At an occasion of a level transition when a second periodic voltage becomes equal to a main reference voltage a first periodic voltage generating circuit starts a first monotonically changing time-period in which a voltage value of a first periodic voltage increases monotonically from 0, which is an initial value, towards a voltage value of the main reference voltage. The resonator can be a one-port resonator if the electrode on both sides is a single electrode, or it can be a two-port resonator if the electrode on one side is a single electrode and the electrode on the other side is a bipolar electrode. The present invention also provides for enhancing biodegradation of sanitary products after use and disposal. After the opening is made in the protective covering at the access location, the optical fibers for distribution are selected.