A susceptor is a material used for its ability to absorb electromagnetic energy and convert it to heat (which in some cases is re-emitted as

infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from aroun ...

thermal radiation Thermal radiation is electromagnetic radiation generated by the thermal motion of particles in matter. Thermal radiation is generated when heat from the movement of charges in the material (electrons and protons in common forms of matter) is ...

). The electromagnetic energy is typically radiofrequency or

microwave Microwave is a form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter corresponding to frequency, frequencies between 300 MHz and 300 GHz respectively. Different sources define different fre ...

radiation used in industrial heating processes, and also in

microwave cooking A microwave oven (commonly referred to as a microwave) is an electric oven that heats and cooks food by exposing it to electromagnetic radiation in the microwave frequency range. This induces polar molecules in the food to rotate and produce th ...

Operation

, susceptors are built into paper packaging of certain foods, where they absorb microwaves which penetrate the packaging. This process raises the susceptor patch temperature to levels where it may then heat food by conduction or by infrared radiation. * Conduction heating occurs with good thermal contact between the susceptor and food. Because of the lower temperatures there is less browning, but more than if there were no susceptor at all. * If there is an air gap (or at least, poor thermal contact) between the susceptor and food, the susceptor will heat to a much higher temperature (due to its smaller effective heat capacity when in poor contact with food), and, at these higher temperatures, will radiate strongly in the

. This infrared radiation then shines onto the food below or next to the susceptor, causing a "broiling" type effect (high skin heating) due to lower ability of infrared to penetrate foods, vs. microwaves. Conversion of some microwave energy to infrared is particularly useful for foods which require a large amount of crust-browning from infrared, such as frozen pies.

Design and use

Susceptors are usually made of metallised film,

ceramic A ceramic is any of the various hard, brittle, heat-resistant and corrosion-resistant materials made by shaping and then firing an inorganic, nonmetallic material, such as clay, at a high temperature. Common examples are earthenware, porcelai ...

s or

metal A metal (from Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. Metals are typi ...

s (such as

aluminium Aluminium (aluminum in AmE, American and CanE, Canadian English) is a chemical element with the Symbol (chemistry), symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately o ...

flakes). The susceptor (which may be located on examination by its gray or blue-gray color, which is different from paper) is the reason products meant to be browned via susceptor-generated

carry instructions to microwave the food while still inside its packaging. Susceptors meant to heat foods by direct conduction, where less browning will occur, may be seen in the gray lining of packaging directly holding the food and in good contact with it. A typical example of the latter is the paper-susceptor–lined dish directly holding a microwaveable pot pie or casserole. Susceptors built into packaging create high temperatures in a

microwave oven A microwave oven (commonly referred to as a microwave) is an electric oven that heats and cooks food by exposing it to electromagnetic radiation in the microwave frequency range. This induces polar molecules in the food to rotate and produce ...

. This is useful for crisping and browning foods, as well as concentrating heat on the oil in a microwave popcorn bag (which is solid at room temperature) in order to melt it rapidly. Among the first microwave susceptors marketed were those from the mid-1980s in a product called McCain Micro Chips by McCain Foods. It consisted of a susceptor sheet which cooked French fries in a

. These sheets are currently used in several types of packaging for heating and cooking products in microwave ovens. Care in package design and use is required for proper food safety. A "crisping sleeve" is a device made of

paperboard Paperboard is a thick paper-based material. While there is no rigid differentiation between paper and paperboard, paperboard is generally thicker (usually over 0.30 mm, 0.012 in, or 12 points) than paper and has certain superior attribute ...

and affixed with a susceptor used both as a rigid container to support the food items within and to focus heat on the foodstuff. They are generally intended for a single use. Hot Pockets is an example of a product which uses crisping sleeves.

References

External links

"Susceptor heating" on commercial website

Cooking appliances Packaging materials Electromechanical engineering Microwave technology American inventions

Operation

Design and use

See also

References

Further reading

External links