Electrostatic Puck: Making An Electret

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You might have heard of electrets being used in microphones, but do you know what it is? Electrets produce a semi-permanent static electric field, similar to a magnet produces a magnetic field. The ones in microphones are very small, but in the video after the break [Jay] from the Plasma Channel makes a big electret and demonstrates it’s effects.

Electrets have been arounds 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 and 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 trop of repeatedly. Moving the aluminum electrodes the the inner surfaces of the molds top and larger distance between the plates eventually produced and electret detectable out to 10 inches.

This was with the original wax recipe, but there are now have 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 build an detector array, with 25 detectors in a 5×5 array, to help him visualize the size and shape of the field. One of the commenters had an interesting idea to use the detector with long exposure photography to visually map the shape of the electric field.

Besides microphones, static electricity is also useful for motors and speakers.



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