  The principle of transformation optics has been applied to various wave
phenomena (e.g., optics, electromagnetics, acoustics and thermodynamics).
Recently, metamaterial devices manipulating dc currents have received
increasing attention which usually adopted the analogue of transformation
optics using complicated resistor networks to mimic the inhomogeneous and
anisotropic conductivities. We propose a distinct and general principle of
manipulating dc currents by directly solving electric conduction equations,
which only needs to utilize two layers of bulk natural materials. We
experimentally demonstrate dc bilayer cloak and fan-shaped concentrator,
derived from the generalized account for cloaking sensor. The proposed schemes
have been validated as exact devices and this opens a facile way towards
complete spatial control of dc currents. The proposed schemes may have vast
potentials in various applications not only in dc, but also in other fields of
manipulating magnetic field, thermal heat, elastic mechanics, and matter waves.
