An electrical connection to the atmosphere.

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I’m playing around with NAIGs (Negative Air Ion Generators) that use ordinary stainless steel sewing needles as ion emitters.

In order to make meaningful measurements, I need an “electrical connection to the atmosphere”. This is very simple in theory: all you need is a flat metal plate. Fine! But what metal? Aluminium quickly oxidizes to a superb insulator, aluminium oxide. Copper does so more slowly, and the end result is certainly “green”. Solder … hmmm … well, I’ve always found it necessary to “poke the probe” into a solder surface.

And PLEASE don’t suggest that I use a “stainless steel plate” unless you’ve discovered secrets about WORKING STAINLESS STEEL that are quite unknown to me.

Any suggestions most welcome.

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Gold leaf?

RS

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Yes, good suggestion. Probably expensive and difficult to work, but a large area of PCB with gold flash might be a cost-effective alternative.

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52midnight:
Yes, good suggestion. Probably expensive and difficult to work, but a large area of PCB with gold flash might be a cost-effective alternative.

Yes, some skill is needed to gild with leaf, and a few dedicated tools, but it isn’t as expensive as you would think.

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I’ll assume that you’ve practical experience with this, whereas I haven’t. I’m open to using leaf, but am thinking along the lines of a small (one inch diameter) area of PCB with gold plating over copper connected to a side terminal to create an ‘atmospheric ion emitter/collector’.

The reason is empirical. It’s quite OK to ‘believe’ that you’ve established a ‘gold-atmosphere’ connection, but quite another to prove it. The test is simply to confirm the law named for our old friend Georg Ohm. It must be possible to MEASURE the resistance of the junction, but probably not easy. Call to mind such things as wind velocity sensors which (as I recall) use ‘ion drift’ across a small discoidal ‘wind tunnel’. This requires that electrons be injected at the top of a disc-shaped cavity through which the prevailing air moves, and measuring the increase in resistance that results from ions being ‘blown away’ from the collector at the bottom.

If two of the above ‘emitter/collectors’ were used simply to measure the impedance encountered by an ‘ion drift’ between them, it would allow the resulting ‘gold-atmosphere’ junction to be characterized, and so used in reliable and repeatable measurements.

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Very interesting. It should be possible to buy small gold plated copper squares, or one could electroplate the copper plates of this size ones self. Very small containers and chemical volumes. I know of no way to bond leaf to another metal for reliable continuity with the substrate

It would be interesting to measure gold plated and just copper to see if the precious metal made a difference. Platinum strips? If non corrosive metal is needed there are options. Detecting electron streams eh? Hmmm

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Boards at oshpark are ENIG (immersion gold) plated.

/mike

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Thanks for the suggestions. I’m doing up some new proto PCBs which I plan to panelize, and thought I’d “fill up the holes” in the panel with something experimental. Looks like I’ve got the makings of a solution here.

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The atmosphere is an extremely high impedance, low current voltage source, with a vertical electric field of typically 100 V/m and current density in the range of 1 to 10 picoamperes/square meter. http://www.feynmanlectures.caltech.edu/II_09.html

How do you plan to measure the voltage due to the charge accumulated on the plate and of what use is the measurement?

If you want to measure the effectiveness of your ion generator, the current into or out of the Earth ground would be informative.

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Hey, thanks for an unexpected and most informative reply.

The atmosphere is an extremely high impedance, low current voltage source,

Very well put.

with a vertical electric field of typically 100 V/m

This has always fascinated me, though the numbers I’ve seen vary.

and current density in the range of 1 to 10 picoamperes/square meter.

Now that’s VERY new, to me at least - food for much further thought.

http://www.feynmanlectures.caltech.edu/II_09.html

The Master Himself, eh? Will certainly take a look.

How do you plan to measure the voltage due to the charge accumulated on the plate

My first thought was simply to prove that ions were being emitted. As it turns out, very simple. Take a piece of blank PCB 1" x 2", cut the copper across the middle to give two 1"" squares, bridge them with a neon bulb and a capacitor (10 - 100n @ >100V), grasp one end and hold the other near the emitters in a darkened room, and you’ll see the neon flash as accumulated ions charge the cap and ignite the bulb.

and of what use is the measurement?

The first ‘roughy’ I built didn’t flash the bulb - calculated at maybe 2kV max. The second calculated at 5 - 7kV gave 2 - 3 flashes per second. I’m still hoping to find the time to get a string of 1kV resistors as V divider input to a hi-Z voltmeter to get a reasonably accurate number, but so many other things …

the current into or out of the Earth ground would be informative.

Yep, that’s why this post; though NOT Earth GND, but current from the emitters direct to the collector plate (the “connection to the atmosphere”) is what I was wanting.

Much appreciated.

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A bit of mulling has turned up an interesting possibility. After running Version 2 of my Ion Generator on a shelf for six months, the surrounding wall became blackened around it. I live near the city centre, so car and diesel fume particles being electrically deposited - the “corollary product” of discharged positive ions - was further proof of its … efficacy? Certainly, but in what respect?

I’d been pondering a portable version, but realized that without a ground - a literal DC one - the continual negative discharge would result in the whole device becoming positively charged; UNLESS this charge could be dissipated to the atmosphere, hence the topic of this post.

If the “positive plate” were literally that - say a 2" square of gold-plated copper on the front of the device - it could serve as a “repository” of airborne contaminants for those wanting to monitor the air in their surroundings.

This is a somewhat “far-out” suggestion - though quite practical - and given the apparent interest in this thread, I’m wondering if any Reader of it would cooperate in exploring this further.

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Air filters that work on the basis of high voltage electrostatic discharge have been around for decades. They are called “electronic air filters” by the HVAC industry.

The air handler in my home has a Honeywell F300A 2025 filter, and it works very well. It uses a wire grid charged to 8000V to ionize dust particles and these are then precipitated when the air passes between condenser plates with one side grounded and the other at 6000V.