| Metadata | Details |
|---|
| Publication Date | 2022-03-29 |
| Journal | Sensors |
| Authors | Zhipeng Li, Xu Meng, Bonan Wang, Chao Zhang |
| Institutions | Northeast Forestry University |
| Citations | 8 |
| Analysis | Full AI Review Included |
- High-Frequency SAW Torque Sensor: A novel three-dimensional Finite Element Analysis (FEA) model is proposed for a Surface Acoustic Wave (SAW) torque sensor utilizing a high-velocity multilayer structure (IDT/128° Y-X LiNbO3/Diamond/Si(100)).
- Performance Leap: The design achieves a high characteristic frequency near 960 MHz, significantly exceeding traditional quartz-based SAW sensors (~433 MHz), aligning with 5G technology requirements.
- Small Shaft Compatibility: The new mechanical structure is optimized for small diameter torsion bars (d = 10 mm), overcoming installation limitations of traditional designs.
- Structural Integrity Improvement: The new sensor structure reduces surface shear stress by 17% compared to conventional cutting-plane designs, enhancing the stability and safety of the axle body operation.
- Optimal Material Configuration: Simulation identified optimal film thicknesses for maximum performance: LiNbO3 at 0.3λ (1.2 ”m) and Diamond at 0.1λ (0.4 ”m), yielding a maximum electromechanical coupling coefficient (K2) of 0.105.
- High Quality Factor: The multilayer resonator demonstrated a high mechanical quality factor (Qm) of 8370, crucial for ensuring long wireless transmission distance between the sensor and the reader.
- Excellent Linearity: The sensor model exhibited excellent strain linearity and a predictable frequency output curve across the full working range of ±40 Nm.
| Parameter | Value | Unit | Context |
|---|
| Multilayer Structure | IDT/LiNbO3/Diamond/Si(100) | - | Layer stack composition |
| Characteristic Frequency (Resonant) | 959.6 | MHz | S11 parameter peak frequency |
| Mechanical Quality Factor (Qm) | 8370 | - | Under initial structural parameters |
| Maximum Electromechanical Coupling (K2) | 0.105 | - | Achieved at optimal film thicknesses |
| Optimal LiNbO3 Thickness (hLN) | 0.3λ (1.2) | ”m | For maximum K2 |
| Optimal Diamond Thickness (hdia) | 0.1λ (0.4) | ”m | For maximum K2 |
| Working Wavelength (λ) | 4 | ”m | SAW device design parameter |
| Torsion Bar Diameter (D) | 10 | mm | Flexible shaft size |
| Full Torque Range | ±40 | Nm | Simulated operating range |
| S-Parameter (S11) Amplitude | -20.5 | dB | Reflection coefficient at 959.6 MHz |
| Maximum Strain (40 Nm) | 6.53 x 10-5 | - | Measured on SAWR1 (compression) |
| Maximum Deformation (40 Nm) | 0.03 x 10-3 | mm | Total displacement on flexible axis |
| Shear Stress Reduction (New vs. Traditional) | 17 | % | Improvement in axle body stability |
| LiNbO3 Density (Ï) | 4700 | kg/m3 | 128° Y-X cut piezoelectric substrate |
| Diamond Youngâs Modulus (E) | 105 x 1010 | Pa | High sound velocity layer |
- Finite Element Modeling (FEM): COMSOL Multiphysics 5.6 was used to establish a 2D model of the multi-layer SAW resonator (IDT/LiNbO3/Diamond/Si(100)) and a 3D model of the complete torque sensor assembly.
- Material Definition: Comprehensive material parameters (density, relative dielectric constant, elastic matrix, coupling matrix) for Aluminum (IDT), 128° Y-X LiNbO3, Diamond, and Si(100) were input into the FEA model.
- Boundary Conditions: Periodic boundary conditions were applied to the IDT structure. A Perfectly Matched Layer (PML) was used for sound absorption. Electrical excitation was set using alternating ±1 V potentials on the IDT fingers.
- Propagation Analysis: The effects of varying LiNbO3 and Diamond film thicknesses (hLN and hdia) on key SAW characteristics were analyzed, including resonant/anti-resonant frequency, electromechanical coupling coefficient (K2), S-parameter (S11), and mechanical quality factor (Qm).
- Torque Application Simulation: The 3D sensor model (10 mm shaft) was subjected to external torque (±40 Nm). One end of the shaft was fixed, and force resistance was applied to the other.
- Strain Measurement: The resulting mechanical strain (shape variable) on the two differentially arranged SAW resonators (SAWR1 and SAWR2, oriented at ±45°) was calculated and analyzed for linearity and magnitude.
- Frequency Shift Correlation: The calculated strain values were introduced back into the multi-layer SAW resonator FEA model to determine the corresponding shift in resonant frequency, establishing the final torque-frequency output relationship.
- High-Frequency Communication (5G/6G): The high operating frequency (960 MHz) makes the sensor suitable for integration into next-generation wireless communication systems requiring high-frequency passive devices.
- Automotive and Transportation: Essential for measuring steering torque in Electric Power Steering (EPS) systems, particularly those utilizing small-diameter flexible shafts.
- Industrial Robotics and Automation: Used for precise, non-contact torque monitoring in compact robotic joints, high-speed spindles, and automated machinery where space is limited.
- Condition Monitoring: Passive, wireless sensing capabilities enable remote monitoring of rotating machinery health in harsh environments (high temperature, high vibration) due to the robust Diamond/Si substrate.
- Advanced Sensor Development: The methodology provides a foundation for developing other high-performance, layered SAW sensors (e.g., temperature, humidity, acceleration) by leveraging the high sound velocity and coupling characteristics of the LiNbO3/Diamond stack.
View Original Abstract
A three-dimensional finite element analysis model of surface acoustic wave (SAW) torque sensor based on multilayer structure is proposed in this paper. Compared with the traditional saw torque sensor with quartz as piezoelectric substrate, the SAW torque sensor with multilayer structure has the advantages of fast propagation speed and high characteristic frequency. It is a very promising torque sensor, but there is very little related research. In order to successfully develop the sensor, it is essential to understand the propagation characteristics and torque sensing mode of SAW in multilayer structure. Therefore, in this study, we first established a multi-layered finite element analysis model of SAW device based on IDT/128° Y-X lithium niobate/diamond/Si (100). Then, the effects of different film thicknesses on the characteristic frequency, electromechanical coupling coefficient, s parameter, and mechanical quality factor of SAW device without changing the wavelength are analyzed. Then, based on the finite element analysis, a three-dimensional research model of a new SAW torque sensor suitable for small diameter torsion bar (d = 10 mm) is established, and the relationship between saw device deformation and torque under the condition of small torque (±40 Nm) is tested. The shape variable is introduced into the finite element analysis model of multi-layer SAW device. Finally, the relationship between saw torque sensor with multi-layer structure and torque is established by using the deformation relationship, which shows the perfect curve of sensor performance.
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