The one area where patent-challengers see continued success is when means-plus-function claims lack appropriate structural support in the underlying patent document. 35 U.S.C. 112(f) allows a patentee to claim a “means” for accomplishing a specified function without reciting the actual structure of the mechanism or material used to accomplish the function.
However, as a rule of construction, the statute indicates that the “means” will be construed to “cover the corresponding structure, material, or acts described in the specification and equivalents thereof.” The impact is that, although the claim appears to broadly cover a “function” it will be construed to be much more limited. When an applicant follows this claiming approach, but fails to specify any corresponding structure within the specification then the claim is deemed invalid as indefinite.
In Eon Corp v. AT&T (Fed. Cir. 2015), the Federal Circuit has affirmed that Eon’s asserted patent claims are invalid for failing to specify the structure associated with a purely functional claim element.