Microphones

1. Overview ‌

Microphone is a transducer device that converts sound wave signals into electrical signals. It is widely used in communication equipment, consumer electronics, medical instruments, and other fields. Its core function is based on the conversion of mechanical vibration caused by sound pressure changes and electrical parameters (such as capacitance and voltage) .

‌2. Classification and Working Principle ‌

1) ‌Dynamic microphone ‌

Principle: Using electromagnetic induction, sound waves drive the diaphragm to drive the coil to move in the magnetic field, generating induced current.

Features: Simple structure and durability, but low sensitivity, poor high-frequency response, suitable for human voice recording.

2) ‌Capacitive microphone ‌

Principle: Sound pressure causes the capacitance between the diaphragm and the backplate to change, and the bias voltage is provided by the charge pump. The signal is output after ASIC amplification.

Subtypes:

√‌MEMS microphone‌: The silicon-based diaphragm is etched using micro-electromechanical technology, and the ASIC chip is integrated. It has the characteristics of small size and good consistency. ‌

√‌Electret microphone ‌: The built-in electret material provides a fixed charge, and no external bias power supply is required. It is often used in consumer electronics products. ‌

3) ‌Piezoelectric microphone‌

Principle: Utilize the mechanical stress-voltage effect of piezoelectric materials to directly convert vibration into electrical signals, and it has been gradually applied to the MEMS field in recent years. ‌

‌3. Structural Features‌

‌MEMS microphone‌:

It is composed of a silicon diaphragm and a perforated backplate to form a variable capacitor. The front cavity/back cavity design affects the frequency response characteristics (such as the large front cavity of the Top type and the low high-frequency resonance point) . ‌

Packaging forms include COB (Chip On Board) and surface mounting, supporting digital/analog output. ‌

‌Electret microphone‌:

It includes an electret backplate and a field effect transistor to simplify the circuit design, but it needs to be matched with an impedance-matching circuit. ‌

‌4. Key Parameters‌

Sensitivity‌: Expressed in dBV (analog) or dBFS (digital) , reflecting the efficiency of converting sound pressure into electrical signals. ‌

‌Frequency response‌: Determines the microphone's ability to capture sound waves of different frequencies, such as the Top type MEMS has a narrow frequency response range.

‌

‌Signal-to-noise ratio (SNR) : Related to thermal noise, MEMS microphones reduce noise by optimizing diaphragm materials (such as silicon nitride) .

‌Maximum sound pressure level (SPL) : The upper limit of sound pressure that a microphone can withstand. Digital MEMS usually supports 120 dB SPL.

5.‌ Application Areas ‌

‌Consumer electronics: Mobile phones, headphones (MEMS-based) .

‌Industrial and medical: Voice-controlled equipment, hearing aids (requires high sensitivity and low noise) .

‌Professional audio: Recording equipment, stage microphones (dynamic/capacitive-based) .

6‌. Development Trends ‌

‌Integration: High integration of MEMS and ASIC chips to improve signal processing efficiency.

‌Miniaturization: Silicon-based processes drive microphone size down to the millimeter level to meet the needs of wearable devices.

‌Multimodal fusion: Combining piezoelectric and capacitive technologies to optimize frequency response and signal-to-noise ratio.