Published on Jan 16, 2016
Thermal imaging (Infrared thermography) is a technique that produces a visible graph or thermographic image of thermal energy radiated from objects. The human eye can only see the narrow middle band of visible light that encompasses all the colours of light in the rainbow. Thermography utilizes a portion of the infrared band of the electromagnetic spectrum between approximately 1 and 14 microns.
Thermal infrared images translate the energy transmitted in the infrared wavelength into data that can be processed into a visible light spectrum video display. Thermal infrared imagers are detector and lens combinations that give a visual representation of infrared energy emitted by all objects. In other words thermal imagers let you "see" heat.
Depending upon the sophistication used, thermography is capable of providing very detailed images of situations invisible to the naked eye. Thermal imaging thus finds its applications in different fields.
Electromagnetic radiation is emission of energy from a source, which could be a solid, liquid or gas. This radiation is given off in the form of alternating electric, magnetic waves produced by the acceleration and deceleration of charged electric particles. Although the electromagnetic spectrum is comprised of many different types of electromagnetic radiation there are similarities that must be recognized. As mentioned all electromagnetic radiation is produced by the movement of electric particles. A second point is that all electromagnetic radiation, unhindered by gases, travels at the speed of light.
As the intensity of the radiation increases, the wavelength becomes shorter and the frequency becomes higher. On the other hand as the intensity decreases, the wavelength becomes longer and the frequency lower. The main difference between the various classes of electromagnetic radiation is the wavelength and frequency, as well as the way it is produced and the "equipment" used to detect it. The chart below depicts the many classifications of electromagnetic radiation and their relation to one another.
The amount of energy in light wave is related to its wavelength. Of visible light violet has the most energy red has least. Just next to visible light spectrum is infrared spectrum
Infrared light can be split into 3 different categories:
NEAR Infrared: closest to visible light wavelength range from 0.7-1.3 microns
MID Infrared: has wavelengths ranging from1.3-3 microns, both near IR and mid IR are used by variety of electronic devices, including remote controls.
THERMAL Infrared: occupying in the largest part of infrared spectrum, this has wavelengths ranging from 3microns -over 3microns.
The key difference between thermal IR and other two is that thermal IR is emitted by an object instead of reflected of it. Infrared rays are emitted because of what's happening at the atomic level.
Atoms are constantly in motion. They continuously vibrate, move and rotate. Even the atoms that make up the chairs that we sit in are moving around. Solids are actually in motion! Atoms can be in different states of excitation. In other words, they can have different energies. If we apply a lot of energy to an atom, it can leave what is called the ground-state energy level and move to an excited level. The level of excitation depends on the amount of energy applied to the atom via heat, light or electricity.
An atom consists of a nucleus (containing the protons and neutrons) and an electron cloud. Think of the electrons in this cloud as circling the nucleus in many different orbits. Although more modern views of the atom do not depict discrete orbits for the electrons, it can be useful to think of these orbits as the different energy levels of the atom. In other words, if we apply some heat to an atom, we might expect that some of the electrons in the lower energy orbitals would transition to higher energy orbitals, moving farther from the nucleus