Low Profile Shear Sensor Monolithic Flexure Beams
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Solution Overview
Problem
Existing shear stress measurement devices, particularly MEMS-based sensors, face limitations in size customization, cost, robustness, and brittleness, making them unsuitable for wide-range and field applications, while single-pivot sensors are prone to misalignment and high costs due to assembly requirements.
Innovation Solution
A low-profile shear-sensing unit with a monolithic construction using flexible, thick, and narrow flexure beams made from non-brittle materials, combined with an optical displacement sensor, allowing for large floating plates and high-resolution measurements, and fabricated using wire EDM for cost-effectiveness and customization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If MEMS-based shear stress sensors are used, then measurement precision and sensitivity are improved, but device complexity and manufacturing cost increase due to photolithography requirements
Solution Approach 1:
The patent replaces complex MEMS photolithography fabrication with wire electrical discharge machining (EDM), substituting a mechanical/electrical machining process for a complex semiconductor manufacturing process. This allows monolithic fabrication of the floating element and flexure beams without requiring cleanrooms, photolithography masks, or specialized MEMS equipment, thereby reducing device complexity while maintaining measurement precision.
2Measurement precision
If MEMS sensors are used, then measurement precision is improved, but ease of manufacture deteriorates due to limited wafer sizes and customization requirements
Solution Approach 1:
The patent enables easy customization by allowing continuous adjustment of geometric parameters (floating element size, flexure beam dimensions, thickness) through wire EDM programming rather than requiring new photolithography masks for each configuration. This parameter-based customization approach maintains measurement precision while dramatically improving ease of manufacture for different application requirements.
3Measurement precision
If silicon-based MEMS devices are used, then measurement precision is improved, but reliability deteriorates due to brittleness and susceptibility to damage
Solution Approach 1:
The patent employs aluminum or other ductile metals instead of brittle silicon, creating a composite-like structure where the monolithic metal body provides both the floating element and flexure beams. This material substitution maintains measurement precision through controlled elasticity while dramatically improving reliability by eliminating the brittleness and fragility inherent in silicon-based MEMS devices.
4Ease of manufacture
If single-pivot shear stress sensors are used, then ease of manufacture is improved through assembly of parts, but measurement precision deteriorates due to floating element misalignment
Solution Approach 1:
The patent merges the floating element and flexure beams into a single monolithic structure fabricated by wire EDM, eliminating the separate assembly step required in single-pivot sensors. This integration ensures perfect alignment between the floating element and pivot point, maintaining measurement precision while still allowing ease of manufacture through direct machining of the complete assembly from a single block of material.
5Ease of manufacture
If assembled shear sensors are used, then ease of manufacture is improved, but reliability deteriorates due to misalignment and increased cost
Solution Approach 1:
The patent combines multiple components (floating element, flexure beams, pivot point) into one monolithic piece machined by wire EDM, eliminating assembly operations entirely. This ensures perfect alignment accuracy while maintaining manufacturing flexibility through programmable wire paths that can create complex geometries from a single material block, thereby improving reliability without sacrificing ease of manufacture.
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 accurate and robust shear force measurement across various surfaces and environments with high resolution and flexibility, suitable for both laboratory and field tests, while minimizing space and cost, and accommodating different materials for durability.
Implementation Method 1
The plurality of flexure beams are shaped to deform in a direction along a plane of the floating plate
Implementation Method 2
a displacement sensor that reads the response
Data Source
AI summary
A low-profile shear-sensing unit includes a floating plate surrounded by a frame and a displacement sensor that measures in-plane movement of the floating plate. Covered with a surface sample, the floating plate is displaced by the friction drag (i.e., shear) on the surface caused by the flow of fluid and the in-plane displacement is measured by the displacement sensor. The shear force on the sample surface is then obtained by multiplying the measured displacement and the spring constant of the flexure beams, which suspend the floating plate. The floating plate and the flexure beams are formed out of one plate or substrate to achieve monolithic construction with a beam geometry that leads to a high-resolution measurement.