Affordable Lens Heats Up Thermal Imaging

Thermal cameras, also referred to as infrared cameras or thermographic cameras, are specialized devices that capture and interpret invisible radiation emitted by objects. Unlike conventional cameras that rely on visible light, thermal cameras operate within the infrared spectrum, enabling them to detect and visualize heat signatures emitted by people and objects. This unique capability sets thermal cameras apart and makes them useful in diverse application areas across a variety of domains.

At a high level, thermal cameras work based on the principle of thermography. All objects with a temperature above absolute zero emit infrared radiation, which is invisible to the human eye. Thermal cameras use special sensors called microbolometers to detect this radiation and convert it into electrical signals. The sensors are made up of an array of tiny, heat-sensitive elements that change their electrical resistance when exposed to infrared radiation. These changes in resistance are then translated into temperature data and displayed as a thermal image.

These technologies are well-established and readily available, however, some of the components that go into higher-quality infrared cameras can be very costly. This expense has the effect of greatly limiting the use cases for which these cameras can be deployed. Low-resolution cameras cannot be used to detect pedestrians, for example, in self-driving cars. But adding the cost of a high-quality thermal camera to a car’s price tag would drive many consumers away.

The specialized lenses needed by thermal cameras are a big part of the reason for their expense. Lenses made of germanium or zinc selenide can cost thousands of dollars, and there is no easy way to get around that. Such lenses have special properties that allow infrared radiation to pass through them, whereas traditional lenses absorb infrared radiation. Further adding to the cost is the fact that the needed raw materials are scarce, and also difficult to work with.

Low-cost thermal cameras may not have to sacrifice quality in the future, thanks to the work of researchers at Flinders University. They have developed a new type of thermal camera lens that is highly-performant and made of abundant raw materials that are simple to work with. And best of all, each lens only costs about a penny. From self-driving cars to agricultural inspections and aerial imaging by drone, this lens could open up thermal imaging to a wide range of applications for which it was previously prohibitively expensive.

The team’s novel lens is composed of a mixture of sulfur and cyclopentadiene. A key innovation that made this unique material possible was using cyclopentadiene in a gaseous form, so that it would react with the sulfur. By precisely controlling this process, they were able to construct a lens with the perfect properties for use with a thermal camera — in fact, this lens has the highest long-wave infrared transmission of any plastic that has ever been reported on.

The choice of materials allow for the lenses to be cast or molded using techniques that are common in the plastics industry. This serves to reduce costs, and also makes it possible to create lenses in any type of complex shape that is desired.

Aside from industrial applications, these lenses are inexpensive enough that future smartphone releases may even be able to include high quality thermal cameras. This work represents a significant step forward for lenses for infrared optics that could have the effect of democratizing the technology in the years to come.