A Missing Limitation Can Matter—If It Is Truly Missing
Patent infringement is analyzed against the claims, not against a general picture of the patented product. For literal infringement, every limitation of the asserted claim must be found in the accused product or process. If a required limitation is genuinely absent, that particular claim is generally not literally infringed.
The engineering mistake is to convert that rule into a visual shortcut: “the patent drawing has four components, ours has three, therefore we are clear.” The claim may define a relationship rather than a separate physical part. A feature that looks deleted may be performed by another structure. A single component may satisfy more than one limitation. Or claim construction may reveal that the limitation is broader or narrower than the engineer assumed.
The first question is not “what did we remove?” but “which claim limitation is no longer satisfied, why, and what product evidence proves that conclusion?”
First Confirm What the Limitation Actually Means
Before declaring a limitation absent, the team needs a defensible construction of the relevant claim language. The ordinary meaning of a word may be affected by the specification, prosecution history, definitions, disclaimers, and the way the claim uses the term in context.
For example, replacing a “separate support member” with a molded portion of a housing may or may not eliminate the limitation. The answer depends on whether the claim requires a distinct component or merely a structure that performs the stated relationship. That is a claim-construction question, not a parts-counting exercise.
Doctrine of Equivalents Can Still Matter
Even when literal infringement is not established, U.S. law recognizes the doctrine of equivalents in appropriate cases. The USPTO’s MPEP summarizes the Supreme Court’s element-by-element inquiry: the accused product may still infringe if it contains elements identical or equivalent to each claimed element. Equivalence is analyzed in the context of the particular limitation, including whether a substitute performs substantially the same role or is otherwise only an insubstantial change.
This does not mean every substitute is an equivalent. The doctrine cannot be used to erase a claim limitation or make the claim cover subject matter that the law treats as materially different. Federal Circuit decisions repeatedly emphasize an all-elements limitation on the doctrine. The practical point for design-around work is narrower: replacing a claimed component with a technically different mechanism needs analysis, not a label saying “different.”
A useful engineering record explains what changed in function, way, result, structure, operating principle, or system interaction—and why that difference is material rather than cosmetic.
Prosecution History Can Narrow the Equivalents Analysis
The patent’s prosecution history can materially affect a design-around. Under Festo, a narrowing amendment made for a reason related to patentability can give rise to prosecution-history estoppel and can limit the patentee’s ability to recapture surrendered territory through the doctrine of equivalents.
That makes the file history valuable to both sides. A product designer should review why a limitation was added, what alternatives were distinguished, and what arguments were made to obtain allowance. A limitation that looks dangerous in the issued claim may have a narrower practical reach because of the prosecution record. Conversely, assuming a limitation is narrow without reviewing that record can produce false confidence.
One Claim Is Not the Entire Patent—or the Entire Family
A design-around that defeats independent claim 1 can still be exposed to another independent claim, a method claim, or a claim in a continuation or other family member. Dependent claims should also be checked because they can reveal how the patent drafter distinguished narrower versions of a feature.
For products entering the United States, the review should therefore identify the commercially relevant U.S. patents and pending applications, map independent claims first, and then examine dependent claims or related family claims that correspond to the redesigned feature. A single claim chart is not a substitute for family-level triage when the patent owner has an active continuation strategy.
The Product Evidence Must Match the Version That Will Be Sold
Design-around conclusions are only as reliable as the product record. A CAD model, prototype, supplier drawing, firmware build, manufacturing BOM, and final retail product can differ. If the legal conclusion depends on the absence of a particular structure or step, the team should preserve evidence showing that the production version actually omits it.
This is especially important for supplier-designed products. A supplier may change a component after the initial review or substitute a functionally similar part without telling the brand owner. The FTO file should identify the version reviewed and define what changes trigger re-review.
A More Defensible Design-Around Workflow
- Identify the exact independent claims creating risk.
- Construe the key limitations using the claim, specification, and prosecution history.
- Map each limitation to the current product with evidence.
- Identify the limitation intended to be removed or materially changed.
- Evaluate literal infringement and, where relevant, doctrine-of-equivalents exposure.
- Review other independent claims, method claims, and relevant family members.
- Record the final production version and define change-control triggers.
Takeaway
Removing one component can be exactly the right design-around. But the legal conclusion should be “this limitation is not satisfied for these reasons,” not simply “our product looks different.” The strongest design-arounds are engineered from a limitation-by-limitation analysis and documented so that the conclusion remains intelligible after the product, supplier, or litigation posture changes.