Human Body Sensor Phase-Shift Detection for Contact Discrimination
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Solution Overview
Problem
Capacitive sensors fail to accurately distinguish between human body contact and contact by other objects like liquids or grounded metals due to quantifying series combined capacitance rather than capacitance between the human body and the sensor.
Innovation Solution
A human body detecting sensor system with a first and second electrode, a drive circuit, a detection circuit, and a comparison circuit that generates and compares signals to detect a touch or approach based on phase and amplitude differences within specific ranges, allowing for accurate differentiation of human body impedance from other objects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a capacitive sensor quantifies the series combined capacitance, then the sensor can detect contact by any conductive object, but the sensor cannot accurately distinguish human body contact from contact by other objects like liquids or grounded metals
Solution Approach 1:
The patent applies parameter changes by measuring both the capacitance value and the phase angle of the impedance, and by operating across multiple frequencies. The phase angle parameter specifically distinguishes human body contact from other conductive objects, as human bodies exhibit characteristic phase characteristics due to their resistive and capacitive properties. This multi-parameter measurement approach resolves the contradiction by maintaining broad detection capability while adding precision for human body identification.
2Device complexity
If a single capacitance measurement is used, then the sensor system remains simple, but the system cannot differentiate between human body impedance and other objects
Solution Approach 1:
The patent transitions from a single-dimensional capacitance measurement to a two-dimensional measurement by incorporating the phase angle of the impedance. This dimensional change allows the system to plot measurements on a complex plane where human body contacts form distinct regions from other objects. The phase angle adds a new dimension of information without requiring completely new hardware, thus improving precision while maintaining reasonable system complexity.
3Ease of operation
If the sensor measures series combined capacitance only, then the measurement process is straightforward, but the sensor cannot quantify the capacitance between the human body and the sensor accurately
Solution Approach 1:
The patent introduces an intermediary measurement approach by using the phase angle as a mediator to extract information about the human body-to-sensor capacitance. Rather than directly measuring the difficult-to-access Cfr, the system measures the overall impedance and its phase angle, which contains information about Cfr. This intermediary measurement method maintains operational simplicity while achieving accurate capacitance quantification through mathematical relationships between the measured parameters.
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 reliably detects human body touch and approach by identifying phase shifts and amplitude changes within prescribed ranges, improving vehicle safety by distinguishing human contact from non-human objects.
Implementation Method 1
a capacitive sensor may not quantify the capacitance Cfr between the human body and the sensor, but rather may instead quantify the series combined capacitance Cfr*Cfg/(Cfr+Cfg) of the coupling capacitance Cfg between the human body and ground and the capacitance Cfr between the human body and the sensor
Implementation Method 2
the comparison circuit is configured to detect a touch and/or an approach of a human body with respect to at least one of the first and second electrodes when a phase difference and an amplitude difference between the first signal and the second signal are within a prescribed range
Data Source
AI summary
A human body detecting sensor system includes a first electrode, a second electrode, a drive circuit, a detection circuit, and a comparison circuit. The second electrode is connected to the first electrode via a capacitor. The drive circuit generates a first signal having a prescribed frequency for driving the first electrode. The detection circuit detects a second signal generated at the second electrode in response to the first signal being supplied to the first electrode. The comparison circuit compares the first signal with the second signal. The comparison circuit detects a touch and/or an approach of an object, which has an impedance in a certain range corresponding to a human body, with respect to at least one of the first and second electrodes when a phase difference between the first signal and the second signal is within a prescribed range.