Conductive Shield for Biosignal Sensing
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Solution Overview
Problem
Capacitive biopotential measurements suffer from strong motion artefacts due to triboelectric effects, which can render reliable measurements impossible for extended periods.
Innovation Solution
An apparatus comprising a first and second electrode, non-inverting amplifiers, an inverting amplifier, and a conductive shield driven to a potential derived from the inverted common mode voltage, which acts as a drain to dissipate triboelectric charges, thereby reducing noise in the output signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If capacitive electrodes are used for biopotential measurement, then non-contact measurement is enabled, but triboelectric charges cause strong motion artefacts and noise
Solution Approach 1:
A conductive shield is introduced as an intermediary component between the capacitive electrode and the user's body. The shield is driven at a potential derived from the inverted common mode voltage to actively cancel triboelectric charges generated at the electrode-body interface, thereby reducing motion artifacts while preserving non-contact measurement capability
Solution Approach 2:
The potential of the conductive shield is dynamically adjusted based on the inverted common mode voltage signal. By changing the electrical parameter (shield potential) in response to detected common mode variations, the system actively compensates for triboelectric effects and maintains measurement reliability
2Productivity
If capacitive electrodes are used for biopotential measurement, then motion artefacts are generated, but extended measurement periods become impossible
Solution Approach 1:
The conductive shield operates continuously to dissipate triboelectric charges throughout the measurement period. By maintaining active charge cancellation rather than periodic correction, the system enables extended measurement periods without interruption while preserving reliability
Solution Approach 2:
The system uses feedback from the common mode voltage signal to drive the conductive shield. The inverting amplifier processes the common mode voltage and applies the inverted signal to the shield, creating a closed-loop system that continuously adapts to varying triboelectric conditions and maintains measurement quality over time
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
The solution effectively reduces noise in biosignal output by dissipating triboelectric charges, enabling more reliable and consistent biopotential measurements.
Implementation Method 1
Capacitive biopotential measurements suffer from strong motion artefacts due to triboelectric effects
Implementation Method 2
the inverting amplifier has a low output impedance compared to the input of the first non-inverting amplifier and acts as a drain to enable triboelectric charges that are transferred to the first conductive shield to be dissipated
Data Source
Figure 1~2
Figure 3A~3E
Figure 4A~4B
AI summary
An apparatus comprising: at least one electrode, having a first potential, arranged to sense a biosignal; a conductive shield provided over the at least one electrode where the conductive shield is configured to be driven to a second potential wherein the second potential is equivalent to the first potential plus a multiple of an inverted common mode voltage; and wherein the conductive shield is coupled to a drain to enable triboelectric charges to be dissipated.