Static Electricity Remembers

As humans we often think we have a pretty good handle on the basics of the way the world works, from an intuition about gravity good enough to let us walk around, play baseball, and land spacecraft on the moon, or an understanding of electricity good enough to build everything from indoor lighting to supercomputers. But zeroing in on any one phenomenon often shows a world full of mystery and surprise in an area we might think we would have fully understood by now. One such area is static electricity, and the way that it forms within certain materials shows that it can impart a kind of memory to them.

The video demonstrates a number of common ways of generating static electricity that most of us have experimented with in the past, whether on purpose or accidentally, from rubbing a balloon on one’s head and sticking it to the wall or accidentally shocking ourselves on a polyester blanket. It turns out that certain materials like these tend to charge themselves positively or negatively depending on what material they were rubbed against, but some researchers wondered what would happen if an object were rubbed against itself. It turns out that in this situation, small imperfections in the materials cause them to eventually self-order into a kind of hierarchy, and repeated charging of these otherwise identical objects only deepen this hierarchy over time essentially imparting a static electricity memory to them.

The effect of materials to gain or lose electrons in this way is known as the triboelectric effect, and there is an ordering of materials known as the triboelectric series that describes which materials are more likely to gain or lose electrons when brought into contact with other materials. The ability of some materials, like quartz in this experiment, to develop this memory is certainly an interesting consequence of an otherwise well-understood phenomenon, much like generating power for free from static electricity that’s always present within the atmosphere might surprise some as well.

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On The Nature Of Electricity: Recreating The Early Experiments

Bits of material levitating against gravity, a stream of water deflected by invisible means, sparks of light appearing out of thin air; with observations like those, it’s a wonder that the early experiments into the nature of electricity progressed beyond the catch-all explanation of magic. And yet they did, but not without a lot of lamb’s bladders and sulfur globes, and not a little hand waving in the process. And urine — lots and lots of urine.

Looking into these early electrical experiments and recreating them is the unlikely space [Sam Gallagher] has staked out with the “Experimental History of Electricity,” a growing playlist on his criminally undersubscribed YouTube channel. The video linked below is his latest, describing the apparatus one Francis Hauksbee used to generate static electric charges for his early 18th-century experiments. Hauksbee’s name is nowhere near as well-known as that of Otto von Guericke or William Gilbert, who in the two centuries before Hauksbee conducted their own experiments and who both make appearances in the series. But Hauksbee’s machine, a rotating glass globe charged by the lightest touch of a leather pad, which [Sam] does a fantastic job recreating as closely as possible using period-correct materials and methods, allowed him to explore the nature of electricity in much greater depth than his predecessors.

But what about the urine? As with many of the experiments at the time, alchemists used what they had to create the reagents they needed, and it turned out that urine was a dandy source of phosphorous, which gave off a brilliant light when sufficiently heated. The faint light given off by mercury when shaken in the vacuum within a barometer seemed similar enough that it became known as the “mercurial phosphor” that likely inspired Hauksbee’s electrical experiments, which when coupled with a vacuum apparatus nearly led to the invention of the mercury discharge lamp, nearly 200 years early. The more you know. Continue reading “On The Nature Of Electricity: Recreating The Early Experiments”

Is That A Triboelectric Generator In Your Shoe?

The triboelectric effect is familiar to anyone who has rubbed wool on a PVC pipe, or a balloon on a childs’ hair and then stuck it on the wall. Rubbing transfers some electrons from one material to the other, and they become oppositely charged. We usually think of this as “static” electricity because we don’t connect the two sides up with electrodes and wires. But what if you did? You’d have a triboelectric generator.

In this video, [Cayrex] demonstrates just how easy making a triboelectric generator can be. He takes pieces of aluminum tape, sticks them to paper, and covers them in either Kapton or what looks like normal polypropylene packing tape. And that’s it. You just have to push the two sheets together and apart, transferring a few electrons with each cycle, and you’ve got a tiny generator.

As [Cayrex] demonstrates, you can get spikes in the 4 V – 6 V range with two credit-card sized electrodes and fairly vigorous poking. But bear in mind that current is in the microamps. Given that, we were suprised to see that he was actually able to blink an LED, even if super faintly. We’re not sure if this is a testament to the generator or the incredible efficiency of the LED, but we’re nonetheless impressed.

Since around 2012, research into triboelectric nanogenerators has heated up, as our devices use less and less power and the structures to harvest these tiny amounts of power get more and more sophisticated. One of the coolest such electron harvesters is 3D printable, but in terms of simplicity, it’s absolutely hard to beat some pieces of metal and plastic tape shoved into your shoe.

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3D Printing Your Own Triboelectric Generators

A triboelectric nanogenerator (TENG) certainly sounds like the sort of thing you’d need to graduate from Starfleet Engineering to put together, but it actually operates on the same principle that’s at work when you rub a balloon your head. Put simply, when friction is applied to the proper materials, charges can build up enough to produce a short burst of electrical energy. Do it enough, and you’re on the way to producing useful power.

In a recent paper, [Leo N.Y. Cao], [Erming Su], [Zijie Xu], and [Zhong Lin Wang] describe how a functional TENG can be produced on a standard desktop 3D printer. What’s even more impressive is that the method doesn’t appear to require anything terribly exotic — just some commercially available filaments and a bunch of PTFE beads.

TENGs can be printed in any size or shape.

So how do your print your own TENG? First, you load up an electrically conductive PLA filament and lay down a base into which a series of channels has been designed. At around the half-way point, you pause the print to insert your PTFE beads, and then swap over to standard filament for a few layers to produce an insulator. Finally, you pause again and switch back over to the conductive filament for the rest of the print, encasing the beads inside the structure.

As [Leo N.Y. Cao] demonstrates in the video below, you then clip leads to the top and bottom of the print, and give it a good shake. If everything went right, LEDs wired up to your new high-tech maracas should flash as the PTFE beads move back and forth inside. But there’s a catch. Going back to the balloon-on-the-head example, the effect at play here produces high voltages but low current — the paper says a TENG containing 60 beads should be capable of producing pulses of up to 150 volts.

Naturally, you won’t get very far with just one of these. Like other energy harvesting concepts we’ve covered in the past, such as vibratory wind generators, it would take a bunch of these working together to generate a useful amount of power. But given how cheap and quickly these printable TENGs can be produced, that doesn’t seem like it would be too much of a challenge.

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Harvesting Mechanical Energy From Falling Rain

Collecting energy from various small mechanical processes has always been something that’s been technically possible, but never done on a large scale due to issues with cost and scalability. It’s much easier to generate electricity in bulk via traditional methods, whether that’s with fossil fuels or other proven processes like solar panels. That might be about to change, though, as a breakthrough that researchers at Georgia Tech found allows for the direct harvesting of mechanical energy at a rate much higher than previous techniques allowed.

The method takes advantage of the triboelectric effect, which is a process by which electric charge is transferred when two objects strike or slide past one another. While this effect has been known for some time, it has only been through the advancements of modern materials science that it can be put to efficient use at generating energy, creating voltages many thousands of times higher than previous materials allowed. Another barrier they needed to overcome was how to string together lots of small generators like this together. A new method that allows the cells to function semi-independently reduces the coupling capacitance, allowing larger arrays to be built.

The hope is for all of these improvements to be combined into a system which could do things like augment existing solar panels, allowing them to additionally gather energy from falling rain drops. We’d expect that the cost of this technology would need to come down considerably in order to be cost-competitive, and be able to scale from a manufacturing point-of-view before we’d see much of this in the real world, but for now at least the research seems fairly promising. But if you’re looking for something you can theoretically use right now, there are all kinds of other ways to generate energy from fairly mundane daily activities.

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Improving Ocean Power With Static Electricity

Water is heavy, so if you think about it, a moving ocean wave has quite a bit of energy. Scientists have a new way to use triboelectric generators to harvest that power for oceangoing systems. (PDF) Triboelectric nanogenerators (TENGs) are nothing new, but this new approach allows for operation where the waves have lower amplitude and frequency, making traditional systems useless.

The new approach uses a rotor and a stator, along with some aluminum, magnets, and — no kidding — rabbit fur. The stator is 3D printed in resin. The idea is to mechanically accumulate and amplify small low-frequency waves into high-frequency motion suitable for triboelectric generation.

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Miracle Of Science: Scotch Tape Improves Generator

We were always amused that one of the biggest scientific discoveries of the recent past — graphene — was started with pencil lead and Scotch tape. Now, researchers at the University of Alabama in Huntsville have determined that double-sided Scotch tape can improve triboelectric power generators. Triboelectric generation, of course, is nothing new. These energy harvesters take mechanical and thermal energy and turn them into tiny amounts of electricity. What’s new here is that PET plastic, aluminum, and double-sided tape can make an inexpensive generator that works well.

Keep in mind we are talking about little bits of power. In the best scenario with the device stimulated at 20 Hz, the generator peaked at 21.2 mW. That was better than some designs that only got to 7.6 mW in the same configuration.

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