Smartphones have a scaling problem. Specifically, the radio-frequency (RF) filters that every phone—and every wireless device in general—uses to extract information from isolated wireless signals are too big, too flat, and too numerous. And without these filters, wireless communications simply wouldn’t work at all.“They are literally the entire backbone of wireless systems,” says Roozbeh Tabrizian, a researcher at the University of Florida in Gainesville.So Tabrizian and other researchers at the...