Capacitive Skin Contact Sensing with Pre-Stored Calibration
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Solution Overview
Problem
Capacitive sensing systems in wearable devices are power-hungry and prone to unreliable operation due to self-calibration issues when in skin contact, leading to inoperability and non-reliability.
Innovation Solution
A skin contact sensing device with a processor that reads calibration parameters from a memory to adjust for environmental changes, allowing the sensor controller to be switched off during non-use periods and conducting auto-calibration only at predefined times, using a capacitive contact sensor integrated into wearable devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a self-calibrating capacitive sensor controller is switched on while in skin contact, then the controller performs self-calibration to compensate for environmental changes, but the existing skin contact is misinterpreted as an environmental change causing over-compensation and rendering the sensing inoperable
Solution Approach 1:
The system performs self-calibration before skin contact is detected, establishing a baseline capacitance value when no skin is present. This preliminary calibration ensures that subsequent skin contact measurements are not affected by environmental variations, resolving the contradiction by preparing the system in advance rather than calibrating during contact.
Solution Approach 2:
Instead of continuously calibrating during operation (which causes over-compensation), the system inverts the approach by performing calibration only when skin contact is absent. This reversal of the calibration timing eliminates the harmful over-compensation effect while maintaining sensing reliability.
2Reliability
If a capacitive sensing controller continuously operates to detect skin contact, then detection reliability is maintained, but power consumption becomes excessive for ultra-low power systems
Solution Approach 1:
The capacitive sensing controller operates in periodic intervals rather than continuously. The controller activates the capacitive sensor only at scheduled intervals to perform measurements, then enters a low-power sleep mode. This periodic operation maintains detection capability while dramatically reducing average power consumption for ultra-low power wearable systems.
Solution Approach 2:
The system uses wake-up triggers (such as motion detection or user interaction) to activate the capacitive sensing controller only when skin contact detection is actually needed. Between triggers, the controller remains dormant, allowing the system to service itself by activating only when necessary rather than running continuously.
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
Significantly reduces power consumption by up to 90% while maintaining reliable skin contact detection, adaptable to varying environmental conditions, and compatible with low-power applications.
Implementation Method 1
Detection of a mechanical contact to a body portion, e.g. to the skin of a person, is typically implemented by way of a capacitive sensor
Data Source
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AI summary
In one aspect the present invention concerns a skin contact sensing device (10) comprising: - a contact sensor (11) operable to generate electrical contact signals being indicative of a skin contact, - a processor (12) connected to the contact sensor (11) and operable to process the electrical contact signals received from the contact sensor (11), - a memory (15) connected to the processor (12) and operable to store at least one calibration parameter, - wherein the processor (12) is operable to ascertain a skin contact by processing of the electrical contact signals on the basis of the at least one calibration parameter and wherein - the processor (12) is operable to read and to obtain the at least one calibration parameter from the memory (15).