Low Frequency Antenna Question

Discussion in 'Wireless & RF Design' started by dtow1, Nov 24, 2010.

  1. dtow1

    Thread Starter New Member

    Apr 27, 2010
    24
    0
    Hello,

    I want to start off by saying that this is a senior design project so I'm really not interested in getting a solution, I'm interested in starting points for things that I can look into and research myself to design. One of our projects parts is a measurement system that will include a measurement of Electric Field. The team member responsible for this section has not completed any work, so I am taking it over, I want to design this section but we do not have any courses in antenna design.

    What I know is this we are looking at low frequencies, of 100khz max, so this gives us a wavelength of 3000 meters, so a quarter wavelength antenna is 750 meters and out of the question as this is a portable device.

    The only potential option we have is an antenna that uses a circular plate, I have googled around and either my search criteria are very poor, or there are not a lot of options on low frequency antenna design. The books I have read have all been those tall antennas that you see at AM radio stations. Im just starting research into this and have no experience in antenna design so would greatly appreciate any information to get me on the correct track.

    Thanks
     
  2. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    5,448
    782
    One can buy isotropic E-field probes off the shelf that purport to have a flat frequency response from 100kHz up to several GHz.

    Exactly what do you want to measure? Near field values adjacent to a transmitter antenna? What sensitvity do you require?

    It's not clear what you really need, although you appear to be simply researching the subject.

    Most good books on antennas would cover the entire spectrum of options rather than just low frequency radio.

    This paper covers some ideas regarding low frequency measurements for geoscience applications

    http://sciencestage.com/uploads/text/SKb1griQkAJ2kPvPNT3m.pdf

    Perhaps try searching for EMC testing equipment which will give a wide range of books and articles with some good background on antennas and monitoring technologies.

    http://books.google.com.au/books?id=O7NYUnPFuSYC&pg=PA115&lpg=PA115&dq=test+equipment+E+field+measurement+below+100+kHz&source=bl&ots=qIWKz9hQXf&sig=W8MDO7SmdXqUR0HXeh3K1HPbuuE&hl=en&ei=BtPtTMa6KozSsAP2hdGtCw&sa=X&oi=book_result&ct=result&resnum=9&ved=0CDcQ6AEwCA#v=onepage&q=test%20equipment%20E%20field%20measurement%20below%20100%20kHz&f=false
     
    Last edited: Nov 24, 2010
    dtow1 likes this.
  3. dtow1

    Thread Starter New Member

    Apr 27, 2010
    24
    0
    I apologize for the lack of actual content to my question.

    We are measuring an electric field from several meters to several tens of meters from the source.

    The expected values are from 1 V/m to 1 kV/m. The frequency band of interest is from a static field up to 100kHz.

    I was trying to stay away from the specifics since I want to make sure I do the design myself, it is a design project so I want to do it correctly. I appreciate the links and will read through them, I have had E&M and a class on wave transmissions which included very brief and simple antenna theory, so I think I should be able to do any required math to design something as long as I have a better understanding of antennas, or I may be over complicating things(not the first time). Thanks again for the feedback.
     
  4. dtow1

    Thread Starter New Member

    Apr 27, 2010
    24
    0
    Oh Also its meant to be a quick setup, something that would allow someone with no computer or engineering experience to deploy and set up in under ten minutes, the idea is to have them just flip a switch and have it work. So its portable self contained, and thats why Im looking for small antennas, this is why Im trying to get familiar with these technologies so that we can see how feasible this is.
     
  5. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    5,448
    782
    I don't want to pour cold water on your enthusiasm for the challenge. However this is a specialised art with many traps for the inexperienced. I expect such a design task would be something done by an RF engineer with some good & proven experience behind them. It's not just about having the mathematical competence. I'd strongly advise against doing your own design if you are looking for a reliable, accurate & consistent solution.

    Good luck all the same!
     
  6. dtow1

    Thread Starter New Member

    Apr 27, 2010
    24
    0
    Well I greatly appreciate the answer and the help. I'm very interested in the subject, so will keep on reading about it, but I will take your advice seriously and see what I can do. Thanks for taking the time to answer.
     
  7. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    3,795
    949
  8. bertus

    Administrator

    Apr 5, 2008
    15,648
    2,347
    Hello,

    You could also take a look in the links of this page:
    http://ac6v.com/antprojects.htm

    You could look for the loop or magnetic loop antennas.

    Bertus
     
  9. Tesla23

    Active Member

    May 10, 2009
    318
    67
    If you want to measure the E-Field then loop antennas are no good. If you know you are in the far-field of your source then you could use a loop to measure H and compute E from E/H = 377 ohms, but in general you can't rely on this.

    It's funny, tell people that you want to sense a magnetic field and a small loop seems easy, the OC voltage is simply given by Faraday's law and if the loop is small the source impedance is set by the inductance. To sense an electric field you essentially use an unshielded capacitor and the OC voltage is set by the external field, and if the capacitor is small the source impedance is set by the capacitance.

    What people seem to use is a short dipole, here is a paper that may get you started, check out Section IV.
    http://www.nist.gov/calibrations/upload/im-34-4b.pdf
     
  10. TIRED ONE

    New Member

    Feb 25, 2010
    5
    0
    Perhaps reading the many books by this respected author will help in your search for antenna knowledge.

    You can also Google his name for other links to his work.

    http://www.cebik.com/


    JIM:)
     
Loading...