How do I drive this cheap ultrasonic probe?

[CFlower]

Hi everyone,

I've acquired a cheap ultrasonic probe (advertised as for a thickness gauge.) It's a temperature resistant probe up to 300C and operates at 5MHz. It came with no documentation or means to drive it. It terminates in two LEMO 00 connectors, and I've acquired 2 LEMO 00 to BNC adapters. I've tried just plugging one cable into a function generator, but got no visible vibration or anything (next time I will maybe try dipping it in water to see.) However I have a strong feeling that the function generator was broken (I tested it with an oscilloscope which admittedly may also have been broken, but saw no results.)

My question is, what would the best way be to get some vibration? I don't need this to be exactly at 5 MHz. It's intended to be used for some experimental sonication. Could the other LEMO 00 be for a voltage source? Was the function generator the right step?


Any suggestions or replies are greatly appreciated!

Thanks,
C

 

[Okefenokee]

Do you have any links or part numbers for the probe? A datasheet would be nice.

 

[CFlower]

I wish I had a datasheet for you, but I've gathered all that I know so far. It was purchased of Amazon (from China.) Keep in mind we only have the probe, no electronics with it.

This was listed on the amazon page:
Frequency: 5MHz
Crystal Diameter:12mm
Measuring Range:3-200mm ( in Steel )
Lower limit: 30mm
Temperature Range: lower than 300℃

However, almost unsurprisingly, we were shipped a different probe than was in the picture. I found on ebay an identical probe to the one we have being sold by what seems to be the same "company." It has the following specs listed

Name: 300ºC High Temperature Probe
Model: GT-12 (Lemo 00 connector)
Frequency: 5MHz
Diameter of the contact proportion: 14mm
Measuring Range: 4.0mm-80.0mm
Avaliable Contact Temperature: Below 00ºC
Application: use for all Ultrasonic thickness gauge

The picture had "Sparker Instruments" watermarked on it, and the model GT12. The seller was called M&A Electronics. I've searched all of these terms extensively and come up with only ebay and aliexpress selling links, so I think the notion that this is a legitimate company is out the window. I'm not too concerned about that, as we only need this to function as a transducer to some capacity for experimental purposes. If we can show some sort of preliminary success we can justify spending more money on a legitimate setup. But for now this is what I'm stuck with. I will keep looking for more information and will post it here if I can find any. I hope this helps! Would it be possible to determine something useful (say, resistance) experimentally? That is probably within my means to do.

Thanks!

 

[256bits]

If it is an ultrasonic probe, it probably has an ultrasonic transducer.

Since it is rated for 5 MHz, the signal will be attenuated at other driving frequency, just due to the fact of how these things work and are made. Whether 5MHz is the fundamental frequency, which I surely suspect it is, you won't obtain an output by driving it an any other frequency from your signal generator.

In fact, one does not use a thickness probe connected up to a signal generator. What you need is a pulse generator. Have you ever heard the 'ping' from the sonar of a movie where a warship is tracking a submarine. These things work the same way. A voltage is applied to the device and released. The transducer resonates at its fundamental frequency for a cycle or 2, sending the sound wave into the material you wish to test. The sound reflects off the back of the material, and re-enters the probe, this time producing an voltage in the probe. The difference in time between the sent signal and the reflected material and the speed of sound in the medium determines the thickness of the material. So what it does is "chirp" out and you get a "chirp" back.

You will have trouble "seeing" effects from a 5 MHz vibration.

Putting the thing in water is of no use as it sets up an impediance mis-match, as water is a liquid, not a solid.

Your probe might send out a compression wave or a stress wave.
Your probe might have a single transducer or a dual, most likely not a matrix.
I do suspect the two connectors are as follows: one should be for output signal from your driving electronics, and one for input signal from the reflected wave.

 

[CFlower]

Thanks for your reply! It has been very informative. The function/signal generator that I have has a pulsed mode (effectively a square wave, right?)

What you've said about water is interesting, I didn't mean I would submerge the probe entirely, just the end of it to get some verification of whether or not the probe is on. I figured if we actually were getting vibration some spray/cavitation would be visible if I dipped the moving part of the probe into the water.

I'll try this now. I have an amplifier that can step up the pulses to 120V, which is closer to but not quite what I suspect is the appropriate voltage for this transducer. I'll try driving the transducer and instead of putting the end in water, I will hook up the output cable to an oscilloscope.

 

[256bits]

Here is a bunch on ultrasonic transducers which you now have me more interested in.
http://www.ndt-ed.org/EducationResources/CommunityCollege/Ultrasonics/EquipmentTrans/transducertypes.htm

And a bit from a company.
http://olympus-ims.com/data/File/panametrics/UT-technotes.en.pdf

You will notice that a transducer can be fashioned to work within a liquid.
See page 43 about the wear plate having to be 1/4 wavelength for an immersion type, but they also say that for the delay line transducer.

 

[CFlower]

Thanks for the information!

Does anyone have any idea what current we might have to drive this at? I've been told pules will have to be around 300-600 V but I can't get a stable reading of resistance for the transducer. It fluctuates wildly between 0 and 300 ohms...