Microphone is an energy converter that converts sound signals into electrical signals. It is just the opposite of horn. Microphone can be divided into grid pole welding type, grid crimping type, pole ring connection type, etc. So what is the working principle of using a microphone?

According to electrostatics, for parallel plate capacitors, there is the following relationship: C= ε． S / L...... ① that is, the capacitance is directly proportional to the dielectric constant of the medium, directly proportional to the area of the two plates, and inversely proportional to the distance between the two plates.
In addition, when a capacitor is charged with a Q amount of charge, the two plates of the capacitor must form a certain voltage, which has the following relationship: C = q / V...... ②
For an electret microphone, there is a capacitor composed of diaphragm, gasket and electrode plate. Because the diaphragm is charged and is a plastic film, when the diaphragm is subjected to acoustic pressure, the diaphragm will vibrate, which changes the distance between the diaphragm and the electrode plate, thus changing the distance between the two electrode plates of the capacitor, resulting in a Δ Therefore, it can be seen from formula ① that there must be a change in D Δ The change of C is also known from formula ② because Δ With the change of C, the charging charge is fixed, so there must be a Δ V change.
In this way, a conversion from acoustic signal to electrical signal is preliminarily completed.
Because the signal is very weak and the internal resistance is very high, it can not be used directly, so impedance transformation and amplification are also required.
FET FET is a voltage control element. The output current of the drain is controlled by the source and grid voltages.
Since the two poles of the capacitor are connected to the S pole and G pole of the FET, it is equivalent to adding one between the S pole and G pole of the FET Δ V, the drain current I of the FET generates a Δ The amount of change in ID, so the amount of change in current produces an error on the resistance RL Δ The change of VD and the change of voltage can be output through capacitor C0. The change of voltage is caused by sound pressure. Therefore, the whole microphone completes an acoustic electric conversion process.