New sensors will be able to distinguish between a wide variety of occurrences, including fires, explosions, or gunshots

By Gary Elinoff, contributing writer

No matter
how efficient electronic circuitry may be, active electronics must always
consume some power. With the advent of the IoT, there will
be more instances of sensors residing in remote or dangerous areas where
maintenance, including battery charging and replacement, will be difficult or
impossible. Supplying power to these sensors, perhaps for years at a time, will
present problems. To get past this issue, a new type of sensor based on
plasmonic nanostructures has been proposed that doesn’t require actively
powered electronics at all. In fact, the presence of the condition that the
sensor is on alert for is what, in itself, turns the sensor on.

Plasmonic
nanostructures are nano-sized structures that react to a very specific
frequency, just like the way a radio tuned to 100 MHz only picks up signals
broadcast at the frequency. The sensors were developed for DARPA by a team from
Northeastern University headed by Professor Matteo Rinaldi using this principle to react to a distinct frequency — wavelength — of infrared light.

As described
by Troy Olsson, manager of DARPA’s N-ZERO program, the sensors will
absorb the infrared energy, turn it into heat, and the heat will cause part of
the structure to bend. The bending causes that part of the structure to impact
another part, effecting an electrical connection. The sensor, which might have
lain dormant for months or even years, comes alive, and only then will the
circuitry begin to draw power. Rinaldi and his team describe the device as a “plasmonically enhanced
micromechanical photoswitch.”

Micromechanical_Photoswitch

A “plasmonically enhanced
micromechanical photoswitch.” Image source:
DARPA.

This
frequency-specific behavior means that the sensors can be tuned to identify
specific IR sources. Gasses present in vehicle emissions, such as CO, CO2, or even water, generate
infrared profiles, as do the oxides of nitrogen, NOX, and sulfur, SOX.
The same is true for the gasses generated by gunshots, fires, and explosions.
Olsson explains that a sensor can be constructed to look for any one of those
individual gas’s infrared profiles.

But the
interesting fact is that each type of event generates its own “spectrum” of gas
emissions. As one might imagine, then, the outputs of sensors tuned for
different gasses can be “wired” together in the manner of digital logic to
react only to a specific type of event. If a fire exhibits two or three gasses,
all three will be required to trip the sensor. Similarly, gunshots and
explosions, with their own unique gas emission profiles, can be targeted with
another set of sensors tuned for each relevant gaseous component. Thus,
although originally developed for military purposes, these sensors will have
widespread commercial applications, too.