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A globar is a heated silicon carbide rod used with a filter to emit mid-IR radiation for spectroscopy. It doesn’t need a vacuum tube and is efficient.
A globar is a heated silicon carbide rod used as a thermal radiation device with emissions in the mid-infrared (IR) frequency range. A globar is used in conjunction with a dichroic or interference filter to emit IR radiation in the mid-IR spectrum. This emitted IR radiation is used in infrared spectroscopy as a diagnostic and measurement tool in research, industrial analysis and forensic applications. Due to the lack of rod oxidation in air, the globars do not need to be enclosed in vacuum tubes as is the case with alternating IR light sources.
All heated matter emits thermal radiation to varying degrees. Thermal radiation is not the same as thermal energy which is perceived as heat, but rather electromagnetic emissions in the infrared spectrum of invisible light. Different materials reflect or absorb this radiation differently depending on the exact wavelength of the emissions and the type of material involved. These known factors allow infrared radiation to be used as a diagnostic tool in the science of spectroscopy. When combined with an interference filter, a globar emits thermal radiation in the mid-IR range spectrum at wavelengths of approximately 4-15 micrometers.
The heated material used in a globe is silicon carbide in the form of a small rod typically 0.2 to 0.4 inches (5–10 mm) in diameter and 0.8 to 1.2 inches (20–50 mm) in length. To initiate the irradiation process, the rod is electrically heated to a temperature between 1.832° and 3.002° Fahrenheit (1.000° – 1.650° Celsius). Due to the lack of oxidation of silicon carbide in air at these temperatures, the rod does not need to be enclosed in a vacuum tube. If it’s closed, it’s simply a security measure. An interference filter is placed between the globe and the test sample which produces a specific known IR wavelength used to conduct the tests.
Alternative mid-IR emitters used in infrared spectroscopy include nickel-chromium alloy coils, high-pressure mercury lamps, and older Nernst lamps. The globar is, however, one of the more practical and efficient sources of mid-range IR radiation, particularly in the new generation of portable spectroscopy equipment. The globar name is also a brand name for a range of silicon carbide resistors manufactured by various companies. Technically however, the term correctly refers to the application of the IR emitter and the reference to the global resistor is simply a trade name.
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