Tilted Piezoresistive Sensor for Shear and Normal Force Measurement
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Solution Overview
Problem
Traditional force sensors can only measure compressive force and are unable to simultaneously measure shear force, which is a critical factor in conditions like diabetic foot complications and pressure ulcers, necessitating a sensor capable of detecting both components.
Innovation Solution
A force sensor design featuring a polymeric substrate with a tilt plane and metal piezoresistors that can measure both shear and compressive forces by utilizing a Wheatstone bridge circuit to differentiate between resistance changes caused by normal and shear forces, allowing for the calculation of pure shear and normal forces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If traditional force sensors are used, then the sensor structure is simple, but the sensor can only measure compressive force and cannot measure shear force
Solution Approach 1:
The sensor measures forces by segmenting the measurement into independent components: normal force is measured by piezoresistors on the base substrate, while shear force is measured by piezoresistors on the tilted interface. This segmentation allows simultaneous measurement of different force components using separate sensor elements arranged in a Wheatstone bridge configuration.
Solution Approach 2:
The invention introduces a tilted interface at a specific angle (e.g., 45 degrees) relative to the base substrate, adding a dimensional transformation to the measurement system. This tilt allows the same piezoresistive elements to respond to both normal and shear force components, effectively converting a unidirectional measurement capability into multidirectional measurement capability.
2Measurement precision
If a sensor measures both shear and compressive forces, then the diagnostic capability is improved, but the manufacturing complexity increases
Solution Approach 1:
The piezoresistive elements serve multiple functions: they measure both normal force and shear force components depending on their orientation and the applied load direction. The tilted interface structure enables the same basic sensor architecture to provide comprehensive force component measurement, eliminating the need for separate specialized sensors for different force types.
3Adaptability or versatility
If metal piezoresistors are deposited on a tilt plane, then shear force measurement is enabled, but the fabrication process becomes more complex
Solution Approach 1:
The tilted interface structure is fabricated in advance during the substrate processing stage, before the piezoresistive elements are deposited. This preliminary creation of the tilt geometry allows subsequent metal deposition to follow the pre-established angled surface, ensuring precise alignment and consistent measurement characteristics without requiring complex real-time deposition control.
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 measurement of both shear and compressive forces, facilitating advanced diagnostic tools for conditions like diabetic foot and pressure ulcers, improving predictive and preventive measures by providing comprehensive force mapping.
Implementation Method 1
at least two metal piezoresistors on the tilt plane
Data Source
AI summary
A force sensor includes a polymeric substrate including a cavity with a tilt plane, at least two metal piezoresistors on the tilt plane, and a contact pad connected to the metal piezoresistors. The tilt plane may include a measured interface of from 15° to 75°.