For an electret microphones, within a diaphragm, gasket and plate capacitor, because filling a charge on the diaphragm, and is a plastic film, so when the diaphragm is the role of sound pressure, the diaphragm to vibrate, thus changing the diaphragm and the distance between the plates, which changed the distance between the two plate capacitor, produced a Δ d change.

In this way, a preliminary conversion from acoustic signal to electrical signal is completed. Because the signal is very weak and the internal resistance is very high, it cannot be used directly. Therefore, impedance transformation and amplification should be performed. FET field effect tube is a voltage control element, the drain output current is controlled by the source and gate voltage.

As a result of the capacitor are two very received FET S extremely extremely and G, so is equivalent to FET S extremely and G between added a Δ v variation, FET drain current (I) is to create a Δ ID variation. This voltage variation can be output through the capacitance C0. This voltage variation is caused by the sound pressure, so the whole microphone completes an acoustic and electrical conversion process.


There is a wide variety of speakers and their prices vary widely. Audio electrical energy through electromagnetic, piezoelectric or electrostatic effects, so that its paper basin or diaphragm vibration surrounding the air to create sound. Press the mechanism of energy exchange and structure of the rotating coil (electric), capacitor (electrostatic), piezoelectric (crystal or ceramic), electromagnetic (spring), electric ion and pneumatic loudspeaker, electric loudspeaker has good electro-acoustic performance, strong structure, low cost advantages, widely used; According to sound radiation materials, paper basin type, drum type, diaphragm type; According to the shape of the paper basin divided into round, oval, double paper basin and rubber ring; According to the working frequency sub bass, alto, treble, some are also divided into recorder, TV, ordinary and hi-fi speaker; The impedance of voice coil is divided into low impedance and high impedance; According to the effect of direct radiation and environmental sound, etc.


Due to the influence of COVID-19, “body temperature measurement” is already a daily need of people. Therefore, the forehead thermometer is another popular product after masks, alcohol, disinfection water and other epidemic prevention materials.

Buzzer is an integrated structure of electronic sounder, using DC voltage power supply, widely used in computers, printers, photocopiers, alarms, electronic toys, automotive electronic equipment, telephone, timer and other electronic products as sound devices. There are two types of buzzers: piezoelectric buzzers and electromagnetic buzzers. The buzzer is represented in the circuit by the letter “H” or “HA” (the old standard was “FM”, “ZZG”, “LB”, “JD”, etc.).