Antenna device and method of setting resonant frequency of antenna device

Abstract

In antenna device, a coil conductor of an antenna coil module and a conductor layer at least partially overlap. A current flows in the conductor layer and blocks a magnetic field generated by a current flowing in the coil conductor. A current, which flows around the periphery of an opening of the conductor layer, flows along the periphery of a slit and around the periphery of the conductor layer due to a cut-edge effect. Since magnetic flux does not pass through the conductor layer, magnetic flux attempts to bypass the conductor layer along a path in which the conductor opening of the conductor layer is on the inside and the outer edge of the conductor layer is on the outside. Accordingly, the magnetic flux generates relatively large loops linking the inside and the outside of a coil conductor of an antenna on a reader/writer side.

1 . An antenna device comprising:
 a coil conductor having a loop shape or a spiral shape in which a winding center portion defines a coil opening; and   a conductor layer that is arranged on a side closer to an antenna on a communication partner side than a location of the coil conductor; wherein   the conductor layer includes a conductor opening and a slit, the slit connecting the conductor opening and an outer edge of the conductor layer; and   when the coil conductor is viewed in plan view, the coil conductor and conductor layer are superposed one on top of the other.   
     
     
         2 . The antenna device according  claim 1 , wherein when the coil conductor is viewed in plan view, the coil opening and the conductor opening at least partially overlap. 
     
     
         3 . The antenna device according to  claim 1 , wherein the coil conductor and the conductor layer are arranged so as to be in a vicinity of each other. 
     
     
         4 . The antenna device according to  claim 1 , wherein an area of the conductor layer is larger than an area of a region in which the coil conductor is located. 
     
     
         5 . The antenna device according to  claim 1 , wherein the coil conductor is wound across a plurality of layers. 
     
     
         6 . The antenna device according to  claim 1 , wherein, when the coil conductor is viewed in plan view, the coil opening and the conductor opening overlap each other over almost entire peripheries thereof. 
     
     
         7 . The antenna device according to  claim 1 , wherein the conductor layer is located on an inner surface or an outer surface of a casing of an electronic appliance. 
     
     
         8 . The antenna device according to  claim 1 , wherein the coil conductor is located on a substrate, a magnetic sheet is stacked on a surface of the substrate on a side that is distant from the antenna of the communication partner side, and an antenna coil module is defined by the substrate and the magnetic sheet. 
     
     
         9 . The antenna device according to  claim 8 , wherein the resonant frequency is lower than a central frequency of a to-be-used frequency band in a state in which the conductor layer is not present and is equal or substantially equal to the central frequency of the to-be-used frequency band in a state in which the antenna coil module has been mounted inside the casing of the electronic appliance. 
     
     
         10 . A method of setting a resonant frequency of an antenna device, the antenna device being configured by mounting, inside a casing of an electronic appliance, an antenna coil module that is formed by stacking a substrate on which a loop-shaped or spiral-shaped coil conductor, in which a winding center portion defines a coil opening, has been formed, on a magnetic sheet, the method comprising the steps of:
 arranging a conductor layer in the casing on a side that is closer to an antenna of a communication partner side than a location of the coil conductor; and   providing a conductor opening and a slit in the conductor layer, the slit connecting the conductor opening and an outer edge of the conductor layer; wherein   when the substrate is viewed in plan view, the coil conductor and the conductor layer are superposed one on top of the other; and   the resonant frequency is set to be lower than a central frequency of a to-be-used frequency band when the conductor layer is not present and is set to be equal or substantially equal to the central frequency of the to-be-used frequency band when the antenna coil module has been mounted inside the casing of the electronic appliance.