Shape-Memory Strain Sensor for Low-Hysteresis Body Motion Monitoring
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Solution Overview
Problem
Existing strain sensors for body movements are limited by low sensitivity, hysteresis, non-linearity, and inability to distinguish strain from pressure, and lack a compact, reliable system for long-term monitoring with strains greater than 5% to 8%.
Innovation Solution
A sensor element using a shape-memory alloy conductor with an insulating coating, embedded in an elastically deformable support, capable of measuring strains up to 15% with minimal interference, featuring a portable electronics unit for data processing and wireless transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If simple strain gauges and stick sensors are used, then the sensor structure is simple and easy to manufacture, but they are only suitable for small strains (less than 0.5%) and fail after a few cycles at large amplitudes
Solution Approach 1:
The patent uses a composite structure combining a conductive polymer material with specific mechanical properties (yield strength >100 MPa, elastic elongation >5%) with a flexible substrate. This composite approach allows the sensor to withstand large strains (>5%) and repeated cycling while maintaining structural integrity and electrical functionality, resolving the contradiction between simple manufacturing and reliability under large strain.
2Measurement precision
If highly elastic resistive strain sensors based on nanomaterials are used, then extensibility and sensitivity are improved, but they display nonlinear behavior and hysteresis
Solution Approach 1:
The patent changes the material parameter from conventional nanomaterial-based conductive layers to a conductive polymer material with specific mechanical properties (yield strength >100 MPa, elastic elongation >5%). This parameter change in material selection eliminates the nonlinear behavior and hysteresis inherent in nanomaterial-based sensors while maintaining high sensitivity and extensibility, achieving both measurement precision and stability.
3Stability of the object's composition
If capacitive sensors with highly compliant dielectric layers are used, then stretchability, linearity, and hysteresis properties are excellent, but sensitivity is very low
Solution Approach 1:
The patent employs a composite material system where a conductive polymer with high yield strength (>100 MPa) and elastic elongation (>5%) serves as both the sensing element and structural component. This composite approach achieves the linearity and low hysteresis of capacitive sensors while simultaneously providing the high sensitivity typically associated with resistive sensors, resolving the sensitivity deficiency of capacitive designs.
4Reliability
If carbon-based networks and nanoparticle networks are used as conductive materials, then elastic strain sensor performance is improved, but they exhibit quite high temperature sensitivity
Solution Approach 1:
The patent changes the conductive material from carbon-based networks and nanoparticle networks to a conductive polymer material with specific mechanical properties. This material substitution reduces temperature sensitivity while maintaining reliable strain sensing performance, as the polymer's electrical properties are less affected by temperature variations compared to carbon-based materials.
5Ease of operation
If the sensor signal under strain and applied pressure are strongly coupled, then pressure introduction occurs (by tight or stretched clothing or external contact), but the effects of strain and pressure become indistinguishable
Solution Approach 1:
The patent applies local quality by designing the sensor with anisotropic mechanical properties through the conductor's geometric configuration (wire- or strip-shaped conductor with specific orientation). The sensor is oriented and configured to primarily respond to strain in the direction of interest while being less sensitive to pressure from clothing or external contact, allowing strain and pressure effects to be distinguished through directional measurement.
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 reliable, high-sensitivity, low-hysteresis strain measurements with minimal pressure interference, allowing continuous monitoring of body movements with strains exceeding 10% and extended use without damage.
Implementation Method 1
The electrical conductor is made of a shape-memory metal, in particular a shape-memory alloy
Implementation Method 2
Changes in the microstructure lead to a change in electrical resistance upon strain
Data Source
AI summary
The invention relates to a sensor element for sensing stretching during a movement of a body part of a living being, which sensor element can be secured on the body part. The sensor element has at least one electrical wire-shaped or strip-shaped electrical conductor, which can be connected to an electrical voltage source, and a device, which is designed to determine the electrical current flowing through the conductor, the electrical voltage and/or the electrical resistance. The electrical conductor is made from a shape memory metal and has an electrically insulating coating on its surface, and by means of the coating can be adhesively secured to the skin of a body part or, connected to a resiliently deformable carrier element, can be secured to the surface of the body part or can be implanted under the skin surface.