DIELECTRIC HEATING EXPLAINED (AND SIMPLIFIED)
Microwave heating works volumetrically, affecting the whole mass of a product simultaneously (assuming full penetration depth). This stands in contract to convection heating, which heats the outside of a product first and then gradually works to the middle.
Excluding materials which are good conductors of electricity, heat is generated when an object is subjected to an electromagnetic field. This is caused by dielectric losses.* These losses are the result of the polarization of ionic particles in the material (millions of times per second) due to the oscillation of the electromagnetic field. This rapid polarization essentially creates molecular friction, which translates into thermal energy, increasing the temperature of the material.
Water molecules are one of the most polar in existence, and are usually more polar and therefore more “dielectrically lossy” than any other molecules found in materials containing water. As a result, they heat the fastest and most efficiently. This is why dielectric heating (read = microwave heating) is excellent for drying applications.
* Dielectric loss quantifies a dielectric material’s inherent dissipation of electromagnetic energy (e.g. heat). It can be parameterized in terms of either the loss angle δ or the corresponding loss tangent tan δ