What Is a Mica Waveguide Cover for a Microwave?

Microwave ovens are relatively simple electronic cooking appliances. The cooking chamber has a hole for the passage of microwaves, generated by a specialized vacuum tube. The mica waveguide cover is a selective filter that covers the hole in the cooking chamber. It allows microwaves to reach the food, while preventing food particles and moisture from entering the electronic components of the oven.

A hole in the waveguide cover can cause a fire in the cooking chamber of the microwave.

Basic Components of a Microwave Oven

Microwave ovens have four basic parts. The shell of the oven, including the cooking chamber, provides structure for the appliance. The magnetron, a specialized vacuum tube, and a high-voltage transformer are encased between the cooking chamber and outer shell of the oven. The fourth component is the operating console, which may be a simple timer switch or a multifunction electronic device that allows the operator to adjust cooking power.

How Microwaves Heat Food

Microwave ovens heat and cook food by bombarding the food with a form of electromagnetic radiation called microwaves. Microwave ovens, unlike conventional cooking appliances, do not have heating elements. Microwaves emitted by a specialized vacuum tube called a magnetron agitate the food molecules, causing heat to be generated by the food itself.

Waveguide Cover

The waveguide cover or shield can be seen by opening the oven and looking on the inside of the cooking chamber. It is typically located on the same side of the chamber wall as the operating console. The waveguide cover looks like a thin sheet of plastic or cardboard, often attached to the chamber with screws. The shield, made of a mineral called mica, prevents moisture and food particles from being deposited on the sensitive electronic components housed between the cooking chamber and the outer shell of the oven.

Waveguide Cover Failure

With use, waveguide covers can become soiled. If food particles deposited on the shield overheat, the cover can actually combust. Arcing, a discharge of static electricity, can also make a hole in the shield. A burned hole in the shield can cause food particles to be deposited on the sensitive circuitry of the magnetron and transformer, causing the oven to fail. If the waveguide cover is broken or burned, inexpensive replacement covers may be available from the manufacturer.