Passing HF current through your body / Tesla Coils / Forums

Forums

4hv.org :: Forums :: Tesla Coils

« Previous topic | Next topic »

Passing HF current through your body

previous 1 2 3 next

Move Thread

LAN_403

Steve Conner

Thu Sept 26 2013, 08:18AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Yes, the thing is that RF current doesn't stimulate nerves, so it doesn't cause electric shock. The amount you can pass through yourself is limited only by IR heating at points of high current density.

Dr. Dark Current

Thu Sept 26 2013, 10:13AM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

I wonder what the microamp-carrying nerves say to the ampere HF currents

A DC ammeter also doesn't respond to high frequency AC signals, but this doesn't mean you can overload it

It will just start to smoke while dispaying "0".

Steve Conner

Thu Sept 26 2013, 12:57PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Yes, this is what I meant by "IR heating at points of high current density". When passing current through your arm, it tends to concentrate in the nerves and blood vessels of the wrist because they are the best conductors, so there is a risk of literally cooking the nerves.

The ANSI recommendations take this into account, they work back from the current that would flow in your wrist on grabbing a grounded object to calculate the maximum safe E-field.

Uspring

Thu Sept 26 2013, 03:07PM

Registered Member #3988 Joined: Thu Jul 07 2011, 03:25PM
Location:
Posts: 711

I'm tempted to speculate, that the shock experience depends on how far ions in the tissue wander before the polarity reverses. The wandering distance would be proportional to current and inversely proportional to frequency.
TC currents are usually pulsed, so RMS currents are much lower than peak currents. That idea would make TCs more dangerous as estimated from RMS currents.

Goodchild

Thu Sept 26 2013, 03:09PM

Registered Member #2292 Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795

hmmm I seem to be alive.

Feathers

Thu Sept 26 2013, 10:06PM

Registered Member #10052 Joined: Thu Feb 07 2013, 11:31PM
Location: Overland Park, Kansas
Posts: 78

I've always wondered about the HF impedance of an ionized liquid, given that so many of us use water-cooled primary coils.

We may fill the system with deionized water, but after months of sitting/flowing continuously through dozens of feet of copper tubing, radiators, silver strips, etc., I'd bet that property is gone.

If the fluids in body tissues display some sort of characteristic impedance based on the way an ionized liquid conducts, you may be much safer with the HF QCW coils than a larger 40-100KHz coil.

radiotech

Fri Sept 27 2013, 06:10AM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546

I think the idea is the propagation of the current at the surface above the skin depth(sic)
which is 2 pi nepers/wavelength attenuation. So it goes over you, not through you.

If you hold the 2 watt fluorescent lamp and it lights, with your other hand on the Tesla
terminal, it does not follow that it would light if you swallowed it, like circus 'geeks' can do.

Or perhaps it does? Where could place that tiny lamp, where a fiber endoscope could
follow it.

Steve Conner

Fri Sept 27 2013, 07:55AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

The skin depth in flesh is about 10 feet at Tesla coil frequencies, so skin effect isn't an issue.

The impedance of water in a cooling circuit is probably so high compared to the copper coil it's flowing in that it can be neglected. You just have to be careful to avoid any DC bias as it'll cause serious electrolytic corrosion in no time.

Proud Mary

Fri Sept 27 2013, 08:43AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Med Biol Eng Comput. 2004 May;42(3):394-406.
Nerve conduction block utilising high-frequency alternating current.
Kilgore KL, Bhadra N.

MetroHealth Medical Center, Cleveland, Ohio, USA. **link**

Abstract

High-frequency alternating current (AC) waveforms have been shown to produce a quickly reversible nerve block in animal models, but the parameters and mechanism of this block are not well understood. A frog sciatic nerve/gastrocnemius muscle preparation was used to examine the parameters for nerve conduction block in vivo, and a computer simulation of the nerve membrane was used to identify the mechanism for block. The results indicated that a 100% block of motor activity can be accomplished with a variety of waveform parameters, including sinusoidal and rectangular waveforms at frequencies from 2 kHz to 20 kHz. A complete and reversible block was achieved in 34 out of 34 nerve preparations tested. The most efficient waveform for conduction block was a 3-5 kHz constant-current biphasic sinusoid, where block could be achieved with stimulus levels as low as 0.01 microCphase(-1). It was demonstrated that the block was not produced indirectly through fatigue. Computer simulation of high-frequency AC demonstrated a steady-state depolarisation of the nerve membrane, and it is hypothesised that the conduction block was due to this tonic depolarisation. The precise relationship between the steady-state depolarisation and the conduction block requires further analysis. The results of this study demonstrated that high-frequency AC can be used to produce a fast-acting, and quickly reversible nerve conduction block that may have multiple applications in the treatment of unwanted neural activity.

GeordieBoy

Fri Sept 27 2013, 08:48AM

Registered Member #1232 Joined: Wed Jan 16 2008, 10:53PM
Location: Doon tha Toon!
Posts: 881

Isn't this how those TENS machines work that are meant to relieve things like persistent back-pain without having to dose yourself up on Codeine?

There's a video here online from about ten years back of myself and Colin Heath fooling about lighting a 230V 40W filament bulb with the RF current flowing between us:

I'm stood nearest to the CW-SSTC with my left arm around 2ft from the toroid. The lamp filament glows white-hot due to the RF current flowing across my body, through the lamp, and to Colin who is much further away and out of the TC's E-field. There's around 2.5kW of power going into the CW discharge and the brightness of the lamp was entirely controllable by lowering or raising my left arm nearer to the toroid!

On two other occasions when I did this demo, I couldn't get a volunteer to man up for the "current sink" part of the team! I can't image why, especially as having already pointed out that I'm the one actually stood close to the hissy crackly sparky thing! On both occasions I grounded the other end of the 40W lamp to a nearby radiator, and on both occasions got the lamp so bright it fused the filament!

A 230V 40W lamp draws about 174mA. My TC was tuned to 175kHz though, so I was alright!

-Richie,

Disclaimer: Don't try this unless you know what you are doing. I was young and foolish then and thought I knew what I was doing. I'm grown up now and have responsibilities. I don't want nerve damage in my wrists so wouldn't risk doing it again now!

previous 1 2 3 next

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob