Sensor and sensor array having improved selectivity
View Patent ↗A sensor for determining the presence of an analyte is disclosed comprising a reactive layer disposed between a base plate and a movable plate. The reactive layer is configured to interact with an analyte effecting a change in capacitance between the base plate and movable plate. When the analyte has a polarity or overall Hildebrand solubility parameter that is similar to the reactive layer, the change in capacitance is caused by a swelling of the reactive layer as analyte is absorbed into the reactive layer. This results in a decrease in capacitance. When the analyte has a solubility parameter not near the reactive layer, the absorbed analyte causes the reactive layer's total polarity to increase, an effect that dominates swelling. This causes an increase in capacitance. A capacitive sensing circuit is included for measuring the change in capacitance which is indicative of the analyte exposed to the sensor.
1. A sensor array for sensing an airborne analyte, the sensor array comprising at least a first sensor and a second sensor, wherein at least the first sensor comprises:
a first conductive plate, which first conductive plate serves as a base plate;
a second conductive plate disposed in spaced relation to and in electrical communication with the first conductive plate, wherein at least a portion of the second conductive plate is moveable in relation to the first conductive plate;
a reactive layer disposed between at least a portion of the second conductive plate and the first conductive plate, the reactive layer being comprised of a polymer film comprised of at least one polymer species and configured to effect a change in capacitance between the second conductive plate and the first conductive plate when the reactive layer is exposed to the analyte; and
a capacitance sensing circuit for detecting a change in capacitance between the first conductive plate and the second conductive plate indicative of the presence of the analyte.
2. A sensor array according to claim 1 wherein the reactive layer of the first sensor is configured to selectively and reversibly absorb the analyte.
3. A sensor array according to claim 1 wherein the change in capacitance in the first sensor is due at least in part to a change in dielectric properties of the reactive layer caused by the analyte being absorbed into the reactive layer.
4. A sensor array according to claim 1 wherein the change in capacitance in the first sensor is due at least in part to a swelling of the reactive layer caused by the analyte being absorbed into the reactive layer.
5. A sensor array according to claim 1 wherein the reactive layer of the first sensor comprises a sol gel.
6. A sensor array according to claim 1 further comprising a readout circuit for displaying results from the sensor array.
7. A sensor array according to claim 1 further comprising a transmitter for transmitting data from the sensor array to a receiver positioned at a location remote from the sensor.
8. A sensor array according to claim 1 wherein the second conductive plate of the first sensor comprises a structure selected from the group consisting of a cantilever, a tethered moveable plate, and a flexible membrane.
9. A sensor array according to claim 8 wherein the second conductive plate of the first sensor is perforated to facilitate access of the analyte to the reactive layer.
10. A sensor array according to claim 1 wherein the analyte is selected from the group consisting of a volatile organic compound, a chemical warfare agent, and a biological warfare agent.
11. A sensor array according to claim 1 wherein the analyte is an emission gas.
12. A sensor array according to claim 1 wherein the polymer species of the first sensor that comprises the polymer film is a compound selected from the group consisting of polycarbonate, polyethylene, polyisobutylene, polypropylene, polystyrene, polyether urethane, ethyl cellulose, polydimethyl siloxane, silicone epoxy, polymethyl methacrylate, a polyamide, polyvinyl chloride, cellulose acteate, polyurethane, polyvinyl acetate, a polyimide, siloxanefluoroalcohol, and polyethylene-co-vinylacetate.
13. A sensor array according to claim 1 wherein each of the sensors comprises:
a first conductive plate, which first conductive plate serves as a base plate;
a second conductive plate disposed in spaced relation to and in electrical communication with the first conductive plate, wherein at least a portion of the second conductive plate is moveable in relation to the first conductive plate;
a reactive layer disposed between at least a portion of the second conductive plate and the first conductive plate, the reactive layer being comprised of a polymer film comprised of at least one polymer species and configured to effect a change in capacitance between the second conductive plate and the first conductive plate when the reactive layer is exposed to the analyte; and
a capacitance sensing circuit for detecting a change in capacitance between the first conductive plate and the second conductive plate indicative of the presence of the analyte.
14. A sensor array according to claim 13 wherein the reactive layer of each sensor differs from the reactive layers of the other sensors.
15. A sensor array according to claim 13 capable of detecting a plurality of airborne analytes.