Provided are a terpyridine monomer that has a strong ability to coordinate with metal atoms, and a polymer material that can be readily switched between a colored state and a colorless state by controlling the electrical potential applied to it and that can be processed. Included in the cover assembly is a belt that substantially extends around the signal receiving and generating assembly, and a connector to hold the belt closed about the signal receiving and generating assembly. The photodiode is formed in a crystalline semiconductor layer over the metal ion-implanted insulating layer. A second n+ diffusion region is in the second nwell. The switch outputs either the positioning or supplemental positioning signals in response to receiving a control signal.