Dual Mode BAW Gyroscope Gap Change Mitigation
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Solution Overview
Problem
Bulk acoustic wave (BAW) gyroscopes are sensitive to changes in air gaps due to external stresses like thermal gradients and mechanical stress, which affect their sensitivity and zero-rate offset, making them vulnerable to manufacturing variations and environmental factors.
Innovation Solution
A BAW gyroscope is designed to operate with two disparate resonant modes, a fundamental mode and a compound mode, using the same set of drive and sense electrodes, where the fundamental mode is differential and the compound mode is common-mode, allowing for gap change mitigation by exploiting polarity differences to reduce the impact of gap changes on offset.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If narrow air gaps are used to efficiently actuate high frequency mechanical modes, then actuation efficiency is improved, but sensitivity to gap changes increases
Solution Approach 1:
The patent changes the operating parameters by utilizing two different resonant modes (fundamental mode at frequency f1 and compound mode at frequency f2) instead of a single mode. This allows the system to operate with narrow air gaps for efficient actuation while compensating for gap changes through mode combination, thereby resolving the contradiction between actuation efficiency and reliability.
Solution Approach 2:
The patent combines signals from two different resonant modes (fundamental and compound modes) to create a composite output signal. This composite approach allows the system to maintain the benefits of narrow air gap actuation while reducing sensitivity to gap changes, as the combined signal provides redundancy and compensation for manufacturing variations.
2Use of energy by moving object
If narrow air gaps are used, then high frequency mechanical modes can be actuated efficiently, but manufacturing precision requirements increase
Solution Approach 1:
By operating at two different resonant frequencies (fundamental mode f1 and compound mode f2), the system can tolerate larger variations in gap dimensions. The dual-mode operation provides redundancy that compensates for manufacturing tolerances, allowing narrow air gaps to be used for efficient actuation without excessively tight manufacturing precision requirements.
Solution Approach 2:
The combination of fundamental and compound mode signals creates a composite measurement that is less sensitive to manufacturing variations. This composite approach allows the use of narrow air gaps for efficient actuation while reducing the impact of gap dimension imperfections on overall performance.
3Reliability
If gap changes occur due to external stresses, then the gyroscope remains operational, but sensitivity and zero-rate offset are affected
Solution Approach 1:
The patent utilizes two different resonant modes with different sensitivities to gap changes. By operating at fundamental mode frequency f1 and compound mode frequency f2, the system can detect and compensate for sensitivity and zero-rate offset changes caused by gap variations, maintaining measurement precision while remaining operational under external stresses.
Solution Approach 2:
The combination of signals from fundamental and compound modes creates a composite output that compensates for gap change effects. Since the two modes respond differently to gap variations, their combination allows the system to maintain accurate sensitivity and zero-rate offset measurements even when gap changes occur due to thermal gradients or mechanical stress.
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 reduces the impact of gap changes on the gyroscope's rate output by using a weighted sum of the sensed modes, improving stability and accuracy across various operating conditions.
Implementation Method 1
Electrostatically actuated BAW gyroscopes typically utilize narrow air gaps (approximately around a few hundred nanometers) to efficiently actuate high frequency mechanical modes
Implementation Method 2
When the sensor experiences external rotation, energy couples from the driven mode of vibration to the orthogonal mode via the Coriolis force
Data Source
AI summary
A BAW gyroscope is configured to operate with two pairs of orthogonal modes instead of a single pair in order to mitigate the impact of changes in gaps (e.g., introduced from external stresses such as thermal gradients, external shocks, mechanical stress/torque, etc.). Specifically, the BAW gyroscope resonator is configured to be simultaneously driven to resonate with a two disparate resonant modes (referred to herein as the “fundamental” mode and the “compound” mode), with the same set of drive electrodes used to drive both resonant modes (i.e., all of the drive electrodes are used to drive the two drive modes). When the sensor experiences external rotation, energy couples from the driven modes of vibration to two corresponding orthogonal sense modes via the Coriolis force. The same set of sense electrodes is used to sense both sense modes (i.e., all of the sense electrodes are used to sense the two sense modes). The fundamental mode is differential with respect to the electrodes, while the compound mode is seen as common-mode with respect to the electrodes. Thus, differential gap change will impact offset of rate measured with the fundamental mode only, while common-mode gap change will impact offset of rate measured with the compound mode only.