Rfid tag having capacitive load

Abstract

The present invention relates to an RFID tag having capacitive load, including: an antenna unit, a capacitive load and an RFID device. The antenna unit includes two metal sheets and a conductive substrate, and the metal sheets are disposed at a corresponding position above the conductive substrate and electrically connected to the conductive substrate. The capacitive load is electrically connected to the metal sheets. The RFID device feeds the antenna unit by electrically connecting to the metal sheets or coupling. This dramatically decreases the operating frequency, so the imaginary part of impedance is higher with the same size of the antenna unit, thereby reducing the size of the RFID tag. As a result, the weight is reduced, the manufacture process is simplified and the subsequent structure can be easily adjusted.

1 . An RFID tag having capacitive load, comprising:
 an antenna unit, including two metal sheets and a conductive substrate, wherein the metal sheets are disposed at a corresponding position above the conductive substrate and electrically connected to the conductive substrate;   a capacitive load, electrically connected to the metal sheets; and   an RFID device, feeding the antenna unit by electrically connecting to the metal sheets or coupling.   
     
     
         2 . The RFID tag as claimed in  claim 1 , wherein the antenna unit further includes two conductive portions electrically connected to the metal sheets and the conductive substrate respectively. 
     
     
         3 . The RFID tag as claimed in  claim 2 , wherein the conductive portions are conductive pillars or conductive sheets. 
     
     
         4 . The RFID tag as claimed in  claim 3 , wherein each metal sheet includes a first side and a second side corresponding to the first side, the first sides of the metal sheets are close to and face each other, and the conductive pillars approach the second sides of the metal sheets respectively and are disposed between the metal sheets and the conductive substrate. 
     
     
         5 . The RFID tag as claimed in  claim 3 , wherein each metal sheet includes a first side and a second side corresponding to the first side, the first sides of the metal sheets are close to and face each other, and the conductive sheets are electrically connected to the second sides of the metal sheets and two corresponding sides of the conductive substrate. 
     
     
         6 . The RFID tag as claimed in  claim 1 , wherein the antenna unit further includes at least one substrate metal layer and a substrate dielectric material, the at least one substrate metal layer is disposed between the metal sheets and the conductive substrate, and the substrate dielectric material is disposed between the at least one substrate metal layer and the metal sheets and between the at least one substrate metal layer and the conductive substrate. 
     
     
         7 . The RFID tag as claimed in  claim 1 , wherein a notch is formed between the metal sheets, the RFID device further includes an RFID chip and a metal strap, two ends of the metal strap are connected to two ends of the RFID chip to form a loop structure, and the RFID device is disposed in the notch formed between the metal sheets and feeds the antenna unit by coupling. 
     
     
         8 . The RFID tag as claimed in  claim 1 , further comprising a dielectric layer, wherein the RFID device further includes an RFID chip and two flank metal sheets, the flank metal sheets are disposed on a surface of the dielectric layer, the RFID chip is electrically connected to the flank metal sheets, the RFID device is spaced apart from the metal sheets by the dielectric layer and disposed at a corresponding position above the metal sheets, and the RFID device feeds the antenna unit by coupling. 
     
     
         9 . The RFID tag as claimed in  claim 1 , wherein the capacitive load is an SMD (Surface Mount Device) capacitor element. 
     
     
         10 . The RFID tag as claimed in  claim 3 , wherein the capacitive load is an SMD capacitor element. 
     
     
         11 . The RFID tag as claimed in  claim 6 , wherein the capacitive load is an SMD capacitor element. 
     
     
         12 . The RFID tag as claimed in  claim 7 , wherein the capacitive load is an SMD capacitor element. 
     
     
         13 . The RFID tag as claimed in  claim 8 , wherein the capacitive load is an SMD capacitor element. 
     
     
         14 . The RFID tag as claimed in  claim 1 , wherein the capacitive load includes a load dielectric material and a load metal layer, and the load dielectric material is disposed between the metal sheets and the load metal layer. 
     
     
         15 . The RFID tag as claimed in  claim 3 , wherein the capacitive load includes a load dielectric material and a load metal layer, and the load dielectric material is disposed between the metal sheets and the load metal layer. 
     
     
         16 . The RFID tag as claimed in  claim 6 , wherein the capacitive load includes a load dielectric material and a load metal layer, and the load dielectric material is disposed between the metal sheets and the load metal layer. 
     
     
         17 . The RFID tag as claimed in  claim 7 , wherein the capacitive load includes a load dielectric material and a load metal layer, and the load dielectric material is disposed between the metal sheets and the load metal layer. 
     
     
         18 . The RFID tag as claimed in  claim 8 , wherein the capacitive load includes a load dielectric material and a load metal layer, and the load dielectric material is disposed between the metal sheets and the load metal layer. 
     
     
         19 . The RFID tag as claimed in  claim 1 , wherein the capacitive load further comprises four first extension sheets, each metal sheet includes a first side, a second side corresponding to the first side and two corresponding third sides, the first sides of the metal sheets are close to and face each other, two third sides of each metal sheet are located between the first side and the second side, each first extension sheet is connected to the third side at place near the first side and extends along the direction approaching the second side, and each first extension sheet is essentially parallel to the third side. 
     
     
         20 . The RFID tag as claimed in  claim 3 , wherein the capacitive load further comprises four first extension sheets, each metal sheet includes a first side, a second side corresponding to the first side and two corresponding third sides, the first sides of the metal sheets are close to and face each other, two third sides of each metal sheet are located between the first side and the second side, each first extension sheet is connected to the third side at place near the first side and extends along the direction approaching the second side, and each first extension sheet is essentially parallel to the third side. 
     
     
         21 . The RFID tag as claimed in  claim 6 , wherein the capacitive load further comprises four first extension sheets, each metal sheet includes a first side, a second side corresponding to the first side and two corresponding third sides, the first sides of the metal sheets are close to and face each other, two third sides of each metal sheet are located between the first side and the second side, each first extension sheet is connected to the third side at place near the first side and extends along the direction approaching the second side, and each first extension sheet is essentially parallel to the third side. 
     
     
         22 . The RFID tag as claimed in  claim 7 , wherein the capacitive load further comprises four first extension sheets, each metal sheet includes a first side, a second side corresponding to the first side and two corresponding third sides, the first sides of the metal sheets are close to and face each other, two third sides of each metal sheet are located between the first side and the second side, each first extension sheet is connected to the third side at place near the first side and extends along the direction approaching the second side, and each first extension sheet is essentially parallel to the third side. 
     
     
         23 . The RFID tag as claimed in  claim 8 , wherein the capacitive load further comprises four first extension sheets, each metal sheet includes a first side, a second side corresponding to the first side and two corresponding third sides, the first sides of the metal sheets are close to and face each other, two third sides of each metal sheet are located between the first side and the second side, each first extension sheet is connected to the third side at place near the first side and extends along the direction approaching the second side, and each first extension sheet is essentially parallel to the third side. 
     
     
         24 . The RFID tag as claimed in  claim 1 , wherein the capacitive load further comprises two second extension sheets, each metal sheet includes a first side, a second side corresponding to the first side and two corresponding third sides, the first sides of the metal sheets are close to and face each other, two third sides of each metal sheet are located between the first side and the second side, the second extension sheets are disposed on the same side of the metal sheets, each second extension sheet is connected to the third side at place near the first side, each second extension sheet extends along the direction approaching the second side which is essentially parallel to the third side and extends backward along the direction approaching the first side, and the second extension sheets extend crisscross to form a finger-crossed structure. 
     
     
         25 . The RFID tag as claimed in  claim 3 , wherein the capacitive load further comprises two second extension sheets, each metal sheet includes a first side, a second side corresponding to the first side and two corresponding third sides, the first sides of the metal sheets are close to and face each other, two third sides of each metal sheet are located between the first side and the second side, the second extension sheets are disposed on the same side of the metal sheets, each second extension sheet is connected to the third side at place near the first side, each second extension sheet extends along the direction approaching the second side which is essentially parallel to the third side and extends backward along the direction approaching the first side, and the second extension sheets extend crisscross to form a finger-crossed structure. 
     
     
         26 . The RFID tag as claimed in  claim 6 , wherein the capacitive load further comprises two second extension sheets, each metal sheet includes a first side, a second side corresponding to the first side and two corresponding third sides, the first sides of the metal sheets are close to and face each other, two third sides of each metal sheet are located between the first side and the second side, the second extension sheets are disposed on the same side of the metal sheets, each second extension sheet is connected to the third side at place near the first side, each second extension sheet extends along the direction approaching the second side which is essentially parallel to the third side and extends backward along the direction approaching the first side, and the second extension sheets extend crisscross to form a finger-crossed structure. 
     
     
         27 . The RFID tag as claimed in  claim 7 , wherein the capacitive load further comprises two second extension sheets, each metal sheet includes a first side, a second side corresponding to the first side and two corresponding third sides, the first sides of the metal sheets are close to and face each other, two third sides of each metal sheet are located between the first side and the second side, the second extension sheets are disposed on the same side of the metal sheets, each second extension sheet is connected to the third side at place near the first side, each second extension sheet extends along the direction approaching the second side which is essentially parallel to the third side and extends backward along the direction approaching the first side, and the second extension sheets extend crisscross to form a finger-crossed structure. 
     
     
         28 . The RFID tag as claimed in  claim 8 , wherein the capacitive load further comprises two second extension sheets, each metal sheet includes a first side, a second side corresponding to the first side and two corresponding third sides, the first sides of the metal sheets are close to and face each other, two third sides of each metal sheet are located between the first side and the second side, the second extension sheets are disposed on the same side of the metal sheets, each second extension sheet is connected to the third side at place near the first side, each second extension sheet extends along the direction approaching the second side which is essentially parallel to the third side and extends backward along the direction approaching the first side, and the second extension sheets extend crisscross to form a finger-crossed structure. 
     
     
         29 . The RFID tag as claimed in  claim 24 , wherein the capacitive load further comprises two third extension sheets, the third extension sheets and the second extension sheets are disposed on two corresponding sides of the metal sheets, each third extension sheet is connected to the third side at place near the first side, each third extension sheet extends along the direction approaching the second side which is essentially parallel to the third side and extends backward along the direction approaching the first side, and the third extension sheets extend crisscross to form a finger-crossed structure. 
     
     
         30 . The RFID tag as claimed in  claim 1 , which is applied to inventory management of metal material products. 
     
     
         31 . The RFID tag as claimed in  claim 1 , wherein the frequency band comprises UHF (Ultrahigh-frequency), 2.45 GHz or 5.8 GHz.