What to do with Your Brand New Ultrasonic Transducer

We wager you haven’t you heard the latest from ultrasonics. Sorry. [Lindsay Wilson] is a Hackaday reader who wants to share his knowledge of transducer tuning to make tools. The bare unit he uses to demonstrate might attach to the bottom of an ultrasonic cleaner tank, which have a different construction than the ones used for distance sensing. The first demonstration shows the technique for finding a transducer’s resonant frequency and this technique is used throughout the video. On the YouTube page, his demonstrations are indexed by title and time for convenience.

For us, the most exciting part is when a tuned transducer is squeezed by hand. As the pressure increases, the current drops and goes out of phase in proportion to the grip. We see a transducer used as a pressure sensor. He later shows how temperature can affect the current level and phase.

Sizing horns is a science, but it has some basic rules which are well covered. The basic premise is to make it half of a wavelength long and be mindful of any tools which will go in the end. Nodes and antinodes are explained and their effects demonstrated with feedback on the oscilloscope.

We have a recent feature for an ultrasonic knife which didn’t cut the mustard, but your homemade ultrasonic tools should be submitted to our tip line.

20 thoughts on “What to do with Your Brand New Ultrasonic Transducer

  1. I’d love to see a writ up on hackaday about how various types of sensors can be used to build images like ultrasound scanners… strikes me it could be interesting…

  2. Would such a transducer be better suited as a seismometer than the more common Piezo discs, when used as a sensor? The reason being that a higher power transducer like this, must produce more signal. Also it is mechanically stronger, so it can support a higher stationary mass so it will be better suited for sub Hertz waves and less susceptible to noise.

    1. I think the issue is more of power requirements than accuracy. A piezo sensor would have very low power requirements and so would be suited for use in a remote (battery and/or solar powered) sensor location.

  3. Interesting video but why do you need to tune to the original frequency?

    The transducer will resonate at whatever frequency it wants to no matter what you stick on the end of it. The original resonant frequency of a bare transducer is of no interest or use assuming you are going to want to use it for something other than measurements. The important thing is to have the minimum number of steps in anything you add and whereever possible make those steps half a wavelength apart so they are all at nodes.

    The difficult thing is finding a node and making your mount, handle, whatever, at that point.

    The cheap Chinese ultrasonic cleaners just alter their frequency so that they run at resonance just like any LC oscillator does.

    I think that you have to look at both ends of the transducer with your mount on the back side preventing oscillations there in order to not lose at least half of your signal down that way anyway.

    Complicated stuff.

      1. I don’t think he is right. The transducer is not designed to be used at the stand alone resonant frequency at all. It is designed to be fastened to something in order to make it useful and that will always change the frequency. The transducer is designed to work over a range of frequencies around the natural stand alone resonant frequency.

        1. The transducer is designed to work within a small band of frequencies — a 40kHz transducer will not work very well if you try to drive it at anything other than it’s resonant frequency. I think he mentions this in the video, showing the transition in resonant frequency with various horns.

          Tuning to the natural frequency, sans attachments, only gives you a ballpark range, and allows you to tune to the 1st harmonic.

          1. (Thanks to HaD for the mention) You’re absolutely correct – the transducer is considered as an entire resonant system, even on its own. If you attach it to something that causes the entire assembly to resonate at a different frequency, yes, you could drive it at that, but it wouldn’t be as efficient. These transducers are carefully designed (but don’t ask me how), in the choice of materials, shape, size, and bolt tension, to operate most efficiently at the specified resonant frequency.

  4. I have messed with these Chinese ultrasonic cleaners a lot and though nominally 40 kHz the first resonance is anywhere between 37 and 45 kHz. What is more interesting is that around 70 kHz they will resonate again and take 50% more power, this repeats at just over 100 kHz where they will take well over double what they draw at 40kHz.

  5. I personally would love to see an article on selecting these to retrofit to non working watch cleaning machines. There’s a lot of people who would find that equally interesting and it’s not something that really anyone publishes, but there’s a lot of old cleaners out there with broken ultrasonic units and I only know of one guy who fixes such things and he’s not very forthcoming with information. Showing us how to turn these modules into working cleaning devices would be very helpful

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