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Ultrasonic Antenna

09/29/2015 7:41 AM

Hello,

I am using a 50 watt 40 khz ultrasonic transducer it to transmit a signal used for leak detection. My question is, what would be the best dimensions and design for an antenna either omni or directional or both - for the max gain - on the transmitter.

Thanks

I

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Guru
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#1

Re: Ultrasonic Antenna

09/29/2015 7:54 AM

<...best..> would depend upon the nature of the terrain, the elevation of both transmitter and receiver, and the positions and natures of intervening objects.

<...40kHz...> is too low to be useful for a radio signal, so much of the concept will also depend upon the radio frequency, the mode of transmission, and the distance between the two antennae as well. Nothing has been mentioned about Licencing either, so the choice of waveband will certainly affect antenna design an selection.

At this juncture, the forum has insufficient information to advise. So a visit by a specialist organisation that has experience, local knowledge and off-the-shelf solutions for sale would seem to be a good way forward. Yellow Pages, perhaps?

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#2
In reply to #1

Re: Ultrasonic Antenna

09/29/2015 8:07 AM

The transmitter is in an en-closer E.g. ships cargo bay. Distance is no more than 10 meters. The objective is leak detection. You have accurately determined the frequency is too low for a radio signal. It is is Ultrasonic not RF. The signal is sound and not electromagnetic.

Does anyone really look at yellow pages any more?

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#3
In reply to #2

Re: Ultrasonic Antenna

09/29/2015 8:39 AM

Repeating information that has already been stated is pointless, as are rhetorical questions in the quest for solutions.

Questions remain over the method of modulating the signal so as to carry meaningful information from the transmitter to a receiver when a cable for an electrical signal is proven technology at that sort of intervening distance.

Those sorts of audio power levels in a confined space might have enormous safety implications for any creature present despite the frequency being too high for most creatures to hear; the modulation would certainly be heard due to interference effects!

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#4

Re: Ultrasonic Antenna

09/29/2015 9:31 AM

You can't have both omni directional and gain. Gain in an antenna comes from concentrating the transmission or reception in a beam in a given direction. An array of multiple transducers with the proper phase shifts (delays) can give you a beam (if that's what you want), steered in the direction determined by the delays. Given a direction, it's simple geometry to figure the delays required using the array spacing and the velocity of sound in the medium (air, water, etc).

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#6
In reply to #4

Re: Ultrasonic Antenna

09/29/2015 10:07 AM

Excellent! - thanks.

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#5

Re: Ultrasonic Antenna

09/29/2015 9:32 AM

You need a high frequency microphone.

4939 - ΒΌ-inch free-field microphone, 4 Hz to 100 kHz, 200V ...

Gain will come from the amp you use with it.

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#7

Re: Ultrasonic Antenna

09/29/2015 11:41 AM

A 5.333 Km high ground plane or a dipole of double that length if you were to transmit or receive radio waves at that frequency would work fine. If you are to transmit or receive ultrasounds, a parabolic reflector on a transducer would also do the trick. S.M.

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#9
In reply to #7

Re: Ultrasonic Antenna

09/29/2015 6:05 PM

Huh? It's ultrasonic sound at a frequency of 40kHz with a wavelength of 0.339inches, a mechanical vibration not RF energy.

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#10
In reply to #9

Re: Ultrasonic Antenna

09/29/2015 7:12 PM

Covered both cases (LOL) S.M.

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#8

Re: Ultrasonic Antenna

09/29/2015 12:48 PM

Like what i said in your previous post, I do not think this is a viable idea (there are so many variables to pass through a clean out put in this one, sound vibrates through the vessel itself-how do you plan to distinguish the leak out of it), but well, give it a try.

Ideally, you may use a fractal antenna(dipole) at generation near wavelength of 8.6 mm.

Here is some paper that may be useful in your pursuit. "Wave experiments using low cost ultrasonic transducers"

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#11

Re: Ultrasonic Antenna

09/29/2015 10:28 PM

Just purchase a quality ultra sound detector and work with the manufacturer to suite it to your requirements. It has been done many times before with full success. I know of several applications on assembly lines to test moving components for proper operation one of them was electric window function to ensure the cable was operating properly on automotive door window mechanisms. Applications are limitless for any moving medium be it mechanical or gas.

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#12

Re: Ultrasonic Antenna

09/29/2015 10:34 PM

Actually you could use a parabolic dish they use on "spying audio" systems placing the transducer at the approximate focus would give a vast improvement in sig to noise and thus gain, of course it becomes highly directional. At 40Khz a dish of say 6 inches in diameter would work fine. This seems a bit like an acoustic radar so your receiving device would need switching off while in transmit and then be switched on while in receive mode.

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#14
In reply to #12

Re: Ultrasonic Antenna

09/30/2015 8:01 AM

Thanks. I agree the parabolic dish would work best for gain and work well on the receiving side. After more thought on the application I'm now focusing on transmission side. I.e. looking for a design for a 40kHz audio omni directional antenna. I've tried flat disks cut in multiples of the wave length and they seem to only attenuate the signal. Another responder has suggested a cone. After some research I find that design is directional.

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#17
In reply to #14

Re: Ultrasonic Antenna

09/30/2015 9:14 PM

Yes I recall years ago in my Air force days that for Omini Directional antennas in the radio Frequency band (VHF and UHF) they used what is called a DISC-CONE Antenna.

Of course whether you can use this geometry for sound may take quite a bit of experimenting. The radio freq antenna was feed via 50 Ohm coax. The centre conductor went to a flat disc which was electrically isolated from the actual cone. I made one about 5 years ago using a metal funnel as the cone and a copper circuit board as the disc. As I said trying to find an acoustic analogue (coned speaker) is going to be tricky.

Good luck with the project

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#18
In reply to #17

Re: Ultrasonic Antenna

09/30/2015 9:20 PM

No. A discone antenna looks more like an umbrella with no cover. A bunch of wires and nothing more.

It will NOT pick up sound waves.

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#19
In reply to #18

Re: Ultrasonic Antenna

09/30/2015 9:37 PM

That is not quite correct disc-cone antenna's can be solid copper sheet. In the airforce they were used a great deal.

I did mention the problem will be how to make an acoustic analogue. For example an electro static speaker can be just flat plates. Maybe a sphere with two layers feed by audio signals might make an approximate omnidirectional source, a spherical speaker? Who knows

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#20
In reply to #19

Re: Ultrasonic Antenna

10/01/2015 3:36 AM

OK. Well, at least I got the spelling right.

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#13

Re: Ultrasonic Antenna

09/30/2015 7:12 AM

Fundamentally what are you trying to do? You stated you are putting a 40 KHz sound source inside the container. You provided a few more details "The transmitter is in an en-closer E.g. ships cargo bay. Distance is no more than 10 meters."

  • Are you checking to verify cargo bay is water tight (weather)? Is your checking intended to verify that tankers are oil/chemical tight?
  • Is this test to be run frequently or just at ship manufacture/acceptance time?
  • Does the audio power level pose any risks to the operator? (don't forget antenna gain, resonances & standing waves)
  • Will the equipment be hand held or mounted on something? Mostly for the stationary case but will there be issues with standing waves and resonances causing less than desired results?
  • Is this just a brainstorming idea or is there similar equipment on the market or similar test data published?
  • With all the effort that would go into this test and I suspect the risk of it not being 100% trust worthy I have to ask, would a garden hose and a little H2O be a better test?
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#15
In reply to #13

Re: Ultrasonic Antenna

09/30/2015 8:09 AM

Thanks for the response and suggestions.

I have had some success using an of the shelf test unit designed just for the application I have in mind. Proximity became an issue so- I was attempting to increase the transmitter power. I'm now just interested in best antenna design for a 50 watt 40khz omni direction antenna.

Thanks

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#21
In reply to #15

Re: Ultrasonic Antenna

10/01/2015 10:00 PM

Please explain what you mean by proximity. Proximity to what; the leak, the walls of the enclosure, the receiver, etc.?

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#22
In reply to #21

Re: Ultrasonic Antenna

10/05/2015 8:36 AM

In this case proximity is 1. The distance from transmitter to receiver. 2. The angle from transmitter to receiver. Angle of the off the shelf is about 30 degrees. In this application there isn't enough free space between transmitter and wall for 100% coverage because of the narrow beam. _ hence I'm looking for an omni antenna for the transmitter.

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#23
In reply to #22

Re: Ultrasonic Antenna

10/05/2015 11:33 AM

Got it. So your problem is the geometry of the space and the rather sharp cutoff of the beam doesn't allow it to reach all surfaces evenly. What you need is an acoustic lens that will disperse your beam evenly; i.e., a point radiator in an omnipolar pattern. Since ultrasonic transducers tend to be flat they have more of cardioid pattern with a dead zone behind it, so you'll need two configured back to back.

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#24
In reply to #23

Re: Ultrasonic Antenna

10/05/2015 2:51 PM

Excellent understanding - exactly on point! - thank you.

Back to back is an option I can work on. As an alternative, Though I may lose some radiation power, Are you familiar with any type ultrasonic antenna that could emit something close to 180 degree signal? - perhaps a dome?

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#16

Re: Ultrasonic Antenna

09/30/2015 8:48 PM

UT is useless with an air couplant. Hydrogen Leak Detection (Mil-spec) is done in a in as close to an "absolute" vacuum as is possible. The hold of a cargo ship would not, in my estimation, provide a suitable environment for this type of process. If you know the particular particulates that you are looking for, you might consider using a sniffer.

I would advise extreme caution; because, cargo holds can contain an explosive environment.

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