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

The Seek Thermal camera comes in a nicely packaged box which includes a compact storage case. The gallery below shows the packaging and the camera housing. The housing is made of magnesium and the lens has a 36 degree field of view. The camera is quite lightweight at 0.5 ounces. In terms of dimensions, the unit has a length of 2.75", depth of 0.84" and height of 0.84".

The Android version of the camera works on any Android device with a micro-USB port supporting USB OTG (On-the-Go) where the USB port can be in the host mode. Unfortunately, Android phones don't have a standard orientation or placement for the microUSB port. On the HTC One M7 and M8, for instance, the thermal camera tags on to the phone facing the same side as the screen. With the LG G2 and Samsung Galaxy phones as well as the Dell Venue 8 7000 series tablet, there were no issues in getting the orientation of the camera right.

The Seek Thermal Android app has gone through multiple feature updates and bug fixes over the last few months. In the initial days, the app would consistently crash, but it has recently been rock-solid on the multiple devices that I have tested it with (LG G2, HTC One M7, HTC One M8, Samsung Galaxy S4 and the Dell Venue 8 7000).

The gallery below shows some screenshots of the app in action on a LG G2 back in November. Note that we have emissivity control - i.e, the software is aware of the efficiency with which infrared energy is radiated depending on the material. This helps in determining the correct temperature of the material. The reference 'black body' has an emissivity of 1. The Seek Thermal camera has a shutter that passes in front of the lens periodically for recalibration based on the surrounding temperature. This makes a clicking sound which is frequent during the initial usage. After warm-up, calibration frequency is reduced.

In any case, this emissivity control seems to be missing in the latest screenshots taken while the app was running on a Dell Venue 8 7000 tablet.

The various interesting aspects of the app are evident in the screenshots above. It is possible to take still images as well as videos. In the latter case, 16:9 settings provides us with 720p video at 13 fps, while 4:3 gives us a 832 x 624 video at 14 fps. However, the real frame rate is less than 9 fps due to export restrictions on VO-based microbolometers. The photo / video can be in different thermography modes - normal (regular thermal images), spot (average temperature around the center spot), high / low (highest and lowest temperatures in the focus area) and threshold (different color for temperatures above/equal to/below a particular temperature).

Seek Thermal's target market includes a host of applications:

• safety and security (scanning areas at night before venturing out)
• home improvement (heating / insulation evaluation, water damage tracing, clogs tracing)
• pet maintenance
• cooking
• boating and other outdoor activities

PC builders and DIY enthusiasts are not in the list provided by Seek Thermal. However, regular readers of our passively cooled PC reviews must have seen seen photographs from the Seek Thermal camera in the thermal performance evaluation section. The camera provides an affordable way to monitor the temperature of the chassis in order to ensure that things are not overheating and creating a hazard.

Sample Thermal Images

A number of comments have come in with requests for thermal image samples taken by the Seek Thermal camera in day-to-day circumstances. A few cases are provided below. It can be seen that the temperature is not very accurate - for example, the temperature of a component in the refrigerator is reported as -13 C, when the compartment is set to be at 0 C. Also, the skin temperature is reported to be around 32 C, when it is obviously around 37 C (updated: see comments section).

Boiling Water in a Stainless Steel Vessel

Refrigerator Freeze Compartment

Child

Lab with IT Equipment

Faucet with Running Water

Miscellaneous Aspects and Concluding Remarks

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. We decided to monitor the battery voltage and current over Wi-Fi while the Seek Thermal camera was connected to the Dell Venue 8 7000. Obviously, the monitoring aspect contributes to power consumption since the Wi-Fi is kept in use all through. In the table below, we show the power consumption of the tablet for various scenarios.

Note that these power numbers are for the system as a whole and not the Seek Thermal camera alone

Related Plays

Seek Thermal was the first to come out with a sub-$200 thermal imaging solution. The price of the camera is now $249. They have also followed it up with the Seek Thermal XR - Xtra Range. It has the same resolution, but only a 20 degree field of view. However, it has an adjustable focus ring to be able to detect temperatures of objects up to 1800 ft. away. The XR model is priced at $299.

At CES 2015, FLIR was showing off its plans for a FLIR ONE that would be compatible with all iOS devices as well as a majority of Android devices. It is expected to land sometime towards the end of summer for a reasonable price point. For reference, the current FLIR ONE for iPhone 5/5s sells for $249. There is also a Kickstarter campaign for an affordable thermal imager from HemaVision, though the sensor resolution seems to be really low. All in all, thermal imagers are becoming more and more affordable, and given the multitude of useful applications, it is good news for consumers.

Scope for Improvement

The Seek Thermal camera is the ideal device for consumers to get started with a thermal imager without breaking the bank. It is more of a useful toy - given the applications that the company suggests that it be used for. We are not very convinced about the accuracy of the temperature readings, but it is good enough for the target market. Improvement aspects include higher resolution and frame rates for the microbolometer and a flexible microUSB connector for compatibility with a wider variety of devices. Finally, readers interested in a deeper technical dive into the camera would do well to peruse the EEVBlog thread here.