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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  • Phiro69 - Sunday, May 3, 2015 - link

    I think you nailed it on the head, thebeastie. It really smells like the reviewer was told to review it and has no passion/interest in the field.

    A review like this would never have seen the light of day under Anand; I believe this is a harbinger of the content of Anandtech now that Anand has left and the site was sold to Tom's Hardware and the new management consists of ex-executives from CNET and Ziff-Davis, I'm removing my Anandtech bookmark. It's been a great ~15 years (yes, I've been reading it that long), but all good things come to an end.

    -Kelly Schoenhofen
  • ganeshts - Sunday, May 3, 2015 - link

    Kelly, Thanks for your valuable feedback - which, btw, tells me nothing that should have been added to the review.

    As for the original comment - I added a new section with pictures after that comment was posted.

    I challenge you to find a review of the Seek Thermal camera on any other site which :

    1. Gives a concise overview of how thermal imagers operate
    2. Track power consumption numbers of a system to which the Seek Thermal camera attaches itself / app is activated.
    3. Continuous use of the Seek Thermal camera for other reviews (we use it in all our passive PC thermal design evaluation if you can follow the link that has been posted in the review)

    The only feedback aspect from other readers - that has been taken note of and immediately responded to (I actually have plenty of thermal images from the Seek Thermal - but, most were taken without the camera image at the same time - so not fit to present for comparison purposes)

    I look forward to your response.
  • PrinceGaz - Saturday, May 2, 2015 - link

    "The Seek Thermal camera connects to the microUSB port of a smart device, and hence, the measurement of the power consumption of the camera is quite challenging."

    Rubbish. Use an in-line USB current monitor, together with the necessary adapters/leads (whichever is most convenient) to connect it to the Android device and the IR camera. That will give a quite accurate continuous reading of how much current the camera itself is using. Given that USB should be more or less 5V, converting that to Watts is straightforwards.

    Measuring the voltage and current drain from the Android device's battery as you did introduces not just factors related to the power the tablet itself is using, but also how efficiently it can provide the 5V to the USB socket, which will vary from device to device.
  • ganeshts - Saturday, May 2, 2015 - link

    'Challenging' is always relative. Most people don't have the stuff that you mention at hand. Once I had the proper SSH server installed in the tablet, my script to track, record and plot the power consumption took less than 15 minutes. - all I needed was a PC to run the script / SSH client on.

    Also, tracking power consumption for the system as a whole makes sense - we don't really know how much of the post processing is done via software on the app side compared to the hardware inside the thermal camera.
  • ganeshts - Saturday, May 2, 2015 - link

    Forgot to add: The tracking of the power consumption of the system helps in estimating how much battery life would be impacted if one were to keep, say, running the app's preview from the thermal camera continuously (obviously assuming that the battery capacity is known). Tracking the power consumption of the camera alone doesn't provide much benefit to the readers.
  • Shalmanese - Saturday, May 2, 2015 - link

    "A few cases are provided below. It can be seen that the temperature is not very accurate - for example, skin temperature is reported to be around 32 C, when it is obviously around 37 C."

    Your internal body temperature is 37C but exposed skin is much cooler, generally around 27 - 35C because it's constantly radiating heat. This can be trivially confirmed by noticing that you armpits and inside of your mouth are much warmer than the back of your hand or your forehead for example.

    I just checked with a reference thermometer and the side of my arm was 31C and my cheek was 34C, so a reading of 32C is fairly accurate.
  • ganeshts - Saturday, May 2, 2015 - link

    Very much possible. Thank you very much for your feedback. I have updated the relevant section of the piece to refer to the obviously erroneous -13 C in the refrigerator compartment.
  • sor - Sunday, May 3, 2015 - link

    Why is ice cream at -13C obviously erroneous? My freezer is set to -18C, and the solids in there are pretty close to that. I would expect the average freezer to be in the -10C to -15C (15 to 5F) range, unless we are talking about a crappy mini fridge/freezer combo.
  • sor - Sunday, May 3, 2015 - link

    Oh, I see. You say your freezer is set to 0C, a setting that in practice probably doesn't even keep the contents frozen. In that case it IS off the mark.

    Sorry, most freezers I know of in the US have settings around 0F.
  • blue_urban_sky - Tuesday, May 5, 2015 - link

    It does look like you have something in the fridge at around 6 deg C which will kick on the cooling. I would imagine that it has a binary cooling system that is cycled to maintain the approximate temp. This may mean that -13 is not so far out.

    You could invest in a cheap thermometer from amazon ;)

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