Capacitive microphone

In capacitive displacement transducers, parallel plate capacitor is used, with one of its plates being subjected to movement by a mechanical primary transducer. Capacitive pressure transducer belongs to this category where a metallic diaphragm forms the movable plate of the transducer. Capacitive microphone is a modified version of the capacitive pressure transducer. Here capacitance changes when the vibratory displacements of the membrane due to pressure changes. Pressure fluctuations can be reproduced effectively by a capacitive microphone. The capacitive microphone membrane is sensitive to only fluctuating components. A provision is made to equalize the pressure on either side of the membrane to avoid system collapse due to atmospheric pressure variations. In a capacitive microphone, a thin metallic membrane is kept under radial tension. A capillary tube is connected to thr chamber behind the membrane. This is for equalizing the pressure on either side of the membrane. The capillary path and the volume of the microphone chamber act as a low pass filter allowing the slow variations of the atmospheric pressure but preventing the pressure variations of acoustic waves from appearance on the backside of the membrane.