Infrared Handbook

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 IR Detectors For Thermographic Imaging Getting The Most From Your IR Camera Filters Extend IR Camera Usefulness Ultra High-Speed Thermography 1 7 14 25 35

Published by FLIR AB This booklet may not be reproduced in anyform without the permission in writing from FLIR Systems, AB. © Copyright. All rights reserved.

Chapter 1
IR Thermography – How It Works
IR Thermography Cameras
Although infrared radiation (IR) is not detectable by the human eye, an IR camera can convert it to a visual image that depicts thermal variations across an object or scene. IR covers a portion of the electromagnetic spectrum fromapproximately 900 to 14,000 nanometers (0.9–14 µm). IR is emitted by all objects at temperatures above absolute zero, and the amount of radiation increases with temperature. Thermography is a type of imaging that is accomplished with an IR camera calibrated to display temperature values across an object or scene. Therefore, thermography allows one to make non-contact measurements of an object’stemperature. IR camera construction is similar to a digital video camera. The main components are a lens that focuses IR onto a detector, plus electronics and software for processing and displaying the signals and images. Instead of a charge coupled device that video and digital still cameras use, the IR camera detector is a focal plane array (FPA) of micrometer size pixels made of various materialssensitive to IR wavelengths. FPA resolution can range from about 160 × 120 pixels up to 1024 × 1024 pixels. Certain IR cameras have built-in software that allows the user to focus on specific areas of the FPA and calculate the temperature. Other systems utilized a computer or data system with specialized software that provides temperature analysis. Both methods can supply temperature analysis withbetter than ±1°C precision. FPA detector technologies are broken down into two categories: thermal detectors and quantum detectors. A common type of thermal detector is an uncooled microbolometer made of a metal or semiconductor material. These typically have lower cost and a broader IR spectral response than quantum detectors. Still, microbolometers react to incident radiant energy and are muchslower and less sensitive than quantum detectors. Quantum detectors are made from materials such as InSb, InGaAs, PtSi, HgCdTe (MCT), and layered GaAs/AlGaAs for QWIP (Quantum Well Infrared Photon) detectors. The operation of a quantum detector is based on the change of state of electrons in a crystal structure reacting to incident photons. These detectors are generally faster and more sensitivethan thermal detectors. However, they require cooling, sometimes down to cryogenic
User Interface

IR In
NIR MWIR LWIR

Detector Cooling Digitization Optics

Video Processing Electronics

User Control Video Output Digital Output Synchronization In/Out System Status

Figure 1. Simplified block diagram of an IR camera

1

Chapter 1
temperatures using liquid nitrogen or a smallStirling cycle refrigerator unit. hygroscopic, and they can be formed into lenses with modern turning methods. As in visible light cameras, IR camera lenses have antireflective coatings. With proper design, IR camera lenses can transmit close to 100% of incident radiation.

IR Spectrum Considerations
Typically, IR cameras are designed and calibrated for a specific range of the IR spectrum. This meansthat the optics and detector materials must be selected for the desired range. Figure 2 illustrates the spectral response regions for various detector materials. Because IR has the same properties as visible light regarding reflection, refraction, and transmission, the optics for thermal cameras are designed in a fashion similar to those of a visual wavelength camera. However, the types of glass...