Piezoelectric Power Generator Compressive Stress Reliability
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Solution Overview
Problem
Piezoelectric power-generating devices face challenges in achieving long-term reliability due to the fragility of ceramic materials under tensile stress, which can lead to cracks and reduced electric power generation, especially when designed for energy harvesting applications that eliminate batteries and wirings.
Innovation Solution
A power-generating device with a vibration plate made of heat-resistant stainless steel, featuring piezoelectric layers subjected to compressive stress through differential thermal expansion, preventing tensile stress and ensuring the layers remain intact during operation, thereby generating sufficient electric power for low-power wireless communication and sensor operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If larger widths of piezoelectric transducer vibrator and piezoelectric board are used, then electric power generation increases, but total device dimensions become too large
Solution Approach 1:
The patent changes the stress state parameter from tensile to compressive by applying pre-compressive stress to the piezoelectric board. This allows the use of thinner, smaller piezoelectric components while maintaining or improving power generation efficiency, thereby reducing device dimensions without sacrificing power output.
2Power
If larger attractive force of magnet and movable element is applied, then displacement amount of vibrator increases and electric power generation increases, but large force applied to piezoelectric board may produce cracks
Solution Approach 1:
The patent applies pre-compressive stress to the piezoelectric board before operation. This preliminary action creates a compressive stress state that counteracts the tensile stresses generated during vibration, preventing crack formation and ensuring long-term reliability while allowing larger displacement amplitudes for higher power generation.
Solution Approach 2:
The patent converts the potentially harmful tensile stress that could cause cracks into a beneficial compressive stress state. By pre-applying compressive stress, the piezoelectric board is protected from tensile damage during operation, and the compressive stress itself enhances piezoelectric power generation efficiency.
3Power
If piezoelectric board made of ceramic material is used, then piezoelectric constant is large, but material is fragile and may produce cracks under tensile stress
Solution Approach 1:
The patent changes the stress state parameter from tensile to compressive by applying pre-compressive stress. Since piezoelectric ceramic materials have higher strength under compressive stress than tensile stress, this parameter change allows the use of high piezoelectric constant ceramic materials while avoiding crack formation.
Solution Approach 2:
The patent applies pre-compressive stress as a cushioning measure before the piezoelectric board undergoes vibration. This beforehand cushioning creates a compressive stress reserve that protects the fragile ceramic material from tensile stress damage during operation, ensuring long-term reliability.
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 device achieves high reliability and efficient electric power generation by applying compressive stresses to the piezoelectric layers, preventing cracks and ensuring consistent performance over time, with electric work exceeding 714 µJ, sufficient for low-power applications.
Implementation Method 1
a power-generating device that changes mechanical energy to electric energy by using piezoelectric effect
Implementation Method 2
featuring piezoelectric layers subjected to compressive stress through differential thermal expansion
Data Source
Figure 1A~1B
Figure 2
Figure 3
AI summary
A power-generating device includes a vibration plate, a lower electrode on the vibration plate, a piezoelectric layer made of piezoelectric material on the lower electrode, and an upper electrode on the piezoelectric layer, a fixing member for supporting a fixed end of the vibration plate. The vibration plate applies compressive stress to the piezoelectric layer when the vibration plate does not vibrate. The power generating device is excellent in long-term reliability.