Underwater electroscope

Discussion in 'The Projects Forum' started by Techspec2, May 16, 2016.

  1. Techspec2

    Thread Starter New Member

    Oct 15, 2015
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    Had an idea and was wondering if it's possible. I would like to pick up a 1mV signal in a bed of water. I looked into MOSFETs but the most sensitive Vgc I could find was 100mV. I think a diff op-amp would work but IMO, little to pricey lol. Any ideas?
     
  2. Externet

    AAC Fanatic!

    Nov 29, 2005
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    That 1 mV signal is to what point of reference underwater ? What conductor, part, component, node, presents the 1 mV ?
     
  3. Techspec2

    Thread Starter New Member

    Oct 15, 2015
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    Sorry let me re-write, was in a rush. A device is generating a 1mV/cm-10mV/cm electric field inbetween 1000Hz-2000Hz, I was thinking of placing a antenna near it(in the water) to produce a potential difference on the antenna caused by the electric field this device is producing. I would like to know if anyone has a good way to pick up this mV. Was thinking of using a FET. I can filter out unwanted frequencies. Just wanna know more about very low-voltage input devices.
     
  4. Externet

    AAC Fanatic!

    Nov 29, 2005
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    Very low voltage input devices... Think of a front end tuner for radio reception; sensitive to microvolts. They use fets, mosfets. 5mV is actually a 'strong' signal, easy to detect.
    Radio frequencies would not be audio range, but the principle is the same.
    Seawater or fresh water behave very different. IF there is such electric field underwater at very short distance, occurs to me that the antennas Tx and Rx (dipole?) would have to be isolated from water conductivity (like inside a hermetic dry bag)

    To better pick such low frequency, antenna resonance would be preferable with large inductance and capacitance.

    Filtering out unwanted frequencies... unless emitted by the same 1-2KHz originator, there will hardy be any to filter out. Electrical waves to not propagate well underwater.

    I would experiment with a metal core coil in parallel with a largish capacitor, tuned to 1.5 KHz, all inside a dry container near the signal source.

    If the transmitter electric field is already creating a current path in the water conductivity (wet electrodes) the receiving antenna could be wet to sense the current, as copper is way more conductive than waters and at low frequencies, range will increase.

    This is all speculating about your intentions.
    Do you have an oscilloscope that can be wired to a dipole (or two plates) underwater and see how much signal can be detected ?
     
  5. BR-549

    Well-Known Member

    Sep 22, 2013
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    I would think that detecting an electrical signal under water would be difficult.

    Wouldn't the constant ionic charge motion cause a high level of noise?

    If you could charge an underwater dipole, how long could the charge be maintained?

    It would be an interesting study. How long would it take for free water charge to neutralize a dipole?

    Would free water charge allow a charge to be built up on a dipole?

    Even with a plastic sleeve, the free charge would accumulate at sleeve border and absorb the field.

    If I'm not mistaken, many militarys have spent billions trying to radio signal thru and under water.

    Still don't understand why you want to detect this signal under water.
     
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