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no image Saturday, November 25, 2017 by Len Murray

Signal generators - how to transmit microwave frequencies into water

I'm new to the world of electronics and related equipment...

I'm looking to experiment with water's "exclusion zone" (see Dr. Gerald Pollack, Univ of WA). With the use of Nafion, microspheres and a stereo microscope, one can see water's exclusion zone form and degrade. 

Initially my goal is to introduce microwave frequencies to small containers of water - the entire microwave range, if possible.  I'm looking to "transmit" these microwave frequencies into the water container - propagating through the air - as opposed to placing electrodes directly in the water. I have the following questions:

1) What type of signal (frequency?) generator is best recommended?

2) How can I transmit these signals? Is some type of antenna and/or transmitter available?

3) Eventually, I'd like to explore the infrared and visible light spectrum, doing the same thing (transmitting these signals). Is this possible? If so, all in one signal generator, or a different component?

Thanks very much  for any help.

Comments

  • by  Rick Curl
    Hi Len-

    I think first you'll need to decide the frequency range and power level that you want to use. Microwave radiation covers a very wide range- 300 Mhz to 300 Ghz (according to Wikipedia, but the definition varies elsewhere).  I don't know of a single signal generator that will cover the entire range. I suggest an eBay search of "Microwave Signal Generators" as a starting point.

    The output power level of these signal generators will generally be very low- much too low to cause heating.  If you need higher power levels you'll need a microwave power amplifier. If you need high power levels there are many safety concerns that will arise.  BE CAREFUL!!!

    Next, you'll need an antenna.  Again, eBay is your friend. You'll probably be looking for a "Horn" antenna. Make sure you can get a cable with one end that fits the signal generator on one end that fits the antenna.  FYI- microwaves get attenuated very rapidly in coaxial cable.  Keep the cable as short as possible and use the lowest loss cable you can get.  Some of the higher frequency microwaves don't use a cable at all- they use a hollow waveguide.

    Since you will be doing scientific research, you probably need to know the exact power level at the point where the microwave energy hits the water.  Getting this reading may be difficult. Other readers can advise you on this better than I can.

    If you will be dealing with more than a few milliwatts you'll also need to make sure you don't interfere with nearby systems that may be on the same frequency.  You'll also run afoul of the Federal Communications Commission (FCC) if you radiate a signal that propagates very far.  Some microwave tests are conducted in a shielded room  that keeps microwaves from escaping.

    Good luck with your experiments!

    -Rick

  • by  Len Murray
    Thanks very much Rick. This is helpful information and a great head start for me.


    Len - 

  • by  Rick Curl
    Hi Len-

    I have a friend who is an expert in Optics, and I asked him about part 3 of your original question.

    You have some options.  Lasers are available in very specific wavelengths. You could start there, even using some inexpensive "laser pointer" types. Tunable lasers exist, but they're not cheap. 

    You could also get a white laser and feed the light it produces into a prism, and by adjusting the angle you can get many different wavelengths.

    If lasers are too expensive, you could try an incandescent lamp and a prism.

    I hope this helps.

    -Rick 

  • by  Len Murray
    Ok Rick - once again thank you. This is very helpful to me. I have some equipment on order, will work my way toward the visible light aspect of my experiments - keeping this in mind!
  • by  Max Maxfield

    I asked "The Mustache of Knowledge" (my chum Ivan) who hangs out in the next bay. He responded as follows:

    --------------------------

    Too big a topic for the length of the reply.

    Tell him that your chum says that the wavelength in air and the wavelength in water are vastly different, since water’s dielectric constant is about 80. If he wants a specific wavelength in the water, he gotta account for that.

    Also, because of the large dielectric difference, there will be a significant reflection off the water’s surface.

    It also matters if it is salt water (dissipative of energy).

    A one nanosecond ultrawideband pulse covers multiple gigahertz in single pulses, without having to produce a chirp. But, it will interfere with all radio services at power levels he will want to use, without correlating / integrating receivers, and it will bounce off the surface.

    Just the tip of the iceberg on the subject… I’m not getting into this stuff…

  • by  Adam Carlson

    I do radio controlled submarines, and have played a bit in this range.  I have an old attachment that talks of the attenuation value of water based upon its conductivity level, unfortunately I cannot find it right at the moment.  I will share with you some details.  For fresh water, an RF signal can propagate through a significant depth while also being able to continue to transmit data. 


    There are currently groups that are operating submarines up to ~430MHz and getting good signal propagation up to about 3-5' depth.  This is while also being at about 30-40' away from the boat and the transceiver at about 3" above ground level.  


    Some have tried to play with devices in the 900MHz range and were not able to get anything that was functional for running a submarine.  This does not mean that the signal did not penetrate the water, just that the attenuation lead to too many dropped packets of information that it did not allow for true operational experience. 


    A few fools have tried to run 2.4GHz for this.  One group put a 5 or 10W amplifier on the boat under the water and were boiling water on the antenna.  The signal attenuation at this point is so high that the energy is just absorbed and converted to heat. 


    I will look for the link on the attenuation rates of RF signals and try to post it later tonight.


    Adam

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