Piezoelectric SAW Sensor on Sapphire for Wireless High-Temperature Sensing
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Solution Overview
Problem
Conventional surface acoustic wave (SAW) devices are limited by an upper temperature boundary, often failing to operate reliably above 300°C, and require a power source or wired connections, which restricts their application in high-temperature environments.
Innovation Solution
A sensor device comprising a piezoelectric transducer attached to a non-piezoelectric base member, such as sapphire, with an excitation electrode that uses surface acoustic waves reflected from tags on the base member to measure physical parameters like temperature without a direct power source, enabling wireless operation and high-temperature functionality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If conventional surface acoustic wave devices are used, then they can detect physical parameters, but they are limited to operate below an upper temperature boundary (often below 300°C)
Solution Approach 1:
The patent employs a composite structure consisting of a piezoelectric material layer deposited on an acoustic substrate. This composite approach allows the device to leverage the piezoelectric effect for sensing while the substrate provides mechanical support and acoustic wave propagation, enabling operation at elevated temperatures beyond what conventional single-material SAW devices can achieve.
Solution Approach 2:
The invention changes the fundamental operating parameters of the sensing device by transitioning from conventional SAW devices to piezoelectric transducers that generate bulk acoustic waves. This parameter change in the acoustic wave type and generation mechanism enables the device to withstand higher temperatures, expanding the operating temperature range.
2Temperature
If piezoelectric transducers are used for high-temperature sensing, then operating temperature range is extended, but the device requires a power source or wired connections which restricts application in harsh environments
Solution Approach 1:
The piezoelectric transducer exhibits bidirectional functionality: it can be excited by an external signal to generate acoustic waves for sensing, and it can also be mechanically excited by the returning acoustic waves to generate an electrical response signal. This self-service capability eliminates the need for separate power sources or wired connections at the sensor location, simplifying the overall system architecture.
Solution Approach 2:
The same piezoelectric transducer serves dual functions as both the excitation source and the detection element. By applying an excitation signal, it generates bulk acoustic waves; when these waves reflect from the target and return to the transducer, it converts the mechanical wave energy back into an electrical signal. This multi-functionality removes the requirement for additional power supply components.
3Ease of operation
If discrete piezoelectric transducers are placed onto an acoustic substrate, then wireless operation is enabled, but the electromechanical coupling value may be insufficient for optimal performance
Solution Approach 1:
The patent optimizes the electromechanical coupling by carefully selecting and controlling the thickness parameter of the piezoelectric layer. By adjusting this geometric parameter, the device achieves strong coupling between the electrical excitation signal and the generated bulk acoustic waves, ensuring optimal sensing performance while maintaining wireless operation.
Solution Approach 2:
The composite structure of the piezoelectric material layer on the acoustic substrate is designed to maximize electromechanical coupling. The specific material combination and layer configuration enable efficient energy conversion between electrical and acoustic domains, achieving high coupling values necessary for sensitive detection while preserving the wireless operational advantage.
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 sensor device can operate reliably above 300°C, providing accurate temperature measurements and other physical parameter detection without the need for a power source or wired connections, enhancing its applicability in harsh environments.
Implementation Method 1
The primary function of an interdigital transducer is to convert electric signals to surface acoustic waves, SAW, by generating periodically distributed mechanical forces via piezoelectric effect in an input transducer
Implementation Method 2
The same principle is applied to the conversion of SAW back to electric signals in an output transducer
Implementation Method 3
The vibration of the piezoelectric member is transferred to the base member and propagates as a surface acoustic wave on the surface of the base member. The surface acoustic wave is reflected at the at least one acoustic wave reflecting tag
Data Source
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AI summary
Disclosed is a sensor device (1) comprising a piezoelectric transducer (3) and a base member (2). The piezoelectric transducer comprises a piezoelectric member with at least one excitation electrode (37, 38) connected to a first face thereof and having a thickness (h) between the first face and a second face. The piezoelectric transducer (3) is attached to a supporting face of the base member (2) with the second face of the piezoelectric transducer adjacent the supporting face of the base member. The base member comprises at least one acoustic wave reflecting tag (21) distant from the piezo-electric member.