Abstract: An object is to provide a ?/4 radio wave absorber that includes a support, a resistive film, a dielectric layer, and a reflective layer, and that has higher radio wave absorption performance. The object is achieved by a ?/4 radio wave absorber that includes a support, a resistive film, a dielectric layer, and a reflective layer, and that satisfies formula (1): ?0.375x+1086.9<y<?0.375x+1140 wherein x represents a resistance value of the resistive film, and y=the thickness of the support×(the relative permittivity of the support)0.5+the thickness of the dielectric layer×(the relative permittivity of the dielectric layer)0.5.

Abstract: An arc furnace is provided with a variable-capacity ring which is placed at the top of a furnace body and which is split into a plurality of circumferential sections which in turn define in combination a top furnace wall portion, and a driving mechanism for causing the ring to move horizontally. As the ring is moved radially outwardly or inwardly of the furnace body, the height of the furnace body is varied and consequently the capacity or the volume of the furnace body can be varied. As a result, the overcharging of the charge (scrap) is much facilitated; that is, the number of back charges can be reduced. Furthermore, when the pile of the charge in the furnace body is lowered, the capacity or volume of the arc furnace is decreased so that unwanted thermal losses and oxidation and resulting wear of electrodes can be reduced to a minimum.