an apparatus and method for generating electric power by using magnetic fields are provided . a sensor node has a coil unit having a spiral structure in a plane that generates an induced electromotive force by using magnetic fields ; a conversion unit configured to convert the induced electromotive force into dc power ; and an integrated circuit for performing operations using the converted dc power . the sensor node may be disposed on a flexible plate substrate or film , and is attached to or placed on readily available electronic appliance cases which serve as magnetic field sources . the plate substrate or film can be provided with a metal shielding film . the metal shielding film may also be grounded , or the plate substrate or film may be provided with a metal shielding film accompanying an impedance - matching rf circuit for preventing reflection of magnetic fields passing through the coil unit .