HOW DOES A THERMAL CAMERA WORK ?

A thermal camera is an electronic device that allows transforming the infrared radiation emitted by any kind of body in a coloured image. Indeed, any body whose temperature is greater than 0 K (the absolute zero) emits radiation in the infrared spectrum. This is what we call heat. The infrared radiation is not visible to the human eye, so we need a particular device to visualize it. And here the thermal camera comes.

But how does a thermal camera works? And how does it allow us to transform this infrared radiation, that is not visible, into a coloured image that we can see on a screen? Let see it more in detail.

How a thermal camera works

The scheme describing how a thermal camera works is the following:

• A sensitive element transforms the infrared radiation, namely, the heat emitted by a body into an electrical charge. This is possible also if the observed body is at a certain distance and really near to the thermal camera;

• This electrical charge is collected on an electronic circuit until it reaches some LED lights which transform this electrical signal into a luminous one; 

• These luminous signals are actually composing the image that we can see on the screen. The higher the temperature of the observed body, the more the image will be red.

Now one can ask: what are these sensible elements? So let see which of these sensible elements are.

Sensible elements

The sensible elements are particular materials that have the capacity to transform heat in an electrical signal, namely, to emit electrical charges when heated.

There are 2 types of such materials:

• Pyroelectric detectors: Cesium Nitrate, Gallium Nitride, Lithium Tantalate, Tourmaline;

• Semiconductors: Silicon, Germanium, Vanadium.

Thermal camera applications

The thermal camera is used in many applications, both amateur or industrial.

The main applications of a thermal camera are:

• Temperature measurements: hotter zones appear red, cooler ones appear blue. We have seen this application during the COVID-19 pandemic, at the entrance of public locations;

• See in the dark: in these applications, the LED are chosen such that a human body appears white into the dark;

• Short circuit identification: this application is used both in small circuits or energy distribution circuits;

• Measure stress inside a material: when we apply a force to a material, generating stress inside it, the material heats. The higher the stress, the higher the reached temperature;

• Flaw identification inside a material: this is used in quality checks and non-destructive inspections in industrial applications;

• Monitoring of production processes.

Conclusions

In this brief article, I wanted to give you a better and more insightful explanation of how a thermal camera works. The working principle is very simple, the material involved are very particular, the applications are very extended.