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Patentee Failed to Provide Expert Testimony to Support Infringement

December 06, 2004

Decision icon Decision

Last Month at the Federal Circuit - January 2005

Judges: Dyk (author), Michel, and Clevenger

In Centricut, LLC v. The ESAB Group, Inc., No. 03-1574 (Fed. Cir. Dec. 6, 2004), the Federal Circuit reversed a finding of infringement, wiping out a damages award of over $2M.

The ESAB Group, Inc. (“ESAB”) owns U.S. Patent No. 5,023,425 (“the ‘425 patent”), which discloses and claims a three-part electrode for plasma-arc cutting of steel. The claims recite an emissive insert, a holder, and a sleeve positioned between the emissive insert and the holder. The sleeve is different from prior art electrodes and is made of a material with a high “work function” relative to the emissive insert. The addition of the sleeve keeps the arc and the emissive insert even as the copper holder becomes oxidized and, thus, increases the electrode’s useful life.

The parties had agreed that the term “work function” referred to the potential step, measured in electrode volts, that permits thermionic emission from the surface of a metal at a given temperature. In other words, work function is the energy required to remove an electrode from inside a material to outside the material. The claims specifically recite an emissive insert composed of a metallic material having a relatively low work function and a sleeve having a work function that is greater than that of the material of the emissive insert.

At a bench trial, neither party introduced any evidence of tests conducted to directly measure the work function of the materials in the accused device. The Defendant introduced a physics professor, who testified that it was not possible to determine the relative work functions because work function is not an intrinsic property of a metal but rather is a property of specific surfaces under specific conditions. For its part, ESAB did not introduce any expert testimony but simply argued that work-function values recorded in a table showed that the metals used in the accused products had low work functions as required by the claims. ESAB also made alternative arguments about tests it had done concerning the useful life of the accused electrodes and other inferences that could be drawn, but did not introduce any expert testimony on these theories.

ESAB’s sole testimony concerning a correlation between the useful life and work function came from the testimony of its inventor. However, this testimony was contradicted by the Defendant’s expert, who testified that a longer useful life could be attributed to a number of different factors, including temperature, the geometry of the electrode, the thermal and electrical conductivity of the sleeve, or the sleeve’s resistance from oxidation, and, therefore, it was not reasonable to conclude that longer useful life was attributable only to work function. Moreover, the inventor admitted that he was not an expert on the issue of work function. He had not studied the subject in college and had not acquired an expert’s knowledge of work function during the course of his employment, nor had he been qualified as an expert under Fed. R. Evid. Rule 702. Thus, none of ESAB’s theories concerning work function that supported its claim of infringement were supported by expert knowledge of work functions. The only expert testimony as to work function suggested that testing was necessary to prove whether the claims were infringed, and ESAB simply failed to offer any such evidence.

The district court relied on the workfunction tables and concluded that although they might not establish to a certainty that the silver used in the accused product has a higher work function than the metals used in its inserts, these tables are sufficiently persuasive to support a finding of infringement by a preponderance of the evidence.

The Federal Circuit recognized that, in many patent cases, expert testimony is not necessary because the technology is easily understandable, but concluded that this was not such a case. Here, the technology was very complex. Although the Federal Circuit declined to state a per se rule that expert testimony is required to prove infringement when the art is complex, in complex cases where the accused infringer offers expert testimony negating infringement, the patentee cannot satisfy its burden of proof by relying on only testimony from those who are admittedly not expert in the field.