Issue 05/2 | January 10, 2005
Expert Testimony May Be Required To Prove Infringement Of A Patent Claiming Complex Technology

Where an accused infringer offers expert testimony negating infringement of a patent involving complex technology, the patentee cannot satisfy its burden of proof by relying solely on argumentation and testimony from non-experts.

Patentees seeking to carry their burden of proving infringement of claims in a complex technology should carefully consider the need for expert testimony to establish that the accused device meets the limitations of the claimed invention.

On December 6, 2004, the federal circuit in Centricut v. ESAB Group., No. 03-1547-1614, (Fed. Cir. December 6, 2004) reversed a district court holding of infringement, finding that ESAB failed to meet its burden of proving by a preponderance of the evidence infringement of its '425 patent relating to the electrode of a plasma-arc cutting torch.

ESAB's '425 patent claims an electrode including an emissive insert, a holder, and a sleeve positioned between the emissive insert and the holder. Specifically, ESAB's '425 patent claimed the improved performance of the electrode attributed to relative work functions of the insert and holder to the sleeve. The claimed sleeve was made of silver and had a work function greater than that of the holder. Centricut's electrode included an insert made of hafnium, a holder of copper, and a ring washer (asserted to be a sleeve by ESAB) of silver. At trial, the district court found infringement by Centricut, and awarded damages of $2.18 million dollars to ESAB. Centricut appealed, arguing that ESAB did not satisfy its burden of proving infringement because it did not show by a preponderance of the evidence that ESAB's device satisfied the work-function limitation of the claims.

On appeal, the federal circuit considered the testimony of Centricut's expert, Dr. denBoer, a physics professor qualified as an expert in work function who stated that tabulated values of work-function were not the most useful way to rank the work functions of specific materials because many other factors affected the actual work function of a specific surface. ESAB offered three theories of why Centricut's accused product met the work function requirement of the claims, none of which were supported by expert testimony, all of which were refuted by Centricut's denBoer.

The federal circuit held that ESAB's lack of expert testimony was fatal to its proof of infringement:

Thus, each of ESAB's three theories suffers from the same deficiency: none is supported by expert testimony. The first theory, adopted by the district court, rests on the district court's own interpretation of the evidence. The latter two theories rest on the testimony of witnesses who were admittedly not experts on work function.

The court declined to adopt a per se rule that expert testimony would be required to prove infringement when the art is complex, but stated that when an infringer offers expert testimony negating infringement, the patentee could not satisfy its burden of proof by relying on non-experts in the field.

To view a copy of the case visit

To discuss these topics further, please feel free to contact the author Michael R. Dzwonczyk, (mdzwonczyk@sughrue.com), at Sughrue Mion, PLLC in Washington DC, USA.

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