Oxygenator Water Technologies, Inc. v. Tennant Company

Case Overview

Case

Oxygenator Water Technologies, Inc. v. Tennant Company, No. 20-cv-00358 (KMM/DJF)

Court

U.S. District Court, District of Minnesota

Judge

Katherine M. Menendez, United States District Judge

Date

September 3, 2025 **Nature of Case:** Patent infringement; post-trial motions

Background

OWT owns three reissued patents — U.S. Patent Nos. RE45,415 ('415 patent), RE47,092 ('092 patent), and RE47,665 ('665 patent) — covering electrolysis technology that generates very small micro- and nanobubbles in water. All three patents stem from a 2003 patent application and share the same specification. Tennant manufactures commercial and industrial floor-cleaning machines, many of which include an 'ec-H2O' module that performs electrolysis to clean floors without detergent.

OWT filed suit in 2020. At summary judgment, the court found that Tennant's newer 'ec-H2O NanoClean' modules did not infringe, narrowing the case to the older 'ec-H2O' modules. Before trial, the parties stipulated that certain claims were infringed by ec-H2O modules with 24-volt batteries, and that certain other claims were infringed by ec-H2O modules with 36-volt batteries. The contested issues at trial were: (1) whether the 36-volt battery ec-H2O modules infringed claims 13, 18, 24, and 26 of the '415 patent (which require a power source producing no greater than about 28.3 volts); (2) whether infringement was willful and when it began; and (3) the amount of damages.

After a six-day jury trial in November 2024, the jury returned a unanimous verdict for OWT on all issues: literal infringement and infringement under the doctrine of equivalents of the '415 patent claims, indirect (induced and contributory) infringement, willful infringement beginning in 2015, and damages of $9,815,595 (18,558 infringing modules × $529/module).

Tennant's Post-Trial Motion: Judgment as a Matter of Law (JMOL) and New Trial

Legal Standards

JMOL (under Federal Rule of Civil Procedure 50(b)) is available only when there is "no proof beyond speculation" to support the verdict; the court must view evidence in the light most favorable to the prevailing party. A new trial (under Rule 59) requires a finding that the verdict was against the clear weight of the evidence, clearly excessive, or the result of passion or prejudice — i.e., that a new trial is necessary to avoid a miscarriage of justice. The court may not simply reweigh the evidence.

JMOL: No Direct Infringement of the '415 Patent

The '415 patent claims require a power source that "produces a voltage no greater than about 28.3 volts." Tennant's ec-H2O modules use a 36-volt battery. OWT's technical expert, Dr. Seth Miller, testified that the module's power source combines a 36-volt battery with an electronic control board that uses pulse width modulation (PWM) — rapidly toggling the power on and off 2,000 times per second — to produce an effective "average voltage" of approximately 2.5 volts at the electrolysis component, far below 28.3 volts.

Tennant argued (1) that no reasonable jury could find a 36-volt battery literally satisfies a claim requiring no more than 28.3 volts, and (2) that Dr. Miller's "average voltage" theory amounted to improper ad hoc claim construction by the jury.

The court denied JMOL. Infringement is a question of fact reviewed for substantial evidence. Dr. Miller provided extensive, unexcluded testimony supporting his theory. Tennant's competing expert presented a contrary view. The jury resolved the expert dispute in OWT's favor, and the court declined to disturb that credibility determination. On the claim construction argument, the court noted that parties did not seek formal construction of "produces a voltage no greater than about 28.3 volts," so these terms carried their plain meaning. The jury's task of applying that plain meaning to the PWM power source was a factual inquiry, not improper claim construction.

JMOL: No Infringement Under the Doctrine of Equivalents

Under the doctrine of equivalents, infringement exists if the difference between the claimed invention and the accused product is "insubstantial," or if the accused product performs substantially the same function in substantially the same way with substantially the same result (the "function, way, result" test). An expert must provide "particularized testimony and linking argument" — generalized comparisons are insufficient.

Tennant argued Dr. Miller's equivalents testimony was too conclusory, spanning less than two pages of transcript. The court disagreed. Dr. Miller explicitly invoked his extensive prior testimony about PWM when offering his equivalents opinion, linking that foundation to his conclusion that any difference between a PWM-regulated 36-volt source and the claimed invention was insubstantial. The Federal Circuit has expressly approved this efficient reuse of prior testimony (citing Paice LLC v. Toyota Motor Corp., 504 F.3d 1293, 1305 (Fed. Cir. 2007)). The court also noted that this case involved relatively straightforward technology, so the equivalents analysis did not require elaborate separate elaboration. JMOL denied.

The court also ruled that Tennant waived a "claim vitiation" argument (the idea that finding equivalents effectively writes the voltage limitation out of the claim) by never raising it during the litigation despite ample opportunity.

JMOL: No Willful Infringement Before 2019

Willful infringement requires deliberate or intentional infringement — specifically, that the infringer acted in the face of a known or obvious risk of infringement. The jury found willful infringement beginning in 2015 (when the '415 patent reissued).

The court summarized the key evidence: A Tennant engineer named Bruce Field bought multiple units of OWT's commercial product (a "Bait Keeper," a patent-marked electrolysis device sold at Cabela's outdoor stores), reverse-engineered it, used its sparger in prototypes, and pursued a design seeking "equivalence" to the Bait Keeper. Field also cited the Bait Keeper and OWT's earlier patent in his own 2007 patent application. OWT approached Tennant for a license in 2010, asserting its patents covered a broad range of applications. Tennant set up patent-tracking alerts for micro- and nanobubble patents from 2012 to 2019, which flagged OWT's earlier patent in 2012. Tennant employees testified they were unaware of the '415 patent, but a Tennant employee had shredded physical copies of patent search results.

The court denied JMOL, noting that while this was not a straightforward case of undisputed knowledge of the specific patent, willfulness can be based on circumstantial evidence and on knowledge of related patents in the same family with the same specification. The jury was entitled to draw the inference that Tennant knew of — or should have known of — the '415 patent once it reissued in 2015, given the totality of these circumstances. The court gave particular weight to the jury's implicit credibility assessment of the witness who had shredded search results.

New Trial Based on Jury "Taint" from Willfulness Evidence

Tennant argued that allowing pre-2019 willfulness evidence to go to the jury inflamed its passions and tainted the verdicts on other issues. The court denied this request, even hypothetically assuming JMOL on willfulness were warranted. The court noted that Tennant never moved for summary judgment on pre-2019 willfulness, never sought to exclude the relevant evidence before trial, and never objected to the evidence during trial. The evidence would have been before the jury regardless. Additionally, the court reviewed OWT's closing arguments and found them explicitly tethered to willfulness, not likely to have spilled over into prejudice on other issues. The court also noted that Tennant's own defense strategy — minimizing OWT's inventor as a "fish tank" hobbyist irrelevant to floor cleaning — likely did more to harm Tennant's credibility with the jury.

The court also noted that Tennant waived any bifurcation argument by never requesting it.

JMOL: No Indirect (Induced or Contributory) Infringement

Indirect infringement requires knowledge of the infringed patent. Because the court upheld the jury's willfulness finding (which itself requires knowledge), the motion for JMOL on indirect infringement failed for the same reasons. Denied.

JMOL: No Damages for Overseas Units (1,825 units)

Patent infringement under 35 U.S.C. § 271(a) requires that the infringing act occur within the United States. The jury heard evidence that Tennant manufactures and tests its ec-H2O modules in Michigan before distributing them worldwide, including units assembled in the Netherlands. OWT argued that testing the modules in Michigan constituted practicing the patented method in the United States. Tennant did not object to this theory or the supporting evidence at trial. The court found the jury had sufficient evidence to include overseas-sold units in the damages base on the theory that they were first used (tested) in the United States. Post-trial challenge treated as a weight-of-evidence argument, not suitable for JMOL. Denied.

JMOL: No Damages for 2,851 Units in the 2015 Royalty Base

This dispute concerned commercial floor scrubbers manufactured before the '415 patent issued in March 2015 but sold afterward, during a transition period when Tennant was phasing out the ec-H2O module in its smaller commercial scrubbers. Because the asserted claims are method claims, mere sale of the units is insufficient to prove direct infringement — Tennant itself would have had to use (operate) the modules. OWT's theory — that the units "could have" been tested or demonstrated — was too speculative.

The court granted JMOL on direct infringement of these 2,851 units. However, the court found this ruling has no practical effect on the verdict: the jury also found indirect infringement (which would occur when Tennant's customers operated the machines), and the verdict form did not ask the jury to differentiate between directly and indirectly infringing modules. The court declined to speculate about whether the jury's 18,558-unit total was based on direct or indirect infringement for any particular units.

New Trial on Damages

Tennant argued that OWT's damages expert, Dr. Timothy Nantell, violated the "entire market value rule" (EMVR) by failing to properly apportion the value of the infringing sparger component from the non-infringing parts of the ec-H2O module.

The EMVR is a narrow exception to the general requirement that patent damages be apportioned to the value of the patented features; it allows damages based on the full value of a product only when the patented feature is the basis for consumer demand. Tennant argued Dr. Nantell improperly claimed the full value of the module.

The court denied a new trial. It found Dr. Nantell did apportion: his royalty base was set against the value of the ec-H2O module (not the entire floor scrubber), and his $529/module royalty figure represented approximately half of the $1,058 in incremental profit Tennant derived from including the module in an industrial scrubber — reflecting his view that the sparger drove roughly half the module's value. Tennant's expert, John Hansen, proposed $56/module based on a very different analysis (including the sparger's low cost of $6.53 and OWT's prior license rates). The jury chose Dr. Nantell's figure. The court held this was a classic "battle of the experts" properly resolved by the jury. The court also rejected a related argument that OWT improperly introduced the full value of Tennant's floor scrubbers, finding only minimal contextual references that did not warrant a new trial.

The court also rejected Tennant's argument that OWT introduced a "new damages theory" at trial, finding that Dr. Nantell had already disclosed an alternative royalty opinion based solely on the sparger in his expert report prior to trial.

OWT's Motion: Enhanced Damages, Attorney Fees, Interest, and Costs

Enhanced Damages (35 U.S.C. § 284)

Section 284 allows a court to increase patent damages up to three times the jury's award for willful misconduct. Courts apply a nine-factor framework from Read Corp. v. Portec, Inc., 970 F.2d 816 (Fed. Cir. 1992). The court analyzed each factor:

1. Copying: Tennant engineers deliberately acquired and reverse-engineered OWT's patent-marked Bait Keeper, used its sparger in prototypes, and pursued "equivalence" to it in commercial design. However, mitigating factors exist: Tennant's engineers had conceived of the electrolysis-for-floor-cleaning idea before discovering the Bait Keeper, the sparger is one component of a larger module, and the parties are not competitors. Modestly favors enhancement.

2. Good-faith investigation of non-infringement/invalidity: Given the jury's finding of willful infringement from 2015, Tennant's failure to investigate the '415 patent weighs against it. Tennant stipulated to infringement of some claims. The court had already granted summary judgment of no invalidity on two bases, and the Patent Trial and Appeal Board twice rejected invalidity challenges. Tennant did not argue its remaining indefiniteness defense to the jury. Favors enhancement.

3. Litigation misconduct: OWT pointed to Tennant raising new defenses after hiring new counsel and other conduct. The court found nothing rising to the level of vexatious or abusive litigation; both parties tried the case professionally. Does not support enhancement.

4. Defendant's size and financial condition: Tennant is a large, publicly held company and raised no financial hardship arguments. Supports enhancement (essentially uncontested).

5. Closeness of the case: Tennant stipulated to some infringement, but the '415 patent infringement and willfulness questions were genuinely contested. The jury could have gone either way on literal infringement and willfulness. Modestly supports enhancement.

6. Duration of misconduct: Infringement spanned the patents' full life until expiration in 2023, but OWT made no enforcement efforts during the pre-suit period and is not a competitor suffering lost profits. The jury's verdict already captures accumulated royalties. Does not favor enhancement.

7. Remedial action: Tennant never stopped infringing until the patents expired. It did remove the sparger from commercial modules (NanoClean), which the court treated as partial design-around, but left the sparger in industrial modules while arguing it was of minimal value — an internal tension the court found unconvincing. Somewhat supports enhancement.

8. Motivation for harm: The parties are not competitors; there is no evidence of pernicious intent. Tennant's conduct is better explained by economic self-interest. Does not support enhancement.

9. Concealment: No significant concealment; Bruce Field openly cited the Bait Keeper and OWT's patent in his own patent application. Does not support enhancement.

Result: Five factors favor enhancement (to varying degrees), four do not. The court also noted that Dr. Nantell's $529/module royalty already sits at the high end of credible valuations. The court enhanced damages by 30%, adding $2,944,679 for a total award of $12,760,274. The court declined to treble damages.

Attorney Fees (35 U.S.C. § 285)

Fees may be awarded in "exceptional cases" — those standing out from others based on the substantive weakness of a party's litigation position or the unreasonable manner in which the case was litigated (Octane Fitness, LLC v. ICON Health & Fitness, Inc., 572 U.S. 545 (2014)).

The court denied fees. It distinguished the enhanced-damages analysis (focused on culpability during infringement) from the fee analysis (focused on litigation conduct). Key considerations: - Tennant's early stipulation to infringement of certain claims was a reasonable litigation choice that weighed against a fee award. - OWT's original infringement theory was substantially broader and was narrowed by the court at claim construction and summary judgment; OWT cannot recover fees for the partially unsuccessful pursuit of a larger case. - Tennant maintained credible defense theories on damages and willfulness throughout. - This was a hard-fought but professionally conducted case, not one involving frivolous or bad-faith litigation. Denied.

Prejudgment Interest (35 U.S.C. § 284)

Prejudgment interest is ordinarily awarded in patent cases from the earliest date of infringement to compensate the patent owner as if a royalty agreement had been in place.

OWT sought interest from March 17, 2015 (date the '415 patent reissued). Tennant argued interest should run only from 2019, when OWT formally accused it of infringement, asserting OWT engaged in "undue delay" by waiting to sue.

The court rejected Tennant's argument. Under Kaufman v. Microsoft Corp., 34 F.4th 1360 (Fed. Cir. 2022), mere delay in filing suit does not alone constitute "undue delay," and a defendant must show prejudice. Tennant showed no prejudice — it made no effort to avoid or mitigate infringement even after the lawsuit was filed. The court awarded interest from March 17, 2015 at the Minnesota statutory rate of 10% per year (Minn. Stat. § 549.09(c)(2)), following this district's standard practice in patent cases.

Post-Judgment Interest (28 U.S.C. § 1961(a))

Statutorily required on all civil money judgments, running from the date of judgment at the weekly average 1-year Treasury yield. Applies to both the damages award and prejudgment interest. Will be included in the forthcoming judgment.

Costs

Awarded to OWT as the prevailing party under Federal Rule of Civil Procedure 54(d)(1), to be calculated upon entry of judgment.

Final Orders