Capacitively-coupled RFID encoder
View Patent ↗In one embodiment, a capacitive encoding system is provided that includes a pair of capacitive elements formed from an arrangement of stripline conductors.
1. A capacitive RFID tag encoder, comprising:
a substrate;
a ground plane on a first surface of the substrate;
a first plurality of serially-connected stripline conductors on a second surface of the substrate, the serially-connected stripline conductors in the first plurality being arranged within a first area of the second surface,
a second plurality of serially-connected stripline conductors on the second surface of the substrate, the serially-connected stripline conductors in the second plurality being arranged within a second area of the second surface, the encoder being configured to drive the first plurality of serially-connected stripline conductors with an RF signal and to drive the second plurality of serially-connected stripline conductors with a phase-shifted version of the RF signal.
2. The capacitive encoder of claim 1 , wherein each of the stripline conductors in the first and second plurality is arranged in parallel with the remaining stripline conductors.
3. The capacitive encoder of claim 1 , wherein the first and second plurality of stripline conductors are each arranged in a fractal pattern.
4. The capacitive encoder of claim 1 , further comprising:
a stripline feed on the second surface for receiving the RF signal;
a first connector stripline connecting the stripline feed to the first plurality of stripline conductors so that the first plurality of stripline conductors is driven with the RF signal; and
a second connector stripline connecting the stripline feed to the second plurality of stripline conductors, wherein the second connector stripline has a different length than the first connector stripline so that the second plurality of stripline conductors is driven with the phase-shifted version of the RF signal.
5. The capacitive encoder of claim 4 , further comprising a variable phase shifter for providing the phase-shifted version of the RF signal.
6. The capacitive encoder of claim 1 , wherein a spacing between each of the stripline conductors in the first plurality is at least as large as a thickness of the substrate, and wherein a spacing between each of the stripline conductors in the second plurality is at least as large as the thickness of the substrate.
7. The capacitive encoder of claim 1 , wherein a characteristic impedance for the stripline conductors in the first and second plurality is at least 50 Ω.
8. A capacitive RFID tag encoder, comprising:
a substrate; and
a plurality of capacitive elements on the substrate, each capacitive element including a plurality of serially-connected stripline conductors, the encoder being configured to drive a first selected one of the capacitive elements with an RF signal and to drive a second selected one of the capacitive elements with a phase-shifted version of the RF signal.
9. The capacitive RFID tag encoder of claim 8 , further comprising:
a processor configured to select the first and second selected ones of the capacitive elements based upon an orientation of an RFID tag.
10. The capacitive RFID tag encoder of claim 9 , further comprising:
an RFID tag imager operable to provide the orientation of the RFID tag to the processor.
11. The capacitive RFID tag encoder of claim 9 , each of the stripline conductors is arranged in parallel with the remaining stripline conductors.
12. A capacitive RFID tag encoder, comprising: a substrate;
a ground plane on a first surface of the substrate;
a first plurality of serially-connected conductors on a second surface of the substrate, the serially-connected conductors in the first plurality being arranged in an alternating fashion within a first area of the second surface such the first plurality of serially-connected conductors presents a substantially resistive and capacitive load to an import port coupled to the first plurality of serially-connected conductors through a first feed conductor;
a second plurality of serially-connected conductors on the second surface of the substrate, the serially-connected conductors in the second plurality being arranged in an alternating fashion within a second area of the second surface such the second plurality of serially-connected conductors presents a substantially resistive and capacitive load to the import port coupled to the second plurality of serially-connected conductors through a second feed conductor, the encoder being configured to drive the input port with an RF signal, wherein an electrical length for the first feed conductor is different than an electrical length of the second feed conductor.
13. The capacitive encoder of claim 12 , wherein each of the conductors in the first and second plurality is arranged in parallel with the remaining conductors.
14. The capacitive encoder of claim 12 , wherein the first and second plurality of conductors are each arranged in a fractal pattern.
15. The capacitive encoder of claim 12 , wherein a spacing between each of the conductors in the first plurality is at least as large as a thickness of the substrate, and wherein a spacing between each of the conductors in the second plurality is at least as large as the thickness of the substrate.
16. The capacitive encoder of claim 12 , wherein a characteristic impedance for the conductors in the first and second plurality is at least 50 Ω.