Ultrasonic transducer help

Discussion in 'Electronic Design' started by kellyruperts@yahoo.com, May 4, 2005.

  1. Guest

    I'm looking for two piezo transducers between 500KHz and 1MHz for use
    in doppler velocity measurement. I'd like to find really cheap piezos
    and put them in my own plastics assembly with polyurethane epoxy to
    match the water's acoustic impedence. Precision is definitely not
    important, does anyone know where to find cheap piezos in this range
    with wire leads? All I am finding are high end transducers with highly
    focused beams, which actually the opposite of what I need. Thanks in
    advance.
     
    , May 4, 2005
    #1
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  2. Don Pearce Guest

    On 3 May 2005 22:43:58 -0700, wrote:

    >I'm looking for two piezo transducers between 500KHz and 1MHz for use
    >in doppler velocity measurement. I'd like to find really cheap piezos
    >and put them in my own plastics assembly with polyurethane epoxy to
    >match the water's acoustic impedence. Precision is definitely not
    >important, does anyone know where to find cheap piezos in this range
    >with wire leads? All I am finding are high end transducers with highly
    >focused beams, which actually the opposite of what I need. Thanks in
    >advance.


    It is not being high end that causes them to have highly focussed
    beams. At these frequencies, with corresponding short wavelengths, you
    would find it hard to make a transducer any other way.

    d

    Pearce Consulting
    http://www.pearce.uk.com
     
    Don Pearce, May 4, 2005
    #2
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  3. Don Pearce wrote...
    >
    > On 3 May 2005 22:43:58 -0700, wrote:
    >
    >> I'm looking for two piezo transducers between 500KHz and 1MHz for use
    >> in doppler velocity measurement. I'd like to find really cheap piezos
    >> and put them in my own plastics assembly with polyurethane epoxy to
    >> match the water's acoustic impedence. Precision is definitely not
    >> important, does anyone know where to find cheap piezos in this range
    >> with wire leads? All I am finding are high end transducers with highly
    >> focused beams, which actually the opposite of what I need. Thanks in
    >> advance.


    You can get the raw custom disks from Channel Industries in
    Santa Barbara, although it's rather technical and you have to
    know what you're doing. http://www.channelindustries.com/ Give
    them a call and ask what they have left around from other jobs.

    > It is not being high end that causes them to have highly focussed
    > beams. At these frequencies, with corresponding short wavelengths,
    > you would find it hard to make a transducer any other way.


    Yes, and no. Most commercial transducers in this frequency range
    that one easily come across are intended for use in the metallurgy
    industry, and they have special short-range focusing structures
    mounted on the piezo element. If instead you simply use a small
    disk, say 10mm dia, the acoustic beam will diverge. The beam-width
    in water is a function of the frequency and the width of the disk.

    The disk's acoustic vibration mode may be complex, depending on
    its thickness, e.g., see http://www.ift.uib.no/~jankoc/thesis/ but
    a piston radiator is an appropriate approximation for many cases.
    Even so, the acoustic directivity may be complex to analyze, e.g.,
    http://www.ndt.net/article/v07n06/karpelson/karpelson.htm however
    you can simplify and assume a 5-degree beam width for a 10mm disc
    at 1MHz, and scale from there.

    To understand acoustic transmission calculations, beam-width and
    the sonar equation, attenuation and other issues, I recommend
    Robert Urich's excellent book, Principles of Underwater Sound.
    On pages 102-111 of the third edition, you'll learn that the
    attenuation in water can be severe, increasing with the square
    of frequency. At 1MHz it's about 0.4 dB/meter (that's 0.8dB/m
    for a round trip). This is in addition to spreading losses.

    Have fun, Kelly, and report back to us as you proceed.


    --
    Thanks,
    - Win
     
    Winfield Hill, May 4, 2005
    #3
  4. James Meyer Guest

    On Wed, 04 May 2005 05:50:34 GMT, (Don Pearce) wroth:

    >On 3 May 2005 22:43:58 -0700, wrote:
    >
    >>All I am finding are high end transducers with highly
    >>focused beams, which actually the opposite of what I need. Thanks in
    >>advance.

    >
    >It is not being high end that causes them to have highly focussed
    >beams. At these frequencies, with corresponding short wavelengths, you
    >would find it hard to make a transducer any other way.
    >


    You can use most of the optical methods, lenses and mirrors, to expand
    or contract ultrasonic beams.

    There is a good source for piezo transducers on eBay. Check out
    http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=42899&item=3865272506&tc=photo.

    You will have to add your own wires, but that's extremely easy to do.

    Go to their eBay store for more items. Their web site has data sheets
    for their transducers. I've ordered from them before and can recommend them
    highly.

    Jim
     
    James Meyer, May 4, 2005
    #4
  5. Guest

    Thanks all for the help, the resources, this is exactly what I was
    looking for. One more question: are there any good
    websites/books/tutorials that describe how to make a transducer from a
    piezo disk? I've it is rather difficult and thought I should try to
    find something with wire leads, but I'd like to know more. Thanks
    again.
     
    , May 5, 2005
    #5
  6. Guest

    Sorry, I answered my own question pretty quickly. It seems they all
    come with electrodes that just require a good soldering connection.
     
    , May 5, 2005
    #6
  7. wrote...
    >
    > Sorry, I answered my own question pretty quickly. It seems they all
    > come with electrodes that just require a good soldering connection.


    And you'll notice that Channel Industries' downloadable
    info booklet has detailed soldering instructions.

    What are you working on?


    --
    Thanks,
    - Win
     
    Winfield Hill, May 5, 2005
    #7
  8. Guest

    > What are you working on?

    I am taking a stab at making a flow meter using continuous wave
    doppler. Mainly to avoid ones on the market that are problematic and
    pretty expensive for what you get. If I can make a transducer
    successfully (and test it out with an oscilloscope), I think I can make
    the A/D, DSP, and interface work pretty easily. Suggestions are always
    appreciated, thanks again for your help.
     
    , May 6, 2005
    #8
  9. James Meyer Guest

    On 6 May 2005 00:35:04 -0700, wroth:

    >> What are you working on?

    >
    >I am taking a stab at making a flow meter using continuous wave
    >doppler. Mainly to avoid ones on the market that are problematic and
    >pretty expensive for what you get. If I can make a transducer
    >successfully (and test it out with an oscilloscope), I think I can make
    >the A/D, DSP, and interface work pretty easily. Suggestions are always
    >appreciated, thanks again for your help.


    I don't think A/D and DSP are entirely necessary. Everything you need
    should be "do-able" with analog devices. Take a look at the spec sheets for the
    LM2907 F/V converter. www.national.com/pf/LM/LM2907.html

    Jim
     
    James Meyer, May 7, 2005
    #9
  10. James Meyer wrote...
    >
    > On 6 May 2005 00:35:04 -0700, wroth:
    >
    >>> What are you working on?

    >>
    >> I am taking a stab at making a flow meter using continuous wave
    >> doppler. Mainly to avoid ones on the market that are problematic
    >> and pretty expensive for what you get. If I can make a transducer
    >> successfully (and test it out with an oscilloscope), I think I can
    >> make the A/D, DSP, and interface work pretty easily. Suggestions
    >> are always appreciated, thanks again for your help.

    >
    > I don't think A/D and DSP are entirely necessary. Everything you
    > need should be "do-able" with analog devices. Take a look at the
    > spec sheets for the LM2907 F/V converter.
    > www.national.com/pf/LM/LM2907.html


    Tell us more, please, oh Jim, the ultra-sound man!


    --
    Thanks,
    - Win
     
    Winfield Hill, May 7, 2005
    #10
  11. James Meyer Guest

    On 7 May 2005 03:51:16 -0700, Winfield Hill
    <hill_a@t_rowland-dotties-harvard-dot.s-edu> wroth:

    >
    > Tell us more, please, oh Jim, the ultra-sound man!


    OK, but remember, you asked for it. :cool:

    Start with a clean source of voltage to drive the transmitt element.
    Harmonic distortion doesn't matter much, but amplitude and frequency "noise"
    should be kept as small as you can. Make it easy to vary the frequency a little
    to hit the "sweet spot" of the transducers, ie. be able to tune for maximum
    smoke.

    The receiver section needs some gain at the ultrasonic frequency with a
    little selectivity. A tuned step-up transformer feeding a JFET with an LC tank
    in its output should be enough.

    Follow that with a simple signal diode envelope detector. The received
    signal will contain a lot of the un-dopplered transmitt signal with the
    dopplered part being 40 to 60 db lower, so most of the system gain needs to be
    after the envelope detector. The un-dopplered carrier will create a large DC
    value at the detector. You don't need that for anything, so throw it away with
    a coupling capacitor. Make the RC roll-off low enough to catch the slowest flow
    rate you are interested in.

    From here on, it's a normal audio frequency signal.

    Next, pass the signal through an active low-pass filter with the upper
    cut-off set to pass the doppler for the highest flow rate of interest. Gain can
    be incorporated in the filter or place a gain stage before the filter with,
    perhaps, another after the filter.

    The F/V converter, if you use a LM2907, only needs a 25 to 50 mV P-P
    signal, so distribute the overall gain to get that value. The output of the F/V
    converter is, of course, an analog version of the flow rate.

    I have done the job by putting the raw amplified ultrasound through a
    fast A/D into a DSP, but I can't recommend that for a DIY project.

    Jim
     
    James Meyer, May 7, 2005
    #11
  12. Guest

    Jim/Winfield,
    Thanks both for the help. The problem with Jim's approach is I am
    much more of a programmer than an electrical enginner and really only
    understood the parts that pertained to signal processing. Here's my
    planned approach, let me know what you think.

    If you sample at the transmit frequency (F), exactly, a velocity of 0
    corresponds to no frequency exactly. A doppler shift of 100 Hz will
    result in a strong frequency around 100Hz in the FFT. You can
    theoretically detect a shift of F/2, but that would be an
    unrealistically high velocity. The other problem is that with a
    relatively small FFT, say 2048, one bin corresponds to a large change
    in velocity.

    Therefore, if you sample at F/2, a doppler shift of 100HZ will result
    in a strong frequency around 50Hz in the FFT, and the maximum
    detectable doppler shift is F/4 (Still very fast in terms of water
    velocity). So my plan is to sample at somewhere around 50KHz, which
    will still give me span of F/20, which in practical terms is about 30
    m/s, depending on the angle. A benefit of this approach is that the
    resolution of each bin is quite, which is desireable.

    Naturally, the signal will have to be amplified before DSP, I will
    determine that gain using an oscilloscope. Any thoughts? I am going
    to try using a rabbit core module (http://rabbitsemiconductor.com), as
    they are pretty easy to program. Please let me know if you see any
    problems, or have suggestions. Thanks again.
     
    , May 8, 2005
    #12
  13. wrote...
    >
    > Jim/Winfield,
    > Thanks both for the help. The problem with Jim's approach is I am
    > much more of a programmer than an electrical enginner and really
    > only understood the parts that pertained to signal processing. ...


    Ahem!


    --
    Thanks,
    - Win
     
    Winfield Hill, May 8, 2005
    #13
  14. James Meyer Guest

    On 8 May 2005 04:58:43 -0700, wroth:

    >
    > If you sample at the transmit frequency (F), exactly, a velocity of 0
    >corresponds to no frequency exactly. A doppler shift of 100 Hz will
    >result in a strong frequency around 100Hz in the FFT. You can
    >theoretically detect a shift of F/2, but that would be an
    >unrealistically high velocity. The other problem is that with a
    >relatively small FFT, say 2048, one bin corresponds to a large change
    >in velocity.
    >


    That's fine as far as it goes. Did you notice that the doppler shifted
    energy will be 40 to 60 db lower than the total signal? That places very harsh
    requirements on the A/D process and the digital processing subsequent to that.

    Jim
     
    James Meyer, May 8, 2005
    #14
  15. James Meyer wrote...
    >
    > On 8 May 2005 wroth:
    >
    >> If you sample at the transmit frequency (F), exactly, a velocity
    >> of 0 corresponds to no frequency exactly. A doppler shift of
    >> 100Hz will result in a strong frequency around 100Hz in the FFT.
    >> You can theoretically detect a shift of F/2, but that would be
    >> an unrealistically high velocity. The other problem is that with
    >> a relatively small FFT, say 2048, one bin corresponds to a large
    >> change in velocity.

    >
    > That's fine as far as it goes. Did you notice that the doppler
    > shifted energy will be 40 to 60 db lower than the total signal?


    Isn't it often worse than that? Jim, for your nice return signals
    have you been using well-chosen send-receive transducer placements,
    with a shield, and with dirty water?


    --
    Thanks,
    - Win
     
    Winfield Hill, May 8, 2005
    #15
  16. James Meyer Guest

    On 8 May 2005 08:19:38 -0700, Winfield Hill
    <hill_a@t_rowland-dotties-harvard-dot.s-edu> wroth:

    >James Meyer wrote...
    >>
    >> That's fine as far as it goes. Did you notice that the doppler
    >> shifted energy will be 40 to 60 db lower than the total signal?

    >
    > Isn't it often worse than that? Jim, for your nice return signals
    > have you been using well-chosen send-receive transducer placements,
    > with a shield, and with dirty water?


    My major effort so far has been with blood flow using reflection from
    red blood cells. Dirty water? I guess that's a pretty good description. The
    transducers are side-by-side and oriented so that the beams converge on an
    artery about 10mm under the skin's surface.

    Jim
     
    James Meyer, May 8, 2005
    #16
  17. James Meyer wrote...
    >
    > Winfield Hill wroth:
    >
    >> James Meyer wrote...
    >>>
    >>> That's fine as far as it goes. Did you notice that the doppler
    >>> shifted energy will be 40 to 60 db lower than the total signal?

    >>
    >> Isn't it often worse than that? Jim, for your nice return signals
    >> have you been using well-chosen send-receive transducer placements,
    >> with a shield, and with dirty water?

    >
    > My major effort so far has been with blood flow using reflection
    > from red blood cells. Dirty water? I guess that's a pretty good
    > description. The transducers are side-by-side and oriented so that
    > the beams converge on an artery about 10mm under the skin's surface.


    No, I suspect even dirty water is a poor backscatterer compared to red
    blood cells. Clean water, even worse unless there are turbulence cells.
    Ahem, the O.P. did say, "with polyurethane epoxy to match the water's
    acoustic impedance," so I'd imagine poor backscatter signal strength
    compared to the transmit signal could be a significant issue.


    --
    Thanks,
    - Win
     
    Winfield Hill, May 9, 2005
    #17
  18. Glen Walpert Guest

    On Sun, 08 May 2005 22:14:51 GMT, James Meyer <>
    wrote:

    >
    > My major effort so far has been with blood flow using reflection from
    >red blood cells. Dirty water? I guess that's a pretty good description. The
    >transducers are side-by-side and oriented so that the beams converge on an
    >artery about 10mm under the skin's surface.
    >
    >Jim


    Nice project, Jim. I hope it works out to be usable for continuous
    monitoring of blood flow to the brain, usable by first responders to
    detect the reduction of brain blood flow which often occurs after head
    trauma. The current method used by first responders, the Glasgow
    scale, is applied correctly less than half of the time (detects less
    than half of the instances of high Intra-Cranial Pressure (ICP)
    causing loss of blood flow to the brain, in a timely manner). Since
    loss of brain blood flow always results in death or severe brain
    damage if not treated promptly, such a device has the potential to
    save many thausands of lives. High ICP, typically caused by
    hemorrhage of small blood vessels when the brain moves in the skull
    due to impact or brain "bruising" and swelling, can be properly
    treated only at major trauma centers having MRI and a surgical team
    prepared to enter the skull, and sucessful outcome is dependent on
    prompt recognition of the problem and rapid transit to an appropriate
    facility. Since there is often no immediate outward sign of this
    problem, and there may not be any other serious injury, appropriate
    treatment is often not provided even if readily available.

    This is just the sort of thing that NIH likes to fund.

    Best regards,
    Glen
     
    Glen Walpert, May 9, 2005
    #18
  19. Guest

    The water is dirty, wastewater (i.e sewage) if you really want to
    know, which should help a bit with the recieve. I am aware the return
    signal will be pretty faint compared to the transmit, I'm not sure how
    faint but am prepared to invest the time to make a transducer, connect
    to an oscilloscope and play around with it until I find out if it is
    possible. My guess is the first few bins of FFT will be all bleed from
    the transmit, so near zero velocity detection will be impossible. I'm
    also trying to read up on transducer design to get a good recieve
    signal. Thankfully it is not as critical as blood flow, but should be
    a good way to learn and possibly produce something useful.
     
    , May 9, 2005
    #19
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