Small is Beautiful - Case Study

The versatility and cost savings to be gained from miniaturised optical gas measurement systems.
To reduce system costs in the field of optical gas measurement there is an ongoing trend for miniaturisation. One key element for optical gas detection is an IR-source providing a high and stable optical output power, based on low electrical power consumption. Optical stability can be achieved with a broadband emitter which is suited for a wide range of gases and applications. We report here on a thermal broadband IR source produced in MEMS Technology. This results in an infrared source of low power consumption, low cost and small size. Because of its stability and the ability of fast modulation, a high signal-to-noise ratio can be achieved.

Cost considerations
Saving system costs is one of the major driving forces in the optical gas detection market. Miniaturisation of the system helps here to reduce costs of all the required components. Moreover, miniaturisation can be delivered as a result of low power consumption. Portable and battery driven optical gas measurement systems can be designed in this way and the Axetris IR source’s low power consumption and small
size demonstrate the important features needed for the miniaturisation of such gas measurement systems.

Signal-to-noise
Besides the specifics of miniaturisation the main challenge for an optical gas measurement system is to achieve a good signal-to-noise ratio. Being a key component of the system the IR-source is focused to optimise this ratio by providing an adequate signal with a stable optical output. While the optical power can be maximised by optimising the system’s optical efficiency, signal variations contribute to the noise. Signal variations with respect to temperature variation; in the light spectrum of the source; and variations over the product’s lifetime should be negligible, or at least controllable. For variation control or compensation many system designs use reference signals.

Both low power consumption and an excellent signal-to-noise ratio can be achieved with the EMIRS200 from AXETRIS. The infrared source is a MEMS based black body emitter with broadband emission  (2 to 14μm). With a high emissivity in the Mid-IR and Far-IR range, numerous gases can be reliably targeted.

Low energy consumption
The low power consumption results from MEMS design with a thin membrane. The membrane has a small thermal mass and good thermal isolation to the MEMS-body. Moreover, the thermal time constants for heating and cooling are within milliseconds – so it can be heated up efficiently and fast. With this thermal behaviour short duty cycles can be achieved. In doing so the power consumption is further reduced and battery driven systems can be realised.