Capacitive Sensor for Local Normal Stress Measurement
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Solution Overview
Problem
Current devices for measuring normal mechanical stress are cumbersome, require multiple steps, and are not suitable for all rheometers, leading to measurement errors and a lack of sensitivity to detect stresses in the range of 10 Pa, especially when measuring fluid pressure under shear conditions.
Innovation Solution
A device comprising a substrate with an electrically conductive lower electrode, a polymeric layer with through-cavities, a dielectric layer, and an electrically conductive upper electrode, forming a deformable capacitor that varies capacitance with normal mechanical stress, allowing for sensitive and localized measurement of stresses without disturbing the contact element.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional devices are used to measure normal mechanical stress, then measurement capability is provided, but the devices require numerous non-optimized steps and are not suitable for all rheometer types
Solution Approach 1:
The patent creates a universal measurement device with a standardized capacitor-based sensor platform that can be adapted to multiple rheometer types (Couette, cone-plate, parallel plate geometries). The device uses a common substrate-electrode structure that interfaces with different rheometer configurations, eliminating the need for separate specialized devices for each rheometer type and reducing implementation complexity.
Solution Approach 2:
The measurement device is segmented into modular components: a substrate with lower electrode, insulating layers, through-cavities, dielectric layer, and upper electrode. This segmentation allows the device to be manufactured using standardized processes and adapted to different rheometer geometries by configuring the electrode patterns and cavity arrangements, rather than requiring complete custom designs for each application.
2Measurement precision
If two measurements are performed to obtain normal stress difference, then local rheological measurement is achieved, but significant measurement error risk increases
Solution Approach 1:
The patent merges the measurement of normal stress difference into a single capacitive measurement event. By positioning electrodes to simultaneously detect stress differences across the fluid sample, the device obtains the normal stress difference directly from one measurement, eliminating the sequential two-measurement process and its associated error accumulation risks.
3Area of stationary object
If conventional rheometers are repositioned to measure different zones, then pressure distribution is mapped, but measurement time and complexity increase
Solution Approach 1:
The patent transitions from sequential one-point measurements to simultaneous multi-point measurement by incorporating multiple through-cavities and electrode pairs across the measurement surface. This allows parallel detection of normal stress at multiple locations (different radial positions in Couette geometry, or across the plate surface) simultaneously, mapping pressure distribution without repositioning and eliminating time loss.
4Measurement precision
If sensors are made sufficiently small for local measurements, then measurement localization is improved, but sensor sensitivity to detect 10 Pa stresses decreases
Solution Approach 1:
The patent optimizes the capacitor parameters (electrode area, separation distance, dielectric constant) to achieve high sensitivity for detecting low stresses (10 Pa range) while maintaining small through-cavity dimensions for localized measurement. The capacitance change per unit stress is maximized by adjusting these parameters, allowing small sensors to detect low stresses reliably.
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
Enables easy, accurate, and localized measurement of normal mechanical stress with a single measurement, suitable for various rheometer geometries, and sensitive to a wide range of pressures, minimizing disturbance to the contact element, such as fluids or solids.
Implementation Method 1
the assembly comprising the through-cavity, the dielectric layer and the lower and upper electrodes forming a capacitor
Implementation Method 2
the structure being elastically deformable so that when a normal mechanical stress is exerted on the surface of the second polymeric layer intended to be in contact with the contact element, the volume of the through-cavity varies so as to modify the capacitance of the capacitor
Data Source
AI summary
The present invention relates to a device for locally measuring a normal mechanical stress exerted by a contact element, said device comprising:—a substrate comprising, over at least a part of its surface, at least one electrically conductive layer, called the lower electrode,—a first electrically insulating polymeric layer having a thickness of between 1 μm and 500 μm and comprising at least one through-cavity, the first polymeric layer being arranged on the substrate,—a structure arranged on the first polymeric layer, the structure comprising the following successive layers.