Bio Impedance Guard Electrode Zone Segmentation
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Solution Overview
Problem
Bio impedance measurement systems face challenges such as high skin impedance, motion artefacts, and electronic noise, which affect the precision and reliability of measurements.
Innovation Solution
A method and device using a sensing electrode, pilot electrode, and guard electrode to control current flow between zones, with a controller managing the guard electrode's potential to stop current flow and reject disturbances at specific frequencies, thereby increasing surface impedance and reducing noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a guard electrode is used to separate surface zones and control potential, then current flow between zones is stopped and surface impedance is increased, but device complexity increases
Solution Approach 1:
The body surface is segmented into distinct zones using a guard electrode that separates the sensing zone from the current injection zone. This segmentation prevents current leakage between zones and isolates the high-impedance sensing area from the current-carrying area, thereby improving measurement precision despite adding device complexity.
Solution Approach 2:
The guard electrode acts as an intermediary element between the sensing electrode and the current injection electrode. By controlling the potential of this intermediate guard electrode, the system prevents direct current flow between zones while maintaining electrical isolation, thus improving measurement accuracy without requiring complete system redesign.
2Reliability
If guard electrode potential is controlled at stopping frequencies, then current flow is stopped and rejection of disturbances is improved, but device complexity increases
Solution Approach 1:
The controller applies periodic potential control to the guard electrode at specific stopping frequencies (e.g., 50/60 Hz mains frequency and injection frequency). This periodic control creates temporal isolation by preventing current flow at critical frequencies when disturbances occur, thereby improving measurement reliability without requiring continuous complex control.
Solution Approach 2:
The system dynamically changes the potential parameter of the guard electrode at specific frequencies to match the sensing electrode potential. By adjusting this electrical parameter periodically at disturbance frequencies, the system achieves frequency-selective current blocking, improving reliability while keeping controller complexity manageable through targeted frequency control.
3Measurement precision
If surface impedance is increased to avoid current flow, then motion artefacts and electronic noise are reduced, but measurement system complexity increases
Solution Approach 1:
The system converts the naturally high surface impedance (which normally causes current leakage and noise) into a beneficial feature by using the guard electrode to control and utilize this high impedance. The high surface impedance, when combined with guard electrode control, becomes a mechanism for current isolation rather than a source of error, improving signal-to-noise ratio while managing system complexity through intelligent electrode control.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances the precision of bio impedance measurements by minimizing the impact of motion artefacts and electronic noise, ensuring accurate results regardless of skin conditions or frequency disturbances.
Implementation Method 1
providing a guard electrode (4) adapted to separate the surface in at least two zones... controlling the potential of said guard electrode... in order to stop current from flowing from one zone to the other
Implementation Method 2
controlling the potential of said guard electrode, at least at given stopping frequencies... The controller provides a high rejection within a narrow band... at the angular frequency ω, it is assumed that there is no disturbance current (e.g., 50/60 Hz) nor injected current (e.g., 50 kHz)
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
Method for bio impedance measurement on a skin surface (1) of a living body, using a bio impedance measurement device comprising a sensing electrode (2) and a pilot electrode (9), comprising the following steps: - placing said sensing electrode (2) and pilot electrode (9) on the surface (1) of said body; - providing a guard electrode (4) adapted to separate the surface (1) in at least two zones, among which a sensing zone including the sensing electrode (2) and a current injection zone including the pilot electrode (9); - providing a controller (27), electrically connected to said electrodes, adapted to control the current source (25); - controlling the potential of said guard electrode (4), at least at given stopping frequencies, in order to stop current from flowing from one zone to the other.