You might have heard of electrets being used in microphones, but do you know what they are? Electrets produce a semi-permanent static electric field, similar to how a magnet produces a magnetic field. The ones in microphones are very small, but in the video after the break [Jay Bowles] from Plasma Channel makes a big electret and demonstrates it’s effects.
Electrets have been around since the 1800s, and are usually produced by melting an insulating material and letting it solidify between two high-voltage electrodes. The original recipe used a mix of Carnauba wax, beeswax, and rosin, which is what [Jay] tried first. He built a simple electric field detector, which is just a battery, LED and FET, with an open-ended resistor on the FET’s gate.
[Jay] 3D printed a simple cylindrical mold and stuck aluminum foil to the outer surfaces to act as the electrodes. He used his custom 6000:1 voltage transformer to hold the electrodes at ~40 kV. The first attempt did not produce a working electret because the electrodes were not in contact with the wax, and kept arcing across, which causes the electric charge to drop off. Moving the aluminum electrodes the inner surfaces of the mold eventually produced an electret detectable out to 10 inches.
This was with the original wax recipe, but there are now much better materials available, like polyethylene. [Jay] heated a a block of it in the oven until it turned into a clear blob, and compressed it in a new mold with improved insulation. This produced significantly better results, with an electric field detectable out to 24 inches.
[Jay] also built an array of detectors in a 5×5 grid, which he used to help him visualize the size and shape of the field. He once pulled off a similar trick using a grid of neon bulbs.
Polyethylene makes good electrets?
Does that mean that hot-melt glue could be used?
I still don’t get it… Does it have to be semi conductive material between plates?
No, the strong magnetic field duing the melting fase allign the molecules so they channel static electricity,
It is an electrostatic field, not a magnetic field. Think of the two metal plates that [Jay Bowles] used as two plates of a capacitor. The voltage applied is DC, so there is no current flow (other than the arc-over events). The electrostatic potential between the two plates establishes an electrostatic field that causes materials with dipole structures (e.g., long-chain molecules with positive and negative charges at different ends) in the candidate material to align to the electrostatic field. This is why the material must be molten for the alignment to occur and for the material to cool while the electrostatic field is still applied.
The Japanese used electrets in the condenser mics of their military radios during WWII.
Yes! Please! That’s the sort of editing issue you’d expect big, old news agencies to be doing, not Hackaday.
Polyethylene makes good electrets?
Does that mean that hot-melt glue could be used?
Does a fulgurite have any charge? What about in a raw state prior to any cleaning or cutting or even being bumped?
Now I’m wondering about a few lightning zapped bits that I tossed into the scrap or trash bin over the years.
I more and more dislike those educational youtubers channels. The videos are structured towards maintaining viewer engagement through a series of trial-and-error experiments rather than building a logical educational narrative. Key concepts (in this case molecular polarization, charge trapping mechanisms, and the role of dielectric materials) are glossed over. Another example is the construction of the simple electric field detector which was added as a cool way to visualize the electric fields but he did not explain how it works on a fundamental level. Those youtubers prioritizes quick demonstrations over in-depth explanation. The content serves more as filler for their advertisements.
Video title: Creating an Exotic Material With A Static Secret (Electret)
What happens in the video: he creates an electret
Why exactly do you feel you are owed?
I’m not clear on why you find it so problematic to show the full experimental process, including failures, forming new hypotheses and testing those hypotheses in subsequent experiments. This gives a realistic picture of science.
When the “recipe” or method is already known and described by others, it’s not exactly science but the application of science, otherwise known as “engineering”.
The trial and error method to engineering is just somewhat bad engineering, at least when the information and instructions are available. Sometimes there is no information and you have to reverse-engineer stuff by trying it out, or it’s faster to just plug it in and see what it does. Every process has its tricks and trials.
However, the point of a youtube video like this isn’t to showcase proper scientific or engineering practices, but to “act dumb” and make those errors to have something to fill a video with. That’s not a “realistic picture of science”, nor of engineering. Content creators get to pretend to be scientists by just throwing something at the wall and seeing if it sticks, whereas real scientists or engineers usually have to do a bit more groundwork and systematic testing so their experiments and prototypes would have a better chance of actually working or proving the thing they’re trying to research.
I find them most entertaining, and they give me ideas in other things. The errors are almost as good as the successes. Sometimes you learn more from the errors than the actual experiment.
I wonder if that clear casting resin would work. You’d have to maintain the HV charge for a while, while it cures.
The first time I heard of an electret was over 50 years ago in a Popular Electronics article which I believe was called “The Not Altogether Forgotten Electret”. IIRC, the article described how to make one by using voltage from the HV section of a TV set to charge a dielectric comprised of latex paint.
It’s good to see a new and up-to-date spin on an old subject like this.
I wonder if these could be made into a Halbach array like magnets to increase static attraction on one side.
Better yet, if you make a ring shaped one and spin it really fast, does it make a magnetic field?
That’s actually a really interesting question. Is it possible to create a static charge distribution within a non-conducting solid body such that rotation of that body will create an electric current that doesn’t cancel itself? I’m sure someone will say there’s a trivial solution that presents itself with a glance at Maxwell’s equations, but it’s not obvious to me.
If nothing else, you can spin them just like magnets to transmit VLF.
Now, spin that dipole really fast and you can create a radio wave.
So, what happens if you make the Electret, but keep the metal electrodes. Will the metal electrodes develop a charge between them that can do work?
The electrodes are not relevant. The charge displacement created when the electret was charged, and its electric field, will exist regardless.
An electret can do work in the same sense that a magnet can do work. You can align or attract (or repel) something once, doing some work. But it’s not like a capacitor: you don’t “discharge” it, just like you don’t “discharge” a magnet.
So you make a permanent magnet by cooling a ferromagnetic conductor in a strong magnetic field… and you make a permanent electret by cooling an insulator in a strong electric field. I find that quite pleasant.
There does seem to be a beautiful symmetry between electric and magnetic fields as witnessed by Maxwell’s equations. Frustratingly, despite being conjectured over a hundred years ago and many people looking, no one has conclusively found a magnetic monopole to mirror the proton and electron.