Capacitive sweat rate sensor

1 . A sweat sensor, comprising:

a first conductor;

a second conductor, wherein the first and second conductors are metallic plates that are parallel with one another;

a supporting layer positioned between the first and second conductors, wherein the supporting layer defines a channel that is configured to receive a sample of sweat, and wherein a measure of capacitance between the first and second conductors changes based at least partially upon a volume and/or rate of the sweat in the channel;

a substrate positioned between the first and second conductors;

a first electrode positioned at least partially within the supporting layer, wherein the first electrode is electrically-connected to the second conductor, and wherein the first electrode is electrically-isolated from the first conductor;

second and third electrodes positioned at least partially within the supporting layer, wherein the second and third electrodes are positioned on a first side of the substrate; and

fourth and fifth electrodes positioned on a second, opposing side of the substrate from the second and third electrodes.

2 . The sweat sensor of claim 1 , further comprising:

a first insulating layer defining an inlet configured to receive the sample of sweat, wherein the inlet is in fluid communication with the channel; and

wherein the first conductor is positioned at least partially between the first insulating layer and the supporting layer.

3 . The sweat sensor of claim 2 , further comprising a second insulating layer defining an outlet, wherein the outlet is in fluid communication with the channel, and wherein the second conductor is positioned at least partially between the second insulating layer and the supporting layer.

4 . The sweat sensor of claim 1 , further comprising a circuit configured to measure the capacitance between the first and second conductors, wherein a rate of the sweat varies with the capacitance.

5 . The sweat sensor of claim 1 , the second and third electrodes are positioned on opposite sides of the channel from one another and configured to be contacted by the sweat in the channel.

6 . The sweat sensor of claim 5 , further comprising a circuit that is configured to measure an impedance between the second and third electrodes, wherein a conductivity of the sweat varies with the impedance.

7 . The sweat sensor of claim 1 , wherein the sweat sensor is configured to simultaneously determine a rate of the sweat and a conductivity of the sweat.

8 . A sweat sensor, comprising

a bottom insulating layer defining an inlet that is configured to receive sweat;

a bottom plate positioned above the bottom insulating layer;

a supporting layer positioned above the bottom plate, wherein the supporting layer defines a channel that is in fluid communication with the inlet;

a top substrate positioned above the supporting layer;

a top plate positioned above the top substrate, wherein the bottom plate and the top plate comprise a conductive material, and wherein the bottom plate and the top plate are parallel with one another;

a top insulating layer defining an outlet that is in fluid communication with the channel, wherein the bottom insulating layer and the top insulating layer comprise a non-conductive material;

a first electrode positioned at least partially within the supporting layer, wherein the first electrode is electrically-connected to the bottom plate, and wherein the first electrode is electrically-isolated from the top plate;

second and third electrodes positioned at least partially within the supporting layer, wherein the second and third electrodes are positioned on a first side of the top substrate;

fourth and fifth electrodes positioned on a second, opposing side of the top substrate from the second and third electrodes; and

a circuit configured to:

measure a capacitance between the bottom plate and the top plate using the first electrode; and

determine a rate of the sweat based at least partially upon the capacitance.

9 . The sweat sensor of claim 8 , further comprising:

a bottom substrate, wherein the bottom plate is coupled to the bottom substrate, and wherein the bottom substrate is positioned between the bottom plate and the supporting layer; and

the top substrate, wherein the top plate is coupled to the top substrate, and wherein the top substrate is positioned between the top plate and the supporting layer.

10 . The sweat sensor of claim 8 , wherein the first electrode is configured to be contacted by the sweat in the channel.

11 . The sweat sensor of claim 8 ,

wherein the second and third electrodes are positioned on opposite sides of the channel and configured to be contacted by the sweat in the channel.

12 . The sweat sensor of claim 11 , wherein the circuit is further configured to:

measure an impedance between the second and third electrodes; and

determine a conductivity of the sweat based at least partially upon the impedance.

13 . A sweat sensor, comprising

a bottom insulating layer configured to be placed in contact with a user's skin, wherein the bottom insulating layer defines an inlet that is configured to receive sweat from the user's skin;

a bottom plate positioned above the bottom insulating layer;

a supporting layer positioned above the bottom plate, wherein the supporting layer defines a channel that is configured to receive the sweat from the inlet;

a top substrate positioned above the supporting layer;

a top plate positioned above the top substrate, wherein the bottom plate and the top plate comprise a conductive material, and wherein the bottom plate and the top plate are parallel with one another;

a top insulating layer defining an outlet that is configured to receive the sweat from the channel, wherein the bottom insulating layer and the top insulating layer comprise a non-conductive material;

a first electrode positioned at least partially within the supporting layer, wherein the first electrode is electrically-connected to one of the bottom plate and the top plate, and wherein the first electrode is electrically-isolated from the other of the bottom plate and the top plate;

second and third electrodes positioned at least partially within the supporting layer, wherein the second and third electrodes are positioned on opposite sides of the channel and configured to be contacted by the sweat in the channel;

fourth and fifth electrodes positioned on an opposite side of the top substrate from the second and third electrodes; and

a circuit configured to:

measure a capacitance between the bottom plate and the top plate using the first electrode;

determine a rate of the sweat based at least partially upon the capacitance;

measure an impedance between the second and third electrodes; and

determine a conductivity of the sweat based at least partially upon the impedance.

14 . The sweat sensor of claim 13 , further comprising:

a bottom substrate, wherein the bottom plate is coupled to the bottom substrate, and wherein the bottom substrate is positioned between the bottom plate and the supporting layer; and

the top substrate, wherein the top plate is coupled to the top substrate, and wherein the top substrate is positioned between the top plate and the supporting layer.

15 . The sweat sensor of claim 13 , wherein the first electrode is isolated from the channel.

16 . The sweat sensor of claim 13 , wherein the capacitance changes based at least partially upon a volume of the sweat in the channel.

17 . The sweat sensor of claim 13 , wherein a first via extends through the top substrate and electrically connects the second and fourth electrodes.

18 . The sweat sensor of claim 17 , wherein a second via extends through the substrate and electrically connects the third and fifth electrodes.

19 . The sweat sensor of claim 18 , wherein the fourth and fifth electrodes are in contact with the substrate and the top insulating layer.

20 . The sweat sensor of claim 19 , wherein the fourth and fifth electrodes are electrically isolated from the top plate.