Piezoelectric Stack Electrode Segmentation for Stress Relief
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Solution Overview
Problem
Existing measuring element stacks for forces or pressures using piezoelectric crystal elements face issues with stress and material weakening due to fixed connections and notch-like chamfers, leading to potential detachment at high temperatures and breakage under high loads.
Innovation Solution
The solution involves dividing each crystal element's side surface electrodes into smaller edge and larger main electrodes, with insulating areas to form flat, plane-parallel support surfaces, eliminating the need for notched chamfers and allowing for a more robust connection without soldering or bonding, and using a method that allows for rough initial dimensions with machining to compensate for length differences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If fixed connections (bonding, soldering, thermocompression) are used to connect reference electrodes between adjacent crystal elements, then electrical connection is achieved, but stresses occur within the measuring element stack leading to detachment of reference electrodes at high temperatures
Solution Approach 1:
The patent removes the harmful fixed connections (bonding, soldering, thermocompression) between reference electrodes and crystal elements. Instead, the reference electrodes are designed to contact only the edge electrodes of adjacent crystal elements, eliminating the stress-causing fixed connections while maintaining electrical functionality.
Solution Approach 2:
The reference electrodes are segmented into multiple smaller electrodes that contact only the edge electrodes of adjacent crystal elements. This segmentation distributes the electrical connection points and reduces the stress concentration that would occur with a single fixed connection across the entire electrode surface.
2Reliability
If notch-like chamfers are applied at the transition from side face to front face to insulate adjacent reference electrodes, then charge collection is enabled, but material weakening occurs leading to breakage of crystal elements under high loads or rapid load changes
Solution Approach 1:
The patent removes the harmful notch-like chamfers from the crystal element geometry. Instead of creating physical indentations that weaken the structure, the insulation between adjacent reference electrodes is achieved through the natural geometry of the edge electrodes and the application of force, which causes charges to accumulate at specific locations without requiring structural modifications.
Solution Approach 2:
The patent creates local charge accumulation zones at the edges of the crystal elements where the force is applied, without modifying the overall geometry of the crystal elements. The edge electrodes are positioned to contact only these local charge accumulation areas, providing insulation between adjacent reference electrodes while maintaining the full structural strength of the crystal elements.
3Manufacturing precision
If individual crystal elements are precisely machined to exact dimensions before coating, then manufacturing precision is achieved, but the manufacturing process becomes complex and time-consuming
Solution Approach 1:
The patent performs the precise machining operation after the crystal elements have been coated with their respective electrodes. This allows the crystal elements to be initially cut with rough dimensions, coated with electrodes, and then precisely machined together as an assembly. The edge electrodes serve as reference surfaces for the joint machining operation, ensuring precise alignment and dimensional accuracy without requiring each individual crystal element to be precisely machined before coating.
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 design enhances the stack's resistance to high temperatures and high forces, prevents material weakening, and simplifies the manufacturing process while maintaining measurement accuracy and structural integrity.
Implementation Method 1
a measuring element stack for measuring forces or pressures made up of a plurality of piezoelectric crystal elements which are stacked using the transverse piezo effect
Data Source
Figure 1
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AI summary
A stack of measuring elements (10) for measuring forces or pressures is presented, consisting of several piezoelectric crystal elements (11) which are stacked using the transverse piezoelectric effect with opposite electrical polarization and have discharge electrodes (12) on their side surfaces (13), wherein first and second end-face electrodes (16, 17) are arranged on opposite first and second end faces (14, 15) which serve to introduce the force and are essentially normal to the side surfaces (13).Each drain electrode (12) is divided by an electrically insulating area (20) into a smaller edge electrode (18) adjacent to one of the two end faces (14, 15) and a larger main electrode (19), wherein one of the main electrodes (19) of the crystal element (11) is adjacent to its first end face (14) and contacts the first end-face electrode (16) and the other main electrode (19) is adjacent to its second end face (15) and contacts the second end-face electrode (17) and wherein the edge electrodes (18) of adjacent drain electrodes (12) are in contact with each other.