1 THE ULTIMATE INFRARED . HANDBOOK FOR R&D. PROFESSIONALS. A Resource Guide for Using INFRARED in the Research and Development Industry Contents IR Thermography How It Works 1. IR Detectors For Thermographic Imaging 7. Getting The Most From Your IR Camera 14. Filters Extend IR Camera Usefulness 25. Ultra High-Speed Thermography 35. Published by FLIR AB. This booklet may not be reproduced in any form without the permission in writing from FLIR Systems, AB. Copyright. All rights reserved. The images displayed may not be representative of the actual resolution of the camera shown. Images for illustrative purposes only. Chapter 1. IR Thermography resolution can range from about 160 120. pixels up to 1024 1024 pixels.
2 Certain IR. How It Works cameras have built-in software that allows IR Thermography Cameras the user to focus on specific areas of the FPA and calculate the temperature. Other Although INFRARED radiation (IR) is not systems utilized a computer or data system detectable by the human eye, an IR. with specialized software that provides camera can convert it to a visual image temperature analysis. Both methods can that depicts thermal variations across supply temperature analysis with better an object or scene. IR covers a portion than 1 C precision. of the electromagnetic spectrum from approximately 900 to 14,000 nanometers FPA detector technologies are broken ( 14 m). IR is emitted by all objects at down into two categories: thermal temperatures above absolute zero, and detectors and quantum detectors.
3 A. the amount of radiation increases with common type of thermal detector is an temperature. uncooled microbolometer made of a metal or semiconductor material. These Thermography is a type of imaging that is typically have lower cost and a broader accomplished with an IR camera calibrated IR spectral response than quantum to display temperature values across an detectors. Still, microbolometers react object or scene. Therefore, thermography to incident radiant energy and are much allows one to make non-contact slower and less sensitive than quantum measurements of an object's temperature. detectors. Quantum detectors are made IR camera construction is similar to a digital from materials such as InSb, InGaAs, PtSi, video camera.
4 The main components are HgCdTe (MCT), and layered GaAs/AlGaAs a lens that focuses IR onto a detector, plus for QWIP (Quantum Well INFRARED Photon). electronics and software for processing detectors. The operation of a quantum and displaying the signals and images. detector is based on the change of state Instead of a charge coupled device that of electrons in a crystal structure reacting video and digital still cameras use, the IR to incident photons. These detectors are camera detector is a focal plane array (FPA) generally faster and more sensitive than of micrometer size pixels made of various thermal detectors. However, they require materials sensitive to IR wavelengths. FPA cooling, sometimes down to cryogenic User Interface IR In Video User Control Detector Cooling Video Output Processing NIR Digitization Digital Output Electronics Synchronization In/Out MWIR.
5 System Status LWIR. Optics Figure 1. Simplified block diagram of an IR camera 1. Chapter 1. temperatures using liquid nitrogen or a hygroscopic, and they can be formed into small Stirling cycle refrigerator unit. lenses with modern turning methods. As in visible light cameras, IR camera lenses have IR Spectrum Considerations antireflective coatings. With proper design, Typically, IR cameras are designed and IR camera lenses can transmit close to 100%. calibrated for a specific range of the IR of incident radiation. spectrum. This means that the optics and detector materials must be selected Thermal Radiation Principles for the desired range. Figure 2 illustrates The intensity of the emitted energy from the spectral response regions for various an object varies with temperature and detector materials.
6 Radiation wavelength. If the object is Because IR has the same properties as colder than about 500 C, emitted radiation visible light regarding reflection, refraction, lies completely within IR wavelengths. In and transmission, the optics for thermal addition to emitting radiation, an object cameras are designed in a fashion similar reacts to incident radiation from its to those of a visual wavelength camera. surroundings by absorbing and reflecting However, the types of glass used in optics a portion of it, or allowing some of it to for visible light cameras cannot be used pass through (as through a lens). From this for optics in an INFRARED camera, as they do physical principle, the Total Radiation Law not transmit IR wavelengths well enough.
7 Is derived, which can be stated with the Conversely, materials that are transparent to following formula: IR are often opaque to visible light. W = aW + rW + tW, IR camera lenses typically use silicon (Si) which can be simplified to: and germanium (Ge) materials. Normally 1 = a + r + t. Si is used for MWIR (medium wavelength IR) camera systems, whereas Ge is used The coefficients a, r, and t describe the in LW (long wavelength) cameras. Si and object's incident energy absorbtion (a), Ge have good mechanical properties, , reflection (r), and transmission (t). Each they do not break easily, they are non- coefficient can have a value from zero to one, depending on how well an object absorbs, reflects, or transmits incident MCT radiation.
8 For example, if r = 0, t = 0, and a PtSi QWIP = 1, then there is no reflected or transmitted InSb Microbolometer radiation, and 100% of incident radiation is absorbed. This is called a perfect blackbody. MWIR LWIR. In the real world there are no objects that are perfect absorbers, reflectors, or m m m m transmitters, although some may come very close to one of these properties. Figure 2. Examples of detector materials and their spectral responses relative to IR midwave (MW) Nonetheless, the concept of a perfect and longwave (LW) bands blackbody is very important in the 2. IR Thermography How It Works science of thermography, because it is the 1 emissivity). Since a perfect blackbody is foundation for relating IR radiation to an a perfect absorber, r = 0 and e = 1.
9 Object's temperature. The radiative properties of a perfect Fundamentally, a perfect blackbody is a blackbody can also be described perfect absorber and emitter of radiant mathematically by Planck's Law. Since this energy. This concept is stated mathematical has a complex mathematical formula, and as Kirchhoff's Law. The radiative properties is a function of temperature and radiation of a body are denoted by the symbol e, wavelength, a blackbody's radiative the emittance or emissivity of the body. properties are usually shown as a series Kirchhoff's law states that a = e, and of curves (Figure 3). since both values vary with the radiation These curves show the radiation per wavelength, the formula can take the wavelength unit and area unit, called form a(l) = e(l), where l denotes the the spectral radiant emittance of the wavelength.
10 Blackbody. The higher the temperature, The total radiation law can thus take the the more intense the emitted radiation. mathematical form 1 = e + r + t, which for However, each emittance curve has a an opaque body (t = 0) can be simplified distinct maximum value at a certain to 1 = e + r or r = 1 e ( , reflection =. T-1000 C. Blackbody spectral radiant emittance T-900 C. T-700 C. T-800 C. T-600 C. T-500 C. T-400 C. T-300 C. T-200 C. 2 3 4 5 6 7 8 9 10 11 12 13 14 15. Visible light Figure 3. Illustration of Planck's Law 3. Chapter 1. wavelength. This maximum can be Emissivity calculated from Wien's displacement law, The radiative properties of objects are lmax = 2898/T, usually described in relation to a perfect blackbody (the perfect emitter).)