MEMS Microphone Basics: Operation and Advantages

This article covers the basics of MEMS Microphones, including their operation, working principles, and advantages compared to conventional microphones.

About Microphones

A microphone is a transducer that converts acoustic signals (sound) into electrical signals. These electrical signals can then be processed within an audio chain, such as in a hearing aid. Various technologies are used for this acoustic-to-electrical signal conversion.

Condenser microphones are known for their accuracy and small size. They use a diaphragm that moves in response to sound waves. This movement changes the capacitance, which in turn generates an electrical signal. The process can be summarized as:

• Acoustic signal → movement → change in capacitance → electrical signal

What is a MEMS Microphone?

MEMS stands for Micro-Electro Mechanical Systems. MEMS microphones are developed using advanced silicon technology. They have gained popularity in the hearing aid industry due to their reduced power consumption and low noise levels.

MEMS Microphone Operation and Working Principle

Figure 1: Cross-section of a MEMS Microphone

Figure 1 illustrates the cross-section of a MEMS Microphone. Here’s how it works:

The MEMS microphone consists of a flexible diaphragm and a backplate, both fabricated on a silicon wafer. The diaphragm is designed to move in response to sound pressure. This structure functions as a variable capacitor.

A fixed charge is applied between the diaphragm and the backplate. When sound waves hit the microphone, the diaphragm moves proportionally to the amplitude of the waves. This movement changes the distance between the backplate and the diaphragm, causing a variation in capacitance. With a constant charge applied, this change in capacitance is converted into an electrical signal.

When compression waves hit the microphone, the capacitance value decreases. Conversely, when rarefaction waves hit the microphone, the capacitance value increases. This relationship can be expressed mathematically:

$C = \frac{\epsilon A}{d}$

Where: $C$ = Capacitance $\epsilon$ = Permittivity $A$ = Area of the plates $d$ = Distance between the plates

MEMS Microphone Advantages

MEMS Microphones offer several benefits over conventional microphones:

• Ultra-small fabrication geometries: Enables miniaturization.
• Low power consumption: Extends battery life in portable devices.
• Excellent stability: Ensures consistent performance over time.
• Low noise levels: Provides clearer audio capture.