The Barkhausen Effect: Hearing Magnets Being Born

solenoid wound pickup coil next to a selection of bolts and a steel rod

The Barkhausen effect — named after German Physicist Heinrich Barkhausen — is the term given to the noise output produced by a ferromagnetic material due to the change in size and orientation of its discrete magnetic domains under the influence of an external magnetic field. The domains are small: smaller than the microcrystalline grains that form the magnetic material, but larger than the atomic scale. Barkausen discovered that as a magnetic field was brought close to a ferrous material, the local magnetic field would flip around randomly, as the magnetic domains rearranged themselves into a minimum energy configuration and that this magnetic field noise could be sensed with an appropriately arranged pickup coil and an amplifier. In the short demonstration video below, this Barkhausen noise can be fed into an audio amplifier, producing a very illustrative example of the effect.

One example of practical use for this effect is with non-destructive testing and qualification of magnetic structures which may be subject to damage in use, such as in the nuclear industry. Crystalline discontinuities or impurities within a part under examination result in increased localized mechanical stresses, which could result in unexpected failure. The Barkhausen noise effect can be easily leveraged to detect such discontinuities and give the evaluator a sense of the condition of the part in question. All in all, a useful technique to know about!

If you were thinking that the Barkhausen is a familiar name, you may well be thinking about the Barkhausen stability criterion, which is fundamental to describing some of the conditions necessary for a linear feedback circuit to oscillate. We’ve covered such circuits before, such as this dive into bridge oscillators.

Thanks to {Keith] for the tip!

21 thoughts on “The Barkhausen Effect: Hearing Magnets Being Born

  1. Back in Electronics school, instead of writing in my notes what was the Barkhausen effect,
    I drew a doghouse and a barking dog.
    IOW, I didn’t learn that part of the lesson.

    1. Bark does not mean the barking of a dog in German, but I guess it helps to remember it creates a sound effect. The closest German word is Barke (also spelled Bark sometimes), and meaning a barque. It’s simply a last name.

  2. What use is this effect to the average hardware hacker? Is it a well defined noise source, is the statistical characteristics of the noise perturbed by other influences such as radio waves thus making it potentially a form of detector? What can I do with this other than demonstrate that it exists, given that the local council turned down my perfectly sensible plans to build a nuclear reactor…

    1. The example in the article describes using it in non-destructive testing in nuclear power plants. Every weld, for example, needs testing to see if it still good. I imagine a good weld would sound a certain way. A bad one, another way.
      Usually this is done with x-rays and takes a lot of time and money.

      Maybe the above is good for quick and easy test.

      1. That is a Radio shack mini amplifier, the old version from the 80s or 90s I think. There’s a newer version that looks a bit different. Inside the old version you’ll find a simple LM741 audio amplifier driving an 8-Ohm speaker, all powered by an 9V battery.

        I have several of these things I scavenged from the scrap bin back in college. No exactly great audio quality but very reliable and robust.

        1. Inside the old version you’ll find a simple LM386 audio amplifier driving an 8 ohm speaker, all powered by a 9V battery.

          The 741 is an op amp. It cannot effectively drive an 8 ohm speaker.

          The LM386 is a low power audio amplifier designed specifically to drive low power speakers.

          I owned a couple of the old Radio Shack amplified speakers. They definitely used an LM386

    1. wikipedia: “The Wiegand effect is a macroscopic extension of the Barkhausen effect, as the special treatment of the Wiegand wire causes the wire to act macroscopically as a single large magnetic domain”

    1. Indeed, and I mention that in the article, as we’ve covered [2] before, but not [1]
      Oh, and I think you’re incorrect about the attributions; I believe they are actually both due to the very same German physicist. Or at least that’s what the font of all knowledge (wikipedia) says.

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