We do not state a per se rule that expert testimony is required to prove infringement when the art is complex. Suffice it to say that in a case involving complex technology, where the accused infringer offers expert testimony negating infringement, the patentee cannot satisfy its burden of proof by relying only on testimony from those who are admittedly not expert in the field. That is what happened here, and the patentee thus failed to satisfy its burden of proof. This case stands as an apt example of what may befall a patent law plaintiff who presents complex subject matter without inputs from experts qualified on the relevant points in issue when the accused infringer has negated infringement with its own expert.
Centricut's expert, physics professor Dr. Marten denBoer, testified that it was not possible to determine the relative work functions of the sleeve and the emissive insert of the accused device without direct testing because many factors affect the work function of a surface. In support of this testimony he submitted tables from various reference texts reporting the work functions of samples of various pure elements, but concluded that these tables established nothing about the relative work function of the sleeve and emissive insert of the accused device. This is because work function is not an intrinsic property of a metal, but is rather a property of specific surfaces under specific conditions. The tables were therefore not representative of the torch under actual operating conditions.
Esab argued "a little half-heartedly" that the district court's reliance on the tables was correct "even though the only expert testimony directly contradicted this conclusion." Based upon the inventor's testimony that the useful life testing was a surrogate for relative work function, Esab also argued that the accused electrode's significantly longer useful life must be because the sleeve had a higher work function than the emissive insert. Finally, Esab argued that the relative work functions of hafnium and silver in the accused device could be inferred from hafnium's use in emissive inserts and silver's nonuse in emissive inserts.
However, Centricut presented "extensive expert testimony by Dr. denBoer that longer useful life could be attributed to a number of different factors." The court also noted that Dr. denBoer "stated unequivocally that, while he did not know why the sleeve affects useful life, the useful life tests conducted by Esab told him "absolutely nothing about work function." Dr. denBoer, "also testified that although they are related, work function and emissivity are not the same."
With regard to the inventor's opposite testimony, the court concluded that
[T]he inventor, was not qualified as an expert witness on any matter under Rule 702 of the Federal Rules of Evidence. More to the point, he admitted that he was not an expert on the issue of work function. He admitted that he had not studied the subject at college, and had no graduate degree. He also did not claim to have acquired an expert's knowledge of work function during the course of his employment. In short, he offered no foundation for offering reliable testimony on work function.In fact, the court noted that none of the witnesses upon which Esab relied upon to establish infringement had an expert knowledge of work function.
Charles Landry identified himself as Centricut's director of engineering and technical support, but affirmatively disclaimed expert knowledge of work function. Daniel O'Hara was Centricut's plasma arc cutting torch expert, but he too admitted to having "a limited understanding of work function." Richard Couch, CEO of Centricut's parent company Hypertherm, testified that, although he was skilled in the art of plasma arc torches, he was familiar with work function only "in a very general sort of way." Patrick Byrne, the former president, CEO, and chairman of the board of Centricut, testified that someone explained work function to him during his first day at Centricut, but that he never discussed work function again in the three years he was there, nor did he have any sort of scientific training. In summary, all of the witnesses upon which Esab relies to support this argument lacked expert knowledge of work function.