SAW Strain Sensor Compliant Interface
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Solution Overview
Problem
Conventional surface acoustic wave (SAW) devices have a limited elastic strain limit of about 0.1%, making them inadequate for measuring larger strains in materials, as many materials can withstand strains exceeding 0.5% without plastic deformation.
Innovation Solution
The use of a compliant interface member with a lower modulus than the SAW device substrate to absorb and convert larger strains from the material-under-test into strains within the acceptable range for the SAW device, allowing for accurate measurement by modifying the stress and strain transfer characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional SAW device is used to measure strain, then the device structure is simple and operation is straightforward, but the measurement capability is limited to strains below 0.1% due to the elastic strain limit of the piezoelectric substrate
Solution Approach 1:
A compliant interface member is introduced as an intermediary between the material-under-test and the SAW device. This interface member has a lower elastic modulus than the piezoelectric substrate, allowing it to deform preferentially and transmit only a portion of the applied strain to the SAW device. This enables the SAW device to measure strains that would otherwise exceed its elastic limit, extending the measurement range from 0.1% to potentially 0.5% or higher while maintaining device simplicity.
2Reliability
If the SAW device is directly attached to the material-under-test, then the attachment is simple, but the device fails when the strain exceeds the substrate's elastic limit of about 0.1%
Solution Approach 1:
The compliant interface member serves as a protective intermediary that absorbs excessive strain through its own deformation. When strain is applied to the material-under-test, the interface member deforms first due to its lower stiffness, limiting the strain transmitted to the SAW device substrate to within its elastic limit. This protects the device from failure while maintaining a relatively simple attachment structure consisting of the interface member bonded between the material and device.
3Adaptability or versatility
If a compliant interface member is used to extend strain measurement range, then measurement capability is improved, but the device structure becomes more complex
Solution Approach 1:
The interface member changes the mechanical parameter (strain transmission ratio) between the material-under-test and the SAW device. By selecting materials with appropriate elastic moduli ratios, the system can be designed to transmit a controlled fraction of the applied strain to the sensor. This parameter-based approach allows a single device configuration to measure a wide range of strains by simply changing the interface material or geometry, rather than requiring multiple specialized devices.
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 the measurement of larger strains by limiting the strain on the SAW device to its elastic limit, effectively extending its measurement capabilities beyond its typical strain-to-failure property, while maintaining accuracy and avoiding device failure.
Implementation Method 1
The IDT 20 launches an incident surface acoustic wave (SAW) 28 onto the piezoelectric substrate 24 in response to the received interrogating signal
Implementation Method 2
an interdigital transducer (IDT) 20 disposed on a piezoelectric substrate 24
Implementation Method 3
The acoustic waves reflect from the reflector array back to the transducer where they are received and processed
Implementation Method 4
The IDT 20 receives and converts the reflected SAW 34 to an electrical signal
Data Source
AI summary
A strain sensor for determining a strain experienced by a body under test in response to forces exerted on the body-under-test. The strain sensor comprises an interface member mounted on a surface of the body-under-test and a SAW sensor mounted on a surface of the interface member. The strain in the body-under-test is translated to strain in the SAW sensor and determined by the SAW sensor. The strain in the SAW sensor is responsive to the strain in the body-under-test.