SAW Torque Sensor Resonator Layout for Higher Temperature Sensitivity
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Solution Overview
Problem
Existing SAW-based sensors for measuring torque and temperature have a significantly lower temperature sensitivity than theoretically predicted due to the finite thickness of the aluminum film, resulting in actual sensitivity of approximately 2.4 kHz/°C compared to the predicted 9 kHz/°C, affecting the accuracy of temperature measurements.
Innovation Solution
The SAW-based sensor uses a substrate with aluminum film thickness in the range of 160 nm to 240 nm, with SAW resonators inclined at specific angles, optimizing the h/λ ratio to improve temperature sensitivity and linearity, achieving an average sensitivity of 10 ppm/°C up to +150°C, and incorporating additional resonators for enhanced temperature and torque measurement redundancy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a finite thickness aluminum film is used for SAW resonators, then the device is manufacturable with practical electrode structure, but the temperature sensitivity is significantly reduced from theoretically predicted 9 kHz/°C to actual 2.4 kHz/°C
Solution Approach 1:
The patent applies parameter changes by optimizing the aluminum film thickness to a specific range (160-240 nm) and controlling the h/λ ratio (0.021-0.032) to restore temperature sensitivity. This involves changing the physical parameters of the aluminum film to achieve both manufacturability and improved temperature measurement capability, resolving the contradiction between practical fabrication and sensor performance.
2Reliability
If aluminum film thickness is increased for better electrode performance, then electrical connectivity is improved, but temperature sensitivity continues to deteriorate
Solution Approach 1:
The patent resolves this contradiction by identifying and implementing an optimal parameter range for aluminum film thickness (160-240 nm) that simultaneously satisfies both electrode reliability requirements and temperature sensitivity needs. This parameter optimization ensures adequate electrical connectivity while restoring the temperature sensitivity close to theoretical predictions.
3Reliability
If multiple SAW resonators are added for redundancy, then measurement reliability is improved, but device complexity and substrate area increase
Solution Approach 1:
The patent applies universality by designing SAW resonators that serve dual functions: torque measurement and temperature measurement. The same resonator structure and aluminum film configuration enable both measurement capabilities, eliminating the need for separate dedicated temperature sensors and reducing overall device complexity while maintaining measurement reliability.
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 optimized sensor design significantly enhances temperature sensitivity and measurement accuracy, providing a linear temperature characteristic and improved torque measurement reliability across a broader temperature range, while maintaining a high Q factor and minimizing substrate area.
Implementation Method 1
SAW based sensors for measuring both torque and temperature
Implementation Method 2
the Al film thickness has a finite value, with fabricated SAW Sensors, which have been publicly available, having an approximate Al film thickness of h=260 nm
Data Source
AI summary
A contactless SAW based torque and temperature sensor comprising a first (2) and second (3) SAW resonator provided on a substrate made of Y+34° cut of quartz. The first SAW resonator (2) has its principle axis inclined at +45° to the X-axis of the substrate, which, in use is either aligned with the longitudinal axis of the device who torque is to be measured or is perpendicular thereto, and the second SAW (3) has its principle axis inclined at −45° to the X-axis of the substrate. A third SAW (4) has its principle axis inclined at an angle of 30 degrees to the X-axis of the substrate. Each said SAW resonator (2,3,4) is formed by laying a film of aluminum on the substrate having a thickness (h) and the SAW resonators have an average operating wavelength λ where the ratio h/λ is in the range 0.021 to 0.032.