Researchers at Stanford University are developing a new way to extend the battery life of wireless devices. They have developed a new solution that can wake up or shut-off the receiver of a wireless device or smart phone at a moment’s notice.Researchers, Angad Rekhi, a graduate student in the Arbabian Lab at Stanford, and Amin Arbabian, assistant professor of electrical engineering, have developed a wake-up receiver that turns on a device in response to incoming ultrasonic signals – signals outside the range that humans can hear. By working at a significantly smaller wavelength and switching from radio waves to ultrasound, this receiver is much smaller than similar wake-up receivers that respond to radio signals, while operating at extremely low power with an extended range. This wake-up receiver has many potential applications, particularly in designing the next generation of networked devices, including so-called “smart” devices that can communicate directly with one another without human intervention.Once attached to a device, the wake-up receiver listens for a unique ultrasonic pattern that tells it when to turn the device on. It needs only a very small amount of power to maintain this constant listening, so it still saves energy overall while extending the battery life of the larger device. A well-designed wake-up receiver also allows the device to be turned on from a significant distance.Scaling down the size of the wake-up receivers while extending its range is a major challenge. But this challenge is worth pursuing, because solving this problem can enable scalable networks of wake-up receivers working in everyday environments. In order to miniaturize the wake-up receiver and drive down the amount of power it consumes, the researchers made use of the highly sensitive ultrasonic transducers provided by the Khuri-Yakub Lab at Stanford, which convert analog sound input to electrical signals. With that technology, the researchers designed a system that can detect a wake-up signature with as little as 1 nanowatt of signal power, about 1 billionth the power it takes to light a single old-fashioned Christmas bulb.The work branched off from a previous Arbabian Lab creation, a tiny chip dubbed the “ant-sized radio” that can send and receive signals over radio waves without a battery. The ant-sized radio has the advantage of being wirelessly powered but needs to remain relatively close to the transmitter with which it communicates. The group has since published a way of using ultrasound to extend the powering range of devices like the ant-sized radio, but that distance is still limiting.By comparison, the ultrasound wake-up receiver requires a battery but has much greater range than the wirelessly powered devices, while still maintaining a long lifetime due to extremely low power draw. These two technologies – wireless power and wake-up receivers – would likely serve different purposes but both hint at a turning point in devices that make up the internet of things. In light of a long-promised future where interconnected, autonomous, widespread, unobtrusive technologies make lives easier, the networked devices available now, like video doorbells and app-enabled lights, seem like rather subtle advances. The researchers believe that technologies like theirs could help reduce the gap between the internet of things as we know it and the internet of things that could be.