Piezoelectric-Triboelectric Heel Insert with Lever Mechanism
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Solution Overview
Problem
Existing footwear-based energy harvesting technologies are bulky, inefficient, and fail to effectively convert human locomotion into usable electrical power due to low power density and poor integration with shoe design, making them unsuitable for emergency responders and outdoor enthusiasts.
Innovation Solution
A heel insert with a lever component comprising composite beams with piezoelectric and triboelectric layers, combined with a mechanical SSHI circuit, which amplifies foot motion to generate electricity through friction, providing a high power density solution that is lightweight and easily integratable into footwear.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If electromagnetic induction systems or piezoelectric mechanisms are used for energy harvesting, then electricity can be generated from locomotion, but the mechanisms become bulky and difficult to integrate into shoes
Solution Approach 1:
The patent embeds the energy harvesting mechanism within the heel insert structure of footwear. The composite beam stacks are nested between the lever component and the heel insert housing, with piezoelectric and triboelectric layers integrated within the composite beam structure itself. This nesting approach allows the entire energy harvesting system to fit within a compact heel insert that can be easily integrated into shoes without adding significant bulk.
2Power
If large pedal length is used to increase power output, then more electricity can be generated, but it causes extra effort and makes walking difficult
Solution Approach 1:
The patent employs asymmetric lever arms with different lengths (first lever arm and second lever arm) to optimize the mechanical advantage. The asymmetric composite beam stacks are positioned to create unequal bending moments during heel strike, allowing efficient energy harvesting from the natural heel strike motion without requiring excessive pedal length or additional user effort.
3Power
If piezoelectric and triboelectric layers are combined in composite beams, then power density increases, but manufacturing complexity increases
Solution Approach 1:
The patent divides the energy harvesting system into multiple discrete composite beam stacks, each containing piezoelectric and triboelectric layers. This segmentation allows each stack to be manufactured independently using standard layering techniques, then assembled into the heel insert. The segmented approach simplifies manufacturing by breaking down the complex multi-layer structure into manageable units that can be produced and tested separately before final assembly.
4Power
If spring compression is used to rotate the lever component, then mechanical motion is amplified, but energy loss through spring deformation occurs
Solution Approach 1:
The patent utilizes the periodic nature of walking motion to compress and decompress the spring in a regular cycle. The spring is compressed during heel strike when the lever component rotates, then decompresses to return the lever to its initial position during the toe-off phase. This periodic action synchronizes with the natural gait cycle, allowing the spring to store and release energy efficiently without significant losses, as the compression and decompression occur at optimal points in the walking motion.
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 achieves a significant increase in energy harvesting efficiency, producing up to 60 mW per foot, enabling the charging of electronic devices like smartphones with just one hour of walking, and offers a reliable, lightweight alternative for powering essential devices in emergency situations.
Implementation Method 1
a first piezoelectric layer bonded to the top surface of the first metallic layer and a second piezoelectric layer bonded to the bottom surface of the first metallic layer, wherein during human locomotion (i) compression of the spring rotates the short arm about the pivot point to flex the stacks into a concave shape
Implementation Method 2
a triboelectric layer bonded atop the surface of the second piezoelectric layer, wherein the flexing (i) and (ii) causes friction between the composite beams sufficient to generate electricity
Data Source
AI summary
The disclosure provides an electricity generating insert for a piece of footwear, the insert can be removably placed in the heel portion, e.g. under the insole. The insert comprises a multilayer piezoelectric stack that alternatively flexes under the compression-decompression that occurs during locomotion, which flexing causes friction in the stack to generate electricity capable of charging electronic devices and the like, e.g. via a port on the footwear.