The Race for a Zero-Power Sensor
Before the tech, there was a contest. The United States Department of Defense needed a wireless sensor with near-zero power consumption to support a network capable of detecting vehicle traffic across a broad area. Existing networks required a constant source of power within each sensor to remain active, an implementation that incurred significant maintenance and energy costs; a problem that was not limited to the needs of the DOD.
Matteo Rinaldi, Director of the SMART Center and professor at Northeastern University, saw an opportunity in this contest and decided to pursue the challenge. He and his team of researchers not only developed a working prototype in a year’s time, an impressive feat in its own right, but developed a technology so versatile as to have since been adapted into the fields of flame detection, agriculture, and surveillance in the years after the contest’s conclusion.
What Rinaldi and his team developed in response to the DOD’s challenge was a sensor that possessed the ability to turn itself on only when there was a signal to transmit. Think of it like a motion sensor that switches the lights in a room on and off: the lights remain off until someone walks in and activates the sensor. Rinaldi’s sensor works in a similar way, except it does not require a power source to monitor whether or not the target stimulus is present in the environment, thereby consuming no power in its standby state.
Rinaldi’s sensors contained two functionalities as required by the contest challenge: i) the ability to detect traffic and ii) the ability to transmit a signal indicating that traffic has been detected. To connect the network of wireless sensors, each device necessitated a radio transmitter to communicate between other sensors in the network, a tech which, while important, required modification rather than raw innovation in Rinaldi’s implementation. The sensor also needed a method of detecting vehicle traffic, a challenge which elicited a more creative approach.
Both parts of the sensor share a novel innovation and contain the core aspect of Rinaldi’s design: a passive switch that requires no external power source to detect incoming signals. To monitor vehicle traffic, the switch was adapted to activate in the presence of a specific infrared signal emitted in the exhaust of passing vehicles. The switch repurposes the small amount of energy in the exhaust’s fumes to connect a larger internal power source to the radio transmitter, which then communicates a signal to other sensors in the vicinity. Similarly, the radio-frequency receiver is fitted with a passive switch that, rather than responding to infrared, senses the radio waves put out by other transmitters in the network and connects the internal battery to the transmitter in its own device, thus relaying the signal throughout the network.
Since these switches are passive, the sensors could effectively remain ‘off’, consuming no power until a signal is detected. The resulting wireless network provides a system of sensors that could run much longer than its active counterparts, preserving overall battery life across the entire network and cutting costs in both maintenance and power consumption.
Rinaldi and his team quickly realized that this sensor could have applications beyond the scenario proposed by the Department of Defense. Throughout the contest, the sensor garnered interest from organizations such as the Gates Foundation, spurring further development and proving broader applicability.
Eventually, Rinaldi and his team managed to modify their sensors for use in agriculture, monitoring personnel, and flame detection. Each of these sensors utilize a switch similar to the switches produced for the DOD, except the switches in the modified devices respond to unique signals from specific sources. Due to the immense versatility of the switch, there may exist more applications where these sensors outperform existing wireless systems that have not yet been considered; their impact has yet to be fully realized.
Written by Joseph Burns
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Feature image – Photo courtesy of José Miguel S. This is a derivative work licensed under the Creative Commons 1.0 license found here.
Image 1 – Photo courtesy of Daniel R. Blume. This is a derivative work licensed under the Creative Commons 2.0 license found here.
Image 2 – Photo courtesy of Nenad Stojkovic. This is a derivative work licensed under the Creative Commons 2.0 license found here.
Image 3 – Photo courtesy of Anthony Clochard. This is a derivative work licensed under the Creative Commons 2.0 license found here.