Literal infringement is the strongest cause of action available to a patentee, but the standard for establishing literal infringement is rather stringent: every limitation set forth in a claim must be found in an accused product, exactly. However, as the U.S. Supreme Court has unequivocally stated, "a product or process that does not literally infringe upon the express terms of a patent claim may nonetheless be found to infringe if there is equivalence between the elements of the accused product or process and the claimed elements of the patented invention." If the patentee can show that an accused infringer has replaced a claimed element with a substitute element that performs essentially the same function, in the same way, and produces the same result, courts may find infringement. This well-established principle is known as the Doctrine of Equivalents.
In a case decided a few weeks ago, the jury in the U.S. District Court of Western Texas was put to the task of determining whether AT&T's U-Verse infringed three patents covering a method of streaming audio and video content. The jury determined that AT&T did not literally infringe a single claim! Nevertheless, the jury found that AT&T infringed two of the three patents under the Doctrine of Equivalents and awarded a $27.5 million verdict for Two-Way Media, the plaintiff.
An important caveat to the Doctrine of Equivalents is that its scope is subject to two complex and often convoluted limitations: a foreseeability bar and prosecution history estoppel. If a patent application is not prosecuted with a scrupulous attention to detail and an eye on the ultimate value of the patent, the benefit of the Doctrine of Equivalents may be lost forever, allowing the competitors to safely navigate around the claims of a patent without facing any real danger of infringement. At Smith & Hopen, we see this time and time again when analyzing patents of our clients' competitors.