A virtual interface is disclosed. A transmitter transmits a second signal that represents the first signal, through a second channel, to a master device. Preferably the composition also comprises inorganic boron, an alkali metal salt of a fatty acid, and an accelerator for phosphate coating. A plunger array assembly is included comprising a plunger array frame and a plunger element. A detachment preventing part is provided on an inhaling fan cover andor a discharging fan cover to prevent either of these covers from being detached from the fan assembly.