Capacitive Proximity Sensing for Body vs Low-Permittivity Objects
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Solution Overview
Problem
Conventional capacitive proximity sensors in portable devices fail to distinguish between body parts and low permittivity objects, leading to incorrect proximity detections and potential unnecessary reductions in RF power or screen disablement.
Innovation Solution
A capacitive proximity sensor system that includes a sense electrode and a shield electrode, capable of measuring capacitance changes with the shield electrode in both connected and high-impedance states, allowing for discrimination between human body parts and low-permittivity objects by analyzing the differences in capacitance readings between the main and auxiliary electrodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional capacitive sensor is used to detect proximity, then the sensor can detect the presence of an object, but it cannot distinguish between body parts and low permittivity objects
Solution Approach 1:
The sensor system is divided into multiple independent sensing elements (first capacitive sensing element and second capacitive sensing element) that can be differentially coupled to the object. This segmentation allows each element to contribute different information about the object's properties, enabling discrimination between body parts and low permittivity objects through comparative analysis of their responses.
Solution Approach 2:
The system changes the coupling parameters between the sensing elements and the object by adjusting the differential coupling configuration. By varying which sensing elements are differentially coupled and how they are connected to the object, the system can extract different capacitive parameters that reveal object type information, thereby improving measurement precision.
2Measurement precision
If a single capacitive sensing element is used, then the device complexity is low, but the ability to discriminate object types is insufficient
Solution Approach 1:
The multiple capacitive sensing elements serve multiple functions: they collectively provide both proximity detection and object type discrimination capabilities. The same sensing elements used for basic proximity sensing are also utilized for extracting differential capacitive information that identifies object type, eliminating the need for separate specialized sensors and minimizing additional device complexity.
Solution Approach 2:
The system introduces an intermediary processing stage that analyzes the differential coupling responses from multiple sensing elements. This intermediary analysis layer extracts object type information from the capacitive measurements without requiring complex hardware modifications, resolving the contradiction between measurement precision and device complexity through software or signal processing techniques.
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
Effectively reduces false proximity detections by accurately differentiating between human body parts and inanimate objects, ensuring appropriate adjustments to RF power and screen functionality based on precise proximity measurements.
Implementation Method 1
the detector is a capacitive sensor arranged for sensing a capacity change of the antenna
Implementation Method 2
the human body having a high dielectric constant with respect to air or vacuum, a capacity rise is generated when a body part approaches the head of the user to a short distance of the portable connected device
Data Source
Figure 1~6
Figure 7~9
AI summary
A proximity sensor, and a portable device equipped therewith, with at least two sense electrodes, one influencing the other. By reading twice the capacity of one electrode, while either setting the potential of the counterelectrode to guard or letting it float, the sensor of the invention discriminates between a body part, or another electrically equivalent object, and low-permittivity objects.