Bio-impedance Estimation Using Parasitic Network De-embedding
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Solution Overview
Problem
Existing bio-impedance measurement techniques face inaccuracies due to parasitic networks and contact impedances, particularly in four-wire measurements, which can lead to imprecise estimation of distally located multiport networks.
Innovation Solution
A method involving multiple two-wire measurements to construct a complete Z-matrix of the network, with calibration using known loads to estimate the intervening parasitic network and store calibration parameters for de-embedding, allowing for precise estimation of the distal network.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If four-wire measurements are used to reduce contact impedance effects, then measurement precision is improved, but parasitic networks still cause inaccuracies in distally located multiport network estimation
Solution Approach 1:
The patent segments the measurement system into distinct components: the measurement device with its parasitic network and the distally located body network. By performing multiple separate two-wire measurements through different port combinations and using calibration with known loads, the system separately characterizes the parasitic network parameters and the body network parameters, allowing for more accurate estimation despite the presence of parasitic elements
Solution Approach 2:
The patent implements preliminary calibration measurements using known load conditions before performing actual bio-impedance measurements. This preliminary action allows the system to pre-determine the parameters of the parasitic network, which are then used to de-embed and correct subsequent measurements, improving the accuracy of distally located network estimation
2Measurement precision
If multiple two-wire measurements with calibration are performed, then accuracy of distal network estimation is improved, but device complexity and measurement time increase
Solution Approach 1:
The patent uses a universal calibration procedure that can be applied to different port combinations and measurement configurations. The same calibration methodology and mathematical framework are used whether performing two-wire, three-wire, or four-wire measurements, simplifying the overall system design despite the multiple measurement types required
Solution Approach 2:
The patent creates a mathematical model (impedance matrix representation) that copies and represents the physical parasitic network and body network. This model allows the system to work with simplified mathematical expressions rather than dealing directly with the complex physical measurements, reducing computational complexity while maintaining measurement accuracy
Data Source
AI summary
Accurately measuring bio-impedance is important for sensing properties of the body. Unfortunately, contact impedances can significantly degrade the accuracy of bio-impedance measurements. To address this issue, a method is provided for estimating an impedance matrix of parasitic network disposed between a first network and a second network of a bio-impedance measurement system, the method comprising determining an impedance matrix for the first network (ZMUX) based on an impedance matrix for the second network (ZLOAD) for at least one known load condition; fitting ZMUX values for ZLOAD for the at least one known load condition to estimate parameters of the impedance matrix of the intervening network.