1, electret effect The key element of acoustoelectric conversion is electret diaphragm. It is an extremely thin plastic diaphragm with a pure gold film on one side. Then, after the high-voltage electric field stops, the opposite charges stop at both sides respectively. The evaporation surface of the diaphragm faces outward and communicates with the metal shell. The other side of the diaphragm is separated from the metal plate by a thin insulating gasket. Thus, a capacitor is formed between the gold evaporation film and the metal plate. When the electret diaphragm encounters acoustic vibration, the electric field at both ends of the capacitor changes, resulting in an alternating voltage that varies with the acoustic wave. The electret acoustoelectric sensor has the advantages of small volume, simple structure, good electroacoustic performance and low price.
2. Piezoelectric effect. The so-called piezoelectric effect refers to the phenomenon that when some dielectrics are deformed by external force in a certain direction (including bending and telescopic deformation), due to the polarization of internal charges, their surfaces will produce charges. The sound is transmitted to the piezoelectric effect element (such as piezoelectric ceramics) of the sound sensor through the air, and a voltage signal varying with the sound is generated. Piezoelectric sensor has simple structure, small volume, low power consumption and long service life.
3. Electromagnetic effect. The sound is transmitted to the diaphragm of the sound sensor through the air, and the diaphragm drives the coil to cut the magnetic field lines in the magnetic field, generating a voltage signal that varies with the sound.
Any one of the above three voltage signals generated by sound waves, after being adjusted by amplification, shaping and other circuits, pushes the switch (such as silicon controlled rectifier) to act and controls the electrical appliances (such as corridor lights) to turn on. This is the working principle of the sound wave sensor. If it is used for corridor lights, the circuit is also designed with a delay function to delay for a period of time after turning on the lights.