Midwave-wavelength infrared (MWIR)

Infrared cameras are categorized or labeled in many ways including camera design (handheld, fixed install, iphone), performance attribute (high speed, high sensitivity, high resolution) or application (non-destructive testing, high temperature metal imaging and measurement, gas imaging, microscopic imaging).

Another approach to categorize cameras commonly used for scientific applications is to identify the spectral region from which the camera receives the infrared emissions used to present its infrared image.  Midwave infrared (MWIR) cameras feature detectors responsive to infrared radiation in the middle of the infrared spectrum and are typically available in the spectral range between 3 and 5 µm.

Mid-wave infrared cameras were sold in large quantities before the release of uncooled long wave microbolometer infrared detector technology to support predictive maintenance and other emerging infrared applications in the early 80’s.  These cameras made use of InSb (indium antimonide) detectors that were cooled thermoelectrically.  They commonly incorporated prism scanning systems that were necessary to produce thermal images from small linear arrays before affordable two-dimensional detector arrays became available in production quantities.

Although impractical when compared to today’s solid state long wave uncooled cameras, these early infrared cameras were much easier to deploy than cameras requiring liquid nitrogen and were largely adopted by utilities and manufacturing facilities for predictive maintenance programs.  Higher resolution variants of these midwave cameras supported research and development applications.

Today, midwave infrared cameras are sold mostly for research purposes or for special applications where spectral response in the mid wavelength is required.

Midwave infrared cameras are popular for demanding research applications that may require high resolution, high thermal sensitivity or high-speed data acquisition.  Although new midwave superlattice infrared detector-equipped infrared cameras are now available, the higher quantum efficiency of Indium Antimonide (InSb) midwave detectors make them a more popular choice when high sensitivity or high speed is important.

These cryogenically cooled midwave infrared cameras are very expensive but they are a viable solution when data collection at 1000 hz. to 3000 hz. (full frame) is required on ambient (and above) temperature targets.  Applications served by these cameras include defense related research on thermal signatures of moving targets, high-speed railway component measurement, tensile testing and munitions testing.

Not all midwave specific applications require expensive high speed hypersensitive cooled detector based cameras.

Measuring the refractory temperatures or the tube temperatures in a process furnace is a challenging application because the products of combustion attenuate the infrared signal particularly when long wave cameras are used to collect thermal image and temperature information.  Carbon dioxide, water vapor and other gases absorb the signal in the same wavelength of the LWIR camera spectral response reducing image quality and measurement accuracy.  Special design midwave cameras with spectral filters tuned to 3.9 µm capture radiating temperatures in a spectral region where attenuation from these gases and vapors is minimal.

These special design midwave cameras make use of microbolometer detectors where the primary detector response is in the long wavelength spectral region.  However, because the typical targets on the inside of a furnace are in excess of 700° Celsius, the long wave response of these detectors can be filtered out leaving only the midwave response region of the detector active.  Even though the midwave response on these detectors is much less than the response in the longer wavelength region, the intensity of the radiation from interior process tubes or refractory walls is more than enough to produce clear thermal images and accurate temperature measurements.

Infrared cameras with midwave detectors will likely remain a small portion of the infrared camera market for the foreseeable future, but will fill an important role for research and development and other special applications served best by midwave detector based cameras.