Today’s sensors have been adapted to do some pretty incredible things, from discerning sound and radio signals to discriminating light wavelengths. The issue is that these sensors require power to operate, whether it is from batteries, biofuel, or sunlight. Along with power consumption are problems with sensors always being on, such as lifetime and maintenance. These issues are especially apparent when sensors are placed in remote areas or underground.
Recently, a research article published in the journal Nature Nanotechnology describes a new type of sensor that has overcome these limitations by consuming near-zero power when not acted upon by the desired sensing range. The sensor is effectively asleep, while capable of sensing events at the same time.
"Tuning" Plasmonic Nanostructures to Be Sensors
The research team responsible for the ambitious sensor hail from Northeastern University and are led by Matteo Rinaldi, an associate professor of electrical and computer engineering. They developed the new smart sensor for the Defense Advanced Research Projects Agency (DARPA) for the N-Zero program, though it has a myriad of applications outside military use.
The technology is based on the use of plasmonic nanostructures. These plasmonic nanostructures are nano-sized metal patches that are used as plasmonic devices in that they react to a specific range of light to oscillate and expand. In their research, the team tuned their nanostructures to take the energy of a distinct wavelength of infrared light. This caused the metal patches on metal switches to absorb heat, bending the switch to create an electrical connection.
While there was no infrared signal, the devices consumed no power. When there was a signal, however, the device was powered by the infrared light. Hence, DARPA calls the sensors "dormant" until activated.
One of the metal patches that react to a specific range of light. Image courtesy of DARPA.mil.
"The technology features multiple sensing elements—each tuned to absorb a specific IR wavelength," said Troy Olsson, who manages the sensor program at DARPA. "Together, these combine into complex logic circuits capable of analyzing IR spectrums, which opens the way for these sensors to not only detect IR energy in the environment but to specify if that energy derives from a fire, vehicle, person or some other IR source."
Applications of N-ZERO Sensors
Impressively, the sensor can also be tuned to sense a myriad of very specific events. One specific test was run on the exhaust coming from a car. The fumes have a specific infrared frequency which the team was able to analyze and target. They then proceeded to design the sensor with patterned gold patches that would absorb the target infrared radiation causing the metal switch to bend, forcing the contacts together and ultimately producing a signal.
Our current smart sensors aren’t capable of discerning signals unless actively powered, and that’s what makes this development so important. While initially designed for DARPA and its use is national security, the sensors can easily be tuned to detect other practical things such as chemicals, magnetic fields, light, and radio signals.
While there are still some engineering issues to work out, the team did design a palm-sized sensor that had a near-zero power consumption of 2.6 nano Watts. The team is currently working on decreasing the infrared detection minimum which could enable the sensors' use in even more applications.
“If we have all these sensors embedded in the infrastructure of the city, that would increase awareness, making everyday life safer and more efficient,” said Rinaldi. “That’s the vision.”