How can I keep my salad cold in the microwave?

Don't put the salad in the microwave.

. . . .

Microwaves essentially pervade the cooking chanmber inside the microwave oven, and excite any polar molecules, especially including water and some polar fats.

Since vegetables—salad—are nearly all water, they are exceptionally easy to heat in a microwave oven.

You might then ask: why not "insulate" the vegetables to keep them from getting warm. After all, you could put them in a regular oven covered by a thick towel, and they would heat more slowly. In truth, even in a conventional oven, the simplest way to not heat something you don't want to be heated is to not put it in the oven.

However, in the microwave it is even less practical to prevent excitation of any given food. Microwave ovens are designed to reflect the microwaves into the food from all angles, including the bottom. Almost all microwave safe cooking vessels (or plates, as show in the picture above) are completely transparent to microwaves, so they will not protect the food.

If the vessel was not transparent to microwaves, it would not be usable in the microwave for the most part.

As others have pointed out, a Faraday Cage (a conductive metal mesh with hole sizes substantially smaller than the wavelength of the microwaves—about 12 cm in most home style microwave ovens) can prevent the waves from penetrating. However, this would have to completely surround the food item, in order to protect it.

It would also have to have no edges or bends smaller than about 1 cm radius in order to prevent arcing due to edge effects. A sphere would be most ideal, and least practical.

The Faraday cage itself heats up due to the movement of electrons within it under the influence of those microwaves that are not reflected. This why the energy does does not penetrate.

Lastly, the other food in the microwave will still heat, and so the oven itself will warm up through the normal modes of convection and air conduction from the heated food, which may warm the food to be protected indirectly.

So the simplest, most practical way is to leave the food you don't want to heat outside of the microwave in the first place.

OK, so the obvious "don't put salad in the microwave" answer has been given. And I agree.

BUT, think about the microwave door. You can see through it, but microwaves don't come buzzing out of it and burn your eyes. You'll notice that the door contains a metal mesh, which creates a "Faraday Cage".

See here for more information about blocking microwaves

You "could" build a dome-shaped Faraday cage to put over your salad, but I suspect that it would not be protected from below. Plus heat will be conducted from your chicken, through the plate, and into the salad. Plus it would probably invalidate the warranty for your microwave oven!

So, to be honest, the best thing is to take the salad off the plate first. When I ran my pub's kitchen, I would prepare the salads on a tray, and then lift them onto the plate just before the food was taken out (e.g. for steaks). This way, the hot food went out really hot, and the salad was only on the plate for 15 seconds before it was at the customer's table.

The simple answer is you can't be selective with how things get heated in the microwave. If you put salad in it will get heated. The device you are looking for to solve this issue is called a bowl, and you put the salad in it while the food in the microwave heats, then use devices called salad spoons to move it from the bowl to the plate.

Most of the answers here are taking the wrong approach. Instead of taking the salad off of the plate, you should move the chicken to its own plate during heating and move it back to the salad plate once it has been heated.

The salad in the picture appears to be fairly delicate. Moving it to another plate may destroy it. When chicken is heated up in a microwave, its liquids tend to make a mess on the chicken's container or plate. By heating the chicken on a plate other than the one you will be eating off of, your eating plate will be cleaner and your salad will remain isolated from any flavor of chicken.