“Processors are overdesigned for most applications,” says University of Illinois electrical and computer engineering professor Rakesh Kumar. It’s a well-known and necessary truth: In order to have programmability and flexibility, there’s simply going to be more stuff on a processor than any one application will use. That’s especially true of the type of ultralow power microcontrollers that drive the newest embedded computing platforms such as wearables and Internet of Things sensors. These are often running one fairly simple application and nothing else (not even an operating system), meaning that a large fraction of the circuits on a chip never, ever see a single bit of data. Kumar, University of Minnesota assistant professor John Sartori (formerly a student of Kumar’s), and their students decided to do something about all that waste.
Researchers at the Coordinated Science Laboratory have designed a sound that is completely inaudible to humans (40 kHz or above) yet is audible to any microphone. The sound combines multiple tones that, when interacting with the microphone’s mechanics, create what researchers call a "shadow," which is a sound that the microphones can detect.