Is it possible to scan humans with ultra low frequencies to study medically one's physique?
one aspect of acoustic waves is that they tend to interact with things on the same order of magnitude of size as them. Infrasonic wave, say 10 Hz, at the speed of sound (340 m/s) are:
340(m/s)/10(1/s) = 34 m
The reason ultrasound (at around 10MHz) works so well is because:
340/10,000,000 = 35 um (that's micrometers) so it can pickup the tissue structures that make up humans.
The human body resonates at a frequency greater than that for "elephant" or "whale" infrasound -- perhaps helpful with communication or even brain feedback, if not directly imaging.
It depends on what cavity you're referring to; the whole human body doesn't have some single natural frequency; it's a complex geometric object full of soft tissues, not a string. For wavelengths on the order of molecular and tissue structures, it's pretty much the same for both humans and elephants. You start talking about a stomach or a lung, of course, and it's a different story. But if you want to image a lung from either an elephant or a human, it will be ultrasound.
infrasound doesn't work for imaging small things:
Even if you've got an infrasonic acoustic wave the order of a lung to transmit and detect for backscatter, it wouldn't detail the lung like an ultrasound does. You'd essentially get one data point representing the lung. With ultrasound, you get several data points representing many pieces of the lung, so you can put an actual image together.
humans can certainly respond to infrasound, but not in a pleasant way
Why should humans (or more precisely human organs) alway be the standard? Bats use sound for 'imaging'. Dogs, birds also perceive higher frequencies than humans. What is infra-sonic to one species is ultra-sonic to another.
That wiki link may explain what happened in Fatima on 13th October 1917 in another thread in this section.
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