Omnidirectional Ultrasonic transmitter

Discussion in 'General Electronics Discussion' started by Sami Tabbakh, May 15, 2018.

  1. Sami Tabbakh

    Sami Tabbakh

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    Hello everyone

    I am looking for a small (diam. <= 10mm) omnidirectional ultrasonic transmitter.
    So far, all the ultrasonic transmitters that I found have relatively small beam width (usually < 60deg), and the omnidirectional ones are those found in marine applications are big (diam. > 35mm).

    Can anybody tell me where I can find such an item?

    Regards
     
    Sami Tabbakh, May 15, 2018
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  2. Sami Tabbakh

    kellys_eye

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    There's a (good) reason why the beam width is 'narrow' - is your requirement for a small (physically) sized transducer or a large beam width?

    The usual ultrasonic transducers used in hobbyist applications are similar to these:

    https://www.sparkfun.com/products/13959

    and around 15mm in diameter. I haven't seen anything smaller. You would be limited in range using one so small anyway. Even the larger suppliers don't have anything smaller than the hobbyist market stuff and the prices are....:eek:

    https://uk.rs-online.com/web/c/auto...C747261736F6E6963207472616E73647563657226&r=f
     
    kellys_eye, May 15, 2018
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  3. Sami Tabbakh

    Sami Tabbakh

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    15mm is fine by me. My problem is that I'm not using it as radar, where the utility of narrow beam width comes in handy. In my application, I want to emit ultrasonic waves in omni-(or semi omni-) directional manner from a hand-held device.
    I found some spherical transmitters for underwater applications. But they are huge! and tend to be very expensive.
    Check http://www.benthowave.com/products/BII-7520omnidirectionaltransducer.html
    I was wondering if I can find something similar but bit smaller.
     
    Sami Tabbakh, May 15, 2018
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  4. Sami Tabbakh

    kellys_eye

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    I would have thought that given the limited applications for devices such as the one you link to there isn't any other market requirement for a smaller version? You might be stuck with using a bigger one!
     
    kellys_eye, May 15, 2018
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  5. Sami Tabbakh

    Alec_t

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    I think the nearest you'll get will be an array of small transmitters pointed in different directions.
     
    Alec_t, May 15, 2018
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  6. Sami Tabbakh

    timff

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    I believe you will find a relationship between ultrasonic transmitter size and frequency. The lower the frequency the larger the transmitter. The lower frequencies provide greater signal strength at a distance. For example 200kHz may give you a 10mm transmitter element, but the signal may only go out 3-4m before it is unusable. A 100mm transmitting element may give you 10m range at 40kHz.

    Most piezo elements used in ultrasonics are driven in a pulse mode for greater range in radar like applications. If you want to operate in a continuous mode and with broad directionality, I would suggest using a ultrasonic element used for cleaning tanks. They are usually big enough to handle the power for continuous applications. The problem is finding any in your target size.

    If you can find a mini transducer intended for cleaning applications, it might be possible to construct a radiating element to bolt it to such that it gives you less directionality.
     
    timff, May 15, 2018
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  7. Sami Tabbakh

    Alec_t

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    Alec_t, May 15, 2018
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    Sami Tabbakh and hevans1944 like this.
  8. Sami Tabbakh

    hevans1944 Hop - AC8NS

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    It might help us to identify a product if you told us what you are trying to do. Omni-directional hand-held device isn't very informative. Is it hand-held in air? Underwater? At what distance must it provide an ultrasonic pressure wave? At what intensity? Is this a medical device? A weapon to ward off dogs? We don't discuss weapons here. What ultrasonic frequencies do you want to emit? Are the ultrasonic waves pulsed or continuous? How much power is required?

    Much more information is necessary to define what transducer (if any) is suitable for your application.
     
    hevans1944, May 15, 2018
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  9. Sami Tabbakh

    Sami Tabbakh

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    It should be a hand-held device in air. I don't require much power, only to ping several other receivers.
    It should emit at a specific frequency (40KHz for example). The distance is not greater than 1 or 1.5 meters.
    My requirements are loose. The hardest requirement is that it should be omni-(or semi omni-) directional and relatively small (<15mm diameter).

    @Alec_t , "like these" are very interesting. Thanks man!
    My concern is that they don't seem to have products that are ready to be used now as an electronic component (like conventional ultrasonic transducers). I will be checking some similar stuff.

    I also Stumbled upon this.

    Please guys, keep me posted if you found something that could help me. I'l be waiting for your answers.
     
    Sami Tabbakh, May 16, 2018
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  10. Sami Tabbakh

    poor mystic

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    Hi
    I think that you need a waveguide. It is difficult to design a waveguide with true omnidirectionality, but easy enough if all you really need is 360° on a plane. Here's an idea how to engineer an anisotropic planar wavefield given a point source transmitter.
    Imagine you have 2 discs, like LP records, lying on one another. Now imagine that the disc on top is lifted a few mm. The transducer is fitted to the hole at the centre of the LP, and we plaster over the matching hole in the lower LP.
    Sound emitted by the transducer spreads out and reaches the edge of the cavity between the discs, and radiates away evenly around the circle.
    :)
     
    poor mystic, May 16, 2018
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  11. Sami Tabbakh

    Sami Tabbakh

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    Sounds interesting.. but I doubt I'l be able to do this myself. I need something that is already manufactured, and then I can use it on my PCB.
     
    Sami Tabbakh, May 16, 2018
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  12. Sami Tabbakh

    hevans1944 Hop - AC8NS

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    @Sami Tabbakh: Are you ever going to tell us what you are trying to do? Or must we continue to play this guessing game of offering possible solutions that you then reject?
     
    hevans1944, May 17, 2018
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  13. Sami Tabbakh

    Sami Tabbakh

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    I'm sorry if this is the impression that I gave.
    As I mentioned earlier, I am designing a hand-held device. It should transmit ultrasonic waves to several receivers that are located in different directions. As for the distance, 1.5 meters are enough. I want the user to be able to send these waves without having to point directly to the receivers.
    Also, I want the receivers to pick up the sound waves from the direct path. Not from an echo.
    You want me to reveal more? or can you guess what I am trying to do? :)
    I don't believe the final goal is relevant to my question.
    BTW, I am glad to have someone to discuss this with. Even if no solution was found, I think it is a nice exchange of ideas.
    PS. : Please I need your ideas because this is very important for me.
     
    Sami Tabbakh, May 17, 2018
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  14. Sami Tabbakh

    poor mystic

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    I think it's pretty easy to engineer this waveguide. It really will work using a couple of LP records! All you need is to fit your transducer to the hole in the middle of the top LP, block up the hole in the bottom LP, and put in a few small spacer blocks to keep the 2 discs the right distance apart.
    If you want a manufactured solution you could look at what's being made for bat and insect studies, but I expect you'd have to pay heaps for such niche market gear, and it's usually directional.
     
    poor mystic, May 20, 2018
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  15. Sami Tabbakh

    poor mystic

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    poor mystic, May 20, 2018
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  16. Sami Tabbakh

    poor mystic

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    I've had a further day to think...
    If you use back-to-back frisbees instead of LP records, you'll get a much better acoustic match between the transducer and the atmosphere, because of the rounded edge of the frisbees.
    If you're interested there are tricks to use to help get the match perfect, which is very desirable.
     
    poor mystic, May 20, 2018
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  17. Sami Tabbakh

    BobK

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    Last time I looked LP records and frisbees were larger than 10 mm.

    Bob
     
    BobK, May 21, 2018 at 12:55 AM
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  18. Sami Tabbakh

    poor mystic

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    Hi Bob. Why does 10mm seem significant? I'm sure it's not... The only job of the pair of discs is to channel sound waves from the centre of the apparatus to the edge, from whence they'll be radiated away to parts unknown, and other ultrasonic stations. Sound waves follow easier rules than transverse electromagnetic waves - they are compression waves and require no special spacing - except to match the waveguide to the source and load.
     
    poor mystic, May 21, 2018 at 8:54 AM
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  19. Sami Tabbakh

    hevans1944 Hop - AC8NS

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    Are we still wasting time playing "guessing games" on this thread, which is going nowhere? I thought this was a discussion forum, yet the OP deigns to not discuss WTF he is trying to do, offering only that a small handheld 40 kHz omnidirectional ultrasonic transmitter is somehow required to do it.
     
    hevans1944, May 21, 2018 at 10:50 AM
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  20. Sami Tabbakh

    BobK

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    From the first line of the original post:
    Bob
     
    BobK, May 21, 2018 at 1:55 PM
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