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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  • Folterknecht - Friday, May 1, 2015 - link

    So now Anandtech is finally able to include IR images of VRMs on GPUs and mobos? High Time - after seeing the IR images on TH with the initial GTX 960 review (100°C +) Reply
  • DanNeely - Friday, May 1, 2015 - link

    Maybe. It depends on if it's just a review loaner or not. If it's something that was bought/donated *one* of the editors could use it for improved thermal measuring. The Anandtech writers work from home at various locations around the world; there's no central office where they can all borrow from a shared set of toys. Reply
  • dave1231 - Friday, May 1, 2015 - link

    Bang goes my rough sleeping in the park bushes. Reply
  • Impulses - Friday, May 1, 2015 - link

    How does this compare to the old DSLR & mirrorless cameras that people convert into IR? Output seems rougher here but I dunno if that actually makes it more useful for testing purposes. Reply
  • RandomUsername3245 - Friday, May 1, 2015 - link

    Those IR DSLRs see the infrared region that is *barely* above what our eyes can see, e.g. we see roughly wavelengths = 0.4-0.7 um. The IR SLRs see ~0.7-1.0um. These SLRs don't see thermal emission until roughly the same temperature as we see it with our naked eye: when things glow red hot. Thermal cameras like the Seek see longwave infrared, which is roughly ~8-14 um. This is a substantially different wavelength region than the SLRs. Reply
  • mike8675309 - Friday, May 1, 2015 - link

    The killer thing these type of cameras can do is take a picture with both visible and IR cameras. Then overlay the IR on the visible image to make it easier to pinpoint where the hot spots are in relation to things. Reply
  • fobosca - Friday, May 1, 2015 - link

    Unfortunately this is just a toy. Expensive one. I am professional thermographer and was using multiple FLIR cameras. Thermal resolution is too low for any practical use. Unless of cuz you wanna take pictures if your cat and you have some money to burn. Good luck trying to get any accurate temperature. Reply
  • sor - Saturday, May 2, 2015 - link

    Am I missing something, or are we being misled by a conflation of the visible and infrared resolutions? At 32k it seems this has a resolution between a FLIR E6 and E8, which range in the thousands of dollars. Reply
  • Daniel Egger - Saturday, May 2, 2015 - link

    I happen to own a FLIR i7 which has a lower resolution but from what I'm reading seems to be vastly more accurate than the Seek Thermal (when set to the correct material/reflectivity) and have a higher resolution for the temperature readout (you can actually locate wirings in brick walls even with only low currents passing through).

    I'd be really interested in a shootout between those add-ons and dedicated IR thermographing gear let's say up to a couple thousand bucks.
    Reply
  • thebeastie - Saturday, May 2, 2015 - link

    Yeah LOL there are a few reviews of this on the web that have heaps better pictures of cars etc.
    Those pics on this review are super boring, I can only assume the reviewer was asked to review this and has absolutely no interest in it.

    What would be really handy for me with this is checking for bad battery cells or links on ebike batteries under load...
    https://www.google.com.au/search?q=18650+e+bike+ba...
    Reply

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