose claims cover a method and device for suppressing feedback noise in hearing aids. At trial, the accused hearing aids, which incorporate laterdeveloped technology for automatically and continuously adjusting the feedback suppression signal, were held to infringe the claims of the ETG patents, literally or under the doctrine of equivalents. The Fed Circuit affirmed.

Hearing aids contain a microphone that picks up sound and converts it to an electrical signal, a speaker that converts the electric signal back into sound waves, and sound-processing circuitry between the microphone and speaker for adjusting the received sound to compensate for hearing impairment. Some of the amplified sound from the hearing aid speaker may travel back to the microphone via an “acoustic feedback path,” producing a distressing whistling sound at the speaker.

The two ETG patents, which share a common specification and a priority date of June 1986, describe a method of reducing feedback in hearing aids by incorporating into the circuitry a programmable filter whose frequency-dependent phase and amplitude values are adjusted—for example, by a host computer—to cancel the feedback signal. The accused hearing aids, which were marketed beginning in 2001, incorporate a chip capable of continuously updating the amplitude and phase values of the cancellation signal. Although the ETG patents didn’t describe an algorithm or chip for continuously updating the feedback-suppression signal, the court noted that nothing in the patent indicates that the step of “determining the effect of amplitude and phase on the cancellation feedback signal” must be performed externally or at a fixed time. The Federal Circuit affirmed the district court’s conclusion that the accused devices infringe the claims under the doctrine of equivalents because they perform the same function (“determine the effect on amplitude and phase of the signal transmission”), in the same way (by “calculating the coefficients”), with the same result of cancelling acoustic feedback.

The case is analogous to Hughes Aircraft Co. v. United States, 140 F.3d 1470 (Fed. Cir. 1998), where the patent at issue involved controlling the position of a satellite using calculations that were, at the time the patent was filed, made at a ground station and relayed to the satellite. Advances in computer technology occurring after the patent issued allowed the same calculations to be made on board, rather than at a ground station. Nonetheless, the method of controlling the position of the satellite was deemed to be an insubstantial change in the way the satellite performed the claimed function.

Notably, the court upheld a damages award in which the plaintiff’s damages expert relied in part on the discredited 25% rule. The court held that the use of the 25% rule did not “irretrievably damage” the method the expert used to calculate a royalty, noting he relied “more prominently on other factors,” and that the jury’s award was not grossly excessive.