Bioimpedance Calibration via Group Delay Correction
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Solution Overview
Problem
Bioimpedance measurements are challenging due to unpredictable and varying group delay in measuring electronics, making it difficult to achieve accurate 'in phase' measurements, especially with temperature variations and equipment aging.
Innovation Solution
A bioimpedance measurement system that includes a reference load with negligible reactance and a switching arrangement to determine and correct for group delay, allowing for accurate bioimpedance value determination through calibrated voltage waveforms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional bioimpedance measurement is performed without group delay calibration, then the measurement process is simple, but measurement precision deteriorates due to unpredictable and varying group delay
Solution Approach 1:
The patent applies preliminary action by performing group delay calibration before actual bioimpedance measurements. The system pre-determines the group delay characteristics of the measuring electronics using a reference load, stores this calibration data, and then uses it to correct subsequent measurements. This preliminary calibration step eliminates the need for complex real-time corrections during measurement, thereby improving measurement precision while keeping the overall system complexity manageable.
Solution Approach 2:
The patent uses an intermediary approach by introducing a reference load with known characteristics as a mediator between the measuring electronics and the actual biological samples. This reference load serves as a calibration standard that allows the system to determine group delay without requiring complex mathematical corrections. The reference load acts as an intermediary element that simplifies the measurement process while improving accuracy.
2Measurement precision
If group delay calibration is performed continuously to maintain measurement accuracy, then measurement precision is maintained, but loss of time increases due to repeated calibration operations
Solution Approach 1:
The system performs group delay calibration as a preliminary one-time operation before actual measurements begin. The calibration data is stored and reused for subsequent measurements, eliminating the need for repeated calibration operations. This approach maintains measurement precision over time while minimizing the time lost to calibration procedures.
Solution Approach 2:
The patent implements periodic calibration where the group delay is determined at scheduled intervals or under specific conditions (such as temperature changes or equipment aging), rather than continuously. This periodic approach maintains measurement accuracy when needed while minimizing the time spent on calibration operations during normal measurement sequences.
3Reliability
If temperature compensation measures are implemented to address Joule heating effects, then reliability is improved, but device complexity increases
Solution Approach 1:
The patent uses feedback by monitoring temperature variations in the measuring electronics and adjusting the group delay calibration accordingly. The system measures temperature changes caused by Joule heating and applies appropriate corrections to the calibration data, maintaining measurement reliability without requiring complex active temperature control systems. This feedback-based approach compensates for thermal effects while keeping the device complexity low.
Solution Approach 2:
The patent addresses temperature variations by changing the calibration parameters based on measured temperature conditions. Instead of actively controlling temperature, the system adapts the group delay calibration values according to the actual temperature environment, maintaining reliability through parameter adjustment rather than physical temperature control.
Data Source
AI summary
Techniques are disclosed for measuring bioimpedance of a biological object with an alternating current (AC) source, a pair of electrodes, a reference load, a switching arrangement switchable between a first switch condition and a second switch condition, and measuring electronics. When the switching arrangement is in the first switch condition, the AC source is applied across the reference load and a group delay of the measuring electronics is determined. When the switching arrangement is in the second switch condition, and the pair of electrodes is in contact with the biological object, a voltage waveform based on the AC source being applied across the pair of electrodes is measured and a calibrated voltage waveform is determined, the calibrated voltage waveform being corrected for the group delay. The bioimpedance value of the biological object is determined based on the calibrated voltage waveform.