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 United States to get a better understanding. He explained that it's nearly impossible for microwaves to leak out of the oven because it's essentially an iron box with only one opening—the door. This door is fitted with a metal mesh, which has holes much smaller than the wavelength of the microwaves used in the oven (~12 cm). According to electromagnetic wave theory, waves cannot pass through holes smaller than their wavelength. However, the theory assumes perfect conductors without resistance, and real-world metals aren't as ideal. Plus, the power output of a microwave can be quite high (hundreds of watts), so some leakage is inevitable.
Recently, I came across an article explaining how to build a simple microwave receiver to detect these tiny leaks. The device is surprisingly easy to make but contains a lot of interesting physics concepts. I tried building one myself, and here’s what I ended up with.
The receiver uses a basic dipole antenna. In the center of the antenna, there's a high-frequency diode (like a 1N4148) that acts as a rectifier, converting the microwave signal into a low-frequency DC voltage. This DC voltage is then amplified using an operational amplifier, typically by around 100 times, and finally measured with a multimeter. The reason we convert the signal to DC is that measuring high-frequency signals directly would require expensive equipment.
Here’s a diagram of the circuit:
The output from the DC signal can be further amplified using another stage with an LM358 op-amp. A 100nF capacitor is also included to smooth out the rectified signal even more.
That's all! Now you can place this device near a microwave oven to detect any leaked radiation.
Before turning on the microwave oven:
After starting the microwave oven (make sure there's something inside, like a cup of water, to absorb the microwaves and prevent damage):
Interestingly, this device can also detect electromagnetic waves from mobile phones, though the effect is much weaker compared to the radiation from a microwave oven. It's fascinating how people are often more concerned about phone radiation, yet microwave ovens are actually a much bigger source of microwave exposure. This project not only helped me understand the science behind it but also made me more aware of everyday electromagnetic fields around us.
Voice Recorder (recordable voice box)
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plush toy,stuffer toys,Children toys,Musical toys,Children book and so
on
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2.Classification:Recordable voice recorder and Pre-record recorders
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Pre-record recorder--means that the clients provide their sound
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