Technical patent infringement expert
Expert class library · Intellectual property · Plaintiff side
Compares the accused products to the asserted claims, element by element, under the court's claim construction, either literally or under the doctrine of equivalents. Usually an engineer or scientist in the relevant field who relies on source code review, product teardowns, and testing.
What this expert is retained to answer
- Does each element of the asserted claim, as construed by the court, appear in the accused product?
- If an element is not literally present, does the accused feature perform substantially the same function in substantially the same way to achieve substantially the same result?
- What does the source code or teardown show about how the accused feature actually operates?
- Is the equivalents theory barred by prosecution history estoppel or by claim scope surrendered during prosecution?
Methods
- Element-by-element claim comparison
- Doctrine of equivalents analysis
- Source code and product teardown review
- Testing of accused products
How the testimony is attacked
- Opinions inconsistent with the claim construction. Opponents move to strike opinions that apply a different claim meaning than the court adopted. In Kraft Foods v. TC Heartland the court struck an expert's infringement opinions that imported limitations from the specification, holding that testimony inconsistent with the court's construction is unreliable and unhelpful.
- Conclusory doctrine of equivalents analysis. Accused infringers argue the report lacks the particularized, limitation-by-limitation testimony the Federal Circuit requires. In EMC v. Pure Storage and WARF v. Apple the courts found the reports explained function, way, and result enough to reach the jury, treating the remaining criticism as going to weight.
- Relying on literal infringement analysis for equivalents. Defendants argue the expert cannot recycle literal infringement opinions to support an equivalents theory. The WARF court held, following Federal Circuit precedent, that an expert may incorporate earlier technical testimony rather than restart the analysis.
- New opinions beyond the report. Opponents seek to confine the expert to what was disclosed. The WARF court allowed the disclosed equivalents analysis but warned that the expert could not offer new equivalents opinions at trial.
- Prosecution history estoppel ignored. Defendants fault the expert for not addressing estoppel. In Smart Vent v. USA Floodair the court held that prosecution history estoppel is a legal question for the court rather than for a technical expert, though estoppel can still defeat the equivalents theory on the merits, as the EMC court held for a separate patent.
What the public record shows
A deliberately narrow CourtListener search, "doctrine of equivalents" AND "infringement expert" AND (Daubert OR "Rule 702"), returned 4 opinions filed since 2015, as of October 2, 2026; broader searches return more. Three that show how courts handle this class of testimony:
| Outcome | Case | Court | Why |
|---|---|---|---|
| Excluded | Kraft Foods Group Brands LLC v. TC Heartland, LLC232 F. Supp. 3d 632 | D. Del. 2017 | The court struck the defendant's technical expert's infringement opinions on the packaging limitations because they imported limitations from the specification that the court had rejected at claim construction. |
| Admitted | EMC Corp. v. Pure Storage, Inc.154 F. Supp. 3d 81 | D. Del. 2016 | The court denied the motion to exclude the patentee's infringement expert's doctrine of equivalents opinion, finding his function, way, and result analysis sufficient and leaving its weaknesses to cross-examination. |
| Admitted | Wisconsin Alumni Research Foundation v. Apple, Inc.135 F. Supp. 3d 865 | W.D. Wis. 2015 | The court refused to preclude the patentee's infringement expert from testifying on equivalents, holding that criticism of his analysis as conclusory went to weight and that he could incorporate his literal infringement analysis. |
Each case links to the free opinion text on CourtListener.
Under amended Rule 702
Since December 1, 2023, Rule 702 says expressly that the party offering an expert must show the court it is more likely than not that the testimony meets each requirement: that it rests on sufficient facts or data, uses reliable methods, and reflects a reliable application of those methods to the case. Questions about the basis of an opinion are no longer automatically matters of weight for the jury. For how the circuits have applied the amendment, see the Rule 702 tracker, which follows each court of appeals; for what that means for preparing or attacking this class of expert, see the guide on amended Rule 702.
Related classes
- Defense patent damages expert
- Patent invalidity and prior-art expert
- Patent reasonable-royalty damages expert
Guides
Simulating this class on a matter
Supreme Mind simulates a class of expert, never a named individual, on your fact pattern and returns the likely opinion, the ranked cross-examination weaknesses, the Rule 702 attack surface and what it means for settlement. Read how it works, or book a demo.
Last reviewed October 2, 2026. How this page is built: rulings are found by searching court opinions on CourtListener, and each one is read in the opinion before it is summarised here; outcomes are labelled by what the court did with the expert's testimony. No individual expert is named. This page summarises public decisions for orientation and is not legal advice; read the opinion before relying on any ruling.