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 calibrating a sensor during a period of sensor transition, the method comprising:
defining an electrochemical impedance spectroscopy (EIS)-based sensor status vector (V) for each one of a plurality of sensor current (Isig)-blood glucose (BG) pairs;
defining an Isig buffer to store Isig values of said plurality of Isig-BG pairs;
defining an BG buffer to store BG values of said plurality of Isig-BG pairs;
monitoring the status vectors for the plurality of Isig-BG pairs over time;
detecting when there is a difference between a first status vector for a first Isig-BG pair and a subsequent status vector for a subsequent Isig-BG pair;
if a magnitude of said difference is smaller than a predetermined threshold, calibrating said sensor based on values of said Isig-BG pairs from a first set of Isig and BG buffers; and
if the magnitude of said difference is larger than a predetermined threshold, calibrating said sensor based on values of said Isig-BG pairs from a second set of Isig and BG buffers, wherein said second set of Isig and BG buffers contains at least the values of Isig and BG from said subsequent Isig-BG pair.
2. The method of claim 1 , wherein said first set of Isig and BG buffers contain values of Isig and BG, respectively, prior to said period of sensor transition.
3. The method of claim 1 , wherein said second set of Isig and BG buffers contain values of Isig and BG, respectively, after start of said period of sensor transition.
4. The method of claim 1 , wherein, for each Isig-BG pair, the sensor status vector includes Nyquist slope and at least one of real impedance and imaginary impedance as elements of the vector.
5. The method of claim 1 , wherein, for each Isig-BG pair, the sensor status vector includes 1 kHz real impedance as an element of the vector.
6. The method of claim 1 , wherein, for each Isig-BG pair, the sensor status vector includes 1 kHz imaginary impedance as an element of the vector.
7. The method of claim 1 , wherein, for each Isig-BG pair, the sensor status vector includes Nyquist slope as an element of the vector.
8. The method of claim 1 , wherein, for each Isig-BG pair, the elements of the sensor status vector include 1 kHz real impedance, 1 kHz imaginary impedance, Nyquist slope, and Nyquist R 2 .
9. The method of claim 1 , wherein the sensor status vector includes a plurality of EIS-based elements, and wherein the plurality of EIS-based elements are substantially glucose-independent.