Inductively tunable antenna for a radio frequency identification tag

Claim 2

A radio frequency identification tag, comprising: an insulated substrate having a surface; a parallel resonant antenna circuit disposed on the surface of said substrate, said parallel resonant antenna circuit having a step-tunable inductor comprising a spiral coil adapted for tuning said parallel resonant antenna circuit to a desired frequency, wherein said step-tunable inductor has trimming branches disposed on the surface of said substrate and entirely inside of said spiral coil, wherein said trimming branches are adapted for adjusting the inductance of said step-tunable inductor; and a semiconductor integrated circuit having electronic logic circuits for storing, receiving and transmitting data, said semiconductor integrated circuit being disposed on the surface of said substrate and connected to said parallel resonant antenna circuit.

Claim 3

The radio frequency identification tag of claim 1 , wherein said step-tunable inductor is a spiral coil disposed on the surface of said substrate.

Claim 4

The radio frequency identification tag of claim 1 , wherein said trimming branches are controlled by transistors.

Claim 5

The radio frequency identification tag of claim 3 , wherein said transistors are controlled with fuse links.

Claim 6

The radio frequency identification tag of claim 3 , wherein said transistors are controlled with a frequency selection circuit.

Claim 7

The radio frequency identification tag of claim 5 , wherein said frequency selection circuit is a microcontroller.

Claim 8

The radio frequency identification tag of claim 1 . wherein said trimming branches are controlled by fuse links.

Claim 9

The radio frequency identification tag of claim 7 wherein said fuse links are opened with a current.

Claim 10

The radio frequency identification tag of claim 7 , wherein said fuse links are opened with a voltage.

Claim 11

The radio frequency identification tag device of claim 1 , wherein said step-tunable inductor comprises a spiral coil having a plurality of coil turns.

Claim 12

The radio frequency identification tag device of claim 10 , wherein all but one of said plurality of trimming branches are disconnected so as to adjust the inductance of said step- tunable inductor.

Claim 13

The radio frequency identification tag of claim 11 , wherein each of said plurality of trimming branches form a different length inner coil turn of the plurality of coil turns of said spiral coil.

Claim 14

The radio frequency identification tag of claim 1 , wherein material for said substrate is selected from the group consisting of PET, mylar, paper, plastic, silicon, kapton, ceramic, polyimide and polyvinylchloride (PVC).

Claim 15

The radio frequency identification tag of claim 1 , wherein material for said step- tunable inductor is selected from the group consisting of copper, aluminum, gold, plated metal, and electrically conductive organic and inorganic materials.

Claim 16

The frequency identification tag of claim 1 . wherein said step-tunable inductor has a plurality of fuse links, each of the plurality of fuse links in parallel with a turn of said step-tunable inductor wherein opening a one of the plurality of fuse links increases said step-tunable inductor inductance.

Claim 17

The frequency identification tag of claim 1 , wherein said step-tunable inductor has a plurality of transistors, each of the plurality of transistor in parallel with a turn of said step-tunable inductor wherein turning off a one of the plurality of transistors increases said step-tunable inductor inductance.

Claim 18

A radio frequency identification (RFID) tag system, comprising: a radio frequency identification (RFID) tag comprising an insulated substrate having a surface, a parallel resonant antenna circuit disposed on the surface of said substrate, said parallel resonant antenna circuit having a step-tunable inductor comprising a spiral coil adapted for tuning said parallel resonant antenna circuit to a desired frequency, wherein said step- tunable inductor has trimming branches disposed on the surface of said substrate and entirely inside of said spiral coil, wherein said trimming branches are adapted for adjusting the inductance of said step-tunable inductor, and a simiconductor integrated circuit having electronic logic circuits for storing, receiving and transmitting data, said semiconductor integrated circuit being disposed on the surface of said substrate and connected to said parallel resonant antenna circuit; a radio frequency interrogator for generating a radio frequency signal at the desired frequency which said parallel resonant antenna circuit is tuned; and an RFID tag reader connected to said radio frequency interrogator, said RFID tag reader detecting data signals from said RFID tag.

Claim 19

A radio frequency identification (RFID) tag system, comprising: a radio frequency identification (RFID) tag comprising an insulated substrate having a surface, a parallel resonant antenna circuit disposed on the surface of said substrate, said parallel resonant antenna circuit having a step-tunable inductor comprising a spiral coil adapted for tuning said parallel resonant antenna circuit to a desired frequency, wherein said step- tunable inductor has trimming branches disposed on the surface of said substrate and entirely inside of said spiral coil, wherein said trimming branches are adapted for adjusting the inductance of said step-tunable inductor, and a simiconductor integrated circuit having electronic logic circuits for storing, receiving and transmitting data, said semiconductor integrated circuit being disposed on the surface of said substrate and connected to said parallel resonant antenna circuit; a radio frequency interrogator for generating a radio frequency signal at the desired frequency which said parallel resonant antenna circuit is tuned; and an RFID tag reader connected to said radio frequency interrogator, said RFID tag reader detecting data signals from said RFID tag.

Claim 20

The radio frequency identification tag system of claim 17 , wherein said step- tunable inductor is a spiral coil disposed on the surface of said substrate.

Claim 21

The radio frequency identification tag system of claim 17 , wherein said step- tunable inductor comprises a spiral coil having a plurality of coil turns and a plurality of trimming branches inside of said spiral coil, wherein said plurality of trimming branches are adapted for adjusting the inductance of said step-tunable inductor.

Claim 22

The radio frequency identification tag system of claim 19 , wherein all but one of said plurality of trimming branches are disconnected so as to adjust the inductance of said step- tunable inductor.

Claim 23

The radio frequency identification tag of claim 20 , wherein each of said plurality of trimming branches form a different length inner coil turn of the plurality of coil turns of said spriral coil.

Claim 26

The method of claim 22 , wherein the step of disconnecting is done by cutting with a laser.

Claim 27

The method of claim 22 , wherein the step of disconnecting is done by ablation.

Claim 28

The method of claim 22 , wherein the step of disconnecting is done by mechanically cutting.

Claim 29

The method of claim 22 , wherein the step of disconnecting all but one of said plurality of trimming branches adjusts the length of an inner coil turn of the spiral coil of said step-tunable inductor.

Claim 30

The method of claim 22 , wherein the step of disconnecting is done by opening fuse links.

Claim 31

The method of claim 27 , wherein said fuse links are opened with a current.

Claim 32

The method of claim 27 , wherein said fuse links are opened with a voltage.

Claim 33

The method of claim 29 , wherein the step of disconnecting is done by controlling transistors.

Claim 34

The method of claim 30 , wherein said transistors are controlled with fuse links.

Claim 35

The method of claim 30 , wherein said transistors are controlled with a frequency selection circuit.

Claim 36

The method of claim 32 , wherein said frequency selection circuit is a microcontroller.