Condenser microphone (mic) is a transducer that uses a capacitor (or condenser) to convert acoustical energy into electrical energy. The sound waves result into electric signals that can be used to drive a circuit or device. The pin connected to the case of mic is connected to ground and the other pin gives the output.
A simple capacitor has two plates with a voltage difference between them. The capacitance depends on the distance between these plates. In condenser mic, a diaphragm (of light material) acts as one of the plates. When sound waves strike the diaphragm, the distance, between the plates, changes and so does the capacitance. When the plates come closer, thereby increasing the capacitance, a charge current is generated. Similarly, the capacitance decreases and a discharge current occur when the plates move apart.
There are two methods of extracting sound signals from mic, namely, DC biased and radio frequency (RF). In DC biased method, the charge within the capsule, i.e.
, diaphragm and fixed plate assembly, remains constant. The voltage variations, across the capsule, are passed through a series resistor and are further amplified. In RF method either the capacitance change modulates the amplitude of output of a low RF oscillator or the capsule is a part of a resonant circuit which modulates the frequency of output. Learn about working and internal structure of a condensor microphone.
The FBI appears to have begun using a novel form
The FBI appears to have begun using a novel form of electronic surveillance in criminal investigations: remotely activating a mobile phone\\\'s microphone and using it to eavesdrop on nearby conversations.
The technique is called a \\\"roving bug,\\\" and was approved by top U.S. Department of Justice officials for use against members of a New York organized crime family who were wary of conventional surveillance techniques such as tailing a suspect or wiretapping himthe eavesdropping technique \\\"functioned whether the phone was powered on or off.\\\" Some handsets can\\\'t be fully powered down without removing the battery; for instance, some Nokia models will wake up when turned off if an alarm is set