Similarity to magnets and capacitors
– Electrets and magnets are both dipoles and produce an electrostatic field.
– When an electret is moved with respect to a magnetic pole, a force is felt perpendicular to the magnetic field.
– Electrets and capacitors both have dielectric layers.
– Electrets exhibit quasi-permanent charge storage or dipole polarization.
– Some materials display ferroelectricity and retain polarization permanently.
– Electrets eliminate the need for a polarization voltage in certain microphone types.
Electret types and materials
– Real-charge electrets contain excess charge on surfaces or within the volume.
– Oriented-dipole electrets contain aligned dipoles.
– Ferroelectrets mimic ferroelectric behavior and display strong piezoelectricity.
– Some materials exhibit both real-charge and oriented-dipole electret properties.
– Electret materials occur naturally, such as quartz and silicon dioxide.
– Most electrets are made from synthetic polymers like fluoropolymers.
– Real-charge electrets contain positive or negative excess charges.
– Oriented-dipole electrets contain oriented dipoles.
– Electrets create quasi-permanent internal or external electric fields.
Manufacture of electrets
– Bulk electrets can be prepared by cooling the material in a strong electric field.
– Materials used for electrets include waxes, polymers, and resins.
– Excess charge within an electret decays exponentially.
– Particle accelerators can embed excess negative charge within a dielectric.
– Commercially produced electrets are often based on fluoropolymers.
– One common method is the corona charging technique.
– Another method involves the use of a high voltage field during the material’s solidification process.
– Some electrets are manufactured by applying a strong electric field to the material at high temperatures.
– Certain polymers can be electretized by stretching or compressing them while they are heated.
– Electrets can also be produced by using a combination of techniques such as corona charging and high temperature treatment.
Definition, properties, and applications of electrets
– An electret is a dielectric material with a permanent electric charge.
– Electrets can retain their charge for long periods of time.
– They can be made from various materials such as polymers, ceramics, and metals.
– Electrets have a wide range of applications in electronics, acoustics, and sensing.
– Electret microphones are widely used in devices such as smartphones, laptops, and voice recorders.
– Electret transducers are used in speakers and headphones.
– Electret sensors are employed in touch screens, fingerprint scanners, and pressure sensors.
– Electret generators are used to harvest energy from ambient sources.
– Electret filters are utilized in electronic devices to remove unwanted noise and interference.
– Electret-based noise-cancelling headphones are popular for reducing ambient noise.
– Electret speakers are used in audio systems, televisions, and public address systems.
– Electret hydrophones are employed in underwater acoustics.
– Electret film-based speakers are used in automotive sound systems and home theater setups.
– Electret-based ultrasonic transducers are used in medical imaging and non-destructive testing.
– Electret-based gas sensors are used in air quality monitoring systems.
– Electret-based humidity sensors are used in weather stations and HVAC systems.
– Electret-based accelerometers are used for measuring vibrations and detecting motion.
– Electret-based pressure sensors are utilized in automotive applications and industrial processes.
– Electret-based proximity sensors are used in touchless switches and security systems.
Additional details on electret manufacture
– Electrets can be manufactured by using a combination of techniques such as corona charging and high temperature treatment.
– The corona charging technique involves exposing the material to a corona discharge.
– Some electrets are manufactured by applying a strong electric field to the material at high temperatures.
– Certain polymers can be electretized by stretching or compressing them while they are heated.
– Electrets can also be produced by cooling the material in a strong electric field.
– Materials used for electrets include waxes, polymers, and resins.
– Excess charge within an electret decays exponentially.
– Particle accelerators can embed excess negative charge within a dielectric.
– Commercially produced electrets are often based on fluoropolymers. Source: https://en.wikipedia.org/wiki/Electret
This article needs additional citations for verification. (September 2013) |
An electret (formed as a portmanteau of electr- from "electricity" and -et from "magnet") is a dielectric material that has a quasi-permanent electric charge or dipole polarisation. An electret generates internal and external electric fields, and is the electrostatic equivalent of a permanent magnet. Although Oliver Heaviside coined this term in 1885, materials with electret properties were already known to science and had been studied since the early 1700s. One particular example is the electrophorus, a device consisting of a slab with electret properties and a separate metal plate. The electrophorus was originally invented by Johan Carl Wilcke in Sweden and again by Alessandro Volta in Italy.
The name derives from "electron" and "magnet"; drawing analogy to the formation of a magnet by alignment of magnetic domains in a piece of iron. 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. Modern electrets are usually made by embedding excess charges into a highly insulating dielectric, e.g. by means of an electron beam, corona discharge, injection from an electron gun, electric breakdown across a gap, or a dielectric barrier.
