Wearable bioimpedance monitoring system using conformal nanowire electrodes
Various examples are related to bioimpedance measurements. In one example, a wearable monitoring system includes electrodes and processing circuitry configured for bioimpedance sensing. The electrodes can include a current source electrode, a current sink electrode, and voltage measurement electrodes aligned between the current source and sink electrodes. The processing circuitry can sense bioimpedance based upon excitation current applied through the current source and sink electrodes and measured voltage obtained through the voltage measurement electrodes across a range of excitation frequencies. The electrodes can be conformal and stretchable. In another example, a method for bioimpedance sensing includes positioning a wearable monitoring system on a surface, applying excitation current through the current source and sink electrodes over a range of excitation frequencies; measuring voltage across the voltage measurement electrodes over the excitation frequencies; and determining the bioimpedance using the applied excitation current and the measured voltage over the excitation frequencies.
1 . A wearable monitoring system, comprising:
a plurality of electrodes comprising one or more current source electrode, one or more current sink electrode, and at least two voltage measurement electrodes aligned between the current source and sink electrodes, the plurality of electrodes being conformal and stretchable nanowire (NW) electrodes; and
processing circuitry configured for bioimpedance sensing based upon excitation current applied through the current source and sink electrodes and measured voltage obtained through the at least two voltage measurement electrodes across a range of excitation frequencies, the processing circuitry comprising excitation voltage circuitry coupled to the one or more current source electrode, voltage measurement circuitry coupled to the at least two voltage measurement electrodes, and current measurement circuitry coupled to the one or more current sink electrode, the processing circuitry comprising an impedance analog front end (AFE) coupled to the plurality of electrodes thereby providing direct current (DC) isolation for each of the one or more current source electrode, the one or more current sink electrode, and the at least two voltage measurement electrodes.
2 . The system of claim 1 , wherein the measurements are obtained at a plurality of frequencies in the range of excitation frequencies.
3 . The system of claim 2 , wherein the processing circuitry calculates an impedance at each of the plurality of frequencies.
4 . The system of claim 1 , wherein the nanowire electrodes comprise a network of silver nanowires (AgNWs).
5 . The system of claim 4 , wherein the AgNWs are inlaid in a soft polymer matrix.
6 . The system of claim 5 , wherein the soft polymer matrix comprises Poly(dimethylsiloxane) (PDMS).
7 . The system of claim 1 , wherein the one or more current source electrode, the one or more current sink electrode, and the at least two voltage measurement electrodes each have a defined area and a defined spacing between the other electrodes.
8 . The system of claim 1 , wherein the processing circuitry calculates an impedance at each of a plurality of frequencies within the range of excitation frequencies.
9 . The system of claim 8 , wherein the processing circuitry transmits data associated with the impedance to a remotely located data aggregator.
10 . The system of claim 1 , wherein the processing circuitry comprises an accelerometer and the transmitted data comprises motion data obtained from the accelerometer.
11 . A method for bioimpedance sensing, comprising:
positioning a wearable monitoring system on a surface, the wearable monitoring system comprising a plurality of electrodes comprising one or more current source electrode, one or more current sink electrode, and at least two voltage measurement electrodes aligned between the current source and sink electrodes, the plurality of electrodes coupled to processing circuitry comprising excitation voltage circuitry coupled to the one or more current source electrode, voltage measurement circuitry coupled to the at least two voltage measurement electrodes, and current measurement circuitry coupled to the one or more current sink electrode, the processing circuitry comprising an impedance analog front end (AFE) coupled to the plurality of electrodes thereby providing direct current (DC) isolation for each of the one or more current source electrode, the one or more current sink electrode, and the at least two voltage measurement electrodes;
applying excitation current through the current source and sink electrodes over a range of excitation frequencies;
measuring voltage across the at least two voltage measurement electrodes over the range of excitation frequencies; and
determining a bioimpedance based upon the applied excitation current and the measured voltage over the range of excitation frequencies.
12 . The method of claim 11 , wherein the measured voltage is obtained at a plurality of frequencies in the range of excitation frequencies.
13 . The method of claim 12 , wherein an impedance is calculated at each of the plurality of frequencies.
14 . The method of claim 11 , comprising transmitting data associated with the bioimpedance to a remotely located data aggregator.
15 . The method of claim 14 , comprising monitoring motion of the wearable monitoring system, wherein the transmitted data comprises motion data obtained by the wearable monitoring system.
16 . The method of claim 11 , wherein the surface is a skin surface.
17 . The method of claim 11 , wherein the plurality of electrodes comprises conformal and stretchable silver nanowire (AgNW) electrodes.
18 . The method of claim 11 , comprising producing multivariate time series measurements of the bioimpedance over the range of excitation frequencies.
19 . The method of claim 18 , comprising producing a bioimpedance profile with continuous resistivity and phase measurements over the range of excitation frequencies.
20 . The method of claim 18 , comprising directly measuring impedance of extracellular and intracellular water components over a small area of the surface.