Wireless sensing devices and method for detecting hydration

1. An RF hydration sensor in an assembly, comprising:

a substrate;

an antenna disposed on the substrate;

an RF circuit electrically coupled to the antenna, the RF circuit comprising a processor;

a thermal source electrically coupled to the RF circuit for changing a thermal condition of a target area; and

a sensing element thermally coupled to the thermal source for sensing a temperature of the thermal source, such that when the thermal source is thermally coupled to the target area, the RF hydration sensor wirelessly receives a first power having a first form from a transceiver, the RF circuit transforms the first power to a second power having a second form different from the first form and delivers the second power to the thermal source, the sensing element senses a time variation of the thermal source temperature, and the processor determines a hydration indicator indicating a hydration level of the target area based on the sensed time variation of the thermal source temperature.

2. The RF hydration sensor of claim 1 , further comprising:

a memory storing a reference data associated with the hydration level, and wherein the processor is configured to determine the hydration indicator using the reference data.

3. The RF hydration sensor of claim 1 , wherein the RF circuit controls a magnitude of the second power.

4. The RF hydration sensor of claim 1 , wherein the RF circuit is configured to adjust a duration of the second power supplied to the thermal source.

5. The RF hydration sensor of claim 1 , wherein the RF hydration sensor is configured to wirelessly receive an unknown first power having a first form from a transceiver, and wherein the RF circuit transforms the unknown first power to a known second power having a second form different from the first form.

6. The RF hydration sensor of claim 1 , wherein the RF hydration sensor is adapted to wirelessly communicate with a remote transceiver emitting power at a first radio frequency, wherein the RF circuit is adapted to detune a resonant frequency of the RF hydration sensor away from the first radio frequency to control a magnitude of the first power received by the RF hydration sensor from the remote transceiver.

7. The RF hydration sensor of claim 1 , further comprising:

a thermal spreader comprising a solid or liquid material,

wherein the thermal source is disposed proximate to the thermal spreader.

8. The RF hydration sensor of claim 7 , wherein the thermal spreader is adapted to substantially uniformly distribute a thermal flux from the thermal source across the target area when the thermal spreader is in thermal contact with the target area.

9. An RF sensor for measuring a liquid level, comprising:

a substrate;

an antenna disposed on the substrate;

an RF circuit electrically coupled to the antenna, the RF circuit comprising a processor;

an absorption element comprising an absorption material,

a thermal source electrically coupled to the RF circuit and thermally coupled to the absorption element; and

a sensing element thermally coupled to the thermal source for sensing a temperature of the thermal source, such that after the absorption element is used to absorb a liquid, the RF sensor wirelessly receives a first power having a first form from a transceiver, the RF circuit transforms the first power to a second power having a second form different from the first form and delivers the second power to the thermal source, the sensing element senses a time variation of the thermal source temperature, and the processor determines an indicator indicating a liquid level based on the sensed time variation of the thermal source temperature.

10. The RF sensor of claim 9 , wherein the absorption material comprises at least one of a porous material, a natural or synthetic sponge, a water-absorbing gel, and a superabsorbent polymer.

11. The RF sensor of claim 9 , wherein the RF circuit controls a magnitude of the second power.