Tuning Fork Resonator Layout to Suppress Harmonic Oscillation
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Solution Overview
Problem
Existing piezoelectric resonators face challenges in miniaturization, as further reduction in size can lead to a decrease in the CI value ratio between the fundamental wave mode and the second harmonic mode, potentially allowing oscillation in the harmonic mode instead of the desired fundamental wave mode.
Innovation Solution
A resonator device with a tuning fork-shaped resonator element, where the vibrating arm and support arm are fixed via conductive adhesives, with specific dimensions and groove configurations to increase the CI value in the second harmonic mode, preventing oscillation in the harmonic mode by restraining antinodes and nodes of vibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the resonator size is miniaturized, then the device dimensions are reduced, but the CI value ratio between fundamental wave mode and second harmonic mode decreases
Solution Approach 1:
The patent applies local quality by creating a wide portion in the vibrating arm with different dimensional characteristics (larger length in second direction) compared to the arm portion. This localized structural variation modifies the vibration characteristics specifically in the region where it is needed, allowing the CI value ratio to be maintained at 1 or more even in miniaturized resonators with vibrating arm length of 1000 μm or less.
Solution Approach 2:
The patent changes specific geometric parameters of the vibrating arm structure, including the width Wa (30-75 μm), thickness T (110-150 μm), groove depths t1 and t2 with specific ratios to T, and the dimensions of the wide portion. By optimizing these parameters within specified ranges, the patent achieves miniaturization while maintaining the CI value ratio requirement.
2Volume of moving object
If the CI value in fundamental wave mode is reduced, then the resonator can be miniaturized, but the CI value in second harmonic mode also decreases
Solution Approach 1:
The wide portion structure creates a localized region with modified mechanical properties that selectively affects the second harmonic mode vibration. This local structural feature increases the CI value in the second harmonic mode relative to the fundamental wave mode, preventing harmful harmonic oscillation while allowing overall miniaturization of the resonator.
Solution Approach 2:
The patent introduces asymmetry by adding a wide portion to one side of the vibrating arm, creating an uneven distribution of mass and stiffness along the arm. This asymmetric structure modifies the vibration modes in a way that suppresses the second harmonic mode while maintaining the fundamental wave mode, thereby preventing harmonic oscillation in miniaturized devices.
3Volume of moving object
If the vibrating arm width is reduced, then the resonator is miniaturized, but the groove depth to width ratio becomes problematic
Solution Approach 1:
The patent specifies precise parameter ranges for the groove dimensions relative to the arm thickness T, with the depth ratio (t1+t2)/T constrained to 0.884-0.990 and the width ratio Wb/T constrained to 0.0056-0.0326. These normalized parameter relationships ensure manufacturability and consistent performance across miniaturized resonators, maintaining manufacturing precision even as overall size is reduced.
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 solution effectively increases the CI value in the second harmonic mode, ensuring the resonator oscillates in the fundamental wave mode, thereby preventing harmonic mode oscillation and achieving miniaturization while maintaining desired resonance frequencies.
Implementation Method 1
a base to which the resonator element is fixed via a conductive adhesive
Implementation Method 2
a piezoelectric resonator including a tuning fork type piezoelectric resonator element
Implementation Method 3
oscillation in the harmonic mode is prevented
Data Source
AI summary
A resonator device includes a resonator element, and a base to which the resonator element is fixed via a conductive adhesive. The resonator element includes a base portion, a vibrating arm that is coupled to the base portion and that extends in a first direction, and a support arm that is arranged with the vibrating arm in a second direction orthogonal to the first direction, that extends in the first direction, and that is fixed to the base by the conductive adhesive. 0.2×L1≤Da≤0.4×L1, in which a position at a base end of the support arm is P0, a central position of the conductive adhesive is Pa, and a length between P0 and Pa is Da in the first direction of the support arm.