Means-Plus-Function Claiming, Expert Opinions

For many years, patent attorneys interpreted claims that included “means-plus-function” language as being very broad because it was not necessary to include the actual structure that performs the function in the claim.  For a long time now, the Federal Circuit has ruled that this interpretation is incorrect.  In fact, the opposite is true.  Such claim language is actually construed much more narrowly than claims including structure.

Means-plus-function clauses are permitted in claims by 35 U.S.C. § 112, ¶ 6:

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.

The Federal Circuit has interpreted this provision to mean that “means-plus-function” clauses cover the exact structure described in the specification as performing the precise function described in the claim, as well as reasonable equivalents thereof.  Based on this interpretation, one can immediately see why the use of “means-plus-function” clauses in patent claims has decreased significantly in recent years.  If the specification is not carefully written, such clauses are fraught with peril.


The Federal Circuit has invalidated numerous patents through the years for failure to comply with these statutory provisions.  For example, if the specification does not include structure corresponding to the function described in the claim, the claim is invalid.  If the specification describes the function somewhat differently from the function described in the claim, there can be no corresponding structure.  When no structure is identified in the specification as corresponding to the function recited in the claim, the claim does not fulfill various parts of § 112.

The original claims are considered a part of the written description of the invention.  Thus, if a structure is included in the claims, but is omitted from the specification, it can be added to the specification without violating the prohibition against adding new matter or new material after the application is filed.  For a claim that contains a means-plus-function clause, however, if the structure is omitted from the specification, it cannot be added later because it was by definition absent from the original claim as well.


As if that weren’t enough, the Federal Circuit issued an opinion on Monday that the patent owner had failed to prove infringement of a claim that includes means-plus-function language.  Intellectual Science and Technology, Inc. v. Sony Electronics, Inc.

Intellectual Science sued Sony and other defendants for infringement of U.S. Patent No. 5,748,575.  Claim 1 of the ’575 patent reads:

An information processing apparatus with multitasking function, the information processing apparatus comprising:

(a) a plurality of turntables, each comprising a disc-setting table for mounting an optical disc;

(b) a plurality of optical units, each comprising a driving means and an optical read head, wherein said driving means is provided for moving said optical read head in a radial direction of said optical disc to a predetermined disc position on a surface of said optical disc;

(c) means for simultaneously controlling a plurality of said driving means to move a plurality of said optical read heads to a plurality of predetermined disc positions on at least two optical discs for retrieving information stored thereon;

(d) a plurality of signal-process systems for converting a plurality of information sets retrieved by said plurality of optical read heads from a compact disc format to the original state of the information; and

(e) data transmitting means for transmitting a plurality of the information sets converted by said plurality of signal-process systems to a host computer.

The “data transmitting means” of clause (e) was at issue on appeal.  The parties basically agreed on the claim construction of this clause.  They agreed that it was a “means-plus-function” clause, they agreed on its function, and they agreed on the corresponding structure in the ’575 patent.  The district court, however, issued a ruling of summary judgment of non-infringement in the defendants’ favor because the Intellectual Science’s expert did not demonstrate specific structure in the defendants’ devices that corresponded to this limitation.

The Federal Circuit affirmed, holding that the expert’s opinion was insufficient to satisfy the summary judgment standard.

To satisfy the summary judgment standard, a patentee’s expert must set forth the factual foundation for his infringement opinion in sufficient detail for the court to be certain that features of the accused product would support a finding of infringement under the claim construction adopted by the court, with all reasonable inferences drawn in favor of the non-movant.

The court held that the expert’s opinion was conclusory and unsupported by evidence.  He did not pinpoint where this claim element was found in the accused device.  Intellectual Science argued that this element was an “off-the-shelf” component, presumably meaning that it was common in many devices.  The court found that this did not satisfy the requirement of proving that each limitation of the claim is found in the accused device.

Without that further identification and explanation, a reasonable juror would not be able to determine that those allegedly infringing components are actually present.

It was necessary for Intellectual Science’s expert to identify the specific structure in each accused device that performed the exact function described in the claim, and, show that this structure is the same as or equivalent to the structure described in the ’575 patent specification.  The expert did not fulfill this obligation.


The lessons here are two-fold.  First, be very careful when using means-plus-function language in claims.  Such clauses should be used rarely and only in circumstances where it is necessary.  The patent should also include other claims that do not contain means-plus-function language.  When using the language, be certain that the specification is well drafted and that it contains specific structure that performs the function recited in the claim.

The second lesson is more general and applies even to patents that do not include means-plus-function claims.  To prove infringement, and even to survive summary judgment, it is necessary for the evidence to specifically demonstrate infringement of each claim limitation.  Expert declaration or testimony must show this with particularity and not in a merely conclusory way.  The purpose of an expert witness is to help the court and the jury to understand his party’s position.  When the expert renders conclusory opinions that are not supported by particular facts and evidence, he has not fulfilled this purpose.

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One Response to “Means-Plus-Function Claiming, Expert Opinions”

  1. Michigan Guy Says:

    Thank you for posting your piece, I found your blog on google. I enjoyed reading your article and found if extremely interesting. I am looking forward to more posts on this topic.

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