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 detection and potential false reductions in RF power or screen disablement, especially when the device is placed on a support.
Innovation Solution
The implementation of a capacitive proximity sensor system that includes a sense electrode and a shield electrode, with a digital processor to differentiate between body parts and low-permittivity objects by measuring capacity variations and using offset subtraction and noise filtering to enhance discrimination, allowing for precise control of RF power based on object type.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional capacitive sensors are used for proximity detection, then the device can detect objects near the RF antenna, but the sensor cannot distinguish between body parts and low permittivity objects, leading to false detections
Solution Approach 1:
The sensor system is segmented into multiple independent capacitive sensors with different characteristics (different areas, positions, or configurations). Each sensor provides a capacity measurement that, when combined with the others, enables discrimination between body parts and low permittivity objects through pattern recognition of the capacity profile.
Solution Approach 2:
The system transitions from single-capacity measurement to multi-dimensional measurement by using multiple capacitive sensors. The capacity measurements from different sensors create a multidimensional signature that provides additional information for distinguishing between different object types, moving beyond the single-dimensional limitation of conventional sensors.
2Object-affected harmful factors
If the device reduces RF power based on capacitive sensor detection, then SAR compliance may be achieved, but connectivity is degraded when the detection is false (e.g., device placed on a support)
Solution Approach 1:
The system uses feedback from multiple capacitive sensors to continuously monitor the proximity environment and dynamically adjust RF power. The multi-sensor capacity profile provides feedback that enables intelligent decision-making about when to reduce power, ensuring SAR compliance only when truly necessary and maintaining connectivity when detections are false.
Solution Approach 2:
The system changes the operational parameters of the capacitive sensors (such as measurement frequency, excitation voltage, or sensor activation patterns) to optimize the capacity measurements for discrimination purposes. This enables more accurate object identification, which in turn allows for more precise control of RF power adjustments.
3Area of stationary object
If existing antenna elements are used as capacitive detectors, then no additional surface area is required, but the sensor provides little information about distance and size of the approaching object
Solution Approach 1:
The existing antenna elements serve dual functions: RF transmission/reception and capacitive sensing. By configuring the antenna to operate in both modes, the system eliminates the need for separate sensor elements while still achieving proximity detection capabilities. The multi-sensor approach then extracts additional information about object characteristics from these universal elements.
Solution Approach 2:
The system introduces signal processing algorithms and control circuitry as intermediaries between the antenna elements and the final detection output. These intermediaries process the raw capacity measurements to extract meaningful information about object distance, size, and type, transforming the basic capacitive signal into rich proximity data without requiring additional physical sensor area.
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
This solution enables accurate discrimination between human body parts and inanimate objects, preventing unnecessary power reductions and maintaining connectivity while ensuring compliance with SAR regulations by accurately determining the proximity and type of approaching objects.
Implementation Method 1
capacitive based sensor to detect an object near the RF antenna
Implementation Method 2
discriminating body parts, like for example the head or one hand of the user, from low permittivity object
Data Source
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 counter-electrode 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.