Contactless Physiological Sensor Circuit for Motion Artefact Reduction
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Solution Overview
Problem
Existing contactless physiological sensors face issues with high power consumption and motion-induced noise due to impedance fluctuations, limiting their use in wearable and long-term applications.
Innovation Solution
A system-on-chip design incorporating a capacitive-sensor electrode with an integrated amplifier and a series-connected artefact-reducing capacitor, which has a lower capacitance than the electrode, minimizes impedance fluctuations and power consumption by neutralizing noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If impedance boosting circuits are used in contactless physiological sensors, then the input impedance is increased and signal amplification is improved, but power consumption increases to around 10 mW
Solution Approach 1:
The patent removes the impedance boosting circuit from the sensor design, extracting only the essential amplification function. This eliminates the power-consuming impedance boosting stage while maintaining signal detection capability through direct coupling of the capacitive electrode to the amplifier input.
Solution Approach 2:
Instead of boosting impedance to improve signal detection, the patent inverts the approach by using a low-impedance direct coupling method. The amplifier is designed to work directly with the capacitive electrode without impedance transformation, fundamentally changing the signal conditioning architecture.
2Object-affected harmful factors
If contactless electrodes are used, then skin irritation is avoided and comfort is improved, but motion-induced impedance changes increase causing severe motion artefacts
Solution Approach 1:
The patent converts the harmful motion-induced impedance changes into a beneficial configuration where the capacitive electrode's inherent capacitance becomes part of the amplifier's input capacitance. Motion artifacts are neutralized because the system is designed to accommodate capacitance variations rather than resist them.
Solution Approach 2:
The patent creates a dynamic system where the amplifier's input capacitance adapts to the capacitive electrode's characteristics. The circuit is designed to handle varying capacitance values during motion, making the system dynamically responsive rather than statically fixed.
3Reliability
If invasive microneedle arrays are used to improve grip onto skin, then skin-electrode impedance variation during motion is reduced, but device complexity and invasiveness increase
Solution Approach 1:
The patent replaces the mechanical microneedle array system with an electrical/capacitive solution. Instead of physically penetrating the skin to improve contact, the system uses capacitive coupling with a simple planar electrode, substituting mechanical complexity with electrical simplicity.
4Measurement precision
If wet electrodes with liquid or gel-based contact medium are used, then skin-electrode impedance is reduced, but skin irritation occurs and long-term use is prevented
Solution Approach 1:
The patent adopts a disposable capacitive sensor design where the sensor can be discarded after use. This eliminates the need for reusable components that require cleaning and maintenance, allowing single-use application that avoids skin irritation while maintaining measurement quality throughout the sensor's service life.
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 reduces power consumption to less than 100 μW, allowing for miniaturized, motion-insensitive sensors suitable for long-term use in various applications, including medical monitoring and personal fitness devices.
Implementation Method 1
a capacitive-sensor electrode having a first capacitance; an amplifier device connected to the capacitive-sensor electrode
Implementation Method 2
an artefact-reducing capacitor connected in series between the capacitive-sensor electrode and an input of the amplifier device, the artefact-reducing capacitor having a second capacitance which is less than the first capacitance
Data Source
AI summary
A system-on-chip contactless physiological sensor (10) is provided which comprises a capacitive-sensor electrode (14) having a first capacitance (C1) and an amplifier device (18) connected to the capacitive-sensor electrode (14), the capacitive-sensor electrode (14) and amplifier device (18) at least in part forming an amplifier circuit for the physiological sensor (10). An artefact-reducing capacitor (20) is then connected in series between the capacitive-sensor electrode (14) and an input of the amplifier device (18), the artefact-reducing capacitor (20) having a second capacitance (C2) which is less than the first capacitance (C1). In this sensor (10), there is no impedance boosting input between the capacitive-sensor electrode (14) and the input of the amplifier device (18).