Patent claims can’t be ambiguous. Under 35 USC 112, the claims (combined with the specification and prosecution history), must clearly teach the invention’s scope.
The government, to encourage science and the useful arts, grants limited monopolies for new inventions for limited periods. Part of the bargain is that the inventor must disclose their ideas to the public. Another part of the deal is that inventors must teach skilled workers precisely what they are claiming.
As previously discussed, failure to teach claims with patentable material will get you a 35 USC 101 rejection. Failure to prove that your claims are novel will get you a 35 USC 102 rejection. Failure to verify that your claims are not obvious will get you a 35 USC 103 rejection. Here we are talking about another common rejection, a 35 USC 112(b) “claim ambiguity” rejection.
What makes a patent claim ambiguous?
To understand this better, let’s look at the 2014 SCOTUS Nautilus v. Biosig and the 2015 Federal Circuit Biosig v. Nautilus decisions. The present law is based on a dispute about a biomedical device patent for a “Heart Rate Monitor.”
Biosig patent 5,337,753: In 1992, Biosig Instruments obtained a patent on an improved heart rate monitor. In this device (see figure), a user grips a cylindrical bar (and electrodes) using both hands. In particular, each hand grips two separate electrodes. Each hand grips one live electrode (9, 13) and one common electrode (11, 15). This arrangement, with suitable electronics, helps reduce noise and improve the heart rate signal.
The setup is well suited for exercise equipment. So much so that Nautilus Inc. decided to use this in their equipment. Biosig sued. Nautilus countered that the Biosig claims were invalid under 35 USC 112. Biosig claimed that the live electrodes and the common electrodes were in a “spaced relationship”. However, Nautilus argued that “spaced” was indefinite, and the clams were therefore invalid.
This otherwise routine biomedical instrumentation patent went up to the Supreme Court! SCOTUS was uninterested in the technology. But, they complained that the earlier 35 USC 112 “insolvably ambiguous” standard had problems. Instead, they articulated the present 35 USC 112 rule. There is a problem when:
“claims, read in light of the patent’s specification and prosecution history, fail to inform, with reasonable certainty, those skilled in the art about the scope of the invention.”
SCOTUS then sent the patent back to a lower court (the Federal Circuit) for further analysis.
So SCOTUS used this to change the 35 USC 112 criteria, but didn’t otherwise rule? What happened?
The Federal Circuit examined the patent’s underlying technology in more detail. They noted that the Biosig patent taught an upper bound on spacing. This was that the live and common electrode separation must not be greater than the width of the user’s hand.
But was there a lower limit? No explicit dimensions were given, but the patent is assumed to be operative. Here, the Federal Circuit gave credit to the inventor’s declaration (presented after filing but during prosecution). During prosecution, the inventor told the examiner that a skilled artisan would configure the spacing to minimize a differential output. If the spacing is too close, this won’t work. So there is a functional lower limit as well. Skilled workers can indeed understand the scope. So the patent survived both SCOTUS and the Federal Circuit!
The Supreme Court probably chose this patent as a “test case” because it was otherwise unexceptional. However, the case also provides a useful object lesson on patent drafting and prosecution. It is good to give limits. Note further the importance of declarations submitted during prosecution. Consider such statements, no matter which side of the argument you are on.