IR IN MODERN TECHNOLOGY 1 Infrared Radiation in Modern Technology Brian D. Dold Brigham Young University - Idaho
IR IN MODERN TECHNOLOGY 2 Abstract Infrared radiation (IR) is invisible to the human eye but has a wide range of uses in modern technology. There are different applications for the different wavelengths of IR radiation. There is a variety of radiation sources used in industry today including blackbody systems, quantum cascade lasers, electrically modulatable IR thermal sources, and light emitting diodes. These IR sources allow for great technical advancements in thermal imaging, motion detection, weapon guidance systems, gas analyzing and monitoring, solar and space imaging, and environmental health analysis. An understanding of Planck s Law is necessary for comprehension of the functionality of these technologies. Future research is suggested. Keywords: infrared, thermal imaging
IR IN MODERN TECHNOLOGY 3 Infrared Radiation in Modern Technology Infrared radiation (IR) is electromagnetic radiation. It is just like the radiant energy we see as visible light but its wavelengths are just beyond what the human eye can detect with wavelengths as small as 700 nanometers and as large as 1mm. Infrared radiation is used in technology far more that some may realize. For instance the common TV remote contains an infrared light emitting diode (LED) that is in the near-infrared wavelength range of 0.75 1.4 µm. Light emitters of this ranger are very common. Another such example would be the light source for a night vision camera. These light sources are visible to any digital camera. The technologies discussed here will deal primarily with IR sources that are short-wavelength (1.4 3 µm), midwavelength (3 8 µm), and long-wavelength (8 15 µm). To get a size comparison to the wavelengths we are dealing with, it is good to know that the typical diameter of a spider web is about 5 µm. Interest in infrared optical technology continues to grow as an ever increasing number of applications are discovered in academia, industry, and the military (Koerperick, 2009). IR Sources There is a large variety of IR sources, each used for different purposes. Every object that is above zero degrees Kelvin is radiating some form of infrared radiation know as thermal radiation. This is what makes Infrared radiation such a powerful resource. It allows for the ability detect and gather information of an environment without the need of visible light. The human body radiates a long-wavelength IR source of about 10 microns or 10 µm. Another common IR source is blackbody radiation. Blackbody radiation will not be discussed here very much but in essence it is a body or object that does not reflect any light or radiation from its environment so that its only output is the thermal radiation from its own temperature. Another common source is
IR IN MODERN TECHNOLOGY 4 an electrically modulatable IR thermal source. These are similar to a common incandescent light bulb but they use a different filament such as tungsten and as they run an electrical charge through the bulb it outputs more thermal energy or heat than light. The filament will glow a dark orange color. Another source is quantum cascade lasers (QCL) which emit mid- and long-wave infrared radiation. Quantum cascade lasers are used for precision sensing, spectroscopy, medical applications, and military applications. The most common IR source is the light emitting diode (LED). This is the primary source used in the technologies discussed here. New and exciting advancements in technology are allowing for IR LEDs with longer and longer wavelengths. Edwin John Koerperick, a graduate student at the University of Iowa states, High brightness light emitting diodes based on the InAs/GaSb superlattice material system have been developed for use in mid-wave and long-wave infrared optoelectronic systems. By employing a multipleactive region device configuration, high optical output has been demonstrated from devices in the 3-5 µm and 7-12 µm spectral bands (Koerperick, 2009). IR Technologies The first fascinating use for infrared radiation is gas monitoring and analyzing systems. These systems are used for testing air samples to see what gasses are contained in that sample. Using an electrically modulatable IR thermal source one can optically filter the thermal energy coming from the heated filament and let that radiation pass through the gas sample to an IR sensor. This using the gathered data it is possible to calculate which IR wavelengths were absorbed by the gas. Each gas absorbs different wavelengths of IR. For example CO2 absorbs 9.4 µm IR light. So if the sensor reads a low amount of 9.4 µm IR light then you know that the gas sample contains a high amount of CO2. The new long-wave IR LEDs are beginning to be used in gas analyzers. These technologies are getting more and more advanced. One example is the
IR IN MODERN TECHNOLOGY 5 photo-acoustic infrared multi-gas monitoring system. The photo-acoustic infrared multi-gas monitoring system (PAS) has been used recently in agricultural air monitoring studies and for accurate and rapid measurements of N2O and NH3 emissions in maize and grasslands. The PAS, a semi-automated system, based on a photo-acoustic infrared detection method, appears to be an attractive alternative to GC. A built-in pump circulates gas from the static chamber to the PAS up to 50 m away, as greenhouse gas concentrations are automatically recorded at selected time intervals. Thus, the PAS avoids large variations involved in manual gas sampling, storage, and analysis in the GC method (Tirol-Padre, 2014). Thermal imaging and thermal motion detection are both rapidly growing technologies. Thermal imaging or infrared thermography is the ability to capture long-range infrared radiation using a special camera and produce a visible image. Since all objects emit infrared radiation in the long-range spectrum it becomes possible to capture images even at night with no visible light. For obvious reasons thermal imaging is widely used among military and hunting. It allows them to see warm bodies easily in contrast to a cold vegetation back ground. It is used in missile aiming systems for air to ground or ground to air. The missile can view and lock on to an infrared light source such as the warm exhaust of a jet aircraft from a very far distance. That is why aircraft in combat zones are capable of shooting off hot flairs as a defense to try to confuse incoming missiles. Thermal imaging is used by firefighters to see where a burning building is too hot to safely enter. Thermal imaging is used for space imaging. By having a thermal imaging camera in a powerful telescope we are able to view distant light sources in our universe that are not emitting enough visible light to see. We can also tell the temperature of distant stars based on the wavelength of IR light the stars may be emitting. The common motion detector simply has a sensor that is monitoring for a quick change in thermal energy or long-wave infrared radiation
IR IN MODERN TECHNOLOGY 6 within its field of view. Almost all of these technologies would not be possible without the use of Planck s law. Planck s Law Planck s law allows thermal imaging technology to calculate the temperature of the object in the field of view from the measured infrared radiation emitted by the object. For a more complete explanation of Planck s law refer to the article, Infrared (IR) image synthesis method of IR real background and modeled IR target in the references. Here is a simpler explanation. There is a relation between temperature of and object and wavelength of the radiation it emits. It is T = 0.0029/λ with T being temperature and λ being wavelength. Planck s law allows you to describe the amount of energy a body gives off as radiation of different frequencies. B ν is the radiation frequency as a function of frequency and temperature. h is the Planck constant which is 6.626070040(81) 10-34 J s k B is the Boltzmann constant which is 1.38064852(79) 10-23 J K 1 C is the speed of light. Conclusion From researching this topic the thing that caused the most interest was the possibility to simulate thermal infrared energy sources with an IR LED. This topic has been research some but is still new in development. Simulation of thermal scenes with wide dynamic range and high frame rates is desirable for calibration of infrared detection systems. Suitable projectors eliminate the need for observation of a live scene for detector calibration, thereby reducing costs and increasing safety. Current technology supports apparent temperature generation of up to
IR IN MODERN TECHNOLOGY 7 approximately 800 kelvin with frame rates of hundreds of frames per second (Koerperick, 2009). The desire to use IR LEDs to simulate thermal scenes have led to recent research. Few publications are available on long-wave IR (LWIR) light emitting diode (LED) devices. Largeformat (512 512) silicon nitride resistor arrays have been used for IR scene projection experiments. However, long-term reliability and maximum temperature of emission are still the largest issues for IR resistor technology for HWIL applications. Digital micro mirror (DMD) arrays are also used to project IR scenes but with limited high-temperature and dynamic-range capabilities. At Army Research Laboratory, we have developed an 8 7 LWIR (10 μm) LED array for possible application in IR scene projection (Das, 2008). The idea that one can use an IR LED to simulate a heat source in thermal imaging by radiating the correct wavelength but not radiating any heat is a fascinating topic. Further studies could be done in the use of IR LEDs to be used as a way to fool motion detection systems for military and law enforcement. If one could have a long-wavelength IR LED slowly light up the field of view of a motion detector then that detector would not be triggered by a human body walking through its field of view because the sensor would not read a large enough change in thermal energy in its field of view. This would allow law enforcement to pass safety through its field of view as they approach the home of a suspected subject by not triggering the motion sensor lights.
IR IN MODERN TECHNOLOGY 8 References Das, N. C., Bradshaw, J., Towner, F., & Leavitt, R. (2008). Long-wave (10μm) infrared light emitting diode device performance. Solid State Electronics, 521821-1824. doi:10.1016/j.sse.2008.09.003 Kim, Y., Bae, T., Kwon, H., Kim, B., & Ahn, S. (2014). Infrared (IR) image synthesis method of IR real background and modeled IR target. Infrared Physics And Technology, 6354-61. doi:10.1016/j.infrared.2013.12.006 Koerperick, E (2009) High power mid-wave and long-wave infrared light emitting diodes: device growth and applications. PhD (Doctor of Philosophy) thesis, University of Iowa. Tirol-Padre, A., Rai, M., Gathala, M., Sharma, S., Kumar, V., Sharma, P. C., &... Ladha, J. (2014). Assessing the performance of the photo-acoustic infrared gas monitor for measuring CO2, N2O, and CH4 fluxes in two major cereal rotations. Global Change Biology, 20(1), 287-299. doi:10.1111/gcb.12347