Microwave receivers and detecting leaking electromagnetic waves?
I remember reading an article about the safety of microwave ovens. I decided to visit a physics professor at a well-known university in the U.S. He explained that it's nearly impossible for microwaves to leak out because the oven is essentially a metal box with only one opening—the door. This door has a metal mesh, which is much smaller than the wavelength of the microwaves used (around 12 cm). According to electromagnetic wave theory, waves cannot pass through holes smaller than their wavelength. However, in reality, the metal isn't a perfect conductor, and the power from a microwave can be quite high—hundreds of watts. So, even though leakage is minimal, some does occur.
Recently, I came across an article explaining how to build a simple microwave receiver to detect this leakage. The design is straightforward but teaches a lot about physics, so I tried making one myself (as shown below).
The device uses a basic dipole antenna. In the center of the antenna, there’s a high-frequency diode (1N4148) that acts as a rectifier, converting the microwave signal into a low-frequency DC voltage. This signal is then amplified by an op-amp circuit (about 100 times), and finally measured using a multimeter. The reason we convert it to DC is that directly measuring microwave signals would require expensive equipment.
Here’s the circuit diagram:
The output can be further amplified using another stage with an LM358. The 100nF capacitor helps filter the rectified signal, making the readings more stable.
That’s all! Now you can place this device near a microwave oven to measure any leaked radiation.
Before turning on the microwave:
After starting the microwave (make sure to put a cup of water inside to absorb the energy and prevent damage):
Interestingly, this same device can also detect signals from mobile phones, although the effect is much weaker compared to microwave leakage. People are often concerned about phone radiation, but this experiment shows that microwave ovens are actually a bigger source of microwave radiation. It’s important to understand where real risks might lie.
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