David Swenson's electrostatic "invisible wall" (1996)

"Invisible Electrostatic Wall"
at 3M adhesive tape plant
    Aug 1996   W. Beaty

David Swenson of 3M Corporation describes an anomaly where workers encountered a strange "invisible wall" in the area under a fast-moving sheet of electrically charged polypropelene film in a factory. This "invisible wall" was strong enough to prevent humans from passing through. A person near this "wall" was unable to turn, and so had to walk backwards to retreat from it.

This occurred in late summer in South Carolina, August 1980, in extremely high humidity. Polypropelene (PP) film on 50K ft. rolls 20ft wide was being slit and transferred to multiple smaller spools. The film was taken off the main roll at high speed, flowed upwards 20ft to overhead rollers, passed horizontally 20ft and then downwards to the slitting device, where it was spooled onto shorter rolls. The whole operation formed a cubical shaped tent, with two walls and a ceiling approximately 20ft square. The spools ran at 1000ft/min, or about 10MPH. The PP film had been manufactured with dissimilar surface structure on opposing faces. Contact electrification can occur, even in idental materials, if the surface textures or micro-structures are significantly different. The generation of a large imbalance of electrical surface-charge during unspooling was therefore not unexpected, and is a common problem in this industry. "Static cling" in the megavolt range!

On entering the factory floor and far from the equipment, Mr. Swenson's 200KV/ft handheld electrometer was found to slam to full scale. Later, when he attempted to walk through the corridor formed by the moving PP film, he was stopped about half way through by an "invisible wall." He could lean all his weight forward but was unable to pass. He observed a fly get pulled into the charged, moving plastic, and speculates that the e-fields might have been strong enough to suck in birds!

echisholm 5/2016
Have a relative (sort of) who works at a 3M plant. Shit still occasionally happens.
> You can't just say that and go away!! How are you not irresistibly
> interested in that?? I would've interrogated that relative so hard
It just came up in passing at Thanksgiving! I don't really know him that well; he's an in-law. He mentioned being able to throw small washers and bolts at the field and watching them get repelled. People got interested, and so someone came with a voltmeter, and after throwing a couple more, they checked for voltage, and there was a residual charge after they finally caught on on a plastic sheet to prevent immediate grounding. It also had a very slight magnetic field. It's apparently fairly common, but engineering hasn't come up with a solid explanation why.

ALSO: dc469 5/2016
I met this guy at an ESD meeting in austin once. He said the strength of the field maxed out his equipment at a distance so he couldn't get a maximum measurement.
After he published the paper he was contacted by NASA and all the three letter agencies asking for more info. He wanted to experiment around with it but no company had millions to throw into such a project (presumably, the government did). It had to be a pretty narrow window of temperature, pressure, humidity, etc. They kept the garage door open so that's where the insects and sparrows got sucked in (which obviously ruined the product).
He said it was actually known to the technicians for awhile before he experienced it and they just were kinda like "meh". Eventually they fixed the grounding issue on the machine and the problem never popped up again.
edit: found the ESD website. David Swenson apparently is still with them on their board of directors. http://centxesdassoc.homestead.com/

LINKS

• WIRED magazine 1/2018
• YT video, attempted replication 2025
• ESD Journal
• Askreddit 2017
• Reddit TIL
• Sticky Electrostatics, classroom physics demos
• Another poly unwind setup (vid)

Problems: coulomb forces would be expected to attract a person into the "chamber" formed by the PP film, and the attractive force should increase linearly across distance. There should be no "wall" in the center, a discrete wall is repulsive, also nonlinear.

If for some reason a person was repelled from the center of the chamber rather than being attracted, there still should be no "wall," since the repulsion force should exist over a large distance; it should act like a deep pillow which exerts more and more force as one moves deeper into it. Large fuzzy fields, this is how magnets and iron behave, and this is how e-fields and conductive objects should also behave.

A thought: unspooling of film typically generates a much higher net charge on the long piece of film than on the small surface of the spool. However, since charge is created in pairs, and net charge is conserved, the imbalances of charge must be equal and opposite. The charge on the entire length of moving film must be equal in magnitude to the charge on the spool. Yet the charge on the film is very large and is continuously increasing. The limited surface-charge on the spool required that opposite charge is being lost through some unseen path.

Very probably the spool is spewing out enormous quantities of ionized air with polarity opposite that of the charge on the moving plastic film.

Charged air would be created by discharge in the cleft between film and spool as the film was peeled from the spool. I wonder if film was being peeled from the top of the spool, so that any ionized air created in the cleft would be launched into the "tent-chamber" region? (If it was peeled from the bottom of the spool, the charged air would end up outside the "tent.") Or, if a corona discharge arises in the cleft between film and spool, perhaps the UV and e-fields of this corona can ionize the air on both sides of the exiting plastic film, and spray the charged air everywhere.

So, if the charged "tent" of film is negative in the above situation, and if a large quantity of positively charged air is being generated by the spool, then perhaps the "invisible wall" is caused by a cloud of suspended air ions held in position by e-fields. Perhaps it's a pressure gradient created by ionized air trapped under the tent by electrostatic attraction. Yet again this effect would be expected to create a diffuse zone of increasing force, not a "wall", but an "invisible pillow." Added note: concrete floors behave as conductors (resistors) in this situation. Where megavolts at microamps are involved, the division between insulators and conductors is at 10^6/10^-6 = 1000 gigaohms. Concrete resistivity is in the realm of megohms, so it behaves like a grounded metal sheet.

However, a volume of charged air is somewhat analogous to iron filings near a magnet. If a solid sheet of iron filings is held in place by a magnet, then a literal "wall" is created, and this wall will resist penetration by nonferrous objects. If in the above manufacturing plant, a sheet of highly charged air is for some reason being held in place by the fields created by the charged film, then a transparent "wall" made of charged air would come into being. It might produce pressures on surfaces, and resist penetration by human bodies.

My question is this: if the entire situation could be turned on its side, so the "invisible wall" became an "invisible floor", could a person *stand* on it? Have we discovered the long-sought "Zero-G waterbed?" :) - B.B.

The 'force field' event was from 1980, while the report was given at an ESD conference in 1995. Where is that machine today? In other words...

Does that 3M sheet-slitter still slits sheets? Single sheet slitted into three slit sheets spooled onto spools called 'jumbos.' The supposed sheet-slitter shift staff says 3M sold that sheet-slitter. It may be surplused and still exist, sitting in SC, slitting and spooling someone else's slit sheets. Or, since OSHA's lawshuits when staff suddenly statically sucked into sheet slitters don't exhisht shouth of the border, it may haved moved to Mehicco.

MORE THOUGHTS:

Also: I wonder if the (I assume) huge quantity of air ions had anything to do with your weird phenomenon. Maybe the "wall" effect involves a plug of ionized air which is held in place by the opposite charge on the film. If so, your repulsion phenomenon would not occur if the "tent" of film was replaced with highly charged metal plates, since the source of oppositely-polarized electric wind would then be missing. I'm still convinced that the charged film should produce an attractive force upon a human body. Repulsion requires that the human be charged with the same polarity as the PP film, yet induction should produce an *opposite* body charge, so attraction is expected. But if a plug of oppositely-charged air was strongly attracted into the "tent" of PP film, it might produce a significant pressure-gradient in the surrounding air. A fraction of a PSI per foot would be more than enough to prevent someone from walking forward. If this is the origin of the effect, then the repulsion forces you experienced involved air pressure rather than electrostatic attraction/repulsion.

This might be an entirely new way to accomplish levitation. Attract a whirling blob of ionized air to an oppositely-charged plate, then use the resulting pressure gradient to lift and manipulate uncharged objects. Sort of like a fluidized bed, but using charged air instead of sand.

Why doesn't the population of opposite ions "plate" itself onto the plastic surface? Maybe it tries to do so, but the air within the moving tent is swirling like a horizontal tornado, so the charged air cannot simply move straight to the plastic film. If true, then the phenomena would not appear if motionless charged air and oppositely charged plastic were present. The tent shape and the motion of the plastic would also be required. Incredible coincidence that all the required components could ever come together in one place! (if this is indeed how it works!)

Speculative, untried experiments: MOVED TO http://amasci.com/freenrg/iontest.html

ALSO SEE:

• HackerNews comments, and Redditand earlier
• Air Threads
• Water Thread Experiment
• Giant Water Threads occur naturally?
• YT vid of invisible wall! Really!!!!