Get electrical signal of a piezoelectric with ultrasound

[hugo_faurand]

TL;DR Summary

What material do I need to measure the signal generated by a piezoelectric device with ultrasounds ?

Hello everyone !
I'm working on ultrasound probes, and I wanted to measure the electrical signal generated by a piezoelectric device (a transducer).
Here is a sketch of the experiment :

The goal of the experiment is to compare the electrical signal of the piezoelectric cell and compare it with a mathematical model.
However, my school can only give me this type of piezoelectric device that you can find in a watch :

I don't think this kind of device will be sensitive to the ultrasounds. So here is my first question, at the place of the square with "Piezo" written in it, what electrical component should I put?
Does this kind of device work ? Here

I also wonder if I should amplify the signal of the piezo... If I have to I don't know how...

Thanks in advance.
Regards :)

 

[Baluncore]

I'm working on ultrasound probes, and I wanted to measure the electrical signal generated by a piezoelectric device (a transducer).

Do you want to measure the ultrasonic sound wave in air or in a liquid?
What range of frequency will you be using?
How accurately do you need to measure the amplitude?

 

[hugo_faurand]

Do you want to measure the ultrasonic sound wave in air?
What range of frequency will you be using?
How accurately do you need to measure the amplitude?

I think I'll plug the ultrasound emitter on the oscilloscope also but I'm not particularly interested in measuring the ultrasonic sound wave. I'd like to use ultrasound wave with a frequency from 1 to 15 MHz ( these frequencies are used in ultrasound). About the accuracy I don't know what to answer. I think the piezo cell will generate a voltage of some mV (I think) so having an accuracy of tens of mV should be fine.

 

[anorlunda]

I would try it with the oscilloscope before asking the question.

 

[Baluncore]

What will the ultrasonic probe be used for?
What "material" is between the probe emitter and the sensor you will use to monitor the signal?

 

[hugo_faurand]

What will the ultrasonic probe be used for?
What "material" is between the probe emitter and the sensor you will use to monitor the signal?

In a first approach there is no probe, just a system acting like transducer that you can find in probes, to analyze the electrical signal received. I'll work in the air in a first time and then in water. But my question is which component should I use to simulate the behaviour of the piezo transducer.

 

[jrmichler]

I suggest that you take a step back and spend a little time studying piezoelectric transducers. PCB has a general discussion that is a good place to start: https://www.pcb.com/resources/technical-information/general-piezoelectric-theory.

After reading through that, you will understand the difference between a piezoelectric crystal with wires attached, and a piezoelectric transducer with integrated electronics. If you have a piezoelectric crystal by itself, you will need a charge amplifier to measure the output. The input impedance of an oscilloscope will short circuit the piezoelectric crystal, so you will read nothing. Try search terms piezoelectric charge amplifier to start learning about charge amplifiers. A good hit to get started is https://www.allaboutcircuits.com/technical-articles/understanding-and-implementing-charge-amplifiers-for-piezoelectric-sensor-s/. It's very much simplified, but is enough to get you started.

If you are working with a transducer that comes with electronics, be aware of the bandwidth of the electronics. Make sure that the electronics bandwidth includes the range of frequencies that you plan to work with.

 

[Tom.G]

If you care to start at a lower frequency to get an idea of what is needed, try using a piezoelectric microphone, also known as a crystal microphone.

There are also crystal earphones which may be easier or cheaper to obtain. Crystal earphones are sometimes called 'high impedance' earphones.

The cheapest ones you can find (under US$10) are fine for getting started. You may want to buy two because they can be used as the transmitter (sender) if you supply a signal, and as a receiver if you connect them to a measuring device (oscilloscope, etc.)

Many, especially the cheaper ones, can be used somewhat above the audio range where they have a mechanical resonance. Operating them at resonance makes them more sensitive.

Cheers,
Tom