The present invention is directed to an apparatus and method for varying the power level of a transmitted signal, such as a transmitted radio frequency signal, of high power, high transmission rate systems in a relatively straightforward, cost efficient manner. A chamber with a semipermeable membrane at the site of brain contact is perfused with a hyperosmolar solution. They provides residual benefits on the hard surface such as soil resistance and resistance to bacteria, molds and biofilms. When short-circuiting of the load occurs, the load control circuit stops feeding the gate voltage to the output transistor. Provided in the housing and the horizontal shield plates of the receptacle connector are slits for allowing insertion of the vertical shield plates. At least one of the first and second diffractive gratings is made of a material having a refractive index distribution in a plane normal direction, and the predetermined expressions are satisfied for a wavelength \u03bb in a visible wavelength range.