is it like magnets? I feel like it’s magnets
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Have you ever tuned a guitar, trying to make two strings sound exactly alike? If so, you’ve heard that when they’re very close but not quite right, you get an undulating sound effect. This is called a beat frequency.
Metal detectors contain two electronic “guitar strings” called oscillators, that you calibrate to play the exact same tone. The tone is inaudible, but if the tuning is out of whack, an audible beat frequency can be heard.
One of the oscillators uses a big coil of wire to determine its tone. The coil sits inside the metal-detecting disc.
If you’ve ever made or seen an electromagnet, you know that current passing through a coil of wire makes a magnetic field. And if you know how an electrical generator or transformer works, you know that if you pass a changing magnetic field thorugh a coil, you get a current. What you may not know is that this happens to any metal, coiled or not. When there is no coil, the generated current just loops around inside the metal. This looping current makes its own magnetic field which affects the current in the original coil. Since the original coil determines the tone of one oscillator, any metallic object sets it out of whack with the other, and the beat frequency is heard, with a higher tone the more and closer metal there is.
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