Application of electrochemical impedance spectroscopy in sensor systems, devices, and related methods
A diagnostic Electrochemical Impedance Spectroscopy (EIS) procedure is applied to measure values of impedance-related parameters for one or more sensing electrodes. The parameters may include real impedance, imaginary impedance, impedance magnitude, and/or phase angle. The measured values of the impedance-related parameters are then used in performing sensor diagnostics, calculating a highly-reliable fused sensor glucose value based on signals from a plurality of redundant sensing electrodes, calibrating sensors, detecting interferents within close proximity of one or more sensing electrodes, and testing surface area characteristics of electroplated electrodes. Advantageously, impedance-related parameters can be defined that are substantially glucose-independent over specific ranges of frequencies. An Application Specific Integrated Circuit (ASIC) enables implementation of the EIS-based diagnostics, fusion algorithms, and other processes based on measurement of EIS-based parameters.
1. A method of calibration of a glucose sensor involving low start-up detection, the method comprising:
performing electrochemical impedance spectroscopy (EIS) procedures for a working electrode of the glucose sensor to obtain values of at least one impedance-based parameter for the working electrode;
performing a bound check for a Nyquist slope and a real impedance value at 1 kHz based on the at least one impedance-based parameter to calculate a reliability index;
performing a first calibration of the glucose sensor in a case where the reliability index is higher than a predetermined threshold; and
in a case where the reliability index is not higher than the predetermined threshold:
calculating a length of time for the Nyquist slope and the real impedance value at 1 kHz to be within a respective range;
performing the first calibration of the glucose sensor in a case where the length of time is shorter than a predetermined duration; and
performing a second calibration with an EIS-based calibration factor adjustment in a case where the length of time is not shorter than the predetermined duration.
2. The method of claim 1 , wherein the reliability index is calculated to be higher than the predetermined threshold when each of the Nyquist slope and the real impedance value at 1 kHz is lower than an upper bound for the Nyquist slope and lower than an upper bound for the real impedance value at 1 kHz, respectively.
3. The method of claim 2 , further comprising: in a case where the second calibration with the EIS-based calibration factor adjustment is performed, gradually offsetting the Nyquist slope to be lower than the upper bound for the Nyquist slope.
4. The method of claim 2 , further comprising: in a case where the second calibration with the EIS-based calibration factor adjustment is performed, gradually offsetting the real impedance value at 1 KHz to be lower than the upper bound for the real impedance value at 1 kHz.
5. The method of claim 1 , wherein the reliability index is calculated to be lower than or equal to the predetermined threshold when at least one of the Nyquist slope or the real impedance value at 1 kHz is not lower than a respective upper bound.
6. The method of claim 1 , further comprising: calculating the length of time for the Nyquist slope and the real impedance value at 1 KHz to be within the respective range based on a trend of the Nyquist slope and of the real impedance value at 1 KHz.
7. The method of claim 6 , wherein the trend of the Nyquist slope and of the real impedance value at 1 kHz is measured during a start-up period.
8. The method of claim 1 , wherein the first calibration is performed after the length of time has passed, in a case where the reliability index is not higher than the predetermined threshold.
9. The method of claim 1 , wherein the predetermined duration is one hour.
10. The method of claim 1 , wherein the second calibration with the EIS-based calibration factor adjustment is performed upon determining that the length of time is not shorter than the predetermined duration.
11. A system for calibrating a glucose sensor involving low start-up detection, the system comprising:
the glucose sensor having a working electrode; and
control circuitry configured to:
perform electrochemical impedance spectroscopy (EIS) procedures for the working electrode of the glucose sensor to obtain values of at least one impedance-based parameter for the working electrode;
perform a bound check for a Nyquist slope and a real impedance value at 1 kHz based on the at least one impedance-based parameter to calculate a reliability index;
perform a first calibration in a case where the reliability index is higher than a predetermined threshold; and
in a case where the reliability index is not higher than the predetermined threshold:
calculate a length of time for the Nyquist slope and the real impedance value at 1 kHz to be within a respective range;
perform the first calibration in a case where the length of time is shorter than a predetermined duration; and
perform a second calibration with an EIS-based calibration factor adjustment in a case where the length of time is not shorter than the predetermined duration.
12. The system of claim 11 , wherein the reliability index is calculated to be higher than the predetermined threshold when each of the Nyquist slope and the real impedance value at 1 kHz is lower than an upper bound for the Nyquist slope and lower than an upper bound for the real impedance value at 1 kHz, respectively.
13. The system of claim 12 , wherein the control circuitry further causes performance of: in a case where the second calibration with the EIS-based calibration factor adjustment is performed, gradually offsetting the Nyquist slope to be lower than the upper bound for the Nyquist slope.
14. The system of claim 12 , wherein the control circuitry further causes performance of: in a case where the second calibration with the EIS-based calibration factor adjustment is performed, gradually offsetting the real impedance value at 1 kHz to be lower than the upper bound for the real impedance value at 1 KHz.
15. The system of claim 11 , wherein the reliability index is calculated to be lower than or equal to the predetermined threshold when at least one of the Nyquist slope or the real impedance value at 1 KHz is not lower than a respective upper bound.
16. The system of claim 11 , wherein the control circuitry further causes performance of: calculating the length of time for the Nyquist slope and the real impedance value at 1 kHz to be within the respective range based on a trend of the Nyquist slope and of the real impedance value at 1 KHz.
17. The system of claim 16 , wherein the trend of the Nyquist slope and of the real impedance value at 1 kHz is measured during a start-up period.
18. The system of claim 11 , wherein the first calibration is performed after the length of time has passed, in a case where the reliability index is not higher than the predetermined threshold.
19. The system of claim 11 , wherein the second calibration with the EIS-based calibration factor adjustment is performed upon determining that the length of time is not shorter than the predetermined duration.
20. A non-transitory computer-readable medium storing instructions which, when executed by one or more processors, cause performance of operations comprising:
performing electrochemical impedance spectroscopy (EIS) procedures for a working electrode of a glucose sensor to obtain values of at least one impedance-based parameter for the working electrode;
performing a bound check for a Nyquist slope and a real impedance value at 1 kHz based on the at least one impedance-based parameter to calculate a reliability index;
performing a first calibration in a case where the reliability index is higher than a predetermined threshold; and
in a case where the reliability index is not higher than the predetermined threshold:
calculating a length of time for the Nyquist slope and the real impedance value at 1 kHz to be within a respective range;
performing the first calibration in a case where the length of time is shorter than a predetermined duration; and
performing a second calibration with an EIS-based calibration factor adjustment in a case where the length of time is not shorter than the predetermined duration.