| 摘要 |
A wireless microphone is provided to operate in response to an RF(Radio Frequency) applied from the outside without a battery and to monitor a situation of a place by wireless. A SAW(Surface Acoustic Wave) transponder(220) transmits a surface acoustic wave generated in response to the received RF signal applied from an external device to a microphone. The SAW transponder generates the transmission RF signal by converting a reflective wave reflected in the inside in response to the variation of an electrical characteristic of a microphone. The microphone(230) changes the electrical characteristic like the variation of the output impedance or the output voltage in response to the received sound signal. A signal processor is arranged in the SAW transponder and the microphone and removes the noise included in all or a part of the output voltage outputted from the microphone, and converts the voltage into the signal to be processed in the external device after amplifying the voltage. A converter converts all or a part of the output voltage outputted from the microphone and supplies the power to the signal processor.
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