harmonic ringing.
Take a good crystal wine glass, dip your finger in some wine and slowly but evenly run your finger around the rim. It will start to ding at its resonant frequency. This is a sine wave being generated.
Now stop and pick up a wooden spoon and start tapping the rim of the same glass with it. It will also ring at the same frequency. Everything has resonant frequencies.
As you tap the glass, vary the rate of tapping. You may find that at certain rates, the ringing appears to be dampened while at other rates, the ring is loud and clear. The sound id loudest and clearest at harmonics and then the harmonics are not right, the ringing becomes dampened.
This is a simple demonstration that while any frequency can cause ringing, the right frequency will cause the maximum effect.
If you have 1 frequency, is that the right frequency or will another frequency produce better results.
Multi-frequency zappers ...
https://huldaclarkparazapper.com
Ella Fitzgerald could shatter a wine glass by singing just the right note. That is what a zapper is supposed to do to microbes.
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