Newly developed tiny non-dispersive infrared (NDIR) gas sensor with metamaterials detects gases at low concentration utilizing minimum energy.

FREMONT, CA:  Researchers have developed a tiny gas sensor which is the smallest of all with no moving parts and operating with minimum energy. It is the first fully integrated sensor developed for IoT application and smart home devices. The newly developed non-dispersive infrared (NDIR) gas sensor comprises of engineered synthetic materials known as metamaterials. The material used drives away the cost spent for dielectric filter while reducing the size and energy consumption of the device. The sensor design is simple, robust, and efficient that can be employed in low-cost markets such as automotive and consumer electronics. Other potential applications include future medical diagnostics and monitoring equipment.

Conventional NDIR sensors work by glowing infrared light through air containing the gas molecules to be measured, in a chamber. The light is allowed to fall on a detector, and an optical filter p

laced in front of the detector detects the wavelength absorbed by the particular molecule, the concentration of which is measured by eliminating the remaining light falling on it. The resultant light to which the detector is exposed gives the concentration of gas in that air. NDIR sensors are typically used to measure air quality, assess vehicle exhaust, detect gas leaks, and support various medical, industrial, and research applications.

This conventional infrared light source and detector have been replaced with microelectromechanical systems (MEMS) technology. In the newly built sensor, researchers integrate metamaterials onto a MEMS platform to further miniaturize the NDIR sensor and thereby, enhance the optical path length. The use of metamaterials simplifies the sensor’s design comprising three vital parts—metamaterial thermal emitter, an absorption cell, and, a metamaterial thermopile detector.

The generation of infrared light is such that when the microcontroller periodically heats the hotplate; metamaterial thermal emitter emits light that travels through the absorption cell and is detected by the thermopile. This, in turn, produces an equivalent electronic signal to that of absorbed light collected by the microcontroller, which streams the data to a computer.

The key to the design is a type of metamaterial known as a metamaterial perfect absorber (MPA) comprising a complex, layered arrangement of copper, and aluminum oxide. This structure enables MPA to absorb light coming from any angle. Researchers designed a multi-reflective cell that reflects the infrared light many times. 

The conventional NDIR sensors require light to pass through a chamber, which is comparatively a few centimeters longer than the newly designed sensors to detect gas at extremely low concentrations. The new design optimizes light reflection to achieve the same sensitivity level in a cavity that is just over half a centimeter long.

The researchers tested the device’s sensitivity by measuring varying concentrations of carbon dioxide in a controlled atmosphere. The device detected carbon dioxide concentrations with a noise-limited resolution of 23.3 parts per million, a level on par with commercially available systems. The energy utilized by the sensor is only 58.6 millijoules of energy per measurement, which is about a five-fold reduction compared to commercially available low-power thermal NDIR carbon dioxide sensors.