Researchers have figured out how make shaped drone rotors that convert audible and ultrasound frequencies into stable mechanical spinning motion, leading to tiny drones that can be completely silent. While scary-sounding (no pun intended) it’s unclear how usable these would be in the real world, since a line-of-sight source of sound waves has to be provided.
“silent”
“powered by sound waves”
Pick one.
Of course it’s silent. It’s doubtful our sonar would pick it up, and if it did, it would sound like whales humping, or some kind of seismic anomaly
They’re powered by sound from other sources but don’t create sound themselves…no?
You claim that your kite operates without making any noise, and yet it is powered by wind, which is quite noisy.
Kites are noisy.
flap flap flap…
Humming string etc.
there is sound we can’t hear. there is also light we can’t see.