Understanding Means-Plus-Function Claims in Patent Law

We previously wrote about product-by-process claims in patent law describing them as an atypical patent claim. See our article here: https://ipfdalaw.com/understanding-product-by-process-claims-in-patent-law/. Another atypical claim is a so-called “means plus function” claim. The M+F claim has a statutory root under 35 U.S.C. Sec. 112(f) (previously under 35 U.S.C. Sec. 112, sixth paragraph). The statute states that: 

(f) Element in Claim for a Combination.—

An element in a claim for a combination may be expressed as a means or step for performing a specified function without the recital of structure, material, or acts in support thereof, and such claim shall be construed to cover the corresponding structure, material, or acts described in the specification and equivalents thereof.

When are M+F Claims Used?

Historically prior to the 1952 Patent Act, patent applicants used functional claim language to claim the invention, not by what it is, but by what function it performed. There were concerns that a functional claim at the point of novelty would preempt every possible means (or structures) to perform that function. The Supreme Court in the 1946 Halliburton case also cast doubt on the approach to functional claim language. The concern for “machine” claims was that the specification required support for the structures in the claim and pure functional claims untethered from adequate support would render the claim unduly broad and invalid. 

For example, suppose the invention is two pieces of wood connected together. The specification discloses only a nail capable of connecting the pieces of wood. But the claim is to two pieces of wood and a “means for” connecting the pieces of wood. Does the “means” actually cover just the nail because that is what is disclosed in the specification or every possible way of connecting the wood pieces despite only disclosing a nail as an example? In the 1952 Patent Act, it reaffirmed that in principle certain types of functional language is permissible. 

Interpretation of a M+F Claim By Courts

Interpretation of M+F claims start with the statutory language. The M+F claim typically does not recite any structure but the statute indicates how the claim is to be construed. It says, “… claim shall be construed to cover the corresponding structure, material, or acts described in the specification and equivalents thereof.” So it would appear that from a statutory scheme, there are two parts to the latter phrase. First, there is the “construed to cover the corresponding structure, material, or acts described in the specification” and the “equivalents thereof.” Does this mean that the construction of the claim covers corresponding structure, material, or acts and then structural equivalents, material equivalents, and acts equivalents? Or does the “equivalent” mean equivalent structures, equivalent materials, or equivalent acts? And perhaps whether the word “equivalent” comes before or after may not matter. This can be shown here:

Means plus function claims seemed all good until the 1990’s. Then claim construction became a hot topic and M+F claims did not escape the Federal Circuit’s attention, and perhaps rendered them less attractive as claims. The Federal Circuit’s attention was directed to when is a M+F claim really a M+F claim, and when is it not. And when it is, what does it actually claim or cover? That is, how is the means and the function to be construed? In Greenberg v. Ethicon Endo-Surgery, Inc., 91 F.3d 1580 (Fed. Cir. 1996), the Court clarified that because of the historical use of “means for” in claims, the Court will presume that when “means for” is used, it is intended to invoke the M+F interpretation under §112(f) [then §112, sixth paragraph]. And if no “means for” language is used, the Court presumes that M+F claim interpretation is not intended. As such, “means” means M+F claiming; and no “means” means no M+F claiming. 

Then in York Products, Inc. v. Central Tractor Farm & Family Center, 99 F.3d 1568 (Fed. Cir. 1996), the Court clarified that even if the term “means” is used, it does not invoke M+F claim interpretation automatically if the claim recites sufficient structure (because M+F claims typically do not recite sufficient structure). In York, maybe in certain cases using “means” didn’t mean M+F claiming after all. 

Continuing with the claim construction theory for M+F claims, the Court then focused on how to determine what the “means” are for performing the claimed function. Post the Supreme Court’s Markman decision in 1996 [517 U.S. 370] and then the Court’s en banc decision in Cybor [138 F.3d 1448], the Court in Chiuminatta Concrete v. Cardinal Industries, 145 F.3d 1303 (Fed. Cir. 1998) stated that determining the “structures” that correspond to the claimed “means” is a claim construction issue for the Court. Similarly, determining the function claimed is also for the Court. In Chiuminatta, the Court also stated that the M+F statute does not permit every possible “means” for performing the claimed function to be within the claim scope. That would convert the required “means” to mean everything possible. The real question is what the structures in the specification are and whether they are the same as or equivalent to, the accused structures. And borrowing from the Doctrine of Equivalents (DOE), the Court said that comparing structures is about whether such differences are insubstantial. 

Many cases since then, such as the Court’s 2014 Robert Bosch [769 F.3d 1094 (Fed. Cir. 2014)] and Williamson [792 F.3d 1339 (Fed. Cir. 2015)] added to the M+F claim interpretations. In Robert Bosch, even though the claim term did not use the “means for” paradigm, nonetheless the Court held that the presumption against M+F interpretation was in fact overcome and that the claim was a M+F claim after all. And because it was now a M+F claim, the Court then invalidated the claim because the claim lacked any corresponding structure recited in the specification and doomed the claim as indefinite under §112, second paragraph. In Williamson, the Court held (en banc in relevant part), that it was not appropriate to consider the presumption of M+F applying or not applying as “strong” and thus should be abandoned. As such, there is no “strong” presumption of application/non-application of the M+F paradigm. The practical effect is that many patent claims that do not use the typical “means for” structure can become M+F claims and thus potentially invalidated if there is no sufficient recitation of structure. 

Infringement Test and Claim Construction 

With the various late 1990’s claim construction cases in hand, one could divine that the test for infringement was the typical two-steps: (1) construe the relevant claim terms; and (2) determine if infringement occurred. In the M+F claim construction context, that means (no pun intended) that the court examines the claim to divine the function claimed and determine the “structures” from the specification that correspond to that function. Structure disclosed in the specification qualifies as “corresponding structure” if the intrinsic evidence clearly links or associates that structure to the function recited in the claim. Even if the specification discloses corresponding structure, the disclosure must be of “adequate” corresponding structure to achieve the claimed function. Under M+F claim interpretation, then if a person of ordinary skill in the art would be unable to recognize the structure in the specification and associate it with the corresponding function in the claim, then the M+F clause is indefinite.  Then in step (2), the fact finder would determine if the accused product performs the identical function and then whether the structure in the accused device is the same as or equivalent to the structure of the “means”. 

Lingering Questions About M+F Claims and Functional Structures

Recently a few M+F cases have pushed back on the Williamson non-presumptions. In Dyfan LLC v. Target Corp., 2022 WL 870209 (Fed. Cir. March 24, 2022), the Court reversed and remanded back to trial court. The trial court initially determined that the though the claim was not in classical “means for” format, nonetheless the claim was devoid of any structural limitations and thus found that the claim was in M+F format. And because it was in M+F format, the specification was also devoid of any corresponding structure and thus invalid as indefinite.  While the case is generally unremarkable, the Federal Circuit stated that Target (the defendant) bore the burden of showing by a preponderance of the evidence that the presumption against M+F format was overcome. Now this, to the author, is strange because the preponderance of the evidence is more of an evidentiary standard in questions of fact whereas claim construction is a question of law. And with the legion of cases saying that questions of law are for the Court perhaps the Federal Circuit was implying that the presumption to overcome is indeed a factual question. 

A day later, the Federal Circuit reversed and remanded again a trial court’s finding that the claims were in M+F format and invalid for the lack of corresponding structures. VDPP LLC v. Vizio, Inc., 2022 WL 885771 (Fed. Cir. March 25, 2022). This time the Court did not reiterate any “preponderance of the evidence” standard. 

Many M+F claim cases and those that avoid the M+F stricture rise or fall based on whether the claim indeed claims a structure or not. And sometimes the key inquiry focuses on a term that looks like a structure (a noun) but may be a functional term instead. For example, many nouns (devices) take their names from the function they perform, such as a lock (a means for locking), a brake (a means for braking), a filter (a means for filtering), etc. In the computer software context, a claim may recite a processor, a buffer, or a display. In the pharmaceutical context a typical formulation claim may include binders, fillers, disintegrants, which obviously function to bind, fill or disintegrate. The specification may recite a litany of binders, many of which function as a binder but do not share any meaningful chemical similarity. So the question remains of when is a functional noun merely a non-structural feature. The answer likely will involve how terms are understood in the art, and perhaps even expert or other extrinsic evidence. And no clarity will be obtained until the Federal Circuit opines on the issue. 

M+F Claims In Infringement – Narrow Versus En Grosse Structures

The crux of an infringement case may be in defining the structure for claim construction purposes and then for infringement. Returning to the above example of the means for connecting pieces of wood and the specification describes a nail, then the accused device would be infringing if it had a nail or an equivalent structure. Perhaps that equivalency may include a rod, screw, or bolt in the accused device. But it may not include Velcro, glue or a snap. But suppose the claim is a medical device capable of imaging the inside of the body, expressed as a means for imaging a body organ. En grosse, the specification may describe the monitor itself upon which the image is displayed, the computer system that correlates the signals received and sends the image to the display, a cord that connects a probe to the computer system to transmit signals, and the probe at the end that touches the skin, which creates the signal sent down the cord. Now what if the accused device has a wireless handheld probe, with no cord system? If the claim is narrowly construed to be just the handheld probe, then there is greater likelihood of infringement because the accused device has the handheld probe. But if the court construction includes the entire system (en grosse), then there is no infringement because the accused device has no cord. 

In the pharmaceutical context, M+F claims may be implicated in drug-device combinations, where the drug product includes a device component. For example, M+F claims may exist in inhalers, injections, implants, or the like. In one case, a generic drug defendant argued that the sustained release formulation was actually a M+F claim and thus limited by the specified formulation (an osmotic dosage form), presumably because it had a different formulation albeit a sustained release formulation nonetheless. It argued that the term “sustained release [drug name] formulation” was functional as it had no specific structure and only described a function (sustaining the release of the drug). See Alza Corp. v. Mylan Laboratories, 349 F.Supp.2d 1002 (WD Va. 2004). 

Practical Tips for Patent Applicants and Litigants

Perhaps modern patent application practice would avoid drafting M+F claims in the first place. While statutorily allowed under §112(f), the case precedent indicates that claims will be construed narrowly. On the other hand, the drafter ought to identify as many different structures capable of performing the claimed function, and further describe the relevant structures narrowly and en grosse. 

For litigants, challengers would seek to convert non-means claims into M+F claims so that either: (i) the accused device does not have the same or equivalent structure; (ii) the claim is invalid as indefinite for failing to recite sufficient structures, or (iii) both. 

How we can help you?

We help clients in patent litigation, appeals, counseling, opinions of counsel, and PTAB proceedings. When your current firm needs help or the client needs a change of counsel, we can help.

About Upadhye Tang LLP 

Upadhye Tang LLP is an IP and FDA boutique firm concentrating on the pharmaceutical, life sciences, and medical device spaces. We help clients with navigating the legal landscape by helping on counseling and litigation. Clients call us to help move drug and device approvals along and to represent them in IP and commercial litigation. Call Shashank Upadhye, 312-327-3326, or by email: shashank@ipfdalaw.com, for more information. 

No Attorney-Client Relationship or Legal Advice

The content of this website has been prepared by Upadhye Tang LLP for informational purposes only and does not constitute legal advice. Nothing shall not be construed as an offer to represent you, nor is it intended to create, nor shall the receipt of such information constitute, an attorney-client relationship. Please call us first with any questions about the firm. 

Nobody should not take any action or choose not to take any action based upon the information on this website without first seeking appropriate professional counsel from an attorney licensed in the user’s jurisdiction. Because the content of any unsolicited Internet email sent to Upadhye Tang LLP at any of the email addresses set forth in this website will not create an attorney-client relationship and will not be treated as confidential, you should not send us information until you speak to one of our lawyers and get authorization to send that information to us.

Individual Opinions 

The opinions and views expressed on or through this website, or any newsletter, are the opinions of the designated authors only, and do not reflect the opinions or views of any of their clients or law firms or the opinions or views of any other individual. And nothing said in any newsletter or website reflects any binding admission or authority.