Doctrine of Equivalence Case - Adam Mahood

Background/Summary of the Case

• Johnston v. IVAC Corp. - 1989
  • Court of Appeals for the Federal Circuit
  • Citation - 885 F.2d 1574
  • Pretty clear case for non-equivalence
  • As I mentioned in class, this case dealt with plastic covers for thermometer probes (the long metal rod probes from your doctor's office).
  • Essentially, the Johnston patent (AMEC Corp.) was for a thermometer that had a jagged edge towards the base of the probe such that when the plastic cover was slid on, the jagged edge would embed itself in the plastic, thus providing the method for retaining the probe cover.
  • The alleged infringing device used a circular ring also at the base of the probe for attachment, instead of the hook.
  • AMEC sued IVAC for infringing claiming that the circular friction lock was equivalent to the hook and thus the claim read on the IVAC device.
    • AMEC engineer examined the IVAC device with a microscope to find indentations to be able to testify that the IVAC device also dug into the plastic.
    • Since he used a 20x microscope and the plastic deformations were superficial and were in no way enough to hold on the probe cover the judge declared non-equivalence.
  • This case makes it clear that just because something performs the same function, it must also do it in a very similar manner as the patented device in order to potentially be held equivalent.