What is an electret microphone

Microphones are devices that amplify sound volume and are ubiquitous. Among their varieties there are professional ones, as well as simpler options for home use. In addition, microphones come in condenser and electret types.

What is an electret microphone

To better understand what kind of device this is, you first need to clarify what an electret is.

Electret is a special material that can be polarized for quite a long time. In addition, it has the property of creating an electromagnetic field.

Conventional condenser microphones have a fairly low impedance, but the electret version has a much higher impedance. Therefore, such devices require connection to amplifiers, which have a fairly high resistance. They also require an external power supply.

There is an amplifier in its case and all the voltage supplied to the device is required to power it. In capacitor versions, it goes for charging.

Operating principle of an electret microphone

The device consists of capacitors, in which some of the plates are made of film. This film is stretched over the ring. Next, it is exposed to charged particles. Electrons penetrate into it to a small depth. As a result, a charge is created in the space around them. This charge can exist for quite a long time.

The top of the film is covered with a layer of metal. It is also used as an electrode. At a short distance from it there is another electrode - a small metal cylinder. Its flat side is turned towards the film.

The polyethylene membrane creates sound vibrations that are transmitted to the electrodes, resulting in the generation of current. The resulting current is extremely low, while the output resistance is high. Therefore, transmitting an audio signal is quite difficult. To match a small current and a large resistance, a special cascade is used. It is made in the form of a unipolar transistor, and is located in the device body, in a special capsule.

The operating principle of an electret device is based on the ability of certain types of materials to change their surface charge under the influence of an acoustic wave. The materials must have a very high dielectric constant.

REFERENCE! Because these devices have very high output impedance, they can be easily connected to receivers and amplifiers with high input impedance. To make sure that a particular amplifier can be used, you need to connect a multimeter to it and look at the obtained values. If, as a result of measurements, the multimeter showed values ​​equal to 2–3 Volts, then this amplifier can be connected to an electret microphone.

Now almost all equipment can work with this type of device.

Electret microphones have almost replaced other options. This is due to the fact that they have an affordable price, but at the same time are reliable in operation. Another advantage is their small size and weight.