Analysis of working characteristics of plasma-based infrared sensor

In order to capture meaningful signals in the surrounding environment, such as specific vibrations, sounds or spectra, most sensors must be active at all times. As you can imagine, this type of work feature greatly limits the life of a single sensor and also brings higher maintenance costs to the entire system.

Researchers at Northeastern University invented a plasma-based infrared sensor that automatically operates when an inductive task needs to be performed and then automatically shuts down when it is not needed (to save energy and extend life). The study was published in the journal Nature Nanotechnology.

Figure 等离子体 Plasma-based infrared sensor (Source: Northeastern University / Nature Nanotechnology)

This device is an event-driven sensor. Normally it is dormant, but it is always in a vigilant state and will only start when a specific signal (signal of interest) is detected. And it only consumes power when it starts up.

Matteo Rinaldi, an assistant professor at Northeastern University in the United States, explained that when infrared light is applied to the device, it is absorbed by the integrated ultra-thin plasma infrared light absorber and converted into heat. This increases the temperature of the sensitive components, causing them to bend and come into contact due to thermal expansion, thereby enabling the detection function.

The ultra-thin plasma infrared absorber is formed by a stack of three materials: the upper layer is a gold nanosheet (50 nm) with a dielectric layer (100 nm) in the middle and the lower layer is a platinum nanosheet (100 nm). After the nanostructure absorbs electromagnetic waves of a specific wavelength, a highly localized gap plasma is excited. These localized plasmas effectively confine the light to a narrower dielectric gap (the gap between the intermediate dielectric layer and the upper and lower metal layers), which in turn causes a high and rapid temperature increase of the absorber.

The gold nanosheet described above is used as a miniature mechanical transfer switch to extract energy from the monitoring signal (ie, absorption of infrared light of a specific wavelength). The plasma plays a key role in the light absorption process of the mechanical transfer switch. Plasma refers to an electric wave that propagates along a metal surface generated by the interaction of free-vibrating electrons existing on a metal surface with photons. Thanks to this property, strong and selective light absorption can be achieved in the microstructure.

Rinaldi said, "It is precisely because of this special selective absorption that our device can be triggered by light in a narrower wavelength range that is pre-set. In addition, based on the settable light absorption characteristics, on the same chip Multiple switches can be triggered by different wavelengths of light to detect and identify different spectral signals."

The Rinaldi team called the sensor developed by the Rinaldi team "infrared digital sensor" because it can detect infrared radiation with a specific intensity and wavelength. It detects and identifies infrared radiation, turns it into a start signal, and does not consume any energy during standby.

This sensor can be used to detect invasive infrared sources such as human bodies and fuel-powered vehicles. It can also be used to detect heat sources (such as flames, explosions, etc.) and trigger an alarm. This technology can also be used for remote control and communication if combined with a laser source. In all of these applications, the sensor can be used as a zero-powered trigger to activate the next stage of electronics (such as wireless communication modules or more sophisticated sensing and signal processing systems).

To be commercialized, vacuum packaging of sensors is critical. Because they require vacuum operating conditions, high thermal insulation is achieved to better perform their performance.

Although there are still some problems, they have developed a battery-powered palm-sized wireless infrared sensor node that consumes almost no power during standby (only 2.6 nW). “At present, our devices are sensitive enough in many applications (detection limit is 500 nW),” Rinaldi said. However, if lower detection limits can be achieved, the application can be further expanded.”