Piezoelectric Energy Harvester Layout and Adaptive Rectification
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Solution Overview
Problem
Existing energy harvesting devices are fragile and unreliable due to the low tensile strength of piezoelectric materials, and their power management circuits are inefficient, leading to insufficient output at low harvester voltages and excessive output at high voltages.
Innovation Solution
The energy harvesting device incorporates a piezoelectric material element located within a cavity of the proof mass, ensuring compression and reducing torque loads, while the power management circuit features a configurable voltage amplification and rectification system that switches between voltage doubler and full wave rectifier modes to maintain optimal output across varying input levels, avoiding inefficient buck-boost operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the piezoelectric material element is located outside the proof mass, then the device structure is simpler, but the centre of mass is offset causing torque loadings that damage the device
Solution Approach 1:
The piezoelectric material element is nested within a cavity formed in the proof mass. This positioning ensures the centre of mass remains aligned with the piezoelectric element, eliminating offset-induced torque loadings during vibration and thereby improving device reliability without excessive structural complexity.
2Device complexity
If the piezoelectric material element is subjected to tensile loading, then the coupling arrangement can be simpler, but the low tensile strength causes the material to break easily
Solution Approach 1:
Instead of allowing tensile loading on the piezoelectric material, the coupling arrangement is designed to apply compressive pre-stress to the material. The clamping arrangement maintains the piezoelectric element under compression throughout its range of motion, exploiting the material's high compressive strength (>600 MPa) rather than its weak tensile strength (35-40 MPa).
3Device complexity
If a simple full wave rectifier is used when harvester output is low, then the circuit is simpler, but the output is insufficient for many applications
Solution Approach 1:
The power management circuit dynamically switches between voltage doubler mode and full wave rectifier mode based on the harvester output voltage level. When voltage is low, the circuit operates as a voltage doubler to amplify output; when voltage is high, it switches to full wave rectifier mode, providing adaptive power management that maintains sufficient output across varying conditions.
4Power
If a voltage amplification circuit is used to combat low output, then the output is enhanced at low voltage, but the output becomes too high when harvester output rises
Solution Approach 1:
The power management circuit employs dynamic mode switching between voltage doubler and full wave rectifier configurations based on real-time harvester voltage levels. This adaptive approach enhances output when voltage is low while preventing excessive output when voltage rises, maintaining optimal operating conditions across the full range of harvester output variations.
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 enhances the reliability and output of energy harvesting devices by maintaining optimal voltage levels and reducing the risk of damage from torque loads, achieving efficient power conversion and extended device lifespan.
Implementation Method 1
movement of the proof mass causes compression of the piezoelectric material element... deformation of the piezoelectric material in a direction resulting in the generation of an electrical output therefrom
Data Source
AI summary
An energy harvesting device is described comprising a piezoelectric material element (22), a proof mass (18) moveable relative to the piezoelectric material element (22) and coupled to the piezoelectric material element (22) by a coupling arrangement such that movement of the proof mass (18) causes compression of the piezoelectric material element (22), wherein the proof mass (18) defines a cavity (20), the piezoelectric material element (22) being located, at least in part, within the cavity (20). A power management circuit (50) suitable for use therewith is also described, the circuit (50) comprising a configurable voltage amplification and rectification circuit and a mode control circuit operable to configure the configurable circuit to operate in a voltage amplification mode or in a rectification mode, the mode control circuit selecting the operating mode depending upon the input or output of the configurable circuit.