Microwaves make use of the dissipation factor by polarizing and depolarizing water molecules.
Dissipation factor is a measure of how inefficient a capacitor’s insulating material is. It generally measures the heat lost when an insulator, such as a dielectric, is exposed to an alternating field of electricity. A capacitor usually has two metal plates and some kind of insulator between them. The relationship between the capacitance when an insulating material is present and when the plates are separated by air or vacuum is often called the dielectric constant. The reciprocal of this relationship defines how the insulating material reacts and what its resistance is at a given frequency, generating a value for the dielectric dissipation factor.
If a material has low dissipation, it generally means that it has better efficiency. This feature is usually set to a certain frequency. To measure the dissipation of a material, a test is usually done with the material between the metal plates and then a test without it. The results can be expressed in a ratio, which is the dielectric constant normally used to test material dissipation. A dissipation factor test can be completed in other ways, such as using equipment such as test cells with different electrode configurations; the test method may vary depending on the application.
When a dielectric material is exposed to an electric field, its molecules rearrange themselves, consuming a significant amount of energy. Once the field is removed, the energy cannot be recovered. Dissipation factor is often referred to as power factor, especially when using an alternating current with a capacitive circuit that is not affected by resistance or induced current. A power factor of zero generally indicates no dissipation. Power losses are usually calculated by multiplying dissipation by voltage and current.
The dissipation factor for air and vacuum is normally zero, although air usually has a small enough loss value to be discounted under most circumstances. This is measured for specific materials like polyester, for example, at a certain frequency. Whenever the use of a specific material in an electrical circuit is considered, it is often important to understand what its energy loss looks like.
There are applications that often make use of the dissipation factor, such as the principle involved in microwave food preparation. The alternating electric fields of a microwave oven cause energy losses through the polarization and depolarization of water molecules. This results in enough heat for the food to cook.