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DARPA’s Dormant but Always-Alert Sensors

DARPA has new sensor that use virtually zero stand-by power. Then ovel sensors could improve situational awareness for warfighters, add smarts to Internet of Things. A research team at Northeastern University, led by Electrical and Computer Engineering Associate Professor Matteo Rinald has built sensors remain dormant and unattended but always alert, even for years, without drawing on battery power.

They are plasmonically-enhanced micromechanical photoswitches.

Nature Nanotechnology – Zero-power infrared digitizers based on plasmonically enhanced micromechanical photoswitches

“What is really interesting about the Northeastern IR sensor technology is that, unlike conventional sensors, it consumes zero stand-by power when the IR wavelengths to be detected are not present,” said Troy Olsson, manager of the N-ZERO Program in DARPA’s Microsystems Technology Office. “When those IR wavelengths are present and impinge on the Northeastern team’s IR sensor, the energy from the IR source heats the sensing elements which, in turn, causes physical movement of key sensor components. These motions result in the mechanical closing of otherwise open circuit elements, thereby leading to signals that the target IR signature has been detected.”

The sensor is a showcase of clever physics and engineering, including a grid of nanoscale patches whose specific dimensions limit them to absorb only particular IR wavelengths. “The charge-based excitations, called plasmons (that can be thought of somewhat like ripples on the surface of water), are highly localized below the nanoscale patches and effectively trap specific wavelengths of light into the ultra-thin structure, inducing a relatively large and swift spike in its temperature,” Rinaldi explained. These temperature spikes, in turn, lead to an upstream sequence of events that culminates in circuit-completing deformations of other parts of the sensor.

“The technology features multiple sensing elements—each tuned to absorb a specific IR wavelength,” Olsson noted. “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.”

Consider the identification of vehicles from their IR emissions. Engines that burn gasoline or diesel fuels emit specific compounds in their exhaust gases. Among these compounds are CO2, CO, H2O, various oxides of nitrogen and sulfur (NOx and SOx, respectively), and hydrocarbons such as methane. “As a result, the infrared emission spectra of the heated tailpipe gases coming out of vehicles such as trucks, cars or aircraft can by themselves act as a signature specific to a vehicle type,” explained Zhenyun Qian, who has been working with Rinaldi and other research team members on the N-ZERO program.

A primary goal of the N-ZERO program is to develop fundamental technologies that open the way to new and more capable sensor systems relevant to national security. The NU team points out in its Nature Nanotechnology paper that the same technology could become important over the coming years as the Internet of Things expands to include hundreds of billions of devices, ranging from cars, to appliances, to remotely deployed sensors. “The capability of consuming power only when useful information is present will result in nearly unlimited duration of operation for unattended sensors deployed to detect infrequent but time-critical events, with a groundbreaking impact on the proliferation of the Internet of Things,” the Northeastern researchers predict in their paper.


Structure of the PMP and working principle.

Abstract

State-of-the-art sensors use active electronics to detect and discriminate light, sound, vibration and other signals. They consume power constantly, even when there is no relevant data to be detected, which limits their lifetime and results in high costs of deployment and maintenance for unattended sensor networks. Here we propose a device concept that fundamentally breaks this paradigm—the sensors remain dormant with near-zero power consumption until awakened by a specific physical signature associated with an event of interest. In particular, we demonstrate infrared digitizing sensors that consist of plasmonically enhanced micromechanical photoswitches (PMPs) that selectively harvest the impinging electromagnetic energy in design-defined spectral bands of interest, and use it to create mechanically a conducting channel between two electrical contacts, without the need for any additional power source. Our zero-power digitizing sensor prototypes produce a digitized output bit (that is, a large and sharp off-to-on state transition with an on/off conductance ratio over one trillion and subthreshold slope over 9 dec nW–1) when exposed to infrared radiation in a specific narrow spectral band (∼900 nm bandwidth in the mid-infrared) with the intensity above a power threshold of only ∼500 nW, which is not achievable with any existing photoswitch technologies.

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