How does an electret retain its charge for years without decreasing?

[arul_k]

How is an electret capable of recharging itself after discharge. I came across an article that stated tha electrets are capable of retaining their charge for years and any number of discharges does not decrease their charge. how does this happen?

 

[GRDixon]

How is an electret capable of recharging itself after discharge. I came across an article that stated tha electrets are capable of retaining their charge for years and any number of discharges does not decrease their charge. how does this happen?

In the case of a bar electret (e.g. one made out of barium titanate) "discharge" might occur when ions in the air are attracted to the ends, thus neutralizing the electret's electric field. This process does not change the bar's permanent, electric polarization. When the electret is "recharged", by stripping away the air ions, the bar's polarization field is restored until "discharge" occurs again. Kept in a vacuum, the electret should remain "charged" indefinitely.

 

[arul_k]

In the case of a bar electret (e.g. one made out of barium titanate) "discharge" might occur when ions in the air are attracted to the ends, thus neutralizing the electret's electric field. This process does not change the bar's permanent, electric polarization. When the electret is "recharged", by stripping away the air ions, the bar's polarization field is restored until "discharge" occurs again. Kept in a vacuum, the electret should remain "charged" indefinitely.

Thanks for your reply. I was thinking in terms of a spark discharge that would occour between the +ve and -ve terminals of the electret, when shorted. The process you suggest seems more like a neutralisation of the electric field.

 

[GRDixon]

Thanks for your reply. I was thinking in terms of a spark discharge that would occour between the +ve and -ve terminals of the electret, when shorted. The process you suggest seems more like a neutralisation of the electric field.

The key to the puzzle may be that the charges responsible for an electret's field are POLARIZATION charges, and are therefore bound charges. As such, shorting the poles as suggested will not result in a loss of the polarization charge. The shorting wire, which does contain conduction electrons, no doubt becomes electrically polarized while in contact (or in close proximity) with the electret's poles. But once removed, it loses this induced polarization and the electret's intrinsic electric field returns to its nominal value. Any conduction charges that "rub off" of the shorting wire, and stick to the electret's positive pole, might be relatively unimportant, as the electret is a dielectric.

But all of the above should be taken with a grain of salt, as I am not experienced with these fascinating devices.

 

[PJC01]

An electret is a special type of dielectric material that has a permanent electric charge. This charge is created by a process called polarization, where the material's molecules become aligned in a way that creates a permanent electric field. This electric field is what allows the electret to retain its charge for years without decreasing.

The key to the electret's ability to retain its charge lies in its molecular structure. The molecules in an electret are arranged in such a way that they have a high degree of internal electric polarization. This means that even when the external electric field is removed, the molecules remain in their polarized state, maintaining the electret's charge.

In addition to its molecular structure, an electret also has a high electrical resistance. This means that it is difficult for the charge to leak out of the material. As a result, the electret can retain its charge for long periods of time without any significant decrease.

Furthermore, an electret is capable of recharging itself after discharge. This is due to its ability to interact with external electric fields. When an electret is exposed to an external electric field, the molecules in the material realign themselves, restoring the electret's charge. This process is known as re-polarization.

In summary, an electret's ability to retain its charge for years without decreasing is due to its unique molecular structure and high electrical resistance. Its capability to recharge itself after discharge is a result of its interaction with external electric fields. These properties make electrets valuable for various applications in science and technology, such as in microphones, speakers, and air filters.