Why MEMS-based IR sources are superior to conventional IR sources


Source: Axetris Ag

MEMS-based sources have many advantages over other technologies, like the bulb, wire wound sources or filament IRS. MEMS-based IRS are especially superior in regard to speed and efficiency. Key factors when it comes to real-time monitoring.

Connecting physical objects to the virtual world opens a whole field of new business opportunities to manufacturers. Industry 4.0 does not just mean new possibilities to automate procedures. It is also a channel to offer new services to customers via near-instantaneous data transfer. Comprehensive and precise data allow for predictive forecasting. Machines can be serviced in exact intervals, minimizing downtime. Whether in the field of manufacturing, Internet of Things (IoT) or sensors worn on the body, so-called wearables, one of the principal challenges remains real-time monitoring. Reliable and extremely fast sensors are indispensable, as they form the basis for gathering data. The state of the art are very small, highly integrated, battery-powered solutions that work autonomously and transmit their data through a wireless network. Energy consumption, efficiency as well as heat management are key factors in these applications.

The “Bulb” type IR source is a miniaturized light bulb. It is often employed in low cost NDIR gas sensors. A common application is the measurement of interior air quality in HVAC. The spiral emitter is encased in glass, which is disadvantageous because transmission through the glass is limited to the spectral band

The well-established bulb source is low-priced yet short-waved, slow and susceptible to shocks.

Open wire-wound IR sources do not share the limitations on transmission, but they have a significantly reduced life span of no more than a few years, rendering them unsuitable for monitoring applications. They are most often employed in analytical devices, where a very high emission performance is indispensable, while energy consumption is not a limiting factor as the device is directly connected to the power grid. They do not have good emissivity across the whole MIR spectrum, however, and their emission patterns are highly divergent.

Wire wound sources are bright but have a high energy consumption and cannot be modulated at high frequencies.

Filament IR sources are most similar to MEMS-based sources, as they are also a surface emitters. The materials used in this model allow for a high operating temperature. This produces great amounts of excess heat (apparent power) which must be dissipated. This is a limiting factor, especially for compact designs. Furthermore, they have a high energy consumption, rendering battery operation unfeasible. The high final temperature lead to long warm-up and warm-down periods, implying smaller reachable modulation frequencies.

Filament IR sources are – similar to wire wound IR sources – bright but also slow (only limited modulation possible).

MEMS-based sources have many advantages over these technologies. They are especially superior in regard to speed and efficiency. Surface emitters possess a dedicated emission layer, rendering them highly energy efficient across the entire spectral band. This makes for an optically efficient system design.

The monolithic structure provides high resistance against shocks and vibration, while also being much easier to integrate. Undesired changes in emission direction due to misalignment are impossible, making them suitable for applications in the automotive industry and measurements in harsh environments.

MEMS based sources are very bright and their speed makes a mechanical modulator unnecessary. The EMIRS50 source has excellent modulation properties, even at frequencies up to 100 Hz. These properties are indispensable, especially when measuring dynamic processes at real-time. It also has a highly reduced energy consumption, especially compared to a bulb source, as the source only needs to be powered for a short time. Due to the short time constants, the necessary output power is reached after only a few milliseconds.

Due to these advantages, MEMS-based sources are suitable for a large number of applications, from medical technology to manufacturing, Internet of Things and wearables. These broad possibilities for applications open possibilities for modular designs and the possibility of implementing Multi Gas NDIR measuring systems.

The advantages of Axetris MEMS-based IR Sources at a glance:

  • High emissivity for the entire spectral range of application
  • High electrical-optical efficiency
  • High modulation depth 
  • Mechanical stability: Insensitive to shock & vibration
  • Long Lifetime and high reliability
  • Stable mechanical alignment after shocks

These advantages turn MEMS-based IRS into the technology of the future.

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