What type of equipment is required to record ultrasound above 1MHz?

[mriver8]

Please give me links if you have them.

[Enthalpy]

Hi mriver8, welcome here!

 

1MHz is nothing special, neither for microphones (piezo elements) nor recorders (hard disk drive). The defining question is whether you consider ultrasound in air, and then 1MHz is really a lot, or in a liquid or solid, for which 1GHz would still be possible and existing technology.

[mriver8]

I'm interested in recording ultrasound travelling through the air.

[Strange]

I'm interested in recording ultrasound travelling through the air.

 

I think you will need to be within a few inches of the source, at that frequency.

[mriver8]

That's fine do you have any links?

[mriver8]

I'm interested in methods of deflecting/shielding ultrasound up to 3GHz traveling through air as a medium. My search lead me to the study of creating impedance mismatches to affect sound wavess. I'm looking specifically for the acoustic impedance neccessary to act as a shield of sorts for materials with an acoustic impedance around one and a half. Some of my searches have said an impedance of around 7 would suffice however I can not find any papers on such tests, and how various materials affected ultrasound travelling through air as a medium at different frequencies. I'm guessing that there have been tests in this area with military applications which would suffice if readily available. To my knowledge this is the best way to affect sound waves, if there are any other methods please feel free to shar

[Sensei]

Where do you have source of sound at such frequencies?

Do you have equipment generating such sound?

Do you have equipment detecting such sound?

If you do so, then start placing different materials between emitter and receiver, to see which one will be working..

Do you know how sound is generated by speaker?

By moving membrane in and out, in and out, as many times as frequency you have in sound.

If membrane would be moving 3 GHz for 1 cm it's 3*10^9 * 2 * 1 cm = 60 mln m/s = 20% speed of light.

For 1 mm distance movement, it's 2% speed of light.

At 16 kHz membrane moving 1 cm in & out, is reaching nearly speed of sound in air.

Edited September 3, 2014 by Sensei

[Enthalpy]

[...] ultrasound up to 3GHz traveling through air [...]

 

That cannot exist, so you don't need to shield it. It exists in liquids and solids.

 

At any frequency including sensible ones, every solid makes a very efficient impedance mismatch with air. Matching air is difficult, mismatching very easy.

If membrane would be moving 3 GHz for 1 cm it's 3*10^9 * 2 * 1 cm = 60 mln m/s = 20% speed of light.

For 1 mm distance movement, it's 2% speed of light.

At 16 kHz membrane moving 1 cm in & out, is reaching nearly speed of sound in air.

 

Which is why displacements are not what you assume. 3GHz is commonly used in non-destructive testing of solids, with a displacement at the transmitter that is nowhere near cm nor mm.

Do you have equipment generating such sound?

Do you have equipment detecting such sound?

If you do so, then start placing different materials between emitter and receiver, to see which one will be working..

 

As 3GHz sound doesn't propagate through the atmosphere, no transmitter exists, no receiver neither, and materials can't be tested.

 

Just for reference, the mean collision frequency of air molecules at ground level is 6.9e9/s, so a 3GHz sound can't exist in the atmosphere.