Single-Sensor Proximity Detection for Human vs Object Discrimination
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Solution Overview
Problem
Existing capacitive proximity sensors in portable devices struggle to reliably distinguish between human body proximity and proximity to inanimate objects, leading to unnecessary reduction in RF output power and connectivity issues due to variations in capacitance caused by high-permittivity objects.
Innovation Solution
A capacitive proximity sensor system with a processor that uses multiple threshold values and stability analysis of the capacitance signal to differentiate between human body and inanimate object proximity, allowing for precise control of RF power levels to maintain Specific Absorption Rate (SAR) within limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If capacitive proximity sensor is used to detect human body proximity, then SAR compliance is improved, but false detection near inanimate objects causes unnecessary RF power reduction
Solution Approach 1:
The system dynamically adjusts the proximity threshold based on detected capacitance values. When an inanimate object is detected (higher capacitance threshold), the system raises the proximity threshold to prevent false detection, while maintaining SAR compliance for actual human body proximity through continuous monitoring and adaptive threshold adjustment.
Solution Approach 2:
The system changes the capacitance threshold parameter dynamically based on the detected object type. By monitoring capacitance variations and comparing against adaptive thresholds, the system distinguishes between inanimate objects and human body proximity, maintaining both SAR compliance and detection accuracy through parameter adaptation.
2Reliability
If multiple sensors are used to improve discrimination between human body and inanimate objects, then detection accuracy is improved, but device complexity increases
Solution Approach 1:
Instead of adding multiple sensors, the system achieves improved discrimination by dynamically changing the capacitance threshold parameter based on detected values. This single-sensor approach with adaptive thresholding provides accurate discrimination between human body and inanimate objects without increasing device complexity.
Solution Approach 2:
The proximity sensor system performs self-adjustment by monitoring its own capacitance readings and automatically adapting the threshold. The system uses the capacitance data from the single sensor to determine object type and adjust its detection criteria, eliminating the need for additional sensors or complex external control systems.
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 system effectively reduces RF power only when a human body is detected, avoiding unnecessary power reduction and maintaining connectivity by accurately distinguishing between human and inanimate object proximity, thus ensuring compliance with SAR limits while maintaining device performance.
Implementation Method 1
Capacitive proximity detectors are used in many modern portable devices... Known capacitive sensing systems measure the capacity of an electrode and, when the device is placed in proximity of the human body detect an increase in capacity
Implementation Method 2
Electrical permittivity of the human body is considerably higher than that of wood, glass, plastic and many other material... the capacity will increase more when the device is close to the body then when it is close to a tabletop
Data Source
Figure 1a~3
Figure 4
AI summary
A capacitive proximity detector for use in a connected portable device such as a telephone, laptop or tablet, in which the capacity seen by the senor electrode is compared with four thresholds: a proximity threshold, set lower than the other, to generate a general proximity flag, and a body detection threshold set higher than the other arranged to generate a body detection flag that indicates that the object in proximity is a part of a human body. Two object detection thresholds in the region between the proximity threshold and the body threshold define a region in which the detector can decide whether the object in proximity is an inanimate object, based on the time variation of the capacity.