The article is sourced from the FLIR website.
There are as many types of infrared – or thermal imaging – cameras as there are scientific applications. So, which type of camera is better suited to your R&D application?
Infrared cameras are often the missing piece needed to truly understand what’s happening in an R&D environment. Because they detect and visualize heat, these cameras provide insight into everything from engineering flaws in printed circuit board designs to the combustion of individual coal particles in a larger flame.
Within the families of science-specific cameras, researchers have a range of choices from entry-level, uncooled thermal cameras to high-performance cameras with a cooled detector. Choosing the correct model depends heavily on your intended application, so consider the variables below.
Defining Cooled and Uncooled Detectors
Cooled infrared (IR) detectors use materials that must operate at cryogenic temperatures. These materials respond to individual photons of light, which makes them very sensitive and very fast—a good choice for high-performance imaging applications. A variety of material choices makes it possible for cooled cameras to operate in the near-infrared, mid-wave, long-wave bands. Their main drawbacks are cost and complexity: the detectors must be packed in a vacuum Dewar, while the cryocoolers are a mechanical device that requires periodic service and consumes significant power.
Uncooled infrared detectors, on the other hand, work at ambient temperature and do not require specialized cooling systems, making them simpler, more affordable, and more durable. These detectors primarily operate in the long-wave infrared (LWIR) range and are commonly used in security cameras, industrial monitoring, and general thermal imaging. While they have lower sensitivity and resolution than cooled detectors, their practicality and cost-effectiveness make them widely adopted across commercial and consumer applications.
Infrared Wavelength Regions
Looking at the electromagnetic spectrum, the infrared region spans wavelengths from approximately 780 nanometers to one millimeter, bridging visible light and microwaves. It is commonly divided into three subcategories: near infrared (0.78–3 µm), mid-wave infrared (3–8 µm), and longwave infrared (8–15 µm). Each infrared wavelength range serves a unique purpose, making infrared technology indispensable across multiple industries and applications.
- Near infrared (NIR) is commonly used in industrial inspections to detect defects or differences in materials that might not be visible to the naked eye, but can also be used in environmental monitoring, agriculture, and scientific research. Its ability to see through layers of paint even allows NIR to be used in art restoration applications.
- Mid-wave infrared (MWIR) begins at 3 µm and is standard for radiometry and high-performance thermography applications due to its excellent thermal contrast and sensitivity, ideal for defense research and electronics design.
- Long-wave infrared (LWIR) starts around 8 µm, where both uncooled and cooled cameras operate. LWIR has better transmission through fog, smoke, and dust, making it suitable for harsh industrial environments and long-range security operations.
Detector Speed
A camera’s speed depends heavily on the detector materials. For SWIR cameras and those imaging up to 1.7 µm, the most common sensor material is indium gallium arsenide (InGaAs). For MWIR, cooled MW mercury cadmium telluride (MCT), indium antimonide (InSb), or MW-tuned Type II Strained Layer Superlattice (SLS) sensors provide fast frame rates and high sensitivity.
For LWIR, there are silicon or metallic-based microbolometers that don’t require cooling, or cooled, high-performance MCT or SLS sensors with fast integration speeds and a wide temperature range.
Microbolometers: sensitive from 7.5 µm to 14 µm, tuned for peak sensitivity at 10 µm for ambient temperature (~30°C). Speed and sensitivity are inversely proportional to thermal resistance; highly sensitive bolometers are often slower. Rolling shutter readout can create distortions for fast-moving objects. For accurate imaging, events should be slower than 60 milliseconds.
Cryocooled detectors: incorporate photon-sensitive detectors with adjustable integration times, ROIC to collect signals, a cold filter to limit sensitivity to wavebands, and a cooling system. Each pixel has an integration capacitor controlling energy accumulation. They allow fast frame rates, precise image quality, and windowing capabilities, suitable for capturing motion without blur while maintaining accurate temperature readings.
Detector Sensitivity
Thermal sensitivity, or NETD (Noise Equivalent Temperature Difference), measures the temperature difference needed to produce a signal equal to the camera’s temporal noise. NETD represents the temporal noise floor in equivalent temperature units. Lower NETD means higher sensitivity.
- Uncooled microbolometers: NETD ~30–50 mK
- Cooled cameras: NETD ~20 mK
Both types experience temporal and spatial noise. Temporal noise occurs randomly over time; spatial noise appears as fixed patterns. Performing Non-Uniformity Correction (NUC) reduces spatial noise. Cooled detectors provide sharper images for low-energy or transient thermal events compared to bolometers.
Detector Spatial Resolution
Spatial resolution, or instantaneous field of view (IFOV)/spot size, defines the area a single detector cell or pixel captures. This principle applies to cooled, uncooled, or digital cameras. Each pixel covers a specific area extending outward into space. Understanding spatial resolution requires knowledge of field of view (FOV).
