How ultrasonic propagates through air?

Opps

Adam,

As Gen. Chuck Yeager once said, "Ya want some whiskey?"

Bob

Why are you thinking so? What is the problem with my question?

That 500Hz sound only propagates spherically if the speaker is small with respect to a wavelength. Ditto for ultrasound. The only difference is the wavelength compared to you, so a 50kHz transducer that's 1/4 wave across is going to look little, while a 500Hz transducer that's 1/4 wave across is going to look BIG.

--
Tim Wescott
Control systems and communications consulting
http://www.wescottdesign.com

Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html

Adam, you should know that sound propagation through air is dramatically attenuated, beyond ordinary spherical spreading, under ordinary conditions, especially at high frequencies, and the attenuation vs frequency is dramatically affected by the air's humidity level.

I have posted detailed tables several times here on s.e.d.

Attenuation at 40kHz is dramatically more than 500Hz. You can just forget any reasonable propagation at all at 40MHz in air.

Thanks sir,

So, what about a source opening equal to the wavelength, and ahain what about a source opening much larger than the wavelenght?

Simple physics will give you your answer. Get a long length of rope say

100ft and try shaking it from one end. What happens if you shake faster ? Now if the rope were air!

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Best Regards:
                     Baron.

See, I know that what will happen, But if someone reply my above question then i'll say you what I mean by my question.

For a flat source much larger than the wavelength, the sound will propagate nearly as a straight beam (with diameter equal to that of the source) for some distance.

At a distance of order: [(opening)^2 / wavelength] and beyond, wave diffraction effects become significant and the sound will begin to spread out.

Regards,

Mark

Exactly the same way, except for much higher attenuation on the path in the air. The path loss exponent is proportional to the square root of the frequency. So the practical frequency range for the ultrasound in the air is below ~100kHz.

Vladimir Vassilevsky DSP and Mixed Signal Design Consultant

If you know what will happen then you have your answer! As others have explained.

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Best Regards:
                     Baron.

Do you know what frequency(s) American Technology Corp. Hyper-Sonic Sound Technology uses to produce highly localized audio from the mixing of ultrasonic beams?

Or, at least, that's what Electronic Design claims they do.

Robert H.