Intermodulation sensor platform based on mechanical resonator
The present invention related to a new passive wireless sensor platform which is based on the intermodulation communication principle. The platform may utilize a quartz crystal or other mechanical resonator. Additionally, the platform allows for a narrow bandwidth and/or ID-code of a sensor. Certain embodiments enable high frequencies and large read-out distances. It facilitates a generic sensor element and can thus be used to monitor virtually any quantity. Additionally, it offers a means to realize a wireless passive sensor using MEMS sensor technology.
1. A wireless sensor comprising;
an antenna,
a mixing element conductively connected to the antenna, to a mechanical resonator and to a sensing element,
wherein the mixing element is capable of providing excitation to the mechanical resonator at the difference of two distinct received signal frequencies.
2. A wireless sensor according to claim 1 , wherein the mixing element is a Schottky diode.
3. A wireless sensor according to claim 1 , wherein the mechanical resonator comprises a quartz crystal or MEMS resonator.
4. A wireless sensor according to claim 1 , wherein the sensing element is a capacitive sensor element, resistive sensor element or inductive sensor element.
5. A wireless sensor according to claim 1 , further comprising at least one additional mechanical resonator and sensing element pair.
6. A wireless sensor according to claim 5 , wherein the mechanical resonator of each pair resonates at a unique frequency.
7. A wireless sensor according to claim 1 , wherein the wireless sensor does not contain a battery.
8. A wireless sensor according to claim 1 , wherein the antenna acts as the sole voltage source for the wireless sensor.
9. A wireless sensor according to claim 1 , wherein the wireless sensor is a passive wireless sensor.
10. A wireless sensor according to claim 1 , wherein the mixing element is capable of mixing a voltage modified by the mechanical resonator and sensing element pair with one of at least two signals received by the antenna.
11. A wireless sensor according to claim 1 , wherein the antenna is coupled to the mixing element and is capable of receiving signals at at least two distinct frequencies simultaneously and re-transmitting a modified form of at least one of said received signals.
12. A wireless sensor according to claim 1 , wherein the mixing element and sensing element are separate elements.
13. A wireless sensor according to claim 1 , wherein the antenna is coupled with a first matching circuit.
14. A wireless sensor according to claim 1 , wherein the mixing element is coupled with a second matching circuit.
15. A wireless sensor according to claim 1 wherein the mechanical resonator and sensing element are configured so as to provide a response at a frequency less than 100 kHz.
16. A wireless sensor according to claim 1 wherein the sensing element is a capacitive sensing element and the mechanical resonator is in parallel with the sensing element in order to form a low frequency circuit.
17. A method of wirelessly reading a sensor element comprising the steps of;
transmitting two signals from a reading device to a wireless sensor, wherein each signal is transmitted at a different frequency,
wherein the difference between the two signal frequencies induces an excitation of a mechanical resonator conductively connected to a sensing element,
receiving an intermodulation response from the wireless sensor,
determining the impedance of a sensing element based on the received intermodulation response, and
providing a readout of the sensor element based on the determined impedance and known resonance of the mechanical resonator coupled to the sensing element.
18. A method according to claim 17 , wherein determining the impedance includes measuring the intermodulation response across a frequency range.
19. A method according to claim 17 , wherein the difference between the frequencies of the two transmitted signals is between 0.1-100 kHz.