10.5 Patent infringement
Both district courts and the USITC adjudicate patent infringement. This section discusses the district court’s role. Section 10.12 discusses the USITC’s role and processes.
District court patent litigation begins with the filing of a civil complaint – either by a patent owner alleging patent infringement or a party that has been threatened with litigation seeking a declaration that a patent is invalid, not infringed, or not enforceable.95 In the latter case, the patent owner defendant will typically file a counterclaim asserting patent infringement.
10.5.1 Claim construction
The construction of patent claims is central to the evaluation of infringement and validity and can affect or determine the outcome of other significant issues, such as unenforceability, enablement and remedies. The Supreme Court’s decision in Markman v. Westview Instruments96 laid the groundwork for modern U.S. claim construction practice. That decision, reinforced by Teva Pharmaceuticals USA, Inc. v. Sandoz, Inc.,97 declared that “the construction of a patent, including terms of art within its claim, is exclusively within the province of the court.”98
The Federal Circuit’s decision in Phillips v. AWH Corp.99 stands as the most authoritative synthesis of the claim construction doctrine. A “bedrock principle” of patent law is that “the claims of a patent define the invention to which the patentee is entitled the right to exclude.”100 The “objective baseline” for construing patent claims is determining “how a person of ordinary skill in the art understands a claim term” “at the time of the invention, i.e., as of the effective filing date of the patent application.”101 “That starting point is based on the well-settled understanding that inventors are typically persons skilled in the field of the invention and that patents are addressed to and intended to be read by others of skill in the pertinent art.”102 Often, other evidence will provide context for characterizing the person having ordinary skill in the art. The “effective filing date” is the earlier of the actual filing date or the filing date of an application from which priority is accorded. The skilled artisan “is deemed to read the words used in the patent documents with an understanding of their meaning in the field, and to have knowledge of any special meaning and usage in the field.”103 Interpreting patent claims thus requires the court to consider “the same resources as would that person, viz., the patent specification and the prosecution history.”104
The proper definition of a claim term is context-dependent. The patent and its prosecution history “usually provide the technological and temporal context to enable the court to ascertain the meaning of the claim to a person having ordinary skill in the art at the time of the invention.”105 Thus, patent claims are to be interpreted in light of this “intrinsic” evidence (i.e., the patent specification and its prosecution history) as well as pertinent “extrinsic” evidence (i.e., evidence showing the usage of the terms in the field of art, such as in dictionaries, treatises, and inventor and expert testimony), but extrinsic evidence cannot contradict or override intrinsic evidence. The Federal Circuit explained why extrinsic evidence is inherently less reliable than intrinsic evidence:
First, extrinsic evidence by definition is not part of the patent and does not have the specification’s virtue of being created at the time of patent prosecution for the purpose of explaining the patent’s scope and meaning. Second, while claims are construed as they would be understood by a hypothetical person of skill in the art, extrinsic publications may not be written by or for skilled artisans and therefore may not reflect the understanding of a skilled artisan in the field of the patent. Third, extrinsic evidence consisting of expert reports and testimony is generated at the time of and for the purpose of litigation and thus can suffer from bias that is not present in intrinsic evidence […] Fourth, there is a virtually unbounded universe of potential extrinsic evidence of some marginal relevance that could be brought to bear on any claim construction question […] Finally, undue reliance on extrinsic evidence poses the risk that it will be used to change the meaning of claims in derogation of the “indisputable public records consisting of the claims, the specification and the prosecution history,” thereby undermining the public notice function of patents.106
U.S. patent law provides for liability for both direct and indirect infringement.
10.5.2.1 Direct infringement
Section 271(a) of the Patent Act imposes direct patent liability upon “whoever without authority makes, uses, offers to sell, or sells any patented invention, within the United States or imports into the United States any patented invention during the term of the patent therefor.” An accused product or process literally infringes a patent if it contains each and every limitation recited in a claim.
A defendant can also be held liable for nonliteral infringement where the accused product or process is close to the patented invention, but does not literally infringe. The doctrine of equivalents evolved in response to the concern that an “unscrupulous copyist” could avoid literal infringement of a patented invention by making insubstantial changes to the invention.107 Under the function-way-result test, an accused element is equivalent to a claim limitation “if it performs substantially the same function in substantially the same way to obtain the same result.”108 Under this test, a finding of equivalence requires that all three prongs be satisfied. The doctrine of equivalents determination is judged on the state of technology as of the time of the infringement, not (as in the case of means-plus-function claims) as of the time the patent issued.
The courts have limited the doctrine of equivalents in several ways. The all-elements rule provides that the test for equivalence under the doctrine of equivalents must be applied on an element-by-element (or limitation-by-limitation) basis. A finding of infringement therefore requires that the accused product or process contain each claim limitation or its equivalent.109 Moreover, the doctrine of equivalents is not available where the patentee has narrowed a claim element during prosecution unless (1) the equivalent was unforeseeable to a person having ordinary skill in the art at the time of the amendment, (2) the rationale for the amendment was no more than tangentially related to the equivalent at issue, or (3) another reason suggesting that the patentee could not reasonably be expected to have described the alleged equivalent.110 Furthermore, under the public dedication rule, a patentee may not invoke the doctrine of equivalents to recapture subject matter disclosed but not claimed in a patent.111
10.5.2.2 Indirect infringement
U.S. patent law also imposes liability upon those who actively induce or contribute to infringement by another person. Section 271(b) of the Patent Act provides that “[w]hoever actively induces infringement of a patent shall be liable as an infringer.” Induced infringement requires that the patentee prove that the defendant “actively and knowingly aid[ed] and abet[ted] another’s direct infringement.”112 The knowledge requirement can be established by showing actual or constructive knowledge of the patent113 or that the defendant acted with “willful blindness.”114 Under the doctrine of “willful blindness,” the inducer must have (1) subjectively believed that there was a high probability of infringement and (2) taken deliberate actions to avoid learning of that fact.115
Section 271(c) imposes liability under the following circumstances:
 Whoever offers to sell or sells within the United States or imports into the United States a component of a patented machine, manufacture, combination or composition, or a material or apparatus for use in practicing a patented process,  constituting a material part of the invention,  knowing the same to be especially made or especially adapted for use in an infringement of such patent,  and not a staple article or commodity of commerce suitable for substantial noninfringing use,  shall be liable as a contributory infringer.
The patentee must prove that the alleged contributory infringer had knowledge of the patent.116 Element  serves as an important defense, immunizing the sale of staple articles of commerce, that is, products that have substantial noninfringing uses. Thus, absent evidence of inducing conduct, sellers of non-patented goods are shielded from liability unless the good “has no commercial use except in connection with [… the] patented invention.”117
Section 282 of the Patent Act provides for the following defenses: (1) noninfringement, absence of liability for infringement or unenforceability; (2) patent invalidity; and (3) any other fact or act made a defense.
10.5.3.1 Patent invalidity
Section 282(a) of the Patent Act provides that patents “shall be presumed valid.” Therefore, the patent owner does not need to prove validity in an infringement action. The challenger bears the burden to prove invalidity by “clear and convincing evidence.”118
10.5.3.2 Other defenses
An alleged infringer can defend on the ground that the patentee has consented to their use of the technology by, for example, granting a license.
Under the first-sale doctrine (sometimes referred to as the exhaustion principle), a form of implied license by operation of law, the first unrestricted sale of a patented product exhausts the patentee’s control over that product, and it can be resold and repaired without implicating the patent owner’s rights.119 The line between permitted repair and impermissible reconstruction is not easily determined, resulting in rather vague, context-specific rulings.120 Such issues arise frequently in the context of contributory infringement claims, where the alleged infringer is providing specialized replacement parts.
Courts have long recognized a common-law defense of experimental use. The Federal Circuit has, however, interpreted this doctrine quite narrowly, limiting it to uses “for amusement, to satisfy idle curiosity, or for strictly philosophical inquiry.”121 In addition to the common-law doctrine of experimental use, § 271(e) creates a limited experimental use exception for submitting information for regulatory purposes.
Section 273 of the Patent Act provides for a prior-use right to a defendant who commercially used the invention in the United States at least one year before the earlier of either (1) the effective filing date or (2) the date of the first public disclosure of the claimed invention. The prior-use defense must be established by clear and convincing evidence.
Even where a defendant cannot prove that the patent has not been infringed or is invalid, it may avoid liability by showing that the patentee engaged in inequitable conduct or patent misuse or by proving another equitable defense (equitable estoppel or prosecution laches). Inequitable conduct may “arise from an affirmative misrepresentation of a material fact, failure to disclose material information, or submission of false material information, coupled with an intent to deceive or mislead the [US]PTO.”122 A determination that inequitable conduct occurred in relation to one or more claims will render the entire patent unenforceable.123
Inequitable conduct claims must be pled with particularity under FRCP 9(b), and these claims “require identification of the specific who, what, when, where, and how of the material misrepresentation or omission committed before the [US]PTO.”124 The accused infringer must prove both materiality and intent by clear and convincing evidence.125 Once these threshold findings are established, the court “must weigh them to determine whether the equities warrant a conclusion that inequitable conduct occurred.”126 “Intent and materiality are separate requirements. A district court should not use a ‘sliding scale,’ where a weak showing of intent may be found sufficient based on a strong showing of materiality and vice versa.”127
The affirmative defense of patent misuse exists to prevent harm to the market caused by a patentee extending a patent’s right to exclude beyond its legal scope.128 The underlying principle of misuse is that an alleged infringer must prove by clear and convincing evidence that a patentee has both “impermissibly broadened the physical or temporal scope of the patent grant” and caused some “anticompetitive effect.”129 Where the patentee’s behavior remains within the grant of the patent right to exclude, however, there can never be patent misuse.130 In response to concerns that this judge-made doctrine was vague, unpredictable, and overbroad, Congress exempted several specific behaviors from the doctrine by adding § 271(d): for example, enforcing a patent or refusing to license cannot constitute patent misuse.131
Equitable estoppel arises when a patentee misleads an alleged infringer into believing that it would not be sued for using the patented technology. The defense may bar all relief on an infringement claim.132 Prosecution laches renders a patent unenforceable where the patentee unreasonably delayed in prosecuting the patent, and the accused infringer or others suffered prejudice by the delay.133