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IRnova – New Sensors, New Discoveries

Last Updated Mar 2021
By: Jörgen Städje

Thermal imagers and related infrared systems are important tools for various applications, such as night vision, surveillance, gas detection, firefighting and remote sensing of heat signatures. The Swedish company IRnova is using Myfab to its advantage, making advanced sensors for many of the world’s great manufacturers of thermal imagers.

On a clear day, except it’s in the middle of night

For some applications the thermal signature alone is not enough to detect and identify an object and therefore additional scene information is needed.

The polarization of the infrared light is one property that has proven to provide such additional information. In contrast to regular thermal imaging, the polarization sensitive imaging also collects information from the surface properties of an object, and not only by its temperature and emissivity. Thus, significantly improved contrast and detection capabilities can be achieved when fusing the thermal and polarimetric information in one image.

In the beginning, there was Acreo, a research institute in electronics, optics and related communication techniques (today part of RISE, Research Institutes of Sweden). Originally being part of Acreo, IRnova has been manufacturing detectors since 1986 in the Myfab Electrum Laboratory of KTH in Kista. IRNova was spun off from Acreo in 2007.

IRnova started volume production of QWIP sensors (quantum well infrared photodetector) in 1999 and has been selling OEM products to manufacturers of strategic products, heat cameras, gas cameras and such, ever since. The quality manufacturing machines of Myfab helped a small company to world renown. Production is run in the lab by IRnova’s own staff.

Since then, IRnova also achieved European leadership in another innovative and ground-breaking new detector material called T2SL (or SLS). This technology is the most demanded technology for SWaP infrared imaging applications. T2SL detectors low Size Weight and Power brings high performance infrared capabilities to battery powered and space constrained systems.

Polarised IR

Polarised IR is used to detect unusual surfaces in nature, that is, things that man has created, intentionally or unintentionally. Nature is random, wrinkly, wavy or noisy, whereas man usually creates plane surfaces or resurfaces wavy surfaces into smooth ones. Smooth surfaces changes randomly polarised radiation into linearly polarised. This helps when you want to detect the items below.

Camouflage Denial

All the world’s military forces have long understood that they have to camouflage their vehicles to avoid being detected with heat cameras. Camouflage has to work in the visible, as well as in the 3–7 µm wavelength band.

But it is impossible to hide the fact that tanks are flat and straight, whereas leaves and grass are randomly oriented. So, whereas grass and leaves will reflect randomly polarised radiation, battle tanks and the like will produce linearly polarised IR surfaces, making them detectable with IRnova’s technology.

Pouring Oil upon Troubled Waters

An ordinary heat camera cannot detect oil on the sea surface, as its temperature differs very little or not at all from the water’s. But it is possible to detect differences in wave height, or a flatter surface. The old proverb of “pouring oil on troubled waters” to calm a choppy sea happens to be completely true. Oil is denser than water, and so will decrease the wave height and thereby increase the level of horizontal polarisation of the reflected IR. The image sequence above demonstrates this.

Drone Against Forested Backdrop

Flying drones are difficult to distinguish against a forest backdrop or the sky. At least in visible light. But the wings of a drone will necessarily have to be flat and so will polarise reflected IR, making them easily detectable against the randomly polarised background.

Buried Land Mines

Mine clearing is a dangerous task. There are various ways of detecting mines directly, and then there is the IRnova way. When a mine is buried, the ground is disturbed and finer particles, usually found deeper into he soil are left on the surface. They are small enough to be able to polarise infrared light, and so can be detected with a polarised detector.

Of course, the de-mining staff will have to be fast about it. The effect vanishes after rain, which will disperse the finer particles.

Face Recognition in Darkness

It would have been nice to be able to do face recognition in total darkness, based only on invisible, infrared radiation. Unfortunately, ordinary thermal IR images do tend to smear out the facial features, making the image unsuitable for face recognition algorithms.

If polarisation is taken into account, and one is able to distinguish the angles of the various facial surfaces, one might be able to distinguish between surfaces, hair etc and create an image suitable for facial recognition. There are obvious advantages to this in police and military investigative work, for example. On top of this polarization brings a new set of parameters that hepls identification even in daytime.

The camera creating the imagery above was developed by IRnova in cooperation with researchers at the FOI (Totalförsvarets forskningsinstitut), the Swedish Defense Research Agency. The problem was how to map all the polarisation information available onto one recognisable image. Several methods were investigated, such as imaging the Degree of Linear Polarisation and the Angle of Polarisation and finally a method of fusing the Degree and Angular images was selected.

The image above shows an unusable thermal image to the left, and the final, fused DoLP+AoP image to the right.

Optical Gas Imaging

Humans can’t see gases. This is a problem in the industry, where leaking gases could present lethal danger, risk of suffocation, or in the case of overland gas distribution, a loss of income and the risk of pipeline explosion.

Various gases absorb energy in various wavelength bands. So, it is possible to make a gas sensitive camera, which is able to “see” various types of gases. The most important industrial gases are Sulphur hexafluoride (SF6, absorbing at around 10.5 µm), Methane (absorbing at around 3.3–3.5 µm) and Carbon dioxide (4.2–4.4 µm).

The image above shows Butane gas emerging from a cigarette lighter. Butane absorbs energy in the 3-2.8 µm band. The image is created with a narrowband sensor OGI camera. Background radiation that should have illuminated the sensor, is instead absorbed by the gas, acting like a grey filter, creating a dark streak on the image.

Semiconductor Manufacturing

There are various types of infrared sensors around, based on Silicon (uncooled bolometric) and Mercury Telluride (MCT) as well as InSb, but all these technologies have problems at longer wavelengths.

QWIP came up as a competing technology, exploiting quantum phenomena. QWIP sensors are manufactured in Gallium Arsenide. Polarisation detection arises from the incoming photons reflecting off the grating on the chip surface, and only the photons with the proper polarisation are reflected into the quantum well, resulting in an image current.

The GaAs chip only contains the quantum wells. After manufacture, the very thin GaAs substrate is cut into separate sensor chips, which are bonded onto Silicon chips, containing all the readout electronics.

Other manufacturers create polarisation sensitive detectors by having a rotating polarising filter in front of the camera. This is a slow method, not useful for high frame rates, depicting moving objects or movie-making. A far more efficient way of sensing polarisation is having an array of pixels directly sensing the four directions, 0, 90, 45 and -45 degrees. This enables the IRnova sensors to use a frame rate of 60 fps, suitable for filming.

The spectral band is determined by varying the thicknesses of the nanometric layers of GaAs and AlGaAs in the chip, as well as the separation of the grating lines.

IRnova manufactures three main chip structures: QWIP LWIR (sensitive around 8 µm) for general purpose applications, such as military intelligence, QWIP LWIR 10.55 (sensitive around 10.55 µm) for detection of Sulphur hexafluoride, and T2SL MWIR (3.3–5.1 µm).


Type II super lattice (T2SL or SLS) is the latest, emerging infrared detector technology, capable of outperforming all existing infrared technologies, and without their main drawbacks, like poor array uniformity, and inability to meet reduced size weight and power demand

T2SL is based on quantum mechanics, just like QWIP, but the substrate is manufactured from Gallium antimonide (GaSb). The result is increased quantum efficiency, decreasing noise and enabling greater frame rates etc.

T2SL detectors works up to 150 K while maintaining equal performance to earlier, colder devices. The idea behind cooling the circuits is to increase the difference between image current and dark current, thereby decreasing noise in the image.

IRnova achieves cooling by using a Stirling engine cooling the detector down to working temperature in about 6 minutes. Of course, the hotter the circuit can work, the smaller the cooling apparatus can be made. The latest sensor, the “Oden MW” an HOR T2SL, is smaller,  lighter and consumes less power than any other MWIR detector product in the market.

The IRnova detectors are used by many of the world’s heat camera manufacturers.

Myfab Making it all Possible

Semiconductor manufacturing requires extremely expensive machinery. IRnova is taking advantage of the Myfab high-performance infrastructure in Stockholm, Uppsala, Lund and Gothenburg to manufacture its circuits.

The availability of high-quality equipment, the fact that the equipment is shared among others and the availability of service personnel significantly increases the yield of IRnova’s investment.

Further reading

Have a look at IRNova:

IRNova on Youtube: