Is the microwave oven heated from the inside out?

The biggest problem of microwave heating food is uneven heating. The microwave oven directly heats food, not air, which is the reason for its high energy efficiency. But it is not heated from the inside out as many people think-it is also heated from the outside in. However, compared with the traditional heating method, microwave has stronger penetration and can be directly heated to a depth of several centimeters. Traditional heating is from the surface to the inside, and the temperature of the outer layer is always higher than that of the inner layer. Because the temperature rises quickly where microwave can reach and slowly where it can't penetrate, the temperature difference between inside and outside may be very large. This is especially obvious when thawing food. Because liquid water absorbs microwave energy much more efficiently than ice, the first melting part of the outer layer is further heated efficiently, while the inner layer can only be slowly transferred to the inside by the heat from the external heated part. If the conventional heating function of microwave oven is used to thaw, the outer layer may be cooked, but the inside is still frozen. In most microwave ovens, there is a special "defrosting function"-for traditional microwave ovens, it is actually to raise the temperature and stop the machine, so that the heat in the outer layer has time to penetrate.