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.

20 thoughts on “Is That A Triboelectric Generator In Your Shoe?

    1. Haha! That reminds me of the final year project of one of my flatmates when I was in my final year of university. He’d decided that he would use the movement of cars for power generation, he wanted to have the road surface get pressed down by the weight of vehicles and that would move a magnet through a coil. I tried to convince him that he was trying to make all roads slightly more of an up hill. He just couldn’t see that the energy he was stealing from cars would have to come from somewhere.

      1. That is the big problem with all these energy harvesting devices for cars, all the energy comes from the car. Sure when braking in a normal car the energy is wasted so there is some merit to putting generators where cars are likely to slow down, but then when you have an electric car with regenerative braking you are just stealing the energy from the car or in places where some cars may not want to slow down you are making them use more energy.

        I am very surprised your flatmate made it all the way through to their final year without knowing the basics of thermodynamics, “energy cannot be created or destroyed, only converted from one form to another”, where did they think the energy they were generating came from?

        It seems a lot of these “green” projects aren’t very well thought out, just look at the solar roadways that EEVBlog covered many times, when even a small amount of dust can significantly diminish a solar panel’s output they thought it would be a great idea to make a cycle path out of solar panels, as expected the surface got dirty and scratched up to the point you might mistake it for concrete and the solar panels were basically non functional then.

      1. Not really. Human-produced electricity costs around $10/kWh in food alone, and that’s with cheap calories and a very efficient generator (which this ain’t).

        And sure, the materials are pretty cheap, but with only a few microwatts output, the payback period is going to be measured in centuries.

    1. I remember wondering about harvesting energy from motion like this after those motion-winding watches started showing up and it seemed like a really fascinating idea, same with those roads that generate electricity as cars drive over them… until I actually heard how little energy actually got harvested (and for the roads, just how expensive they were to maintain for that slightly better trickle). I still love the idea and hope someone finds a way to make all of them cost effective but physics seems to be stacked against it being both effective and cheap enough to be worth it.

      1. ugh that comment originally sprung off your comment more Garth and then my brain started editing and meandering and yeah, what’s the link besides the article itself? I don’t even remember

      2. The problem with energy harvesting roads is that they are inefficient and that the energy has to come from somewhere, from the car itself, so fossil fuel cars may have to use more fuel and electric cars will lose out on some regenerative braking or use more power. I think I would much rather the car’s kinetic energy go into efficient regenerative braking which is built into the car anyway, rather than waste most of the energy and waste a lot of money on energy harvesting roads.

        A far better option (although not perfect either) is just to put solar panels on more roofs.

  1. That doesn’t behave like a triboelectric generator, where charge carriers (electrons) are transported between electrodes, and can make a DC current. It looks much more like a piezoelectric effect, where deforming a polymer changes the electric field and the voltage potential on the capacitor plates. Repeated deformations produces an AC current. Still energy harvesting, but different mechanism.

    1. No, this is a pretty standard triboelectric nanogenerator. The spring-like deformation of the device is to assist contact and separation. The electrodes could be attached to solid blocks and moved together and apart with the same effect. The tape is not essential, as you can move charge between electrodes with just paper though it’s not as effective. You can see this effect more clearly by alternately touching two electrodes with a loose scrap of paper and observing the voltage.

      1. The video shows AC voltage being generated, not DC. There is no evidence of charge carriers being transferred between electrodes, so fails on the definition of triboelectricity. The effect demonstrated is more consistent with piezoelectric generation, not triboelectric.

        It’s still generating some voltage, and even a a few microwatts of power, but by a different mechanism than described.

  2. I saw somewhere where the military is interested in this for infantry and powering the tech they now have to carry. It was a few watts they were getting if I remember.

    1. Then that energy needs to come from the soldier. If the energy would just be wasted then that is ideal but the human body is pretty efficient already, with elastic muscles and other things that increase the efficiency of walking and running. Considering the human body uses 100-150 W depending on what it is doing (with a lot of that being used for internal functions rather than motion), stealing a few watts or enough to power most modern equipment would actually put noticeable strain on a person.

      The only way I could see this working is if it used heat to generate power, then the soldier getting hot and sweaty and the body trying to get rid of heat (sweating) would provide a good beneficial way of generating electrical power, since the body is trying to waste that extra heat that is generated through evaporative cooling. If the generator could help get rid of that heat whilst generating power from it then it could actually help the soldier, either prevent them overheating or mean they have to sweat less and hence waste less water.

      1. If the generator is sucking any significant amount of heat from the body, it is necessarily going to end up being the coolest spot on the body: the whole body must be hotter than that heat dump (otherwise the body heat won’t flow to it). How much skin surface to you need? (all of it?)

        Then the generator is going to try to harvest some power from that relatively cool heat source and dump it in the ambient air. Carnot is going to buck you here, hard.

        How about using the hot exhaled air instead? It’s already close to 37 degrees, and carrying away 5-20 watts of heat (or more), depending on work load and ambient temperature.

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