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Beam width!

Discussion in 'Electronic Design' started by Adam, Oct 17, 2006.

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  1. Adam

    Adam Guest

    I have few 40kHz T and R ultrasonic transduces, and don't have any
    info about thier beam width,
    can anyone let me know how to measure their beam width please?

    Thanks in advance
  2. Jim Thompson

    Jim Thompson Guest

    If they're like the bunch I have in my junk box... pretty wide. I
    used them as motion detectors for an alarm system design, and they
    covered a 4' hallway within a few feet away from the transducer.

    "Measure"? I don't know :-(

    ...Jim Thompson
  3. Measure ... lets see, if you position both of them in
    free space, meaning without refections from anything,
    and have them rotateable around 3 axis,
    then operating them should give you an idea. Beam
    width means where the signal drops off by 3dB.

  4. Joerg

    Joerg Guest

    Hello Adam,

    Basically by CW transmission and then rotating the receiving tranducer
    on a circular arch around the transmitter. Ideally you'd want a
    professional sound pressure sensor as a receiver but a crystal should do
    for a rough overview. Lots of web resources, such as this one:
  5. qrk

    qrk Guest

    You can get a rough idea about the beamwidth of simple circular
    transducers with the following equation:

    bw = 2*asin(lambda/(2*D))

    where lambda = wavelength = c/f
    D = diameter of the active face of the transducer

    In air at room temp, lambda is appx (345 m/s)/(40kHz) = 0.00863 m =
    8.63 mm.

    Be sure wavelength and diameter use the same units (e.g. meters,
    inches, rods, ...).

    If you want a slightly more accurate answer, the "2" in the equation
    is closer to 1.9436.
  6. Rich Grise

    Rich Grise Guest

    Set up a test bench in a soundproofed room - maybe hang blankets on
    the walls or something, and ping the TX and move the RX around and
    see what you get.

    Good Luck!
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