A New Method to Perform Direct Efficiency Measurement and Power Flow Analysis in Vibration Energy Harvesters

Area of Science:

• Energy Harvesting
• Materials Science
• Mechanical Engineering

Background:

• Piezo energy harvesters (PEHs) efficiency measurement is challenging.
• Current methods often simplify power consumption, ignoring mechanical losses.
• Accurate efficiency assessment is crucial for optimizing PEH performance.

Purpose of the Study:

• To develop a novel measurement system for accurate, definition-based efficiency of PEHs.
• To enable direct efficiency measurement without needing PEH parameters.
• To identify and quantify sources of energy loss in PEHs.

Main Methods:

• Designed a measurement system to directly determine definition-based efficiency.
• Input power is measured from the vibration source, not PEH parameters.
• Tested the system on PZT and PVDF piezoelectric harvesters.

Main Results:

• The novel system achieves <0.5% absolute uncertainty and quantifies losses.
• Direct measurement revealed discrepancies compared to simplified efficiency calculations, especially for PVDF.
• Identified air damping and thermal losses (internal/interlayer friction) as main loss sources.

Conclusions:

• The developed method provides a more accurate assessment of PEH efficiency.
• Standard methods can overestimate efficiency by neglecting mechanical losses, particularly in low-stiffness devices.
• Understanding loss mechanisms is key to improving PEH design and performance.