How Do Microwaves Work?

The microwave is probably the most critical tool that many have in their kitchen, especially for someone who needs to heat up a meal quickly. But, while just about every house and apartment you will ever enter will have a microwave many people don’t understand how they work or misunderstand how they function.

Microwaves work by producing microwaves in an electron tube. The waves are then reflected within the metal interior of the oven where they are absorbed by food. Microwaves cause water molecules in the food to vibrate, producing heat that cooks or heats up the food.

Now, even with this explanation, it can still be very confusing to understand how the microwave works, but don’t worry as throughout the rest of the article I will explain how each of the steps works in using a microwave, along with many of the possible dangers that come with microwaves. Along with that, I will give a brief history of how the microwave was created, allowing us to reheat our leftovers.

Do Microwaves Produce Radiation?

Yes, microwave ovens produce a type of radiation called electromagnetic radiation. Microwaves are a form of “electromagnetic” radiation, in other words, they are waves of electrical and magnetic energy moving together through space. The size of electromagnetic radiation waves varies greatly, spanning from very long radio waves to very short gamma rays. The reason that many aren’t aware of electromagnetic radiation is that our human eyes are only able to see a very small amount of the spectrum, which we call visible light.

However, we utilize other spectrums in many aspects of our life, like using radio to detect a different portion of the spectrum and using an X-ray machine, which detects uses yet another portion of the spectrum.

Types of Electromagnetic Radiation

Visible light, microwaves, and radio frequency (RF) radiation are forms of non-ionizing radiation.  Non-ionizing radiation does not have enough energy to knock electrons out of atoms. X-rays are a form of ionizing radiation. Exposure to ionizing radiation can alter atoms and molecules and cause damage to cells in organic matter. 

How Microwaves are Used

Microwaves are used to detect speeding cars and to send telephone and television communications. Industry uses microwaves to dry and cure plywood, cure rubber and resins, raise bread and doughnuts, and cook potato chips. But the most common consumer use of microwave energy is in microwave ovens.

Microwaves have three characteristics that allow them to be used in cooking: they are reflected by metal; they pass through the glass, paper, plastic, and similar materials; and foods absorb them. This is crucial as when the food absorbers the microwaves, it causes the atoms to shake, heating up the food.

How Microwaves Cook Food

As mentioned earlier, the simplest way to explain how microwaves work is that the food absorbs the microwaves, causing the atoms to vibrate which heats up your food.

Microwaves are produced inside the oven by an electron tube called a magnetron. The microwaves are reflected within the metal interior of the oven where they are absorbed by food. Microwaves cause water molecules in the food to vibrate, producing heat that cooks the food. That’s why foods that are high in water content, like fresh vegetables, can be cooked more quickly than other foods.

The microwave energy is changed to heat as it is absorbed by food, and does not make food “radioactive” or “contaminated. So you don’t need to worry about your food becoming radioactive or dangerous. The only way to do that is through overcooking.

Although heat is produced directly in the food, microwave ovens do not cook food from the “inside out.” When thick foods are cooked, the outer layers are heated and cooked primarily by microwaves while the inside is cooked mainly by the conduction of heat from the hot outer layers.

Microwave cooking can be more energy efficient than conventional cooking because foods cook faster and the energy heats only the food, not the whole oven compartment. Microwave cooking does not reduce the nutritional value of foods any more than conventional cooking. In fact, foods cooked in a microwave oven may keep more of their vitamins and minerals, because microwave ovens can cook more quickly and without adding water.

Materials That Makeup the Microwave Oven

Glass, paper, ceramic, or plastic containers are used in microwave cooking because microwaves pass through these materials. Although such containers cannot be heated by microwaves, they can become hot from the heat of the food cooking inside. Some plastic containers should not be used in a microwave oven because they can be melted by the heat of the food inside.

Generally, metal pans or aluminum foil should also not be used in a microwave oven, as the microwaves are reflected off these materials causing the food to cook unevenly and possibly damaging the oven. The instructions that come with each microwave oven indicate the kinds of containers to use. They also cover how to test containers to see whether or not they can be used in microwave ovens.

Microwaves Safety Standards

The FDA received reports in the past of serious skin burns or scalding injuries around people’s hands and faces as a result of hot water erupting out of a cup after it had been overheated in a microwave oven. Super-heated water (water heated past its boiling temperature) does not appear to be boiling and occurs when water is heated by itself in a clean cup.

If super-heating has occurred, a slight disturbance or movement such as picking up the cup, or pouring in a spoon full of instant coffee, may result in a violent eruption with the boiling water exploding out of the cup. Adding substances such as instant coffee or sugar before heating greatly reduces this risk.

You will want to closely follow the precautions and recommendations provided in the microwave oven instruction manuals, specifically regarding heating times.

Have Microwaves Caused Radiation-Related Injuries?

Microwave radiation can heat body tissue the same way it heats food. Exposure to high levels of microwaves can cause a painful burn. Two areas of the body, the eyes, and the testes are particularly vulnerable to RF heating because there is relatively little blood flow in them to carry away excess heat. These types of injuries – burns and cataracts – can only be caused by exposure to large amounts of microwave radiation.

Consumers should take common sense precautions regarding the handling of hot foods and beverages. Most injuries related to microwave ovens are the result of heat-related burns from hot containers, overheated foods, or exploding liquids. Most injuries are not radiation-related.

That said, there have been very rare instances of radiation injury due to unusual circumstances or improper servicing. In general, microwave oven radiation injuries are caused by exposure to large amounts of microwave radiation leaking through openings such as gaps in the microwave oven seals. However, FDA regulations require that microwave ovens are designed to prevent these high-level radiation leaks.

Microwave Ovens & Pacemakers

The reason that I bring up pacemakers is that at one time there was concern that radiation leakage from microwave ovens could interfere with certain electronic cardiac pacemakers. Similar concerns were raised about pacemaker interference from electric shavers, auto ignition systems, and other electronic products.

While FDA does not specifically require microwave ovens to carry warnings for people with pacemakers, this problem has largely been resolved as today’s pacemakers are designed to shield against such electrical interference. However, patients with pacemakers are encouraged to consult their physicians if they have concerns.

Microwaving the Wrong Materials

  • Aluminum Foil. The most commonly-used household item you should never put in the microwave is aluminum foil. It’s essentially a very thin metal that, when exposed to microwave radiation, will reflect the energy instead of absorbing it. This, in turn, can create sparks that could ruin the appliance, or worse, start a fire.
  • Anything With Metal or Stainless Steel. Plates with shiny metal rims and stainless-steel travel mugs can also cause a fire if put inside a microwave. Moreover, these vessels will prevent your food and beverage from warming up.
  • Single Use Plastics. Plastic bags and containers like yogurt tubs should never be microwaved because they may contain bisphenol A, more commonly known as BPA. These materials can easily melt inside the appliance releasing BPA into your food
  • Takeout Containers. Chinese restaurant takeout containers tend to have a metal rim and are sometimes lined with plastic materials. However, the containers that most restaurants use are usually microwave-friendly. To be sure, always check for the microwave safe sign which usually looks like a box with squiggly lines in the middle.
  • Styrofoam. Styrofoam (a.k.a. polystyrene foam) isn’t just bad for the environment, it also melts quickly if exposed to radiation. Much like plastic, this can release dangerous chemicals into your food and potentially cause long-term illnesses.
  • Uncovered Pasta Sauces. The most notorious culprit responsible for a messy microwave is tomato-based pasta sauces. If warmed uncovered, they can spit and splatter all over the appliance. This is because the thick consistency of the sauce can trap the steam until it explodes. Instead, reheat your pasta or pasta sauce in a pot or saucepan on the stove.

Leakage & Other Possible Safety Problems

There is little cause for concern about excess microwaves leaking from ovens unless the door hinges, latch, or seals are damaged. The FDA recommends looking at your oven carefully, and not using an oven if the door doesn’t close firmly or is bent, warped, or otherwise damaged.

The FDA also monitors appliances for radiation safety issues and has received reports of microwave ovens that appear to stay on – and operate – while the door is open. When operating as intended, microwave ovens have safety features to prevent them from continuing to generate microwaves if the door is open.

However, if an oven does continue to operate with the door open, consumers cannot be 100 percent sure that microwave radiation is not being emitted. Thus, if this occurs, the FDA recommends immediately discontinuing the use of the oven.

If you suspect a radiation safety problem with your microwave oven, you may contact the microwave oven manufacturer. Manufacturers who discover that any microwave ovens produced, assembled, or imported by them have a defect or fail to comply with an applicable federal standard are required to immediately notify FDA. In addition, manufacturers/importers are required to report all accidental radiation occurrences to the FDA.

Who Invented the Microwave

Like many great inventions, microwave ovens were an accidental discovery. Back in the 1950s, American electrical engineer Percy Spencer (1894–1970) was carrying out some experiments with a magnetron at the Raytheon Manufacturing Company where he worked. At that time, the main use for magnetrons was in radar: a way of using radio waves to help airplanes and ships find their way around in poor weather or darkness.

One day, Percy Spencer had a chocolate bar in his pocket when he switched on the magnetron. To his surprise, the bar quickly melted because of the heat the magnetron generated. This gave him the idea that a magnetron might be used to cook food. After successfully cooking some popcorn, he realized he could develop a microwave oven for cooking all types of food. He was granted a series of patents for this idea in the early 1950s, including one for a microwave coffee brewer

Spencer’s early equipment was relatively crude compared to modern wipe-clean microwaves—his first oven was around 1.5 meters (5 ft) high! Since then, microwave ovens have become much more compact and millions of them have been sold throughout the world.

It’s easy to put Spencer’s invention down as a “mere” happy accident, but there was more to it than that: it takes the right kind of inventive mind to seize on discovery and make something of it. As Reader’s Digest magazine later reported, Spencer “demonstrated that nothing is beyond the grasp of a man who wants to know what is going on, and who feels a sense of responsibility for doing something about it.”

The 130 patents he was granted in his lifetime attest to that, and to his inventive ability to put scientific ideas into practical action.