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  • Uday Sirohi

Functional Claiming - What is "Structure" and Why is it Important?

What is a Functional Claim?

A functional claim limitation describes an invention in terms of what it does, rather than describing its structural components. Functional language may also be employed to limit the claims without using the means-plus-function format. Unlike means-plus-function claim language that applies only to purely functional limitations, functional claiming often involves the recitation of some structure followed by its function. The U.S. patent statute (35 U.S.C. Section 112(6), pre-AIA; Section 112(f) post-AIA) allows a claim drafter to recite an element of a claim “as a means or step for performing a specified function without the recital of structure.” There is one important requirement, however, when using functional claiming: a structure for performing the claimed function must be described in the patent’s specification. The functional limitation is not limited to only those structures described in the specification. The patent statute says that the patent must disclose at least one corresponding structure, but the claim will be read to cover not only that structure but also any “equivalents thereof”.

What is Structure and Why is it Important?

Structure of the invention explains the structural components of what is claimed in the patent. The federal courts have a history of viewing functionally claimed inventions with varying degrees of skepticism. The broad scope of functional limitations is why the patent statute requires disclosing a corresponding structure in the patent’s specification. The “benefit of the bargain” of using broad, functional claiming is that the patent drafter must tell the reader what specific structures perform the recited function.

A patent that uses a functional claim limitation without describing in the specification a corresponding structure for performing the function can be found invalid as indefinite. Importantly, the entire claim can be found invalid even if only a single functional limitation is unsupported.

Functional Claiming in the Aftermath of Williamson

On 16 June 2015, the US Court of Appeals for the Federal Circuit issued an en banc opinion in Williamson v Citrix Online LLC, 792 F.3d 1339 with a seemingly subtle change in means-plus-function claim analysis, i.e, in the post-Williamson cases non-means claims can receive means-plus-function treatment.

In the Williamson decision, the whole Federal Circuit overturned this “strong” presumption that applied when the words “means for” were not used. Under the new standard, courts will still apply a presumption, but the presumption is no longer “strong”. Instead, courts will use a “balanced scale” to evaluate whether the claim itself recites what an ordinary skilled person would interpret as “sufficiently definite structure” for performing the claimed function. If a challenger shows it does not recite such definite structure, the claim is subject to the means-plus-function rules. Applying this new analysis to the “distributed learning control module for [performing a function]” limitation at issue, the Federal Circuit found that the “module” did not recite sufficient structure and should be construed as a means-plus-function limitation.

The Federal Circuit’s restructure of the means-plus-function analysis in Williamson creates uncertainty for functional claiming. In Williamson’s aftermath, innovators and practitioners should evaluate three questions to determine Williamson’s impact on their patent strategy. First, what does Williamson mean for issued software or hardware patents claimed functionally? Second, how should software and hardware patents be claimed to avoid unintentional means-plus-function construction? Third, how does this decision impact strategies that software patent owners and challengers have been developing surrounding the new “abstractness” doctrine following last year’s Alice v. CLS Bank decision from the U.S. Supreme Court?

Suggestion for Drafting Means-Plus-Function Claims

So how do we deal with some of the potential land mines resulting from Williamson? Following are a few suggestions to consider when drafting and filing new patent applications if means-plus-function claim interpretation is not desired:

  • Avoid placeholder words – placeholder words (eg, device, module, mechanism, element, unit, component and member, among others) continue to be red flags for means-plus-function interpretation.

  • Use words with known structural connotations – for example, consider claiming a ‘spring’ rather than a ‘biasing element’, then consider broadly defining ‘spring’ in the specification to encompass other types of biasing element.

  • Disclose function-performing structure – do this for any functional language in the claims, whether it is associated with a physical claim element or not. An accused infringer will be looking for functions recited in the claims that do not have a corresponding structure in the specification when mounting a means-plus-function attack. Even if the challenged claims receive means-plus-function treatment, function-performing structure can preserve their validity. Where the function is computer-implemented, disclosure of even a simple algorithm capable of performing the function can save the claim.

  • Use dependent claims to recite structure – even if a claim with functional language receives means-plus-function treatment and is held to be indefinite, dependent claims with function-performing structure can remain valid. Courts have also looked to dependent claims as evidence of whether a claim term in the independent claim represents a class of structures to avoid means-plus-function treatment.

  • Be wary of fanciful claim terms – while patent practitioners have a long-enjoyed tradition of acting as their own lexicographers and specially defining claim terms in the specification, there is some danger in this activity when the claim term is coupled with functional language. The test is whether the claim term would connote sufficient structure to one of ordinary skill in the art. This means extrinsic evidence can trump intrinsic evidence in functional claim interpretation, which is counter to the now-familiar claim construction guidance set forth in Phillips v AWH Corp (415 F.3d 1303 (Fed Cir 2005)).



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