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 calculating a single, fused sensor glucose value based on respective glucose measurement signals of a plurality of redundant sensing electrodes, comprising:
performing respective electrochemical impedance spectroscopy (EIS) procedures for each of the plurality of redundant sensing electrodes to obtain values of at least one impedance-based parameter for each said sensing electrode;
measuring the electrode current (Isig) for each of the plurality of redundant sensing electrodes;
calibrating each of the measured Isigs to obtain respective calibrated sensor glucose values;
calculating a bound-check reliability index and a noise-check reliability index for each said sensing electrode based on said measured Isig and said values of the at least one impedance-based parameter;
calculating a dip reliability index for each said sensing electrode based on one or more of said at least one impedance-based parameter;
calculating a sensitivity-loss reliability index for each said sensing electrode based on one or more of said at least one impedance-based parameter; and
calculating said single, fused sensor glucose value based on the respective bound-check reliability index, noise-check reliability index, dip reliability index, sensitivity-loss reliability index and calibrated sensor glucose values of each of the plurality of redundant sensing electrodes.
2. The method of claim 1 , wherein said at least one impedance-based parameter includes at least one of real impedance, imaginary impedance, and Nyquist slope.
3. The method of claim 1 , wherein said at least one impedance-based parameter is 1 kHz real impedance.
4. The method of claim 3 , wherein calculation of said bound check reliability index and said noise check reliability index include determining whether each said measured Isig and said values of the 1 kHz real impedance fall within respective predetermined ranges for said bound check and noise check.
5. The method of claim 4 , wherein said predetermined range for the 1 kHz real impedance bound check is between 0.3 e+4 and 2 e+4.
6. The method of claim 1 , wherein said at least one impedance-based parameter is imaginary impedance.
7. The method of claim 6 , wherein said imaginary impedance is measured at about 1 kHz over a period of time.
8. The method of claim 7 , wherein calculation of said bound check reliability index and said noise check reliability index include determining whether said values of the 1 kHz imaginary impedance fall within respective predetermined ranges for said bound check and noise check.
9. The method of claim 8 , wherein said predetermined range for the 1 kHz imaginary impedance bound check is between −2 e+3 and zero.
10. The method of claim 1 , wherein each said Isig is calibrated by using a blood glucose (BG) value.
11. The method of claim 1 , wherein, prior to calibrating the measured Isigs, said Isigs are first filtered to remove any EIS-induced spikes therein.
12. The method of claim 1 , wherein a low-pass filter is applied to the said single, fused sensor glucose value.
13. The method of claim 1 , wherein each said respective EIS procedure is performed for a range of frequencies.
14. The method of claim 1 , wherein one or more of the at least one impedance-based parameter are substantially glucose-independent.
15. The method of claim 1 , wherein calculation of said dip reliability index is additionally based on the measured Isig for each said electrode.
16. The method of claim 1 , further including calculating, for each of the plurality of electrodes, a weight based on said electrode's bound-check reliability index, noise-check reliability index, dip reliability index, sensitivity-loss reliability index.
17. The method of claim 16 , said single, fused sensor glucose value is calculated based on the respective weights and calibrated sensor glucose values of each of the plurality of redundant sensing electrodes.