A foldable keyboard having a plurality of folding keyboard sections. The capacitor body includes a plurality of insulator layers laminated, a signal inner electrode and a first grounding inner electrode which are arranged so as to oppose each other with at least one insulator layer in between, and a second grounding inner electrode arranged so as to oppose the signal inner electrode or first grounding inner electrode with at least one insulator layer in between. The electrode is in electrical communication with one of the conductors and has an outer contact adapted for contacting adjacent body tissue of a patient.