How to check if your microwave oven has a radiation leak

The secret comes from the namesake of the machine — microwaves. In case you are unaware, these are electromagnetic radiation (like light and radio waves) that lie towards the longer wavelength of the EM spectrum. 

Microwaves have frequencies ranging from about 1 billion cycles per second (1 GHz) up to 300 times that and have wavelengths (the distance between peaks) of between 12 inches (30 cm) and 0.04 inches (1 mm). To put that into perspective, radio waves typically have wavelengths varying from 1 mm to 100 km, and the light visible to our human eyes roughly falls between 380 to 700 nanometers (a sheet of paper is typically 100,000 nanometers thick).

Inside a microwave oven, microwaves are generated in a piece of tech called a magnetron and are beamed into the metal interior of the microwave oven. Anything you put inside the microwave oven (food, drink, etc.) absorbs these rays. These microwaves excite the water molecules within the food/drink, causing it to heat up rapidly. The higher the water content inside the target food/drink, the faster they tend to cook, so moist items cook much faster than desiccated items. 

For bigger chunks of food, the microwaves only cook the outermost layers, with the inner bits cooked via the conduction of heat from the outside. With all that radiation shooting inside the microwave oven, it is not ideal to have much of it leaking outside the box. For this reason, devices like microwave ovens must undergo rigorous testing before they can be released for general use.

How do you test your microwave for radiation leakage?

While very high standards are typically set for tolerable levels of microwave leakage from microwave ovens, some microwaves can, and inevitably will, escape. So, how do you test how effective the microwave shielding is on your microwave? As it turns out, there is quite a simple test. 

A fascinating, if not slightly disconcerting video by Physics Girl shows us why we should probably all check our microwave ovens. Her simple experiment shows us that there is an easy and effective way to check the integrity of the radiation shielding on your kitchen appliance. And all it takes is a little bit of lateral thinking. 

Microwave ovens, like cell phones, emit radiation in a specific band of EM frequencies — specifically radio waves. All things being equal, you should expect that by placing your phone inside a microwave and closing the door, the signal would be blocked by the shell of the microwave oven.

If this is the case, it would also be reasonable to assume that you shouldn’t be able to ring the phone once it is safely locked inside. It turns out this is not the case. Somehow and somewhere, EM radiation can reach the phone’s antennae, resulting in you being able to call it from outside! But how? 

As it turns out, the main form of shielding built into the microwave is a device called a “Faraday cage.” These devices work by dissipating the charge from EM radiation around their structure. This happens because electrons in the metal are excited by the radiation and move throughout the metal structure of the cage, creating an electric field that opposes and cancels out the external wave or field of anything inside it. 

In this sense, Faraday cages are effectively hollow conductors. Any breach in the structure of this cage can, theoretically, allow small amounts of EM radiation to “leak” inside (or outside)the cage. According to this experiment, this is indeed the case for some microwave ovens. 

Do all microwave ovens leak radiation?

This simple experiment is interesting, but it is impossible to quantify exactly how much leakage your microwave oven may have. For this reason, more sophisticated means of investigation are required. For example, are all microwave ovens equal? Perhaps yours is of a lower quality than others? 

If you repeat the experiment using different ovens, as Physics Girl did, you will likely find that some block the cellphones while others do not. 

Building on her findings, she decided to find which part of the microwave was letting the radiation escape. Using aluminum foil to act as a near-perfect Faraday cage, she completely wrapped her phone. Sure enough, no one was able to call her phone. 

The next step was to wrap certain parts of the microwave oven to narrow down and seek out the “leaky” parts. By systematically leaving parts of the microwave unwrapped, they hoped to find the leak. It turned out that the door was the most likely culprit.

What are some other simple tests for microwave radiation leaks? 

To confirm her theory, Physics Girl employed a self-professed hacker’s services to use a HackRF radio transmitter and receiver to conduct a more sophisticated experiment. These devices can receive and transmit signals from 1 MHz to 6 GHz. Using the device and a bona fide Faraday cage, they demonstrated that you shouldn’t be able to call a phone shielded by one — if it is fully intact.

Next, they tested whether commonly used Wi-Fi signals can enter the microwave’s door. Wi-Fi signals use a similar frequency to microwave ovens, so this is an exciting test. Microwaves typically operate around 2.45 Gigahertz, while cellular signals are around 1.9 Gigahertz or 850 Megahertz.

Sure enough, they could FaceTime the phone through the microwave door. Interestingly, older microwave ovens have been shown to affect the quality of your domestic Wi-Fi routers and devices! But, we digress. Using the same detector, they could also directly detect microwave energy outside of the microwave oven.

They hypothesized that the radiation could be exploiting holes in the shielding of the door, allowing the microwave oven to leak radiation. As Physics Girl points out, her experiments show that some microwaves let the specific frequencies of mobile phones through, providing clear evidence that some form of radiation leakage is possible within these appliances. Physics Girl notes that their experiment had a tiny sample size and did not consider the microwave oven’s age or proximity to a cellular tower. These variables could affect the results.

Should you be worried if you find that your microwave is leaking?

FDA regulations allow for a small amount of leakage over the lifetime of the microwave, of about five mW/cm2 at approximately 2 inches (5 cm) from the oven surface. The radiation itself is non-ionizing, so that it won’t damage your DNA directly, rather it will excite the water within your soft tissues. 

The FDA does warn that high exposure to microwaves can lead to a painful burn. Organs like eyes and testes are particularly vulnerable because they have relatively little blood flow to carry away the heat. Also, the lens of the human eye is susceptible to heat. High levels of microwaves could cause cataracts.

The FDA also notes that this kind of damage would require much radiation. So, should you be concerned if your microwave oven leaks radiation? In short, No. You are more likely to hurt yourself from a heated glass of water than the radiation. The radiation will not be high enough to cause you any harm. 

So, even if you discover that your microwave leaks some radiation, it is of such a small amount and a non-mutagenic kind that you shouldn’t lose sleep over it. Though, standing very close to your microwave when it is in operation should probably be avoided.

And that is your lot for today.

So does your microwave oven leak? Even if it does, it’s important to note that microwave energy is classified as non-ionizing radiation and is generally considered safe. Whatever the case, it’s advisable to exercise caution and follow the manufacturer’s instructions when using any electrical appliance, including microwaves.