Flexible Strain Gauge with Resistive Layer Cuts for Cross-Sensitivity Control
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Solution Overview
Problem
Conventional strain gauges face issues with cross-sensitivity, relaxation, and temperature coefficient, which affect their accuracy and reliability in measuring mechanical parameters, particularly in stress analysis and temperature variations.
Innovation Solution
A strain gauge with a flexible substrate and a resistive layer that includes a measuring resistor with a conductor track, featuring strategically placed cuts or incisions to control strain transmission and resistance changes, allowing for adjustable sensitivity and reduced creep behavior.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a layer resistor with carbon-containing material and conductive clusters is used, then the k-factor is increased to more than 20, but the cross-sensitivity increases to up to 50% of the sensitivity in the longitudinal direction
Solution Approach 1:
The resistive layer is segmented into multiple conductor tracks arranged in a grid pattern, where each track can independently respond to strain in different directions. This segmentation allows the longitudinal and transverse sensitivity to be decoupled and controlled separately through the grid configuration.
Solution Approach 2:
Different regions of the resistive layer are assigned different functional properties through the grid pattern. The conductor tracks are oriented to provide high sensitivity in the longitudinal direction while the grid structure limits transverse sensitivity, creating local quality variations that achieve directional selectivity.
2Object-affected harmful factors
If conventional metal foil strain gauges are used, then the cross-sensitivity is negligible, but the k-factor is limited to 2
Solution Approach 1:
The patent uses a composite resistive layer combining carbon-containing material with conductive clusters (such as metal particles or carbon aggregates). This composite structure provides both the high k-factor needed for sensitivity and the grid pattern configuration that suppresses cross-sensitivity, achieving a combination of properties not available in conventional metal foils.
3Reliability
If the elastic element is subjected to constant load and constant ambient conditions, then the sensor signal should remain stable, but the elastic after-effect causes continuous change in the sensor signal over time
Solution Approach 1:
The strain gauge pattern is designed with preliminary geometric features (such as cuts or incisions in the adhesive layer) that pre-compensate for the elastic after-effect. These geometric modifications create a relaxation effect that opposes the elastic after-effect, thereby stabilizing the sensor signal over time under constant load conditions.
4Temperature
If the temperature changes, then the elastic element dimensions change thermally, but this causes deformation of the strain gauge even without external force, affecting measurement accuracy
Solution Approach 1:
The patent modifies geometric parameters of the strain gauge structure, specifically introducing cuts or incisions in the adhesive layer that change the thermal expansion characteristics. These parameter changes allow the strain gauge to better accommodate thermal dimensional changes of the elastic element, reducing spurious deformation signals during temperature variations.
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 solution minimizes cross-sensitivity and temperature coefficient, enhancing the accuracy and reliability of strain gauge measurements by controlling strain transmission and resistance changes, thereby reducing errors due to relaxation and temperature variations.
Implementation Method 1
The specific resistance of the resistive layer is dependent on an elongation of the resistive layer and with the resistive layer exhibits a change in resistivity both when stretched in a longitudinal direction and when stretched in a transverse direction perpendicular thereto
Implementation Method 2
The conductive material, for example nickel, forms clusters in the layer, which are separated from one another by carbon
Data Source
Figure 1~2
Figure 3~4
Figure 5a~5b
AI summary
The invention relates to a strain gauge (10) comprising a flexible substrate (12) and a resistance layer (14) which is arranged on the flexible substrate. At least one measuring resistor (18) with a conductor track (15), which comprises at least one straight conductor track section (40) and/or at least one curved conductor track section (42), is formed in the resistance layer by structuring the resistance layer, wherein the specific resistance of the resistance layer is based on an elongation in the longitudinal direction (34) and an elongation in a transverse direction (36) perpendicularly thereto. The strain gauge has at least one cutout (28) in the shape of a thinned region or at least one incision (30), and the at least one cutout is arranged within the at least one conductor track section (40, 42) or at a distance from the at least one conductor track section, said distance being smaller than ten times the thickness (D) of the flexible substrate. The depth (d) of the at least one cutout is at least 1/100 the width (B) of the at least one conductor track section when seen from the side on which the resistance layer is arranged. The invention additionally relates to sensor elements comprising at least one such strain gauge, to a method for adjusting the creep behavior of such sensor elements, to a method for minimizing the temperature coefficient of a measuring resistor of such sensor elements, and to a method for minimizing the transverse sensitivity of such sensor elements.