A floor covering made up of at least two layers bonded to one another, including a bottom layer of electrically conductive rubber arranged under a light-colored top layer of rubber, where the top layer is interrupted in partial areas distributed over its area in a pattern, and formed by electrically conductive rubber there. By this means, it is possible to perform demodulation processing based on the effective reception power of a modulated signal, enabling the precision of demodulation of modulated signals to be improved. Once the vessel is filled, the wafer is then processed utilizing the processing fluid.