Wireless Passive RF Strain Sensors Using Rigid Substrates
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Solution Overview
Problem
Conventional strain sensors are prone to deformation and fatigue, limiting their long-term performance and suitability for structural health monitoring applications, and often require physical connections that are susceptible to corrosion and damage.
Innovation Solution
Multi-layer strain sensors with rigid substrates and insulating interlayers, such as elastomers or air, that resonate electromagnetically to detect strain without deforming, allowing for wireless monitoring and extended fatigue life.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional resistive metal foil strain gauge sensors are used, then the sensors are low-cost and easy to install, but they require a physical connection between the sensing element and the interrogation unit which is prone to corrosion and fracture
Solution Approach 1:
The patent replaces the mechanical/physical connection system with an electromagnetic field-based wireless sensing system. The sensing element uses electromagnetic coupling to transmit strain information without physical contact to the interrogation unit, eliminating the physical connection that is prone to corrosion and fracture while maintaining ease of installation.
Solution Approach 2:
The patent introduces an electromagnetic field as an intermediary between the sensing element and the interrogation unit. This electromagnetic field serves as a mediator that transfers information without requiring direct physical contact, thereby improving reliability while maintaining ease of installation.
2Measurement precision
If deformable metallic sensing elements are used, then the sensors can detect strain through physical deformation, but the fatigue life of the metallic elements limits long-term performance
Solution Approach 1:
The patent replaces the mechanical deformation-based sensing mechanism with an electromagnetic resonance-based mechanism. Instead of relying on metallic elements to physically deform and fatigue, the sensing element uses electromagnetic resonance frequency shifts to detect strain, eliminating the fatigue life limitation while maintaining strain detection precision.
Solution Approach 2:
The patent changes the sensing mechanism from measuring physical deformation of metallic elements to measuring electromagnetic resonance frequency shifts. This parameter change from mechanical displacement to electromagnetic frequency allows for indefinite operational life while maintaining measurement precision.
3Reliability
If wireless sensors are implemented, then physical connection issues are eliminated, but conventional resistive or capacitive strain gauges cannot operate without a clear line of sight or physical connection
Solution Approach 1:
The patent uses electromagnetic fields as an intermediary that can penetrate obstacles and operate without clear line of sight. The electromagnetic coupling between the sensing element and interrogation unit allows wireless operation in environments where conventional wireless sensors would fail, providing both reliability and adaptability.
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 sensors provide reliable, long-term strain measurement capabilities suitable for structures like bridges and aircraft, with improved resistance to deformation and the ability to detect cracks wirelessly, enhancing structural health monitoring.
Implementation Method 1
The sensing layers are coupled together electromagnetically (i.e., capacitively and/or inductively) to form a structure that resonates at a resonance frequency that depends on the relative displacement between the first and second sensing layers
Implementation Method 2
form a structure that resonates at a resonance frequency that depends on the relative displacement between the first and second sensing layers
Implementation Method 3
The insulating interlayer can be a flexible elastomer or other suitable material... tensile and compressive loads cause the interlayer to deform. Unlike the sensing layers, which are typically metallic, the interlayer can be made of an elastomer or other insulating material capable of undergoing millions of deformation cycles before failure
Data Source
AI summary
Wireless strain and displacement sensors wirelessly monitor structural health and integrity, and are made by printing inductor-interdigital capacitor sensing circuits on a variety of substrates, including ceramic substrates, with thermally processable conductive inks. Sensors of the invention can be employed to detect strain and displacement of civil structures, such as bridges and buildings. The sensors include sensing elements that are mounted or printed on stiff, inflexible substrates, which prevent the sensing elements from bending, stretching, or otherwise warping when the sensor is strained. An interlayer between the sensing elements allows the sensing elements to move with respect to each other during application of strain. Thus, strain causes the sensing elements to move but not to deform, causing changes in sensor resonance that can be detected through wireless radio-frequency interrogation. Because the sensing elements do not change shape when under strain, the sensor can undergo millions of measurement cycles before breaking.