In the microwave technology (frequency band 300 MHz to 300 GHz), the polarity of certain molecules such as water, various salts, fats, etc. is used to put them with high-frequency electric fields in rotation or vibration in a way that warms up the entire product.
In Germany, the frequencies 915 MHz and 2.45 GHz are approved for industrial use.
Depending on the desired depth of penetration, and depending on the product characteristics, the optimum frequency is selected.
If the dimensions of the housing e.g. of a continuous heating system, in which the electrical energy is coupled, is smaller than half the wavelength (λ = c / f, wavelength equal to the speed of light divided by the frequency, wavelength at 915 MHz = 328 mm, wavelength at 2.45 GHz = 122 mm) , it is called a "mono-mode-systems". Mono-mode-systems have the advantage over multimode systems (housing dimensions larger than the wavelength) that the electric fields in the chamber are forming with almost the same field strength through the entire chamber cross-section, and thus lead to a complete heating of the product. In mono-mode-systems there are no so-called “hot spots”, which are locations in space where waves overlap each other, and no "cold" places where waves cancel each other out by interference.
If it is necessary to use multimode equipment due to the dimensions of the products to be treated, Fricke & Mallah uses so-called microwave antennas. Microwave antennas are waveguide tube pieces made of stainless steel, which are closed at the end and have a cutout on the long side, which is closed with a Teflon plate. The electromagnetic wave enters the reaction chamber through this Teflon plate.
To determine the number, size and position of the antennas, Fricke & Mallah uses special simulation software that ensures optimum efficiency.
In the following section we will concentrate on the applications of microwave technology in food production.
The nature of the microwave is related to the UVC radiation, because in both cases it is to electromagnetic radiation, but with completely different wavelengths.
The penetration depth of electromagnetic rays also increases with increasing wavelength.
The wavelength of UVC radiation (254 nm) basically penetrates only in the uppermost cell layer of the food, but is able to penetrate the cell membrane of microorganisms.
Therefore the microwave technology is used, where you want to penetrate deeper into the product to be heated.
This is the case of bulk solids, pasty liquids and solids.
Typical applications for microwaves in the food production:
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Continuous microwave plant from Fricke & Mallah
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