Introduction to Thermal Imaging

The costs associated with thermal imaging systems have restricted their usage and kept it out of reach of the average consumer / impulse-buy territory. However, there have been some recent advancements in this field that have made the prices of such system more palatable to the non-professional users. Thanks to the advent of smart mobile devices, the costs associated with the storage, control and user-interface for these systems could be taken out for most markets. One of the first forays into this space was the $250 FLIR ONE personal thermal imager from FLIR Systems. Unfortunately, by restricting the hardware design to work only with the Apple iPhone 5 and 5s, they lost out on widespread market appeal. Seek Thermal entered the market with a splash by launching their first smartphone-attached infrared camera for just $199. Two distinct models carrying the same features and capabilities were launched, only differing in the connector - one with a microUSB interface for Android devices and another with a Lightning connector for iOS devices. Before talking in detail about the Android version of the camera and the associated mobile app, let us take a moment to understand how thermal imaging works - particularly since this is not something we have covered on our site before.

All materials emit infrared energy and the intensity is a function of its temperature. In simple terms, the higher the temperature, the greater the intensity. Thermal imaging systems utilize a sensor to convert the emitted infrared energy into electrical impulses for further processing. In general, these sensors are called bolometers - they are made of materials whose electrical resistance is dependent on the temperature. The heating is triggered by the power of the incident electromagnetic radiation. Note that bolometers can be used for any type of electromagnetic radiation, though they are typically best suited for infrared and microwave frequencies. A microbolometer is a particular type of bolometer suitable for infrared wavelengths, making them suitable for use in thermal imaging systems. The microbolometer in the Seek Thermal camera responds to long-wave infrared (i.e, wavelengths between 7.2 and 13 microns).

A microbolometer consists of an array of pixels. The Seek Thermal camera has a 206 x 156 array (for around 32K thermal pixels). Each pixel has multiple layers, as shown in the cross-sectional diagram below.

"Cross-sectional microbolomter". Licensed under Public Domain via Wikipedia

Depending on the manufacturer, the manufacturing procedure and absorbing materials can differ. Amorphous silicon and vanadium oxide (VO) are the two commonly used infrared radiation detecting materials. Despite being lower in performance and longevity compared to amorphous Si, VO is preferred as it has been around for quite some time (more mature) compared to a-Si. The Seek Thermal camera also uses VO as the IR radiation detecting material. The pixel array in the microbolometer is usually encapsulated in a vacuum to increase the life of the device. The construction of the microbolometer also determines the supported temperature range. The Seek Thermal camera can detect temperatures between -40 C and +330 C.

As one of the graphs in the a-Si link above shows, we have also seen a decrease in the dimensions of the individual pixels. While older devices had a pixel pitch of 45 um, newer devices such as the Seek Thermal have a pixel pitch of just 12 um. With decreasing pixel size, the number of pixels per unit area increases to provide higher resolution images.

Unlike regular cameras (which use regular glass or plastic lenses), thermal cameras can't use materials that reflect thermal radiation. The commonly used materials for thermal lenses are germanium, zinc selenide, zinc sulphide and chalcogenide glass - all of these have good transmission capabilities for the infrared wavelengths. The Seek Thermal camera uses a chalcogenide lens (a type of glass containing one or more of sulphur, selenium or tellurium).

Seek Thermal - Hardware, Setup and Usage Impressions
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  • icrf - Friday, May 29, 2015 - link

    Now that G+ Photos has exited G+, it's easier to share links to videos. Here's the one of the water boiling:
  • ganeshts - Saturday, May 2, 2015 - link

    One of our fellow readers has provided a nice set of images. I have also added a page prior to the concluding section with some sample images.
  • slashbinslashbash - Friday, May 1, 2015 - link

    Having experienced crashing my car into a moose on a dark Colorado highway, I am extremely interested in this technology as some kind of early warning system for night driving in areas where there are likely to be deer or other large animals. I would love to see some samples of the output for far-away warm objects such as humans or other animals.
  • Daniel Egger - Saturday, May 2, 2015 - link

    You'd have to mount it outside of the car though as even the reflectivity of regular glass completely throws off the sensor, let alone car windshields and windows which usually usually coated with vaporized metal specifically to block IR and UV.
  • DanNeely - Friday, May 1, 2015 - link

    How are they getting a 720p video out of a 206x156 sensor? Unless they're able to jiggle the sensor back and forth a fraction of a pixel to interpolate a higher resolution, wouldn't 720p offer nothing except resizing artifacts over a lower resolution version?
  • ganeshts - Friday, May 1, 2015 - link

    It is upsampling with some tricks, as explained in this paper:

    In higher-end thermal imagers, the optical image sensor output is also used along with the thermal sensor's output to do a better job of the upsampling.
  • nathanddrews - Friday, May 1, 2015 - link

    Save some money:
  • ganeshts - Friday, May 1, 2015 - link

    No doubts about that for certain applications, but for a majority of the use cases (checking for moving animals in the dark, finding the hotspots in a PC quickly, tracing clogs in plumbing etc.), the IR thermometers just won't cut it :) Trust me, I have used both - for different purposes :)
  • carlwu - Friday, May 1, 2015 - link

    I have this device. Around doors and windows, you can plainly see where there is heat loss in the winter time. Some areas you can address, others you can't.
  • SilthDraeth - Friday, May 1, 2015 - link

    I love how the guy in the comments has taken more useful pictures than the reviewer. Sure, taking the pictures the reviewer took contains data. But for god sake, take pictures of animals at night. Etc. For instance, I was contemplating this device, I was curious if on a pitch dark night, if I could see a coyote at 300 feet away in the darkness based on his heat signature. Obviously, coyotes aren't going to play nice, but, if a person would show up on an empty field at 300 feet it would be enough information for me to go off of.

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