Capacitive Proximity Sensor Parasitic Capacitance Reduction
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Solution Overview
Problem
Capacitive proximity sensors used in motor vehicles to trigger tailgate opening are prone to reduced sensitivity due to parasitic capacitances, especially when contaminated with dirt, salt, and moisture, leading to unreliable detection of the operator's foot.
Innovation Solution
A capacitive proximity sensor design with an elongated sensor electrode arrangement and an auxiliary electrode, where the sensor electrode and auxiliary electrode are arranged parallel to each other at a predetermined minimum distance, and the sensor electrode is covered by an insulating material to reduce parasitic capacitances and ensure hermeticity, with specific spacing and potential configurations to enhance sensitivity and directional detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the sensor electrode is placed behind the vehicle apron to enable foot detection, then the sensor can trigger tailgate opening, but parasitic capacitances from the circuit arrangement and feed lines deteriorate sensitivity and detection reliability
Solution Approach 1:
The patent extracts the sensor electrode from direct contact with the vehicle apron surface by placing it inside a hollow insulating body that is inserted into the apron. This separation removes the parasitic capacitances associated with feed lines running along the apron surface, while the insulating body itself acts as a capacitor with the apron surface, enabling detection without the harmful parasitic effects.
Solution Approach 2:
The hollow insulating body serves as an intermediary between the sensor electrode and the vehicle apron. It provides a controlled capacitive coupling through its wall thickness while isolating the electrode from direct contact with contaminated surfaces and feed line parasitics. The insulating body's dielectric properties mediate the detection function while eliminating harmful electrical pathways.
2Measurement precision
If an auxiliary electrode is added to increase sensitivity and achieve directional effect, then detection sensitivity improves, but additional parasitic capacitances from the auxiliary electrode and its leads further reduce detection certainty
Solution Approach 1:
The patent merges the auxiliary electrode with the insulating body structure itself, where the inner surface of the hollow insulating body serves as the auxiliary electrode. This integration eliminates the need for separate auxiliary electrode leads and connections, thereby avoiding additional parasitic capacitances while maintaining the directional sensitivity function through the configured electrode arrangement inside the hollow body.
Solution Approach 2:
The hollow insulating body with its thin dielectric wall functions as a flexible capacitive structure that provides both sensor and auxiliary electrode functions. The thin wall allows sufficient capacitive coupling for sensitive detection while the hollow structure provides space for electrode configuration and maintains isolation from external parasitic influences.
3Ease of manufacture
If the sensor is mounted on the rear of the vehicle apron in a coaxial arrangement, then cost is reduced, but contamination with dirt, salt, and moisture creates conductive layers that further degrade sensitivity
Solution Approach 1:
The patent implements a nested structure where the sensor electrode and auxiliary electrode are positioned inside the hollow insulating body, which is itself inserted into the vehicle apron. This nested arrangement protects the electrodes from direct exposure to contamination while maintaining the cost-effective coaxial geometry. The insulating body wall acts as a barrier against dirt, salt, and moisture that would otherwise create conductive layers on the electrode surfaces.
Solution Approach 2:
The hollow insulating body creates an inert electrical environment around the sensor electrodes by isolating them from the contaminated external atmosphere. The dielectric material of the insulating body prevents conductive contamination layers from forming on the electrodes, maintaining stable capacitive coupling conditions even when the vehicle apron surface is contaminated with dirt, salt, and moisture.
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 design significantly improves the sensor's sensitivity and reliability, even on dirty and damp surfaces, by minimizing parasitic capacitances and maintaining hermeticity, ensuring accurate detection of the operator's foot movement.
Implementation Method 1
The electric field generated by the capacitive proximity sensor is influenced by the movement of the foot under the vehicle apron with the proximity sensor, so that the capacitance changes.
Implementation Method 2
The electric field generated by the capacitive proximity sensor is influenced by the movement of the foot under the vehicle apron with the proximity sensor
Implementation Method 3
a capacitive proximity sensor which is arranged behind a cladding (10) made of an insulating material (a dielectric)
Data Source
Figure 1~2
Figure 3~4
AI summary
An elongated sensor electrode assembly (4) has sensor and auxiliary electrodes (5,6) arranged at a predetermined minimum distance. Electrode assembly is connected to a control circuit. Sensor electrode is connected respectively to low electric potential node and capacitor at specific time periods. Auxiliary electrode is connected to a high electric potential node. An insulator cover (10) is arranged on a cover (2) for hermetically sealing the electrode assembly. Distances (12,13) of sensor electrode from outer surface (11) and front surface of cover are about 10 mm.