The Operating Principles and Design of the Electret Condenser Microphone

The electret condenser microphone (ECM) is a widely used transducer in audio and sensing systems, converting acoustic pressure variations into corresponding electrical signals. This paper provides a comprehensive explanation of ECM operation, including the physical transduction mechanism, electret charge physics, circuit modeling, and system-level design considerations. Detailed mathematical derivations are presented to describe the relationship between diaphragm displacement, capacitance variation, and output voltage. Equivalent circuit representations are provided to elucidate the interface between the mechanical, electrical, and electronic domains. This discussion concludes with comparisons to MEMS microphone technology and practical notes on biasing, sensitivity, and noise optimization.