SAW Strain Sensor with Perpendicular Reflector Arrays
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Solution Overview
Problem
Existing surface acoustic wave (SAW) devices face challenges in accurately distinguishing between strain deformations caused by stress forces and those caused by temperature changes, as both types of deformations affect the reflected signal in similar ways, making it difficult to obtain precise strain measurements.
Innovation Solution
The use of multiple SAW sensors with strategically positioned reflector arrays and a specific coding scheme, combined with digital signal processing, allows for the differentiation between strain and temperature-induced effects by analyzing the time domain responses and creating a database of matched filters to correlate with real-world strain deformations, while the SAW sensors are mounted in a well to enhance bonding and accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single SAW sensor is used to measure strain, then the device complexity is low, but the measurement precision deteriorates because temperature and strain effects cannot be distinguished
Solution Approach 1:
The measurement function is segmented between two specialized sensors: a strain-sensitive SAW sensor with reflectors aligned in a first direction and a temperature-sensitive SAW sensor with reflectors aligned in a second direction perpendicular to the first. This segmentation allows each sensor to specialize in detecting specific physical quantities, enabling precise strain measurement by eliminating temperature interference.
Solution Approach 2:
The temperature-sensitive SAW sensor acts as an intermediary that measures temperature effects separately. Its output is used to compensate for temperature-induced phase shifts in the strain measurement, effectively mediating the interference between temperature and strain measurements and enabling accurate strain detection.
2Measurement precision
If multiple SAW sensors with different orientations are used to distinguish temperature and strain effects, then the measurement precision improves, but the device complexity increases
Solution Approach 1:
The system changes the orientation parameter of the reflector arrays in different sensors to create distinct measurement characteristics. By orienting reflectors in perpendicular directions, the sensors respond differently to temperature and strain, creating separable signal parameters that simplify the differentiation process through phase comparison.
Solution Approach 2:
The strain-sensitive and temperature-sensitive sensors are designed with asymmetric reflector orientations relative to the direction of applied strain. This asymmetry creates differential phase shift characteristics that allow straightforward mathematical separation of temperature and strain contributions from the combined measurements.
3Measurement precision
If SAW sensors are mounted directly on the surface, then the ease of manufacture is high, but the measurement precision deteriorates due to poor bonding and reduced accuracy
Solution Approach 1:
A recess (well) is pre-formed in the host structure at the desired measurement location before mounting the SAW sensor. This preliminary action creates a dedicated mounting cavity that ensures proper positioning and bonding surface area, thereby improving measurement accuracy without significantly complicating the manufacturing process.
Solution Approach 2:
The SAW sensor is nested within a recess in the host structure, with the sensor substrate fitting into the pre-formed well. This nesting arrangement maximizes the bonding interface between the sensor and host structure while maintaining a compact configuration, thereby improving strain transfer efficiency and measurement accuracy.
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
This approach enables more accurate and sensitive strain measurements by effectively separating temperature-induced effects from strain-induced effects, providing precise deformation data in multiple directions and improving the predictability of surface strain on the object.
Implementation Method 1
An interrogating signal comprises a radio frequency (RF) signal pulse transmitted by an RF transceiver. The interrogating signal is received by an antenna connected to an interdigital transducer (IDT) disposed on a piezoelectric substrate. The IDT launches an incident surface acoustic wave (SAW) onto the piezoelectric substrate in response to the received interrogating signal.
Implementation Method 2
The waves propagate on the surface of a material (referred to as a substrate and which may comprise lithium niobate, for example) to a reflector array.
Implementation Method 3
The acoustic waves reflect from the reflector array back to the transducer where they are received and processed.
Data Source
AI summary
A sensor system for determining deformation of an object subject to forces. The sensor system comprises an object upon which forces are exerted and a cavity within the object, a first substrate for supporting surface acoustic waves in an upper surface of the first substrate, the first substrate disposed in the cavity, a first surface acoustic wave transducer disposed on the upper surface and responsive to an interrogation signal for generating an incident surface acoustic wave in the upper surface, a first reflector array responsive to the incident surface acoustic wave for creating reflected surface acoustic waves on the upper surface, the reflected surface acoustic waves received by the transducer and having characteristics indicative of strain deformation of the object due to a force exerted on the object.