Patent ID: 8639185

Claim:
A communication system for wideband communications, comprising: a transmitter configured to apply an electric field to a transmission medium, the electric field corresponding to a voltage signal obtained by a wideband modulation of an information signal; and a receiver configured to detect the electric field from the transmission medium and obtain a demodulation signal corresponding to the information signal by a wideband demodulation; wherein the transmitter includes: a transmission electrode configured to apply the electric field to the communication medium by capacitively coupling to the transmission medium; a transmission circuit configured to output the voltage signal corresponding to the information signal; and a first frequency band controller coupled to the transmission circuit, configured to control a frequency band of the voltage signal to be supplied to the transmission electrode, and wherein, if the transmission medium is in contact with the transmission electrode, the first frequency band controller provides the voltage signal with a first bandwidth that allows the receiver to perform the wideband demodulation, and if the transmission medium is not in contact with the transmission electrode, the first frequency band controller provides the voltage signal with a second bandwidth narrower than the first bandwidth, the second bandwidth not allowing the receiver to perform the wideband demodulation, and wherein the first-frequency band controller has a resonator, and performs a resonance control so that, if the transmission medium is in contact with the transmission electrode, a Q factor of the resonator has a first value, and if the transmission medium is not in contact with the transmission electrode, the Q factor of the resonator has a second value hither than the first value.