Piezoelectric Bimorph Switch Symmetrical Stack Depoling Prevention
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing piezoelectric bimorph switches face issues such as depoling due to electric fields not being applied in the same direction as the poling direction, high sensitivity to ambient temperatures, and residual stress gradients, leading to limited control over the initial gap and restoring forces, which affects switching performance and reliability.
Innovation Solution
A piezoelectric bimorph switch with a symmetrical layer stack where the electric field is always applied in the same direction as the poling direction of the piezoelectric layers, compensating for residual stress and thermal expansion coefficients, allowing for active opening and closing with increased contact forces and reduced sticking probability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If piezoelectric layers are driven against the poling direction with high electric field, then larger actuation force is achieved, but depoling occurs reducing reliability
Solution Approach 1:
The patent employs a symmetrical bimorph structure where two piezoelectric layers with opposite poling directions are bonded together. This symmetry allows the structure to experience equal and opposite stresses during actuation, preventing residual stress accumulation and depoling while maintaining high actuation forces. The symmetrical design ensures that neither layer is consistently driven against its poling direction.
Solution Approach 2:
The patent controls the electric field parameters by applying voltages that keep the electric field direction aligned with the poling direction of each piezoelectric layer. By carefully managing the voltage application timing and magnitude, the system achieves large actuation forces without exceeding the coercive field threshold that would cause depoling, thus maintaining reliability.
2Force
If initial gap is made smaller to increase contact forces, then switching performance improves, but capacitive coupling increases and restoring forces decrease
Solution Approach 1:
The patent applies a preliminary voltage to the piezoelectric layers before contact is made, causing the cantilever to deflect and actively open the switch. This preliminary action creates a larger initial gap that can be precisely controlled, allowing small gap sizes for high contact forces while maintaining adequate restoring forces and controlling capacitive coupling through the piezoelectric actuation.
Solution Approach 2:
The patent uses dynamic control of the piezoelectric actuation to actively adjust the initial gap and restoring forces. By applying voltages during operation, the system can dynamically optimize the gap size to achieve high contact forces while maintaining adequate restoring forces and controlling capacitive coupling, rather than relying on fixed mechanical preloading.
3Ease of manufacture
If residual stress gradient is present in the layers, then manufacturing is simplified, but bending moment increases affecting precision
Solution Approach 1:
The patent employs a symmetrical bimorph structure where residual stress gradients in the two piezoelectric layers counterbalance each other. The symmetrical design ensures that bending moments caused by residual stresses are equal and opposite, resulting in net zero bending moment. This allows simplified manufacturing with residual stress gradients while maintaining precise gap control.
4Adaptability or versatility
If thermal expansion coefficients differ across layers, then material selection is easier, but bending moment varies with temperature reducing stability
Solution Approach 1:
The patent uses a symmetrical bimorph structure where layers with different thermal expansion coefficients are arranged symmetrically. This symmetry causes thermal expansion effects to counterbalance each other, eliminating temperature-dependent bending moments. The design maintains switch stability across temperature variations while allowing flexible material selection for optimal electrical and mechanical properties.
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 enhances the switch's reliability by preventing depoling, maintaining low capacitive coupling, and increasing contact forces, while allowing for faster switching times and reduced adhesion issues, thus improving overall performance and lifespan.
Implementation Method 1
A piezoelectric bimorph switch for operating the MEMS, which switch comprises piezoelectric layers (121, 122), which piezoelectric layers form a symmetrical stack
Data Source
AI summary
The present invention relates to a piezoelectric bimorph switch, specifically a cantilever (single clamped beam) switch, which can be actively opened and closed. Piezoelectric bimorph switch are known from the prior art. Such a switch may be regarded as an actuator. Actuators are regarded as a subdivision of transducers. They are devices, which transform an input signal (mainly an electrical signal) into motion. Electrical motors, pneumatic actuators, hydraulic pistons, relays, comb drive, piezoelectric actuators, thermal bimorphs, Digital Micromirror Devices and electroactive polymers are some examples of such actuators. The switch of the invention comprises piezoelectric stack layers (121, 122), which form a symmetrical stack, wherein an electric field is always applied in the same direction as the poling direction of the piezoelectric layers.