A recent Federal Circuit panel decision in Williamson v. Citrix Online, LLC altered the evidentiary standard for determining whether a patent claim employs means-plus-function language. Specifically, the court expressly overruled its own precedent, eliminating the strong presumption that the absence of the term "means" in a patent claim would render the means-plus-function standards inapplicable to the claim at issue.

The Federal Circuit's decision requires additional diligence in patent drafting to avoid unintended impacts that may occur based on the means-plus-function standards being applied to the claim. On the other hand, the new standard provides a stronger basis for challenging patent claims that employ functional claiming without including specific means-plus-function language based on indefiniteness.

Means-plus-function claiming is a statutorily authorized technique allowing an element in a claim for a combination to be expressed as a means or step for performing a specified function without the recital of structure, material or acts in support thereof. In exchange for allowing functional claiming, the statute limits the scope of a means-plus-function claimed element to only the structure, materials or acts described in the specification as corresponding to the claimed function and equivalents thereof. Thus, the use of means-plus-function language limits the claim scope and requires specific disclosure of structure in the specification to avoid being deemed indefinite.

Absence of "means": Then and Now Prior to Williamson, Federal Circuit precedent employed a strong presumption that the absence of the term "means" in a patent claim would render the means-plus-function standards inapplicable to the claim at issue. This presumption could only be overcome with an evidentiary showing that the claim limitation at issue was essentially devoid of anything that can be construed as structure. Thus, a claim that did not include the word "means" was unlikely to be viewed as a means-plus-function claim with the attendant consequences thereof.

In Williamson, however, the Federal Circuit indicated that the test to determine the applicability of the means-plus-function statute is whether the words of the claim are understood by persons of ordinary skill in the art to have a sufficiently definite meaning as the name for structure. The Federal Circuit determined the claim term "distributed learning control module" invoked the means-plus-function standard. Further, the court found the claim invalid as indefinite as the specification lacked sufficient disclosure of structure corresponding to the term. The court noted that the claim term was in the traditional format for means-plus-function limitations, as the distributed learning control module was followed by functional language. Further, the court viewed the term module as a direct substitute for the term means. The court noted that other similar generic terms, such as mechanism, element, and device, may be indicative of means-plus-function claiming, as they typically do not connote sufficiently definite structure.

In view of the Federal Circuit's decision, care must be taken to avoid invoking means-plus-function claiming where such an interpretation is not intended. Such an interpretation can lead to limited claim scope and potential invalidity if the structure is not sufficiently defined in the specification. To the extent possible, claims should avoid the means-plus-function format along with generic terms that do not disclose structure. Further, any elements in a claim that could be potentially interpreted as means-plus-function should be accompanied by sufficient structure in the specification. For example, the specification should describe how the element interacts with other components or provide specific algorithms that can inform the structural character of the limitation.