SAW Sensor Strain-Temperature Decoupling via Local Fixation
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Solution Overview
Problem
Conventional surface acoustic wave (SAW) sensors face challenges in simultaneously measuring strain and temperature using a single device, as strain-induced frequency changes are masked by temperature changes, requiring multiple SAW devices and complicating mounting and signal processing.
Innovation Solution
A SAW sensor design featuring a substrate with a propagation portion fixed to the measurement subject and electrodes not fixed, allowing strain to be measured through phase changes while temperature is measured through resonant frequency changes, using a single SAW device by isolating strain effects from temperature effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single SAW device is used to measure both strain and temperature, then device complexity is reduced, but measurement precision deteriorates because strain-induced frequency changes are masked by temperature changes
Solution Approach 1:
The SAW device is segmented into three distinct functional regions: a drive electrode region, a propagation portion, and a reflector region. By fixing only the propagation portion to the measurement subject while leaving the electrodes unfixed, the device separates the measurement of strain (via phase changes in the propagation portion) from temperature effects (which affect the entire device uniformly), enabling simultaneous measurement with a single device.
Solution Approach 2:
Different regions of the SAW device are given different fixation properties: the propagation portion is fixed to the measurement subject to experience strain, while the electrodes are left unfixed to avoid strain interference. This local differentiation allows the device to selectively measure strain through phase changes while remaining insensitive to strain-induced frequency changes at the electrode regions.
2Measurement precision
If multiple SAW devices are used to distinguish strain and temperature effects, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The single SAW device is designed to perform multiple measurement functions simultaneously. By configuring the propagation portion to be fixed while electrodes remain unfixed, the device can measure both strain (through phase changes in the propagation portion) and temperature (through resonant frequency changes of the entire device), eliminating the need for multiple separate devices.
Solution Approach 2:
The invention adds a dimensional distinction in the fixation state: the propagation portion is fixed in position to the measurement subject, while the electrodes are left free. This creates a gradient in fixation rigidity along the device structure, allowing differential response to strain and temperature stimuli within a single device architecture.
3Stability of the object's composition
If electrodes are fixed to the measurement subject, then structural stability is improved, but measurement precision deteriorates because strain affects resonant frequency
Solution Approach 1:
The fixation property is made local rather than uniform: only the propagation portion is fixed to the measurement subject to provide structural stability, while the electrodes are left unfixed to avoid experiencing strain. This localized fixation strategy maintains the necessary structural integrity for SAW propagation while preventing strain-induced frequency changes at the electrode regions.
Solution Approach 2:
The device is segmented into fixed and unfixed regions. The propagation portion is fixed to ensure structural stability and proper SAW transmission, while the electrodes are separated into an unfixed region. This segmentation allows each part to fulfill its specific function without interference from strain effects.
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 simultaneous measurement of strain and temperature using a single SAW device, simplifying the mounting process and reducing signal processing complexity.
Implementation Method 1
When an excitation signal (burst signal) corresponding to a resonant frequency of the drive electrode is transmitted from the oscillation circuit, an electrical signal is converted to a mechanical oscillation by the drive electrode. Then, a SAW is excited on the surface of the piezoelectric substrate.
Implementation Method 2
The SAW excited by the drive electrode is transmitted along a propagation portion on the surface of the piezoelectric substrate, and is reflected by the reflector.
Implementation Method 3
The reflected SAW is converted to an electrical signal by the drive electrode, and the converted electrical signal is outputted toward the phase detection circuit.
Implementation Method 4
a phase of the SAW outputted from the SAW device is changed by an electrical or mechanical characteristic change of the propagation portion. Therefore, a physical quantity to be measured can be detected by the phase.
Implementation Method 5
the resonant frequency of the SAW is significantly changed according to a temperature change. Therefore, at least two SAW devices are used so as to reduce the resonant frequency change generated by the temperature change
Implementation Method 6
when a strain is generated in the propagation portion of the SAW device, the resonant frequency of the SAW device is changed according to the strain generated in the propagation portion
Data Source
AI summary
In a SAW device, a first area placed at a surface of a measurement subject directly under a propagation portion is fixed to the measurement subject, and a second area placed at the surface of the measurement subject directly under both a drive electrode and a reflector is not fixed to the measurement subject. When a strain is generated in the measurement subject, a strain is generated only in the propagation portion, and a phase change is generated in a surface acoustic wave reflected by the reflector. Because the phase change is hardly affected by a temperature change, the strain of the measurement subject can be measured based on the phase change. Because a resonant frequency of the SAW device is changed by the temperature change, but is not affected by the strain of the measurement subject, a temperature can be measured based on a resonant frequency change.