Under the United States Code, you are a direct infringer if you make, use or sell within the United States an invention – whether a device or process – protected by a patent that hasn’t expired. If your invention contains every characteristic of the patented one, you may be charged with literal infringement. It won't matter if your invention is a process that has additional steps or doesn’t work as well as the patented process. Likewise, even if you prove that you did not know the patent existed, you can still be found guilty of direct infringement.
Induced infringement is a form of indirect patent violation that involves third parties. It requires proof of harmful intent. You induce infringement by encouraging others to perform acts of direct infringement. For example, assume a patent exists for the consumption of yogurt as a digestive aid. If you are a supplier of yogurt and you advertise that yogurt helps people digest their food, you can be charged with induced infringement. Your advertisements induced consumers to directly infringe a patent by using the yogurt as the patent intended.
Contributory infringement is another indirect act that occurs when an infringer sells materials to be used with a patented invention. An example would be a dough-kneading attachment designed for use with a patented artisan bread mixer. To prove contributory infringement, a patent holder must show that the accused infringer knew the materials would be used to infringe a patent and that there are no other commercial uses for the materials. If the accused materials are made up of several parts and not every part infringes a patent, the alleged infringer can still be found guilty.
Doctrine of Equivalents
If you attempt to avoid violating a patent by making or selling an invention that's similar but not identical, you can be charged with patent infringement under the “Doctrine of Equivalents.” The equivalency doctrine permits a court to find infringement if your invention performs “substantially the same function in substantially the same way to obtain the same result” as a patent. The doctrine does not require the patent holder to prove you acted with intent.
If you make or sell an invention without having first taken steps to confirm it's not patent-protected, you can be convicted of willful infringement and required to pay damages three times greater than the patent holder’s actual damages. To establish willful infringement, the patent holder must prove, first, that you took a risk to infringe his patent and, second, that you knew of the risk or it was obvious enough that you should have known.