| 摘要 |
PURPOSE:To allow the microphone device to be used for detecting a very small static capacitance such as that in the order of 10<-5>pF by employing a ceramic resonator for both a resonator of an oscillating circuit and a resonator for a modulation section and detecting a change in a static capacitance equivalent to a sound pressure detected by a sound pressure detection section through the use of change in a tuning point of the ceramic resonator. CONSTITUTION:An oscillation circuit 1 is oscillated by using a signal of a high frequency as a carrier signal and gives the signal to a ceramic resonator 2 being a modulation section. A sound pressure detection section 3 consists mainly of a diaphragm 7 receiving a sound pressure signal and making vibration and a fixed electrode 9 at a rear pole opposite to the diaphragm 7 at a prescribed interval thereto, the diaphragm 7 connects to ground and the fixed electrode 9 connects to an output electrode of the ceramic resonator 2. An oscillated frequency f1 of the oscillation circuit 1 is set to be slightly deviated with respect to the resonance frequency fo of the ceramic resonator 2. The resonance frequency fo of the ceramic resonator 2 is deviated in response to a change in the static capacitance detected by the sound pressure detection section 3 and when the static capacitance changes by DELTAC, a voltage change of DELTAV is extracted from the ceramic resonator 2. |
