Eight Things Engineers Should Know About Thermal Imaging

Thermal imaging is a technology that has existed for many years but is now being applied to a far broader range of applications, partly due to Teledyne FLIR OEM incorporating embedded System on Chip (SoC) electronics into compact relatively low-cost cameras. Recent advancements have made thermal cameras smaller, lighter, and more affordable for industrial, commercial and consumer use. It's important to understand the broad capabilities thermal imaging offers. With that, and other advancements in infrared (IR) technology it has become an essential tool not only for traditional use cases like military and law enforcement, but also for a range of industries including automotive, industrial sensing, security and home automation. If you’re considering integrating a thermal camera into your next project, here are eight key things you should know.

1. Thermal imaging identifies heat—not light. Both day time and night time

Thermal cameras create images from the differences in the heat energy transmitted in a scene. Anything that emits or reflects heat and is above -80K can be seen with the appropriate thermal camera. People, animals, electro-mechanical systems, and industrial processes all have individual heat signatures that can be seen with a thermal camera. They can also see through particulate in the air like smoke dust and most fog, making them essential for firefighting and search-and-rescue operations.

For privacy-sensitive applications like residential security, thermal cameras are ideal, they don’t reveal facial features and can’t see through windows. Beyond imaging, thermal technology can also act as a discrete sensor. It complements visible cameras, LIDAR, and radar to reduce false alarms in security systems and supports emerging technologies like Advanced Driver Assistance Systems (ADAS) and self-driving vehicles.

Because thermal sensors don’t require light to illuminate a scene it makes them useful in all sorts of conditions, for all sorts of applications as described below.

2. What is Thermal Imaging

Unlike standard cameras that rely on light, thermal imagers detect and display differences in IR energy being emitted or reflected from an object. This allows them to function in total darkness, through smoke, dust, and fog and create greyscale or pseudo-colour images.

IR radiation emitted by an object with a temperature above absolute zero (thermal radiation) makes up a part of the electromagnetic spectrum. The wavelength of the thermal radiation emitted is related to the temperature of the object and as objects heat up the wavelength emitted gets shorter. It’s only when objects get very hot that the wavelengths emitted are visible to the human eye. Objects at room temperature for example do not emit wavelengths of thermal radiation that are visible, but they are detectable by a thermal camera. Thermal radiation at room temperature and all relatively low temperatures is called longwave IR and takes a part of the electromagnetic radiation range.

Visible light is the type of electromagnetic radiation that humans are most familiar with. Visible light is a very narrow waveband—0.39 to 0.75 micrometers (μm). IR waveband is much larger by comparison, beginning near 1.0 μm and ending at 1,000 μm.

• Shortwave  IR (SWIR) waveband from approximately 0.9 – 3 μm
• Midwave  IR (MWIR) waveband from 3 - 8 μm
• Longwave  IR (LWIR) waveband from 8 - 14 μm

3. How Thermal Cameras Work

Thermal cameras capture the IR energy that is all around us and use that energy to create images or data points through digital or analogue video outputs. A thermal camera is typically only sensitive to one of the wavebands we discussed earlier: either MWIR from 3-5 μm or LWIR from 8-14 μm.

A thermal camera consists of a lens, a sensor, processing electronics, and a housing. IR energy is focused onto and captured by the sensor, which then converts it into a digital signal that can be represented as a visible image on a digital display. LWIR cameras are common for applications where relatively low temperatures are being detected and the sensor typically does not need to be cooled, while MWIR cameras require cryogenic cooling to reduce noise for adequate sensitivity and performance.

Teledyne FLIR OEM’s LWIR detectors are made of Vanadium Oxide (VOx), the most sensitive material for detecting longwave IR radiation. VOx is typically free of image artefacts that are associated with detector materials like Amorphous Silicon. These detectors come in pixel arrays, commonly 320x256 or 640x512, which is defined as their resolution. Higher resolutions are being developed and are not far away.

These resolutions are low compared to modern visible-light cameras and it is because thermal detectors require larger sensor elements (12 – 17 μm vs. 1 – 4 μm in visible sensors) to detect the longer wavelengths of IR energy. Thermal cameras generally have lower resolution but deliver detailed thermal data.

Once thermal energy hits the detector with each pixel acting like a single thermistor, thermal energy adjusts the resistance of that pixel and by measuring the resistance the sensor can measure the heat coming from the object at that point. Readout electronics convert resistance changes into electrical signals. In advanced models like the FLIR Boson+, this signal is processed onboard using system-on-a-chip (SoC) technology, enabling features like image processing and analytics without external hardware.

Thermal camera lenses are made from Germanium or Chalcogenide, materials that transmit longwave IR radiation well, unlike glass, which blocks it. This is also why thermal cameras can't see through standard windows.

4. Choosing the Right Thermal Imager

Choosing the right thermal imager, depends on what you need the camera to do. There are a wide range of thermal cameras, starting with imagers that go into smart phones at the low performance end to high-performance cameras used in critical search and rescue applications.

Resolution:
The camera’s resolution will relate directly to image detail and potential detection range. If you just need to detect presence of an object, a single pixel may be enough to do the job. If you need to recognize what an object is, say, a person, an animal, or a vehicle you’ll need a larger group of pixels in the image to fit inside the object. Typically, it is the shape of the object that enables recognition and one pixel is not enough to determine shape. At Adept Turnkey we typically use a rule-of-thumb, that the resolution of the camera needs to allow for between 5x and 10x pixels across the smallest dimension of the object to be recognised, but this depends greatly on the shape and the level of subtlety in shape difference between objects. For example, a subtle difference might be detecting if a person is armed or not. Another example is determining if that vehicle is a Tesla or a BYD. These would require more pixels than simply determining if it’s a person, a dog or a car.

Dividing the width of the scene in the Field of View (FOV) by the horizontal number of pixels on the sensor will allow you to determine you the smallest feature that can be detected at the required working distance. You can also use a specification called the “instantaneous FOV” (iFOV) to get the angular size of a single pixel and calculate its size at a given range.

Sensitivity:
A thermal camera’s sensitivity is specified as the Noise Equivalent Differential Temperature (NEDT). It’s a signal-to-noise metric that tells you the temperature difference required to produce a signal equal to the camera’s temporal noise, and – by extension – the minimum temperature difference the camera can resolve. NEDT is usually expressed in milliKelvin (mK), with lower numbers indicating superior performance than higher numbers. The Boson+ Industrial Grade thermal camera has industry-leading sensitivity of less than 20 mK NEDT.

Lower-cost imagers like FLIR’s Lepton are ideal for smartphones and compact devices, while high-performance models like the Boson+ series provide greater detail and range for mission-critical tasks.

5. View a Thermal Gradients or Measure Temperature - Imaging vs. Radiometry

Basic thermal cameras provide images that show heat differences, but radiometric cameras go further by offering calibrated temperature measurements for each pixel. This capability is crucial for applications like industrial inspections, where precise temperature readings can detect overheating components before failure. On the other hand, for example, search and rescue only requires an image showing the thermal difference in a scene in order to detect presence of a human.

Teledyne FLIR OEM thermal camera modules are available with varying degrees of radiometric capability and accuracy – from imaging only, to a simple centre spot meter function, to advanced radiometry and improved accuracy – and many Teledyne FLIR OEM cameras can be ordered as either imaging or radiometric.

6. Finding the Right Supplier

An important part of the choice in choosing the right thermal camera is to choose the right imaging supplier. Consider factors such as product reliability, engaged technical support and after sales service, access to detailed product information, quality of software development kits (SDKs), supplier reputation, commitment to continuous development and industry-specific expertise to name a few. Teledyne FLIR OEM and Adept Turnkey have a strong track record of providing high-quality products with extensive documentation and support and more importantly with sales and technical after sales service that is responsive and reliable.

7. Understanding Total Cost of Ownership

The value of a product is not only determined by the initial purchase price but by the total cost of ownership which includes other short and long-term costs. There are hidden development costs caused by integration complexity that not only increase the total cost but delay the time to market and potentially threaten project viability.

The initial product cost should be competitive, but it should also be backed by detailed high quality documentation, enthusiastic technical support and accessibility to application engineers.

Warranties, product lifetimes and product reliability all factor into the total cost of ownership and so need to be considered when determining the right choice of product.

8. Export Regulations and Compliance

Export regulations in recent years have tightened with a greater awareness being demanded by authorities with ever-increasing penalties. Certain thermal imaging products require export licenses due to these government regulations. If your product integrates thermal cameras, ensure compliance with export laws, especially if you plan to sell outside of your country of manufacture. Companies like Teledyne FLIR OEM and Adept Turnkey provide guidance on trade regulations to help customers navigate these requirements.