Angular Rate Sensor Ageing Stabilization via Capacitance Matching
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Solution Overview
Problem
MEMS angular velocity sensors using PZT transducers face limitations due to ageing and temperature drifts, leading to gain variations and phase accuracy issues, which restrict their use to low-performance applications with short timescale stability, such as in GPS aided navigation systems.
Innovation Solution
The design incorporates primary and secondary sensor elements with different volumes of material, where the primary element is smaller and includes extra padding capacitance to match capacitances between channels, minimizing the impact of material deterioration on gain and stabilizing the sensor against ageing and hysteresis effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If PZT transducers are used to achieve high signal levels and good signal-to-noise ratio, then the sensor performance is improved, but ageing and temperature drifts cause gain variations and phase accuracy issues
Solution Approach 1:
The patent changes the physical parameters of the PZT transducers by creating asymmetric volumes between primary and secondary elements, and adjusting capacitance values to achieve frequency matching. This parameter optimization reduces the impact of ageing and temperature drifts on gain variations and phase accuracy, thereby improving reliability while maintaining high signal-to-noise ratio performance
2Measurement precision
If PZT transducer volume is increased to improve signal level, then signal to noise ratio is improved, but capacitance mismatch between primary and secondary channels increases
Solution Approach 1:
The patent applies local quality by making the primary and secondary PZT transducers asymmetric in volume while compensating with additional capacitance in the primary channel. This localized capacitance adjustment ensures that despite different volumes and signal levels, the capacitances are matched between channels, eliminating quadrature errors while maintaining high signal levels
3Reliability
If temperature compensation is added to correct thermal instabilities, then temperature drift is reduced, but device complexity increases
Solution Approach 1:
The patent implements self-service by designing the sensor with inherently symmetric capacitance characteristics through optimized PZT transducer geometry and matching. This self-compensating design eliminates the need for external temperature compensation systems, achieving temperature stability while maintaining simple device architecture
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 effectively stabilizes the scale factor of the gyroscope against ageing and hysteresis, ensuring improved accuracy and reliability by matching the capacitances and gains between primary and secondary channels, thereby overcoming the limitations of PZT transducers.
Implementation Method 1
Typically the MEMS ring type structures are formed from crystalline silicon and incorporate transducers formed from Lead Zirconate Titanate (PZT) materials
Implementation Method 2
angular velocity sensors incorporating a MEMS type ring are known... for detecting turning rate, linear acceleration and angular acceleration. Turning rate is sensed by detecting vibrations coupled by Coriolis forces
Implementation Method 3
the primary channel comprising primary driver means for initiating and maintaining resonant oscillations in the primary sensor elements
Data Source
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AI summary
An angular velocity sensor is described with improved ageing and hysteresis properties. The sensor may be of a ring type driven by a driver circuit, the sensor further comprising primary and secondary portions having corresponding signal pickoffs. The gain of the primary pickoff signal and the capacitance of the primary portions of the sensor are controlled relative to the gain of the secondary pickoff and the capacitance of the secondary portions of the sensor. Control electronics is provided that enables matching of the relative signals from the respective channels. In this way, temperature hysteresis and ageing effects of materials used in forming the sensor are overcome.