Coupling frames for RFID devices
A transponder chip module (TCM) comprises an RFID chip (CM, IC), optionally contact pads (CP), a module antenna (MA), and a coupling frame (CF), all on a common substrate or module tape (MT). The coupling frame (CF) may be in the form of a conductive layer having an outer edge (OE) and a slit (S) or non-conductive stripe (NCS) extending from the outer edge to an inner position thereof which may be a central opening (OP). The coupling frame (CF) may be arranged so that the slit (S) or non-conductive strips (NCS) overlaps at least a portion of the module antenna (MA). A suppressor diode or capacitor may be connected across the slit (S). Methods and apparatus are disclosed.
1. An RFID device comprising:
a transponder chip module (TCM) comprising an RFID chip (IC) and a module antenna (MA); and
a coupling frame (CF) comprising a conductive surface and having an electrical discontinuity comprising a slit (S) or non-conductive stripe (NCS) extending through the surface from an outer edge thereof to an inner position thereof, wherein the coupling frame is disposed so that the slit (S) or non-conductive stripe (NCS) overlaps at least a portion of the module antenna (MA), further comprising a capacitor connected across the slit (S).
2. The RFID device of claim 1 , wherein the coupling frame (CF) is disposed in a card body (CB) of a smart card (SC).
3. The RFID device of claim 1 , wherein the coupling frame (CF) is disposed on a module tape (MT) of the transponder chip module (TCM).
4. The RFID device of claim 1 , wherein the slit (S) or non-conductive stripe (NCS) extends to an opening (OP) in the coupling frame (CF).
5. The RFID device of claim 1 , wherein the slit (S) or non-conductive stripe (NCS) extends to an interior position of the coupling frame (CF).
6. The RFID device of claim 1 , wherein the slit (S) or non-conductive stripe (NCS) overlaps at least some turns of the module antenna (MA).
7. The RFID device claim 1 , wherein:
the transponder chip module (TCM) includes a module tape (MT) supporting the RFID chip (IC) and module antenna (MA); and
the coupling frame (CF) is disposed on an opposite side of the module tape (MT) from the module antenna (MA, PA).
8. The RFID device claim 1 , wherein:
the transponder chip module (TCM) includes a module tape (MT) supporting the RFID chip (IC) and module antenna (MA); and
the coupling frame (CF) is formed from a conductive layer (CL) on the module tape (MT) which is one of the (i) conductive layer used to form contact pads (CP) on the face-up side of the module tape (MT) and (ii) the conductive layer used to form the module antenna on the face-down side of the module tape (MT).
9. The RFID device claim 1 , wherein:
the module antenna (MA) comprises an etched planar antenna (PA) having a number of tracks (traces) separated by spaces;
wherein:
a track width is less than 100 μm; and
a spacing between adjacent tracks is less than 75 μm.
10. The RFID device of claim 1 , further comprising:
a capacitor (CAP) connected with the module antenna (MA) or with terminals of the RFID chip (IC).
11. The RFID device of claim 1 , wherein the capacitor comprises a silicon capacitor.
12. A method of improving coupling between an RFID device comprising a transponder chip module (TCM) and an external reader, the transponder chip module (TCM) comprising an RFID chip (IC, CM) and a module antenna (MA), characterized by:
providing an open-loop conductive coupling frame (CF), wherein the coupling frame (CF) has a slit (S) or non-conductive stripe (NCS) extending from an outer edge (OE) thereof to an interior position thereof and coupling frame (CF) is positioned so that the slit (S) or non-conductive stripe (NCS) overlaps at least a portion of the module antenna (MA, PA, LES); and
connecting a suppressor diode or capacitor across the slit (S).
13. The method of claim 12 , wherein:
the coupling frame (CF) has an opening (OP) at the interior position thereof, and the opening defines an inner edge (IE) of the coupling frame (CF); and
the slit (S) or non-conductive stripe (NCS) extends from the opening (OP) to the outer edge (OE) of the coupling frame (CF).
14. The method of claim 12 , wherein the coupling frame is incorporated into the transponder chip module (TCM).
15. In conjunction with an RFID device comprising an antenna having a number of tracks or turns separated by spaces, a coupling frame (CF) comprising a conductive surface and having an electrical discontinuity comprising a slit (S) or non-conductive stripe (NCS) extending through the surface from an outer edge thereof to an inner position thereof, wherein the coupling frame is disposed so that the slit (S) overlaps at least a portion of the module antenna (MA); further comprising a capacitor connected across the slit (S).