Addressing claim constructions across two patents that ultimately led to noninfringement findings by a district court, the US Court of Appeals for the Federal Circuit affirmed one construction because it was supported by the prosecution history but reversed another because it was unsupported by the specification. SSI Techs., LLC v. Dongguan Zhengyang Elec. Mech. Ltd., Case Nos. 21-2345, 22-1039 (Fed. Cir. Feb. 13, 2023) (Reyna, Bryson, Cunningham, JJ.)

SSI owns two patents directed to sensors for determining the characteristics of fluid in a container such as a fuel tank. One patent, referred to as the transducer patent, describes an exemplary sensor system containing a “level” transducer and a “quality” transducer. The two transducers use ultrasonic sound waves and time of flight to determine both a level of fluid in a given tank and a quality (i.e., concentration of diesel exhaust fluid). The other patent, referred to as the filter patent, describes a similar system but attempts to address the problem of erratic measurement results that may occur because of air bubbles embedded in the fluid. This patent claims a “filter” covering the sensing area that substantially prohibits gas bubbles from entering the sensing area.

Dongguan Zhengyang Electronic Mechanical (DZEM) produces systems that determine the quality and volume of diesel exhaust fluid that are used in emission-reduction systems for diesel truck engines. SSI accused DZEM of infringing both patents. In the district court action, DZEM brought a motion for summary judgment of noninfringement based on the court’s construction of certain terms that appear in the asserted claims. With reference to the transducer patent, the claims recite the need to “determine whether a contaminant exists in the fluid based on . . . a dilution of the fluid [] detected while the measured volume of the fluid decreases.” The district court determined that this claim element required that the contaminant determination actually consider the measured volume of the fluid. The district court predicated its determination on the prosecution history, having found that this term was amended to include the disputed term and that the applicant’s intention was to incorporate the specific error-detection capability recited in the specification. The parties had previously agreed that the DZEM products did not base the contamination determination on any consideration of the measured volume. As a result, the district court granted DZEM’s motion for summary judgment of noninfringement on the transducer patent.

Regarding the filter patent, the district court adopted DZEM’s construction of the term “filter,” which was “a porous structure defining openings, and configured to remove impurities larger than said openings from a liquid or gas passing through the structure.” DZEM’s accused sensors includes a rubber cover with four apertures. The district court found that the rubber cover was not “porous” because the apertures were “relatively large” when compared with the disclosed embodiments in the specification. As a result, the court granted DZEM’s motion for summary judgment of noninfringement on the filter patent. SSI appealed.

SSI challenged both constructions. Regarding the transducer patent, SSI argued that [...]

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