Principle of Infrared or Far Infrared Heating

Infrared (IR) radiation refers to electromagnetic waves with wavelengths ranging from 1 millimeter to 760 nanometers (nm), lying between microwaves and visible light. It is non-visible light emitted by substances above absolute zero (-273.15°C). Modern physics categorizes IR as thermal radiation, which in medical applications divides into near-infrared and far-infrared. A common source of IR in daily life is the sun, which transmits its heat to Earth primarily through IR, providing warmth and earning IR the nickname “light of life.” As depicted in the diagram, IR extends beyond red light in the spectrum (with ultraviolet beyond violet), remaining invisible to the naked eye.

IR can be classified into four types based on the emitting source:

1. Incandescent Emission Range (Actinic range): Also known as the “photochemical reaction zone,” this includes radiation emitted by incandescent objects, spanning from visible light to infrared. Examples include tungsten filament lamps and the sun.
2. Thermal Emission Range (Hot-object range): Radiation emitted by non-incandescent objects such as electric irons and other electrical heaters, typically operating at an average temperature of around 400°C.
3. Heat Conduction Range (Calorific range): Radiation produced by boiling water or steam pipes, with average temperatures below 200°C. This zone is also termed the “non-actinic region” due to its absence of photochemical reactions.
4. Warm Radiation Range (Warm range): Radiation emitted by humans, animals, or geothermal sources, typically at an average temperature of about 40°C.

IR radiation, with longer wavelengths compared to radio waves, microwaves, and visible light (arranged in increasing order of wavelength), elicits a sensation of warmth due to its thermal effects. Despite claims suggesting penetration into atomic or molecular interiors causing expansion or disintegration, IR’s low frequency and energy levels prevent such effects. Instead, IR penetrates the gaps between atoms and molecules, accelerating their vibration and increasing intermolecular spacing. Macroscopically, this results in melting, boiling, or vaporization of substances, without altering the fundamental nature of atoms and molecules. This thermal effect of IR allows for applications such as food grilling and inducing denaturation in organic polymers. However, IR cannot induce photoelectric effects or alter atomic nuclei.

In summary, the penetration range of waves increases with shorter wavelengths, higher frequencies, and greater energy levels. Conversely, longer wavelengths, lower frequencies, and lower energy levels limit penetration capabilities.

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