Dual track surface acoustic wave RFID/sensor
A SAW RFID tag or sensor has an antenna for receiving and propagating an RF signal, an input/output IDT electrically connected to the antenna, and a dual track reflective IDT having a first track and a second track located adjacent and acoustically coupled to the input/output IDT. An RF signal received from the antenna by the input/output IDT is transformed by the input/output IDT into an acoustic way which is propagated to the dual track IDT. One track of the dual track IDT is in-phase with the phase reference of the input/output IDT and the other track is in quadrature phase with said phase reference. The input/output IDT receives two orthogonal complex modulated acoustic waves reflected from the first and second tracks and transforms them to a modulated orthogonal complex RF signal which is propagated from the antenna.
1. A SAW RFID tag or sensor, having:
an antenna for receiving and propagating an RF signal;
an input/output interdigital transducers (IDT) electrically connected to the antenna; and
a dual track reflective IDT having a first track and a second track located adjacent and acoustically coupled to the input/output IDT, whereby said RF signal received from the antenna by the input/output IDT is transformed by the input/output IDT into an acoustic wave which is propagated to the dual track IDT; and
one track of the dual track IDT being in-phase with the phase reference of the input/output IDT and the other track being in quadrature phase with said phase reference, whereby the input/output IDI receives two orthogonal complex modulated acoustic waves reflected from the first and second tracks and transforms them to a modulated orthogonal complex RF signal which is propagated from the antenna.
2. A tag or sensor according to claim 1 wherein one of the tracks is positioned to produce a half-bit effect time delay of the data therefrom.
3. A tag or sensor according to claim 1 wherein each track has an individual modulated identification code embedded within the geometries thereof.
4. A tag or sensor according to claim 1 wherein the in-phase track has an individual modulated identification code rooted into the reflected acoustic wave propagated to the input/output IDT.
5. A tag or sensor according to claim 1 wherein the quadrature phase track has an individual modulated identification code rooted into the reflected acoustic wave propagated to the input/output IDT.
6. A tag or sensor according to claim 1 wherein the first and second tracks have separate load impedances connected thereto.
7. A tag or sensor according to claim 6 wherein variation of the load impedance varies the reflection coefficient of the IDT.
8. A sensor according to claim 1 wherein the tracks have separate sensors connected thereto.
9. A sensor according to claim 8 wherein the sensors measure two independent physical environments.
10. A sensor according to claim 8 wherein the sensors measure a single physical environment with one of the sensors being configured as a reference.
11. A sensor according to claim 8 wherein the sensors measure the differential output of a single physical environment.