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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  • willis936 - Friday, May 01, 2015 - link

    Neat. Reply
  • paul878 - Friday, May 01, 2015 - link

    Could you please post some better pictures taken by the camera, such as people, house, animals. Reply
  • Phiro69 - Friday, May 01, 2015 - link

    Holy smokes, yes. Nothing says "this would be useful" than screenshot after screenshot of nearly uniform orange backgrounds.

    I would love to know if this would be capable of thermally scanning your dwelling for temperature leaks, for instance.
    Reply
  • icrf - Friday, May 01, 2015 - link

    This is the wall around my fireplace. You can see the two porthole windows and the stone hearth as being cooler than average, but the rest looks okay. There's a little more loss in the corner on the right going up the cathedral ceiling, too, but not much I can do about that.

    https://lh3.googleusercontent.com/-AjXbZjNBMJI/VMF...

    Everything is a bit fuzzy (hey, it's a cheap low-res camera), and I'm not sure about the minimum temperature difference it can detect, or if slight variations just get lost in the noise. If you want to find an insulation problem, it would probably have to be a bad one to be obvious.
    Reply
  • icrf - Friday, May 01, 2015 - link

    Here's what that wall looks like (the split screen photo option in the app saves two separate photos if viewed outside the app, but the FOV and exact location is different): https://lh3.googleusercontent.com/-ezEjypVpl0Q/VMF... Reply
  • Gunbuster - Friday, May 01, 2015 - link

    But then you could see how terribad the resolution is... Reply
  • icrf - Friday, May 01, 2015 - link

    The FLIR was interesting in that it would combine the visible photo with the thermal photo and use the higher resolution visible image to enhance detail and overlay some thermal information. I think the sensor in that camera was actually lower than this one, so you actually get less thermal data (assuming similar quality sensors), but it's processed into something much prettier.

    Honestly, getting any thermal camera south of a $1,000 seems like a good start.
    Reply
  • soccerballtux - Saturday, May 02, 2015 - link

    thermal photos could actually be just as high resolution as your cellphone's normal photos but an IR filter is intentionally placed over the CCD to remove the IR, and with Camera addons like this one, an aftermarket blur is intentionally added to the image to reduce resolution Reply
  • hammer256 - Saturday, May 02, 2015 - link

    CCDs can capture near IR, but not the far IR for good thermal imaging. Reply
  • Daniel Egger - Saturday, May 02, 2015 - link

    Please read the article before posting this nonsense. It actually explains the difference in hardware between real thermal imaging and fake IR imaging which can be achieved by removing the IR filter from the sensor of a regular camera. Reply

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