Designing around a patent means engineering a product or process that delivers similar functionality without falling inside the patent’s claims. Federal law grants inventors a limited monopoly and, in the same breath, invites competitors to work outside its boundary. Doing that safely takes three things: a careful read of the claims, a change to at least one claimed element that holds up under the doctrine of equivalents, and usually a written opinion from a patent attorney confirming the new design is clear.
Confirm the Patent Is Still Enforceable
Before spending a dollar on redesign, check that the patent is alive. A utility patent lasts 20 years from its filing date, not its issue date, so a patent that spent years in prosecution has already burned part of its term.1Office of the Law Revision Counsel. 35 USC 154 – Contents and Term of Patent Owners also have to pay periodic maintenance fees; miss one and the patent expires early.
The USPTO publishes a free patent term calculator and public databases showing each patent’s payment history and current status. If the patent has lapsed or expired, the technology is in the public domain and there is nothing to design around. That is the cheapest possible outcome, and it is worth ruling in or out first.
Read the Claims Element by Element
If the patent is active, the numbered paragraphs at the end of the document (the claims) are what you have to work around. They set the legal boundary of the patent the way property lines set the boundary of a deed. Everything inside belongs to the patent holder; everything outside is public.
Independent claims stand on their own and describe the invention at its broadest. Dependent claims refer back to an independent claim and add extra limitations, which makes them narrower but also more resilient if the parent claim is later invalidated. Focus first on the independent claims, because those set the outer edge of protection.
The rule that makes design-around possible is the all-elements rule: literal infringement requires that the accused product contain every single limitation in at least one claim.2World Intellectual Property Organization. Patent Judicial Guide – United States of America Five elements in the claim, four in your product, no literal infringement of that claim. So list each element in each independent claim, then figure out which one you can plausibly remove, replace, or genuinely rebuild.
One warning about claim language: the words do not always mean what a general reader assumes. In litigation, judges construe disputed terms in a claim construction hearing under the Supreme Court’s decision in Markman v. Westview Instruments, and their construction can be broader or narrower than everyday usage.3Justia. Markman v Westview Instruments Inc, 517 US 370 (1996) If the patent has already been through claim construction, or if similar language has been construed in related patents, those rulings tell you where the real boundary sits.
Change at Least One Element, and Change It for Real
Omitting an Element
The cleanest design-around drops a claimed element entirely. Because literal infringement needs every element, taking one out breaks the claim. A designer studying a patented assembly might realize that one component in the claim is not actually necessary for the device to do its job, and build a version without it.
Omission only works if the element is genuinely gone, not renamed or folded into another part, and if the resulting product still functions well enough to sell. When it does work, it often produces a simpler design, because you are forced to reach the same outcome with fewer parts.
Substituting a Different Mechanism
When you cannot remove an element, replace it. A hydraulic actuator claimed in the patent might become an electric motor driving a lead screw in your product. The load still moves; the mechanism is different.
The word carrying the weight here is fundamentally. Swapping one hydraulic fluid for another, or shaving a millimeter off a piston, is not a design-around. Courts look past cosmetic changes, and a superficial swap will be pulled back in under the doctrine of equivalents (below). The substitution has to rest on a genuinely different approach.
Software and Means-Plus-Function Claims
Software patents are harder to redesign around because their claims often describe what a component does rather than what it is. Some are drafted as means-plus-function limitations under 35 U.S.C. 112(f), which by statute cover only the specific structure disclosed in the patent’s specification, plus equivalents of that structure.4Office of the Law Revision Counsel. 35 USC 112 – Specification That narrow construction is an opening: if the specification describes a particular algorithm or data structure, a fundamentally different algorithm or architecture that reaches the same result can sit outside the claim. Read the specification closely to pin down exactly what the inventor disclosed, then build something that works differently.
Functional claims that are not written in means-plus-function form are construed more broadly and are harder to work around. They do, however, carry a matching vulnerability: functional language that describes a goal without specifying how to achieve it may be invalid for indefiniteness, which can make a validity challenge more productive than a redesign.
The Doctrine of Equivalents
Avoiding the literal text of the claims is necessary but not enough. Patent protection reaches beyond the exact words through the doctrine of equivalents, which captures products that make only insubstantial changes to a patented invention. Courts apply the doctrine element by element, comparing each claim limitation against the corresponding feature of the accused product.2World Intellectual Property Organization. Patent Judicial Guide – United States of America
The test comes from Graver Tank & Manufacturing Co. v. Linde Air Products Co.: an accused element infringes as an equivalent if it performs substantially the same function, in substantially the same way, to achieve substantially the same result as the claimed element.5Legal Information Institute. Graver Tank and Mfg Co Inc et al v Linde Air Products Co All three parts have to line up for the equivalent to catch you. Break any one of them (usually the “way,” by operating through a different mechanism) and the chain breaks.
This is where most design-arounds are won or lost. A change that feels significant in the engineering meeting can look trivial to a judge if the function, method, and result all end up in the same place. A modest physical change that runs on a different physical principle can create real distance. Substantive difference is the whole question.
Use the Prosecution History Against the Patent Holder
Every patent has a file wrapper: the public record of back-and-forth between the applicant and the USPTO examiner during prosecution. It shows what the applicant said the invention was, what the examiner objected to, and what the applicant gave up to get the patent granted. It is one of the most useful documents you can pull.
Prosecution history estoppel stops a patent holder from using the doctrine of equivalents to recapture claim scope they surrendered on the way to allowance. In Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., the Supreme Court held that when an applicant narrows a claim to satisfy the Patent Act, a presumption arises that the applicant gave up everything between the original and amended claim.6Justia. Festo Corp v Shoketsu Kinzoku Kogyo Kabushiki Co, 535 US 722 (2002) The patent holder can rebut that presumption only by showing a skilled drafter could not reasonably have written a claim literally covering the equivalent at the time.
Practically, every amendment and every argument distinguishing prior art creates a safe zone. If the applicant told the examiner “the invention is different because it uses titanium rather than steel,” the patent holder cannot later argue that a steel product is equivalent to titanium. Read the file wrapper for those concessions and design toward them on purpose.
Prior Art as a Backstop
Two more defenses live in the prior art, and both are worth mapping alongside your redesign.
The first is the ensnarement defense. A court will not stretch the doctrine of equivalents to reach a product that would have been unpatentable over the prior art in the first place. The test is whether a hypothetical claim broad enough to literally cover your product would have been anticipated or obvious in light of what already existed when the patent was filed. If yes, equivalents cannot reach that far, and the patent holder carries the burden of showing the hypothetical claim would have been patentable. This defense is strongest when your design closely tracks technology that predated the patent.
The second is practicing the prior art directly. If a prior art reference already describes exactly what you want to build, either the claim has to be construed narrowly enough to miss your product or it is invalid for covering something that already existed. The catch is precision: your product has to closely replicate the prior art. Any gap between your design and the reference gives the patent holder room to argue the claim covers the gap.
Get a Written Opinion of Counsel
A design-around that goes wrong does not just cost the redesign budget. A patent holder proving infringement is entitled to damages adequate to compensate, in the form of lost profits or a reasonable royalty. Worse, under 35 U.S.C. 284 a court can increase damages up to three times the compensatory amount.7Office of the Law Revision Counsel. 35 USC 284 – Damages In Halo Electronics, Inc. v. Pulse Electronics, Inc., the Supreme Court held that enhanced damages are reserved for egregious cases of willful misconduct, with district courts given broad discretion based on the totality of the circumstances.8Justia. Halo Elecs Inc v Pulse Elecs Inc, 579 US ___ (2016) In exceptional cases the court can also award the patent holder’s attorney fees.9Office of the Law Revision Counsel. 35 USC 285 – Attorney Fees
A design-around attempted in good faith, on reasonable analysis, generally weighs against a willfulness finding. A pretextual redesign where internal documents show the team knew it was still infringing can make things worse.
The strongest evidence of good faith is a written non-infringement opinion from a qualified patent attorney. By statute, failing to obtain such an opinion cannot be used to prove willfulness.10Office of the Law Revision Counsel. 35 USC 298 – Advice of Counsel The reverse cuts hard in your favor: a competent opinion letter can effectively defeat a willfulness claim and take treble damages off the table.
To carry weight, the opinion has to be thorough. The attorney needs to construe the claims defensibly and compare the accused product’s technical details against each limitation. A one-page letter declaring “no infringement” is worse than nothing, because it reads as a rubber stamp. A real opinion typically runs $10,000 or more depending on the technology, which is small next to the exposure it neutralizes.
When Licensing Beats Redesigning
Not every patent is worth designing around. Sometimes the independent claims are broad enough that any commercially viable product will land inside them, or the doctrine of equivalents closes the remaining gap. In those cases, a license can be cheaper than the combined bill for redesign, retooling, delayed launch, and the residual risk that the new design still infringes.
Speed matters too. A redesign eats engineering time, prototype cycles, and sometimes a fresh round of regulatory approvals; a license can close in weeks. The honest way to make the call is to price both paths against each other: total royalties over the expected product life against total redesign cost plus remaining infringement risk. Companies that skip that comparison and reflex into a redesign sometimes spend more than the license would have cost and still end up in court.