Help driving a mysterious ultrasonic transducer probe?

Thread Starter

CFlower

Joined Jun 3, 2014
11
Hi everyone, I'm new here so bear with me and thanks for any advice you can give.

I've acquired a cheap ultrasonic probe. 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 in to a function generator, but got no visible vibration or anything. 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
 

bertus

Joined Apr 5, 2008
22,276
Hello,

Without any further information on the probe, it will be very difficult to give advice.
As far as I know most ultrasonic devices work at frequencies between 30 and 200 kHz and not the mentioned 5 MHz.

Bertus
 

Thread Starter

CFlower

Joined Jun 3, 2014
11
Hi Bertus,

Thanks for the reply! I know what you mean, things are very difficult with the amount of information that I have. Most transducers for things like ultrasonic cleaners are indeed around the range you mentioned, but there do exist ultrasonic thickness probes/gauges that claim they operate at 5 MHz. Here is an example:
http://uk.rs-online.com/web/p/thickness-gauges-meters/6850918/
Though this is a different probe, you can see in the picture it is also connected by LEMO 00 ports.

What other information should I try to find? Speaking very generally, would a signal generator and/or voltage source work in theory with any transducer?

Thanks!
 

Thread Starter

CFlower

Joined Jun 3, 2014
11
You're right Bob, I definitely don't expect to see anything at 5 MHz. I was unclear, I had hooked the setup up to an oscilloscope and looked for the signal there. I also was told that putting one end of the transducer in water would generate spray, and tried that to "see" the vibration.
 

alfacliff

Joined Dec 13, 2013
2,458
we use ultrasonic probes here to check for voids in composits. they operate at 5 mhz, but to drive them, you need a few hundred watts, and water cooling. without knowing anything except what connectors yours uses, they could be anything.
 

Thread Starter

CFlower

Joined Jun 3, 2014
11
Hi Alfacliff,

Very interesting! Do you mind telling me a little bit more? Do you know roughly what kind of voltage you are putting across the elements? (I assume it is also quite high.) I also am not too worried about the water cooling, this probe was advertised as resistant to temperatures up to 300C, so as long as we can maintain it below that it should work, in theory. Are the transducers you use driven with a sine wave or a pulse sequence at 5 MHz?
 

alfacliff

Joined Dec 13, 2013
2,458
pulses about 300 to 600 volt pulses. the water is more for conduction of the ultrasonic through the composite, two sprays, one on each side, with the transmit probe in one and the recieve probe in the other.
 

Thread Starter

CFlower

Joined Jun 3, 2014
11
Thanks for the information! I suppose the next thing I ought to try and figure out is how to step up my function generator signal with something like 300V pulses. I found an old amplifier that steps to 120 V but after testing I still saw no results when putting the probe in a little water. Maybe this voltage is still not high enough, or maybe the amplifier is broken (a real possibility.) Any recommendations on how to proceed? Are such amplifiers common?
 

Thread Starter

CFlower

Joined Jun 3, 2014
11
I've put together a "datasheet" of everything I know. I hope this may help explain my situation a little better.

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. Would it be possible to determine something useful (say, resistance) experimentally? That is probably within my means to do.
 

RichardO

Joined May 4, 2013
2,270
Any recommendations on how to proceed? Are such amplifiers common?
A couple of quick thoughts...

To get started testing a 5 MHz transducer, you want a pulse that is shorter than 100 nS and has a risetime of less than 70 nS.

Assuming that this is a piezoelectric transducer, the easiest way to do this is to charge the capacitance of the transducer to a high voltage using a resistor to limit the charging current and then discharging the transducer's capacitance by shorting it with a transistor.

The amplifier must have a bandwidth of greater than 5 MHz and must have an input that can withstand the high voltage pulse.
 
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Thread Starter

CFlower

Joined Jun 3, 2014
11
Thanks for the information!

Do you have any idea what the current through something like this might be like? I cant get a good measurement of the resistance unfortunately... it fluctuates wildly between 0 and 300 ohms.
 

RichardO

Joined May 4, 2013
2,270
Thanks for the information!

Do you have any idea what the current through something like this might be like? I cant get a good measurement of the resistance unfortunately... it fluctuates wildly between 0 and 300 ohms.
Are both Lemo connectors the same? Do they both measure the same?

One Lemo may be the transmitter transducer and the other the receiver transducer.

The fluctuation may indicate that there is active electronics in the "transducer".
 
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