[HN Gopher] Electret
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       Electret
        
       Author : thunderbong
       Score  : 43 points
       Date   : 2022-07-07 09:01 UTC (2 days ago)
        
 (HTM) web link (en.wikipedia.org)
 (TXT) w3m dump (en.wikipedia.org)
        
       | xigoi wrote:
       | I'm studying for an electromagnetism exam right now, so this
       | article came just at the right time :)
        
       | nine_k wrote:
       | <<Historically, electrets were made by first melting a suitable
       | dielectric material such as a polymer or wax that contains polar
       | molecules, and then allowing it to re-solidify in a powerful
       | electrostatic field. The polar molecules of the dielectric align
       | themselves to the direction of the electrostatic field, producing
       | a dipole electret with a permanent electrostatic bias.>>
        
       | Animats wrote:
       | The big application for electrets right now is N95 masks. One of
       | the inner layers is an electret. It will attract and hold
       | particles smaller than the holes in the mesh. It doesn't take
       | much of a static charge, because the particles only have to be
       | pulled a few microns to be caught.
       | 
       | This is the huge difference between N95 masks and the cheapies.
        
         | xigoi wrote:
         | How much does this increase effectiveness? And does it also
         | work as a protection from the outside?
        
           | Animats wrote:
           | https://1lnfej4c7wie44voctzq1r57-wpengine.netdna-
           | ssl.com/wp-...
        
         | stdbrouw wrote:
         | ... though I imagine that the big application in general is
         | electret microphones?
        
       | dvh wrote:
       | Interesting, water is also polar molecule, could we make electret
       | from water ice?
        
         | CamperBob2 wrote:
         | Seems likely: https://en.wikipedia.org/wiki/Thermo-
         | dielectric_effect
        
       | klyrs wrote:
       | > However, when an electret is moved with respect to a magnetic
       | pole, a force is felt which acts perpendicular to the magnetic
       | field, pushing the electret along a path 90 degrees to the
       | expected direction of "push" as would be felt with another
       | magnet.
       | 
       | The heck?? Why was I not exposed to this as a kid? (After
       | searching awhile) Why does nobody make these for sale?
        
         | CamperBob2 wrote:
         | The perpendicular force might not be strong enough to notice in
         | most cases, would be my guess. I've never heard of it either.
        
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       (page generated 2022-07-09 23:01 UTC)