Piezoelectric Compliant Mechanism Energy Harvesters Excited Under Large Base Accelerations Xiaokun Ma* Susan Trolier-McKinstry† Christopher D. Rahn* *Department of Mechanical and Nuclear Engineering †Department of Materials Science and Engineering The Pennsylvania State University August 22 nd 2016 1/21
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PCM with optimal stiffness has most uniform strain
Linear Model Validation:Displacement & Strain
• Introduction
• Piezoelectric Compliant Mechanism (PCM) Under Small Base Excitation Review
• PCM Nonlinear Model
• PCM Under Large Base Excitation Results
• Conclusions
Outline
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• Maximum power is obtained under large base excitations• Linear model is only valid for small displacements• The compliant mechanism introduces a stretching effect under large excitations, which may enhance the
generated power
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Understanding Nonlinearity: The Key to High Power Harvester Design
Proof Mass Cantilever
PCM
𝒂𝒎𝒊𝒏 𝒂𝒎𝒂𝒙
Softening effect
Wide bandwidth harvests more energy
Stiffening effect
Cantilever experimentPCM experiment
• Nonlinear axial strain
PCM Nonlinear Governing Equations
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Strain due to stretching
Strain due to bending
• Equation of motion
• Electrical circuit equation
Mechanical coupling
Axial stretchingLarge curvature
for the pinned-pinned beam
𝑘→ ∞
• Assumed mode:
• Time domain model:
PCM Time Domain Model
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A function of base excitation and voltage
Analytical 1st mode
• Introduction
• Piezoelectric Compliant Mechanism (PCM) Under Small Base Excitation Review