Thermography
When viewed through a thermal imaging camera, warm objects stand out well against cooler backgrounds; humans and other warm-blooded animals become easily visible against the environment, day or night.
Some alternative medicine practitioners promote its use for breast screening, despite the FDA warning that "those who opt for this method instead of mammography may miss the chance to detect cancer at its earliest stage".
Specialized thermal imaging cameras use focal plane arrays (FPAs) that respond to longer wavelengths (mid- and long-wavelength infrared).
Older bolometers or more sensitive models such as InSb require cryogenic cooling, usually by a miniature Stirling cycle refrigerator or liquid nitrogen.
However, in the case of infrared thermography, the above equation is used to describe the radiant power within the spectral wavelength passband of the thermal imaging camera in use.
[5] For example, clean metal surfaces have emissivity that decreases at longer wavelengths; many dielectric materials, such as quartz (SiO2), sapphire (Al2O3), calcium fluoride (CaF2), etc.
Some specification parameters of an infrared camera system are number of pixels, frame rate, responsivity, noise-equivalent power, noise-equivalent temperature difference (NETD), spectral band, distance-to-spot ratio (D:S), minimum focus distance, sensor lifetime, minimum resolvable temperature difference (MRTD), field of view, dynamic range, input power, and mass and volume.
[7] Without cooling, these sensors (which detect and convert light in much the same way as common digital cameras, but are made of different materials) would be 'blinded' or flooded by their own radiation.
The pressurised gas is expanded via a micro-sized orifice and passed over a miniature heat exchanger resulting in regenerative cooling via the Joule–Thomson effect.
Modern uncooled detectors all use sensors that work by the change of resistance, voltage or current when heated by infrared radiation.
Current improvements of uncooled focal plane arrays (UFPA) are focused primarily on higher sensitivity and pixel density.
However, by utilizing the "trailing" area of their spectral sensitivity, namely the part of the infrared spectrum called near-infrared (NIR), and by using off-the-shelf CCTV camera it is possible under certain circumstances to obtain true thermal images of objects with temperatures at about 280 °C (536 °F) and higher.
Given the super-linearities of the black-body radiation, active thermography can also be used to enhance the resolution of imaging systems beyond their diffraction limit or to achieve super-resolution microscopy.
Fewer pixels compared to traditional cameras reduce the image quality making it more difficult to distinguish proximate targets within the same field of view.
[23] Thermography finds many uses, and thermal imaging cameras are excellent tools for the maintenance of electrical and mechanical systems in industry and commerce.
Power line maintenance technicians locate overheating joints and parts, a telltale sign of their failure, to eliminate potential hazards.
Healthcare-related uses include: Thermography is often used in surveillance, security, firefighting, law enforcement, and anti-terrorism:[35] In weapons systems, thermography can be used in military and police target detection and acquisition: In computer hacking, a thermal attack is an approach that exploits heat traces left after interacting with interfaces, such as touchscreens or keyboards, to uncover the user's input.
[37] Other areas in which these techniques are used: Higher-end thermographic cameras are often deemed dual-use military grade equipment, and are export-restricted, particularly if the resolution is 640x480 or greater, unless the refresh rate is 9 Hz or less.
Thermography, by strict definition, is a measurement using an instrument, but some living creatures have natural organs that function as counterparts to bolometers, and thus possess a crude type of thermal imaging capability.
A significant step in the development of detectors occurred in 1829, when Leopoldo Nobili, using the Seebeck effect, created the first known thermocouple, fabricating an improved thermometer, a crude thermopile.
The first civil sector application of IR technology may have been a device to detect the presence of icebergs and steamships using a mirror and thermopile, patented in 1913.
[52] In 1929, Hungarian physicist Kálmán Tihanyi invented the infrared-sensitive (night vision) electronic television camera for anti-aircraft defense in Britain.
While several approaches were investigated to improve the speed and accuracy of the technology, one of the most crucial factors dealt with scanning an image, which the AGA company was able to commercialize using a cooled photoconductor.
Although unsuccessful in its intended application of submarine tracking by wake detection, it was applied to land-based surveillance and became the foundation of military IR linescan.
This work was further developed at the Royal Signals and Radar Establishment in the UK when they discovered that mercury cadmium telluride was a photoconductor that required much less cooling.
Honeywell in the United States also developed arrays of detectors that could cool at a lower temperature,[further explanation needed] but they scanned mechanically.
In 1969 Michael Francis Tompsett at English Electric Valve Company in the UK patented a camera that scanned pyro-electronically and which reached a high level of performance after several other breakthroughs during the 1970s.
[57] Tompsett also proposed an idea for solid-state thermal-imaging arrays, which eventually led to modern hybridized single-crystal-slice imaging devices.
One, similar to what is called a "vision chip" when used in the visible range, allow for preprocessing using smart sensing techniques due to the increase in growth of integrated microcircuitry.
There was a dramatic lowering of costs for uncooled arrays, which along with the significant increase in developments, led to a dual-use market encompassing both civilian and military uses.
