Wireless sensing devices including stable near-field antenna
Wireless sensing devices including stable near-field antennas are provided. A spacer layer is attached to a portion of the substrate adjacent to the antenna. The spacer layer has a thickness T, a relative permittivity k, and a figure of merit defined as the ratio of T (in micrometers) by k. The spacer layer has the figure of merit no less than 20 (micrometers).
1. A radio-frequency (RF) sensor device comprising:
a substrate;
an antenna having at least a portion disposed on a first portion of the substrate;
a sensor disposed on a second portion of the substrate, the sensor being at least partially surrounded by the antenna, the sensor including an RF component electrically coupled to the antenna; and
a spacer layer attached to the first portion of the substrate adjacent to the antenna,
wherein the spacer layer has a thickness T, a relative permittivity k, and a figure of merit defined as the ratio of T (in micrometers) by k, the spacer layer has the figure of merit no less than 20 (micrometers).
2. The RF sensor device of claim 1 , wherein the spacer layer has the figure of merit no less than 50.
3. The RF sensor device of claim 1 , wherein the relative permittivity of the spacer layer is in the range from about 1.01 to about 4, and the thickness of the spacer layer is in the range from about 250 micrometers to about 1.0 mm.
4. The RF sensor device of claim 1 , wherein the spacer layer comprises one or more low-dielectric constant materials including one or more of polymers, non-woven materials, woven materials, aerogels, or glasses.
5. The RF sensor device of claim 1 , wherein the spacer layer is water-vapor resistant and configured to prevent moisture to penetrate therethrough to reach the antenna.
6. The RF sensor device of claim 1 , wherein the spacer layer has a frame shape with a width corresponding to the width of the first portion of the substrate, the frame shape defining a window to accommodate a portion of the substrate on which the sensor is disposed.
7. The RF sensor device of claim 1 , wherein the spacer layer includes a ribbed structure.
8. The RF sensor device of claim 1 , wherein the spacer layer includes a closed-cell foam.
9. The RF sensor device of claim 1 , wherein the spacer layer is disposed on the antenna to cover at least a portion of the antenna.
10. The RF sensor device of claim 1 , wherein the spacer layer is disposed on the side of the substrate opposite to the antenna.
11. The RF sensor device of claim 1 , further comprising a layer of insulating media to cover the sensor disposed on the substrate.
12. The RF sensor device of claim 1 , further comprising a cover film to wrap components disposed on the substrate.
13. The RF sensor device of claim 12 , wherein the cover film has a peripheral portion with an adhesive surface.
14. A radio-frequency (RF) sensor to measure a hydration level, comprising:
a substrate;
an antenna having at least a portion disposed on a peripheral portion of the substrate;
an absorption element comprising a fluid absorption material;
a spacer layer attached to the peripheral portion of the substrate adjacent to the antenna, the spacer layer has a thickness T, a relative permittivity k, and a figure of merit defined as the ratio of T (in micrometers) by k, the spacer layer has the figure of merit no less than 20; and
a sensor element disposed on the substrate, the sensor element being disposed on the absorption element and configured to measure the hydration level of the fluid collection media, the sensor element being at least partially surrounded by the antenna and electrically coupled to the antenna.
15. The RF sensor of claim 14 , wherein the spacer layer has a frame shape with a width corresponding to the width of the peripheral portion of the substrate, the frame shape defining a window within which the sensor element is disposed and in contact with the fluid collection media.
16. The RF sensor of claim 14 , wherein the spacer layer is sandwiched between the substrate and the absorption element.
17. The RF sensor of claim 14 , wherein the spacer layer is disposed around a periphery of the absorption element.
18. The RF sensor of claim 14 , wherein the spacer layer is disposed on the antenna to cover a least a portion of the antenna.
19. The RF sensor of claim 14 , wherein the spacer layer is disposed on the substrate at the side opposite to the antenna.
20. The RF sensor of claim 18 , further comprising a barrier layer to separate the substrate from the absorption element.