Introduction What is a transducer? A device which converts energy in one form to another. Transducer Active Passive Generates its own electrical voltage during conversion Needs external power to operate to produce voltage

Capacitive Transducer What is Capacitive Transducer? A capacitor with variable capacitance. The capacitive transducer comprises of two parallel metal plates that are separated by the dielectric material. Change in Position Change in Capacitance Change in Voltage

Uses a capacitor to convert acoustical energy into electrical energy. Require power from battery or external source. Capacitive Audio Sensor

Flexible Diaphragm Fixed Plate Input Voltage Electrical Signal Operation of Capacitive Microphone What we need ?

Flexible Diaphragm Fixed Plate Input Voltage Mathematical Modelling Electrical Signal

Flexible Diaphragm Fixed Plate Input Voltage t V Electrical Signal If diaphragm move close to plate

Flexible Diaphragm Fixed Plate Input Voltage t V Electrical Signal If diaphragm move far from plate

Flexible Diaphragm Fixed Plate Input Voltage Overall operation t V Electrical Signal

Advantages Simple and cheap to construct High accuracy and noise immunity Can used in different medium Effective for high frequency variations Advantages of Capacitive Audio Sensor

Simple to construct Diaphragm Magnet surrounded by coiled metal wire

High Accuracy and Noise Immunity C= KA/d K = Dielectric constant A = Area D = Distance between surface High noise immunity means low disturbance to system

Can Used in Different Medium Can detect liquid and air vibrations Capacitive Micromachined Ultrasonic Transducers (CMUTs) for Underwater Imaging Applications

Effective for High Frequency Variations Can detect: Low Frequency (infra-sound) Low Frequency (infra-sound) High Frequency (ultrasound) High Frequency (ultrasound)

Disadvantages Sensitive to temperature variation Long lead length can cause errors or distortion in signals Sensitive to dirt and other contaminants Disadvantages of Capacitive Audio Sensor

Sensitive to temperature variation Changes of temperature will alter the dielectric properties. The changes of dielectric properties thus changes the value of capacitance.

Long lead length As the length of the lead increases, the capacitance build up on it will introduce sufficient capacitance to the sensor circuit. This will cause the vibration signal to develop distortion.

Dirt and Contaminants Dirt Contaminants such as water droplet and metal particle It may have a higher dielectric constant than the dielectric material used in the transducer. Change in the dielectric constant will severely affected the transducer performance.

Application of Capacitive Audio in Condenser Microphone.

Condenser Microphone  Microphones are a types of transducer.  Transducer: a device which converts energy from one form to another.  Condenser means capacitor.  Condenser microphone: use capacitor to convert acoustical energy (sound waves) into electrical energy (audio signal).  More sensitive and responsive than dynamic microphone.  Not ideal for high volume work. (Their sensitivity make them prone to distort).

Cross-Section of a Typical Condenser Microphone

How Condenser Microphones Work The capacitor has (2) plates with voltage between them. One of this plate made of very light material and act as diaphragm. Diaphragm vibrates when struck by sound wave. Distance between (2) plates became closer. Capacitance increase and charge current occurs.

Distance between (2) plates are further apart Capacitance decrease and discharged current occur. Voltage required across the capacitor so the system can work.