I remember reading an article about the safety of microwave ovens. I visited a professor of physics at a famous university in the United States. The professor said that it is impossible to have microwaves leaking out of the microwave oven because the microwave oven is an iron box with only one opening. The side of the opening (ie the door of the microwave oven) is equipped with a metal mesh. The mesh is much smaller than the wavelength of the electromagnetic wave in the microwave oven (~12 cm). According to the electromagnetic wave theory, the electromagnetic wave cannot pass through a metal hole having a diameter smaller than the wavelength. But perhaps because the metal assumed in the theory is a conductor without resistance, and the actual metal is not such a good conductor; and the microwave power generated by the microwave oven is huge (on the order of hundreds of watts), so there is always some leakage.
I recently saw an article on how to make a simple microwave receiver to detect these leaking electromagnetic waves. The device is very simple but can embody many physical meanings, so I also made one (as shown below).
The receiving device is a simple dipole antenna. In the middle of the dipole antenna, a high-frequency diode (1n4148) acts as a rectification function, that is, converts the received microwave frequency signal into a quasi-direct current. Then send a voltage amplification (~100 times) composed of an op amp, and then read the DC voltage value with a multimeter. Note that the reason we convert it to DC is because if you want to directly record the signal in the microwave band, you need a very expensive instrument.
The circuit is shown below.
The output voltage of the DC can also be amplified once by another carrier on the LM358. The 100nF capacitor in the figure acts to further filter the rectified electrical signal.
This is all done! We can put it near the microwave oven to detect the leaked microwave intensity.
Before the microwave oven is turned on:
After the microwave oven is started (note that a microwave should be placed in the microwave to absorb the microwave to prevent the microwave from burning out):
The electromagnetic waves generated by the mobile phone can also be detected by this device. However, the effect of cell phone radiation is far less than the effect of electromagnetic waves leaked from microwave ovens. We are always very wary of the radiation of mobile phones, it can be seen that microwave ovens are more important sources of microwave radiation.
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