Ultrasonic detection

[Esteban]

I remember Alonso built an ultrasonic long range detector with 2 audio brute tweeters, transmitter and receiver, medium heavy machine and many batteries. This discriminates for gold and silver at good depth. He seal this, don't know what happens.

I post this in march:

I think the next generation of detector will be via ultrasonic ray for to measure density. Different density mean different absorption in ultrasonic, a kind of "ultrasonic" densimeter. So, if each material absorbs a quantity of ultrasonic ray, will be more easy the "classification" of materials, extended for no metal items.
http://thunting.com/geotech/forums/showthread.php?p=44997#post44997

Please red this article:
http://web.mit.edu/newsoffice/2006/land-mines-1220.html

[hung]

Thanks Esteban, great article. Altough they don't mention the range capabilities, I believe this is a very promising aproach. As an audio engineer, I can envision even a way of image scanning using ultrasound. In fact we know how low frequencies do penetrate matter, for instance in the 50 to 100 Hz range, the wave can measure more than 30 feet long.

They mention that at 1 meter away, the SPL is around 155db. Well that's real loud as my main monitors in the studio goes up to 120 db and it's LOUD!

Also very smart decision of using lasers to measure the slightest move of ground.

Food for thought: If the resonant frequencies for different metals are known, then how sucessful would be to employ such a thing with a high amplitude?

[Esteban]

Ooops!

red.
Really the word must be read.:o

[Leto]

Attenuation lost?

Hello..
Ultrasonic treasure finder eh?
For soundwaves short enough to discern manmade objects attenuation in soil is just too big.
Of course is great for shallow items as mines.
Attached is most optimistic report. -> For resolution in range of 5cm (Freq. range 1.7 to 5.2 kHz) image depth of 30 - 40 cm is feasible.

[JC1]

BOOM !!!

Hi Guys,

Interesting, not sure how they make this "beam".

Even constructive interference won't amplify but they

are self demodulating whatever that means in this case.

the air in front of the acoustic beam converts the ultrasound to much lower frequency audible tones that sound like extremely loud tuning forks.

lower frequency? tuning forks?

Have to look into it. Thanks for the information Esteban.

the vibrations from the mine, resonating from the sound waves, push up on the ground and can be measured remotely with a laser system called a Doppler vibrometer.

Unlike ultrasound, the low-frequency sound can penetrate the ground, causing detectable vibrations in the mine's plungers and membranes.

{Is this a "smart" thing to do? vibrate the mine and guts.}

Lower freq may penetrate futher in the ground.

I don't know. 155 db is pretty dang loud. audible freq.

Playing with this in your backyard may wakeup the

neighbors.

Oh, and keep in mind that with federal funding in this case

DARPA all sorts of things get investigated which don't

always pan out.