A magnetically shielded room (MSR) is constructed by combing superconducting panels with normal conductive junctions. The MSR is composed by vacuum insulation panels, a tank for liquid nitrogen for superconducting panels and a ferromagnetic door. Thermally insulating vacuum panels, a reservoir of liquid. nitrogen to cool the superconducting panels and ferromagnetic door make up the MSR.
The superconducting panel is made of 0.2mm thick Bi₂Sr₂CaCu₂Ox film coated on both side of a silver sheet (600mm×800mm× 0.5mm). The MSR are constructed by connecting panels by soldering on the edge of the silver sheet 50mm in width. Measurement results of shielding factors of MSR to ac magnetic fields did not agree with a simple computation supposing that the MSR is shielded by superconductors with perfect connection. We developed an equation to compute the shielding factors taking account of leakage magnetic fields through the normal conductive junction. The computation fundamentally agreed with the measurement results so that the equation is applicable to evaluate a shielding performance of a superconducting MSR.
As well known, a double layer permalloy MSR must keep a fair distance between the two layers to keep effective shielding factors of each layer. A double layer MSR composed of a ferromagnetic shield layer and a superconducting layer gives the best shielding factor when the distance is zero and the factor exceeds multiplication of factors of each layer. We demonstrated the distance effect by experiments.