Three-Electrode Bioimpedance Sensor with Short-Circuit Compensation
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Solution Overview
Problem
Existing bioelectric impedance measurement technologies face challenges in miniaturization, particularly for wearable devices, where the decrease in electrode size increases contact impedance, reducing measurement accuracy and limiting the application of four-electrode methods due to space constraints.
Innovation Solution
A bioelectric impedance measurement apparatus and method using three electrodes, where a first electrode applies current, a second electrode measures voltage, and a third electrode is used for both current application and voltage measurement, with a short-circuit unit allowing the first and second electrodes to be short-circuited, enabling impedance calculation using a bioelectric impedance calculation equation derived from contact impedance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If electrode size is decreased for miniaturization, then device compactness is improved, but contact impedance increases reducing measurement accuracy
Solution Approach 1:
The patent divides the measurement function into two separate electrode pairs: a first electrode pair for applying current and a second electrode pair for measuring voltage. This segmentation allows the current application function and voltage measurement function to be performed by different electrodes, enabling accurate impedance measurement even with miniaturized electrodes by separating the high-current path from the high-precision measurement path.
Solution Approach 2:
The patent introduces a separate voltage measurement electrode pair as an intermediary between the current application electrodes and the measurement instrument. This intermediary electrode pair measures the voltage drop without carrying the full measurement current, thereby avoiding the impact of contact impedance on the voltage measurement and enabling accurate impedance calculation despite small electrode size.
2Measurement precision
If four-electrode method is used for accurate measurement, then measurement accuracy is improved, but device complexity increases due to space constraints
Solution Approach 1:
The patent merges the functions of the four-electrode method into a three-electrode configuration by combining the functions of the second and fourth electrodes into a single third electrode. This third electrode serves both as a voltage measurement electrode and as part of the current application path, thereby simplifying the electrode configuration while maintaining the measurement accuracy benefits of the four-electrode method.
Solution Approach 2:
The third electrode is designed with multi-functionality, serving both as a voltage measurement electrode and as a current application electrode. This universal electrode reduces the total number of electrodes required from four to three, simplifying the device structure while preserving the ability to perform accurate impedance measurements through the separation of current and voltage measurement functions.
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 compensates for the increased contact impedance in miniaturized devices, maintaining measurement accuracy and enabling the use of bioelectric impedance measurement in compact wearable devices like wristwatch-type devices, while also allowing for the measurement of additional signals like ECG and GSR.
Implementation Method 1
a first voltage measurer configured to measure a first voltage between the second electrode and the third electrode generated by a current applied to an object through the first electrode and the third electrode
Implementation Method 2
a short-circuit unit configured to short-circuit the first electrode to the second electrode
Implementation Method 3
a second voltage measurer configured to measure a second voltage between the short-circuited first electrode and the third electrode generated by a current applied to the object through the short-circuited first electrode and the third electrode
Data Source
AI summary
An apparatus and method for measuring a bioelectric impedance is provided. The apparatus may measure the bioelectric impedance using three electrodes. The apparatus may measure the bioelectric impedance by compensating for a change of a contact impedance.