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  • Transducer design.

    I have disassembled some commercial transducer


    from well known companys.


    The crystals was glued with silver epoxy


    on a steel bar. On the sides and back it


    was acoustic isolated with a hard foam


    probably of polyurethane. The rest was


    made of a poluurethane, probably


    Conathane EN-9. The advantage of using


    EN-9 is that have almost the same proprties


    as water.


    Another transducer from another well known


    company that sells cheaper sidescans did have


    a plastic U-shaped "chassi". In this they put


    cork sheat on side, bottom and between the


    crystal. This was then covered with epoxy.


    Both transducer have the same principal:


    Isolate bottom and side with something


    ultrasound absorbing and then let the side


    against water be transparent for sound.


    Both unfilled epoxy and hard polyurethane


    is transparent and cork and corkoprene is


    absorbing.


    Sture

  • #2
    Re: Transducer design.

    Sture,


    This is very helpful! I had a few follow on questions..


    Did you notice the dimensions of the steel bar? Do you think this is important? I was thinking that the waves might resonate in the steel. Perhaps, by using the right dimensions, the transducer could become more efficient.


    Also, how important is the alignment of the elements. I would imagine with a beamwidth of less than 1 degree, this would be important. I could see why a steel bar might be used to keep things lined up. How do you deal with element alignment in your current design?


    Thanks!


    -Bob


    By the way, if anyone is interested in Conathane EM-9, go here:


    http://www.conap.com/cona_156.htm


    There is also a list of distributors on their website.

    Comment


    • #3
      Re: Transducer design.

      The steel bar:


      By some rough calculation I found the steel bar


      thicknees to be 1/4 wawelenght, probably to awoid


      "standing wawes " in it. The steel bar was also


      sliced between each crystal. This is probably


      to avoid longitudinel resonances.


      The gaps was filled with cork.


      The aligment:


      Since directivity becomes from inteferences between


      different part of the transducer I belive that


      the tolerances should be calculated in degrees or


      rather COS(degrees). 10 degrees will then give


      a angle error of around 10% and for 500KHz this


      is 0.1 mm. A normal workshop easily do better than


      that.


      Sture

      Comment


      • #4
        Re: Transducer design.

        Sure,


        1/4 wavelength at 500 KHz would be .75mm. That seems like a pretty thin bar! What size were the cuts?


        Perhaps this was a lower frequency transducer..


        Also, if the bar needs to be rigid enough to stay within .1mm of perfectly straight, the steel would have to be very strong.. Perhaps the absorber behind it also helps to support the array. Do you know of an absorbent material that is also mechanically strong?


        -Bob

        Comment


        • #5
          Re: Transducer design.

          Bob


          In steel the speed of sound is 6000 m/s.


          For 500K you have a 1/4 wawelenght of 3 mm.


          Sture

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