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IoT battery life drastically lengthened by ultrasound wakeup call

Waking up ‘internet of things’ (IoT) devices using inaudible ultrasound patterns could drastically improve standby battery life according to a team at Stanford University in California.

The system works by using a wake-up receiver that can turn on a shut-off device at a moment’s notice after responding 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 and with extended range.

This wake-up receiver has many potential applications, particularly in designing the next generation of networked devices, including smart devices that can communicate directly with one another without human intervention.

Once attached to a device, the 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.

“As technology advances, people use it for applications that you could never have thought of. The internet and the cellphone are two great examples of that,” said Angad Rekhi who worked on the project. “I’m excited to see how people will use wake-up receivers to enable the next generation of the Internet of Things.”

Arbabian said that designing these electronic devices posed a number of challenges. “Scaling down wake-up receivers in size and power consumption while maintaining or extending range is a fundamental challenge,” he said. “But this challenge is worth pursuing, because solving this problem can enable scalable networks of wake-up receivers working in our everyday environment.”

In order to miniaturise 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 analogue 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.

Given the increased interest in networked devices, researchers and industry organizations are starting to define what features and techniques will become standard. Regardless of whether this ultrasound wake-up receiver is among these standard designs, it is likely wake-up receivers of some kind will be integrated into commercial applications soon, Rekhi said.

This 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.

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.

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