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Scientists are working to develop increasingly smaller IoT devices, such as microscopic sensors capable of tracking almost any object. These sensors have tiny batteries that are hard to replace, so engineers are integrating wake-up receivers to keep devices in "sleep" mode when not in use, extending battery life.

Researchers at MIT have created a new wake-up receiver, just a tenth the size of previous ones, consuming only a few microwatts of power. This receiver also includes a built-in authentication system that protects the device from a type of attack that could quickly drain the battery.

The MIT team built a receiver using terahertz waves, about a tenth the wavelength of radio waves, measuring just 1 square millimeter. This wake-up receiver was used to demonstrate efficient wireless communication, with a signal source located several meters away.
The wake-up receiver could be used in micro-robots that monitor environmental changes in small or dangerous areas. Using terahertz waves, the receiver can be applied in emerging applications, such as field-installable radio networks that collect localized data. "Using terahertz frequencies, we can create a very small antenna and integrate these antennas onto a chip, creating a fully integrated solution," says Eunseok Lee, the study's lead author.

The wake-up receiver, measuring only 1.54 square millimeters and consuming less than 3 microwatts, uses a dual-antenna configuration, maximizing performance and facilitating signal reading. The chip amplifies a terahertz signal and converts analog data into a digital signal for processing. The digital signal carries a symbol, which is a string of bits (0s and 1s). If the symbol matches, the wake-up receiver activates the device.

To increase security, researchers added an authentication block that randomizes the device's symbol, using a key shared with trusted senders. This key acts as a password to send the right signal. The team tested the receiver's sensitivity, sending terahertz signals up to 10 meters away. "We performed demonstrations at distances of 5 to 10 meters, larger than usual, using a small device with low energy consumption," says Lee.

However, for maximum efficiency, terahertz waves must strike the detector directly. If the chip is positioned at an angle, some of the signal is lost. Therefore, researchers paired the device with a recently developed steerable terahertz array by Han's group, to precisely direct terahertz waves. This way, communication could be transmitted to multiple chips with minimal signal loss.

In the future, Lee and colleagues want to address signal degradation issues. If they can maintain signal strength when the receiver chips move or tilt slightly, device performance could be improved. They also want to test the wake-up receiver in extremely small sensors and adapt the technology for use in real devices.

"We have developed a rich portfolio of technology for future millimeter-sized sensing, tagging, and authentication platforms, including terahertz backscattering, energy collection, and electric beam steering and focusing. Now, this portfolio is more complete with Eunseok's first terahertz wake-up receiver, which is essential for saving the limited energy available on these mini-platforms," says Han.

Other co-authors include Muhammad Ibrahim Wasiq Khan, a PhD student in 2022; Xibi Chen, a master's student in EECS; Ustav Banerjee, a PhD student in 2021 and assistant professor at the Indian Institute of Science; Nathan Monroe, a PhD student in 2022; and Rabia Tugce Yazicigil, an assistant professor of electrical and computer engineering at Boston University. 

Team PromoBusiness

Photo: Jose-Luis Olivares/MIT with figure courtesy of the researchers