US Military superiority is underpinned by advanced engineering and technology. Innovations in infrared imaging have given American warfighters the advantage for decades, and the technology continues to advance.
When longwave and midwave (LWIR or MWIR) thermal cameras were first developed and used for military applications, the sensors needed to be cryogenically cooled to liquid nitrogen temperatures (77K or -200C) to increase the thermal sensitivity and reduce noise. Initially, the systems had either single or multi-element sensors or linear arrays and there were mechanical scanning devices used to “paint” a complete thermal image. This resulted in a complex device that was quite large and bulky, had frequent maintenance issues, and was very costly. The technology at the time made it impossible to have a truly portable soldier system.
In the early 1990s, the technology evolved from scanning-based systems to staring systems with the advent of two-dimensional focal plane array systems. They had to be cooled to the same 77K, but advanced mechanical coolers were developed. It was a step in the right direction and created somewhat more portable systems—but they were still far from ideal.
MWIR was well suited for many applications, but not ideal for all. LWIR was preferred for many terrestrial military applications as there was typically more LWIR flux at colder temperatures, there was a clearer path through the atmosphere in LWIR and, most importantly, LWIR could penetrate smoke, dust, and battlefield obscurants better than MWIR. At that time, there was no practical LWIR solution as there were no practical two-dimensional LWIR sensors. However, with the development of practical microbolometer technology in the late 1990s, that began to change.
Microbolometer Technology: The Advent of Practical LWIR Systems
(Image courtesy of FLIR.)
A microbolometer detector is a thermal detector that reacts to the changing temperature of the scene, as opposed to a photonic detector (like an MWIR sensor) that collects photons emitted from a target. Essentially, each microbolometer pixel is like a miniature thermometer that physically changes temperature when the corresponding projected pixel on the scene changes temperature.
When the pixel changes temperature, it changes resistance, and this can be quantified to produce a thermal image. The best part of microbolometer technology is that it operates at room temperature, which in the 1990s eliminated the need for large mechanical cryogenic cooling devices that were expensive, bulky, and needed periodic maintenance.
In addition, microbolometers are spectrally independent and can be “tuned” to operate in the LWIR wavelength. These innovations finally allowed the promise of affordable LWIR soldier system.
LWIR Microbolometers - Disadvantages
LWIR devices are used for general purpose applications including googles and weapon sights. (Image courtesy of FLIR)
However, LWIR microbolometers had some initial disadvantages. They were free from cryogenic cooling devices, but their inherent sensitivities were lower than cooled devices. This resulted in the need for optics with larger apertures to allow more energy onto the detector, resulting in larger lenses.
Because these lenses had to be transmissive in LWIR and in many cases made of germanium, the lenses were expensive. As a result, it became impractical for uncooled LWIR systems to use the very long focal length lenses used for distant imaging.
In addition, LWIR microbolometer systems had frame rate limitations while cryogenically cooled MWIR systems could operate at hundreds or even thousands of frames per second. This led to MWIR devices being used for more demanding applications (airborne or ground based long range intelligence, surveillance and reconnaissance (ISR), missile seekers, aircraft warning, etc.) and LWIR used for more general purposes (thermal weapon sights, enhanced night vision goggles, driver vision enhancement on vehicles, etc.)
Cutting Edge LWIR: New Developments in Microbolometer Technology
In recent years, advances in microbolometer camera technology have allowed wider adoption of the LWIR sensors for more warfighter solutions.
FLIR Systems, after the acquisition of Indigo Systems in 2004, grew to be the world leader in the production of microbolometers. The technology evolved into smaller pixel-based systems that could reduce the overall size, weight, power, and cost of the camera. Reducing the size, weight, power, and cost (“SWaP-C”) made the technology practical for more widespread applications in the military, furthering the US military goal of ensuring overmatch capability for every warfighter.
FLIR’s recent microbolometer advancements resulted in the Boson product line. This miniature camera module, about the size of a sugar cube, was possible because of significant technological improvements on many fronts. First, FLIR was able to reduce the size of the microbolometer pixel to 12µm, compared to the typical pixel sizes of 17 µm or 25 µm. The reduction in the pixel pitch reduced the size of the entire focal plane array, which then allowed reduction in the size of optics as well as a reduction in power to drive the microbolometer.
In addition, FLIR was able to perfect wafer level packaging of the Boson microbolometers. All microbolometers must be packaged in a vacuum to operate. Traditionally, a microbolometer chip, or die, is mounted on either a ceramic leadless chip carrier or a metallic package from which a vacuum is pulled. The process to package in this manner has many steps and can lead to less than ideal yields. FLIR’s wafer level packaging essentially places the window (and therefore the vacuum) during the microbolometer production at the wafer level. This significantly reduces the physical size of the packaged microbolometer, but also reduces costs and—most importantly—produces higher yields.
The FLIR Boson contains a 12um microbolometer.
The FLIR Boson also uses an advanced microprocessor to perform all image calibrations and image processing functions. Traditionally, most thermal cameras use field programmable gate arrays (FPGA) to do these calculations. While FPGAs are mature and have fine performance, they can be physically large, have high power consumption, and be costly.
FLIR had an early relationship with Movidius, now Intel, and adopted their Myriad processor for use in all Boson products. The Myriad uses SHAVE (Streaming Hybrid Architecture Vector Engine) technology, which has 12 parallel processors. The Myriad was originally designed for intensive gaming, but proved perfect for demanding video processing. In addition, the Myriad processors are well suited for machine learning or artificial intelligent processing “on the edge,” which is the wave of the future in imagery.
The resulting FLIR Boson is a truly miniature thermal camera module. It measures 21mm x 21mm x 23mm, weighs as little as 50 grams, and delivers high performance with low power consumption.
The combination of all these factors make the Boson LWIR module ideal for soldier systems such as thermal weapon sights, thermal monocular or binoculars, and small unmanned aircraft systems (sUAS) payloads.
FLIR Systems is currently developing a modified version of the Boson for use in future variants of the US Army’s Soldier Borne Sensor program. The Soldier Borne Sensor program utilizes a miniature hand-launched UAS for short range tactical operations. Even though the standard Boson is small, it is too large for operation on such a small airframe. The modified Boson for this deployment will be <5g. For UAS operations, SWAP optimization is key, as a reduction in weight equates to longer mission profiles.
Cutting-edge thermal vision technology continues to develop and serve as an integral part of the warfighter’s arsenal for detecting, identifying, and tracking threats.
For more information, check out our story Overmatch Capability for the Warfighter: Thermal Vision and Infrared Imaging, or visit the FLIR Systems website.
FLIR Systems has sponsored this post.