Stacked Capacitive Sensor Layout for Object Permittivity Detection
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Solution Overview
Problem
Conventional proximity sensors in portable devices and wearables struggle to accurately distinguish between different objects based on their permittivity, leading to false detections and inability to discriminate between conductive and dielectric bodies, which affects the reliability of proximity detection and power management.
Innovation Solution
A capacitive proximity sensor with a stacked structure featuring a first electrode and an internal electrode, where the first electrode has openings for partial capacitive coupling, allowing for the determination of capacitance and permittivity of objects in the detection region, using shield control units and readout circuits to differentiate between objects of varying permittivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional capacitive proximity sensors are used to detect body proximity, then the sensor structure is simple and easy to integrate, but the sensor cannot discriminate between different objects (conductive vs dielectric bodies) leading to false detections
Solution Approach 1:
The sensor is divided into multiple independent capacitive electrodes (first electrode, second electrode, third electrode) with distinct functions. The first and second electrodes detect capacitance changes, while the third electrode measures permittivity. This segmentation allows the system to distinguish between conductive and dielectric objects by comparing measurements from different electrodes, thereby improving detection accuracy without requiring a completely complex new sensor design.
Solution Approach 2:
The patent introduces permittivity measurement as an intermediary parameter to differentiate between object types. By measuring both capacitance (which changes with both distance and object type) and permittivity (which is intrinsic to the material), the system can distinguish whether a capacitance change is due to distance or object material properties, reducing false detections while using standard capacitive sensing components.
2Measurement precision
If conventional proximity detection methods are used, then the implementation is simple, but the sensor cannot distinguish between objects at different distances vs. objects of different permittivity
Solution Approach 1:
The system dynamically switches between different measurement modes and configurations. The third electrode is selectively activated to measure permittivity when needed, and the system adapts its interpretation of capacitance changes based on the measured permittivity values. This dynamic approach enables precise object discrimination without continuously operating all sensors at full complexity.
Solution Approach 2:
The patent changes the measurement parameter from simple capacitance to a combination of capacitance and permittivity. By introducing permittivity as an additional measurable parameter, the system gains the ability to distinguish between objects with different material properties. The readout circuit is configured to extract both parameters, transforming a single-parameter measurement system into a multi-parameter system that provides superior discrimination capability.
3Reliability
If optical detection techniques are used for proximity sensing, then discrimination between different objects is possible, but power consumption increases and integration becomes more complex
Solution Approach 1:
The patent replaces optical detection mechanisms with electrical capacitive sensing. Instead of using light sources, photodetectors, and complex optical paths that consume significant power, the system uses passive capacitive electrodes that detect changes in electrical fields. This substitution maintains object discrimination capability through permittivity measurement while dramatically reducing power consumption and simplifying integration into portable devices.
4Reliability
If the first electrode completely covers the internal electrode, then shielding is maximized, but capacitive coupling with detection region objects is reduced
Solution Approach 1:
The first electrode is designed with non-uniform local properties: it has openings or apertures in specific locations where capacitive coupling to the detection region is desired, while maintaining continuous coverage in other areas for shielding. This local quality variation allows different regions of the same electrode to serve different functions - some regions provide shielding while others provide sensing capability, optimizing both shielding effectiveness and measurement precision simultaneously.
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 enables accurate discrimination between objects of different nature, reducing false detections and improving the reliability of proximity sensing, while being compact and energy-efficient, suitable for integration in portable devices and wearables.
Implementation Method 1
a readout circuit configured to determine a first capacitance of either the first electrode or the internal electrode by applying the shield potential to the other electrode and a second capacitance of either the first electrode or the internal electrode while keeping the other electrode at a fixed potential
Implementation Method 2
to determine a permittivity of a body in the detection region based on said first capacitance and second capacitance
Implementation Method 3
the first electrode has a plurality of openings that allow a partial capacitive coupling between the internal electrode and conductive and/or dielectric bodies in the detection region
Data Source
Figure 1~3
Figure 4~6
AI summary
A capacitive proximity sensor with a stacked electrode structure where an inner electrode is partially screened by an upper one. The self-capacitances of selected electrodes is measured while other electrodes are held to ground or to a shield potential. In this manner, the proximity sensor estimates a value of the dielectric permittivity of the approaching body.