1
\$\begingroup\$

How do piezoelectric transducers in ultrasound probes fail? I have a machine whose elements are being driven by an amplifier that is very noisy. The signal I see arriving from the power amplifier has white noise and also a popping/clicking characteristic.

I was wondering if driving an element outside of its resonant frequency would damage it. In principle, if the resonant frequency is 5MHz and you drive it with 8MHz, could that cause damage? What if there are multiple frequencies like in white noise... if you drive an element with high power white noise, would that damage the transducer too?

Any other way these elements could fail?

\$\endgroup\$
1
  • 1
    \$\begingroup\$ Anecdotally, I took a look at an 8MHz probe for something like vascular doppler sensing and it had failed open. Maybe the ceramic cracked. \$\endgroup\$
    – Spehro 'speff' Pefhany
    Commented May 9, 2016 at 1:30

1 Answer 1

Reset to default
2
\$\begingroup\$

The 5 typical failure modes for piezoelectric crystals are:

1) Cracking of the wafer from being over-driven, signal is too strong.

2) By being driven by a signal with too much DC content, which distorts the shape of the wafer, making it easier to crack even with normal AC drive signals.

3) Being driven by too low of a frequency, such that it is out of the crystals natural resonate frequency range, making it prone to cracking.

4) Being driven by too hi of a frequency, such that it is out of the crystals natural resonate frequency range, making it overheat until it cracks or the metal coating melts.

5) Corrosion. These wafers have a thin tin or platinum plating that corrodes quickly if it is not in a sealed container, such that only the ultra-sound can enter or exit the container.

Some designs include resistive heaters behind the crystal to prevent moisture from forming on its surface.

\$\endgroup\$
5
  • \$\begingroup\$ Very thorough response! And great knowledge! So let me ask: If you drive it with too strong of a signal, will you create microscopic cracks which build over time? Or will the entire element be destroyed? I like your idea about DC content. Will that create a bowing which pre-stretches the material? I wonder if ultrasound probes are capacitively coupled to their drivers? I remember hearing that a transurethral probe needed surge protection caps in-line. Thanks for the corrosion idea. Lastly, how does off-resonance frequency damage it? There is no energy being deposited... just reflected. \$\endgroup\$
    – PJazz
    Commented Jun 12, 2016 at 22:50
  • \$\begingroup\$ @PJazz. At maximum power levels the crystal will develop 'micro-cracks' which will lead to the entire crystal cracking-and stop working. Adding DC to the AC signal just puts more stress on the crystal. Other than corrosion, the normal fail mode is the crystal begins to put out spurious LF noise that gets worse with time until the crystal cracks and stops working. Spurious LF noise is a sign the crystal may already have micro-cracks. If my answer was what you needed please add +1 or click on the star under the bottom arrow. \$\endgroup\$
    – user105652
    Commented Jun 12, 2016 at 22:59
  • \$\begingroup\$ @PJazz. A suitable capacitor-inductor filter in line with the crystal will at least filter out DC and out-of-band (off-resonance) frequencies that can hurt the crystal. The crystal acts as a capacitor type load so it tries to absorb and resonate to any frequency you feed it. It bows or heats up with out-of-band frequencies, but some can cause a LF reflection as the crystal tries to stay in a 'flat' shape. \$\endgroup\$
    – user105652
    Commented Jun 12, 2016 at 23:09
  • \$\begingroup\$ I have ordered some piezo Buzzers that were handled roughly and show crack on the piezo-wafer. I have tested them and they create a signal, but should I use them for my build? How will the cracks affect their performance? \$\endgroup\$
    – Da Spotz
    Commented May 18, 2018 at 14:47
  • \$\begingroup\$ @DaSpotz. A cracked piezo wafer will only get worse with time. There is no self-healing. They may sound 'shrill' and tinny while playing music. At some point you will have to replace them. \$\endgroup\$
    – user105652
    Commented May 18, 2018 at 18:05

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.