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Developing a Biomechanical Energy Harvester
Transcript of Developing a Biomechanical Energy Harvester
By Georges Gauthier
How Piezoelectric Material Works
The Macro Circuit
The Micro Circuit
Mimicking Piezo Outputs
Interfacing the Apparatus with a Shoe
The Final Product
I am an active person
I am interested in renewable energy and electronics
I plan to major in electrical engineering
This project is a precursor to the type of work I hope to be doing in the future
Over the course of the summer, fall and
winter of 2012, I researched energy
harvesting from the human body
Why the human body?
What resources are available?
The human body dissipates a large amount of energy
Developing a wearable energy harvesting device would allow for more mobile applications
Wasted light energy that strikes the body can be gathered through solar photovoltaic cells
Wasted thermal energy can be scavenged through the use of the seebeck effect
Wasted kinetic energy can be harvested through either piezoelectric material or electromagnetic generators
Piezoelectric material is a ceramic that produces electrical charge when bent or flexed.
I chose to use piezo material mounted in a shoe for my project
Developing a Circuit
The output of a piezo inserted in the heel of a shoe is shown below.
This output is AC, and constantly varies in voltage
I needed to transform the AC output of my piezos to DC
I needed to both store the electrical energy and boost the stored electrical energy to something usable
I needed to take the stored electrical energy and put it out at a flat, well regulated DC voltage
AC-DC Charge pump
Converts the stored energy from AC-DC and boosts it for final storage
Low Dropout Regulator
Outputs stored electrical energy from the capacitor at a well regulated 3.3 volts
Uses the Linear Technology LTC3588 energy harvesting IC on a Sparkfun breakout board
Accepts an input voltage of 4.5 to 20 volts AC, puts out a 3.3 volt DC signal.
The LTC3588 IC contains a much smaller and more efficient energy conversion circuit
The IC and breakout board compared to a quarter (shown above) and IC example circuit (shown to right)
The only additional components required for this circuit are a storage capacitor, piezo, and load. In my case, I used a 10µF capacitor and a 3v rechargeable Li-ion battery
One difficulty I ran into while testing was that I broke several piezos
This poses a problem, since each costs between $90-150 and takes several weeks to receive from a manufacturer
The Arduino Circuit
My solution was to use an arduino microcontroller to create a square wave
I then used a Sallen-Key filter to filter the square wave into a sine wave
The pink line shows the square wave output from the arduino. The yellow line shows the filtered square wave
Sallen-Key (active low-pass) filter
Arduino microcontroller and square-wave shield
Artificial vs Real Piezo Outputs
Although the output from the piezo has higher voltage peaks and is AC, both put out at a relatively similar duty cycle, and the artificial piezo circuit is capable of powering both the macro and micro circuits
When it came to creating a wearable prototype, I needed to be able to monitor my circuit and keep a piezo mounted in my shoe.
I ended up using a thick, disk shaped piezo and phone cable to connect the mounted piezo to the circuit
My final product interfaced my macro circuit with a storage capacitor and rechargeable coin-cell battery
This prototype was built so that I could swap out the piezo-transducer powering the circuit
Several important skills that I learned through this project included:
Using an Oscilloscope
This project would not have been possible for me to complete without the help and support of my mentor, Dr. John DiCecco