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Offline ramTopic starter
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« Reply #10 on: May 29, 2011, 10:39:44 am »
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thank you for the idea homefire, i have to try it your idea.

ram,

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« Reply #11 on: August 05, 2014, 07:57:44 am »
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Just to ask to experts, if you think is posible to build a GPR based on baby monitor that works on 49 Mhz? Tis are the ones thats are a transmiter and a receiver.
Thanks
Nelson


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« Reply #12 on: August 06, 2014, 01:35:23 am »
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Well here's something interesting, ultrasonic ranges from 20 Khz through to 150 Khz but VLF is from 3 Khz through to 30 Khz so when building a VLF detector you are in fact building an ultrasonic metal detector. Just though this was interesting and decided to post it here since this thread is about ultrasonic.

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« Reply #13 on: August 06, 2014, 05:39:14 pm »
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You have the frequencies right Xavier, and technically you would be correct except for this detail. VLF uses electromagnetic and electrostatic waves whilst Ultrasonic uses air pressure waves. VLF can travel in outer space, but ultrasonic cannot. A  25 kHz ultrasonic receiver would need a pressure transducer to receive a signal and a 25Khz VLF receiver would use a coil/capacitor to receive the signal. Does anyone know that Ultrasonic sound can be generated up into the gigahertz range? YEP! Medical Ultrasound is in the megahertz range. Remember it is sound pressure, not electromagnetic/electrostatic transmission.
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Posted on: August 06, 2014, 04:11:42 pm
I was wondering from things that I have read about ultrasonic, that it might be possible to use ultrasonic sound waves to detect metal not by measuring the reflected pulse delay return time (such as distance measurement) but measure the difference in reflected frequency change or phase or a completely different frequency. I have not tested this theory yet, but it seems to me that bouncing a sound pressure wave of different objects, you should be able to get them to vibrate at a frequency depending on their composition. If you strike a 12 inch metal rod it will vibrate at a specific frequency depending on what type of metal it is. If you strike a 12 inch wooden rod of the same diameter it will vibrate at much different frequency than the metal one would. The reflected signals would definitely be in the audio ranges. I know you are going to give me the argument that this would be true if it was in open air, and gold and coins are buried in the ground so they can't vibrate. But is that really true? It seems to me that the amplitude would definitely be muffled and the reflected frequency would be shifted much lower than in open air. Anyone want to start a joint project to test this out with me? They said no one could build a machine to see inside the body and yet today we have X-ray and Ultrasound technology that lets us do that.

Golddustcarl

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« Reply #14 on: August 06, 2014, 09:13:02 pm »
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GDCarl the oil companies already use that system.  On dry land they have huge truck that roams around a potential area and stopping and jacking it's self up.  The transducers are probably in legs of the beast, then it smacks the ground with a big ram and listens for the return waves which are interpreted by software and printed out in graph form.  At sea they just lower a unit to the bottom and use a humongous woofer to bans the bottom.  This procedure drives the Cetacean lovers out of their collective minds.

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« Reply #15 on: August 07, 2014, 01:55:17 pm »
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Thanks Gramps for reminding me of that. I can just see myself in the playground with one of those trucks. Everybody for blocks would jump out of their shorts, and the kiddies would need therapy for years. Grin Grin. While that is a little overkill I suppose, the general principles work the same way.

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« Reply #16 on: August 07, 2014, 06:54:11 pm »
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I have seen a much smaller unit used by archeologist hunting for subterranean hollow areas that might contain goodies.  It's a gizmo with an approx. 1' square plate with a pipe extending up about 30" and a hole cut in the plate where the tube attaches.  The top of the pipe has a chamber that takes a 12 ga. shotgun blank.  Then the barrel extends down, inches ?, to an sliding weight closed at the bottom and I assume a spring that holds the weight up.  The operator would chamber a load stand on o either side of the pipe and touch it off driving the weight into the ground.  A guy pushing or pulling the sensor would be close by and capture the returns.  Had to be a gutsy dude having a shotgun shell go off so close to George and the twins.

Dennis

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« Reply #17 on: August 08, 2014, 02:48:14 pm »
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Quote:Posted by golddustcarl
VLF uses electromagnetic and electrostatic waves whilst Ultrasonic uses air pressure waves.

Golddustcarl

I knew that I was doing something wrong when I hit the send button LOL

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« Reply #18 on: August 09, 2014, 08:16:16 pm »
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 Not pointing out mistakes intentionally but it was an easy mistake for someone make because your logic always sounds so good and most of time you are 100% on the right track.  Great

golddustcarl

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« Reply #19 on: January 13, 2015, 02:09:21 pm »
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Just some added thoughts about RF metal detectors and similarities to ultrasound. Ultrasonic methods ping a device that generates sound pressure frequencies then waits for a return signal. Pulse induction sort of works similarly where we switch a large current through a coil to generate an electromagnetic-electrostatic signal, and then wait for a return signal. That is the only similarity. In Vlf, BFO, or IB we generate a constant electromagnetic-electrostatic signal while monitoring it's phase or frequency. Gradiometers measure the change in the earth's magnetic field. The only other method I know of is electro-resistive methods that are used either to measure the change in resistance of the soil or a minute voltage change in the presence of buried metal.

Dusty Carl  Wise

Here is another tidbit. RF signals are not the same as ultrasonic signals. The only thing they share in common is they are referenced to by the same terminology: frequency. Ultrasonic waves are regular periodic changes in air pressure and only travel through air, gases or solids. Rf  signals do all of these, plus travels in a vacuum.

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« Last Edit: January 13, 2015, 02:28:21 pm by golddustcarl »
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