Piezoelectric Energy Harvester

**Patent Pending - United States 61928067**

Introduction

What is piezoelectric energy harvesting?
Piezoelectricity translates to “electricity from pressure.” The prefix piezo in Greek means to press or squeeze. Piezoelectric materials exhibit the piezoelectric effect. This allows a mechanical force to be applied to the material to deform it slightly and the material will produce an output electric power. This is done by rearranging the dipoles of the piezoelectric material. This rearrangement causes a change in the dipole density and therefore a change in the electric field between the dipoles. Because of this change in the electric field, the piezoelectric material produces an output electric power.

What will be accomplished in this Instructable?
Completion of this Instructable will result in a piezoelectric energy harvesting "boot." With use of other electronic components, this unit will be able to power other small devices that have a low power consumption. Total project cost (for 1 unit) is ~ $100.

Decide What Size the Unit Should Be. Draft It in a CAD Program, Both in 2D and 3D.

When drafting, be sure to know the size of the piezoelectric disks that will be used. Consider spring placement and sizes of springs. The springs that were used in this unit were about 1.5cm in diameter. Think ahead to all aspects of design from disk placement, spring placement, to where guide bolts will be placed and connecting bolts will be placed. Also think about wire management. The wires can sit next to the disks, but it doesn’t look neat and clean. It will be helpful to see all of this digitally when it comes to assembling the unit.

Draft the Stoppers and Holders and Impact Rods.

These will need to be created in a 3D program such as AutoCAD or equivalent, as they need to be made with precision. They will be exported to a 3D printer. One impact rod will be needed for every disk used, and the stoppers and holders will be needed for each spring. The stoppers and holders must be a cup shape and one will be needed for the top plate and one for the bottom plate. The cup shape is used to hold the spring in place. The additional function of these holders is to act as a stopper for the descending top plate so that the impact rods do not deform the piezoelectric disks to fracturing point. The impact rods were made 1mm longer than the sum of the length of the top and bottom stoppers and holders. This allowed the impact rods to deform the piezoelectric disks 1mm, which is a safe and highly effective deformation distance for the disk elements used in this model.

CNC the Top and Bottom Plates.

MDF board was used since it can be purchased flat, while other boards can be slightly warped. The CNC machine requires likely either a .dwg or a .dxf file to be loaded into software to create a tool path. The entire plate was milled – from the details to the actual cutting of the edges. It would be smart to have the holes for screws and bolts drilled with the CNC as well, as this would greatly increase the accuracy of the holes. After the boards are cut out, be sure to sand the insides of the troughs and holes if the CNC did not make them very flat. Higher end CNC machines will likely take care of this for you.

Assemble and Test the Mechanical Assembly.

Attach the spring holders and stoppers to the plates. Holes must be drilled in them first to allow the bolts through. Place one 1/4 inch washer on the 1/4 inch by 3 inch bolt before putting it through the plate. Once through the plate and the cup, place a 3/8 inch washer on the bolt and then another 1/4 inch washer, followed by a nut. Do this for each of the 8 cup bolts. Tighten finger tight with a socket wrench. Place a spring in each holder and stopper, then place the top plate on the springs making sure that each spring is sitting in both a bottom and top part of the holders and stoppers. Put two 1/4 inch washers on each of the 1/4 inch by 6 inch carriage bolts. Place the carriage bolts in the corner holes of the top and bottom plates, inserting them up through the bottom plate and then through the top plate. Place two more 1/4 inch washers on the carriage bolt and then a nut on each. Tighten so there is about 1 inch of space between the washers and the end of the carriage bolts.

Attach the Impact Rods.

The unit will have to be disassembled to do this. Be sure to drill small holes in the impact rods before trying to screw them in. If the holes are drilled in the MDF board from a CNC, disregard the next sentence. If the holes for the screws were not drilled with the CNC, a printout of the 2D CAD file with circle centers marked will have to be taped to the top plate. This will allow for relatively accurate holes to be drilled manually. Screw in all of the impact rods.

Solder All of the Piezoelectric Disks in Parallel.

It was found to be much easier to solder 3 elements together at a time, leaving 6 groups of disks wired in parallel. Then solder these groups in pairs, leaving three groups of six piezoelectric disks. Lay these three groups out how they will appear on the base plate, and then solder them together. Lastly, solder two longer wires to the end of the disk circuit. These will be the output wires to the load circuit. Note that the leads on the disks are very fragile and will break with too much tugging. Be careful, of there will be a lot of wire stripping and re-soldering to do.

Apply Electrical Tape to the Solder Joints.

The wires will be very close together in the unit and can move easily. Applying a small strip of electrical tape over each solder joint will ensure isolation and prevent any shorts.

Test the Circuit.

Before adhering the disk circuit to the base plate, test the circuit with a multi-meter. Be sure to test each individual disk for an output voltage. Simply tap on them and there should be some voltage. Doing this will ensure that each disk is connected properly in the circuit and that there are no faults in the circuitry.

Hot Glue the Piezoelectric Disks to the Base Plate.

Apply a small dab of hot glue to four sides of the circles on the base plate. Press the disk down on the hot glue. Repeat for all of the disks. It is easier to start with the middle disks as wires begin to get in the way quickly. Be careful with the wires as well, as they can break off easily – no hard tugs! Use a piece of wire or other means to tie or attack the center circuit wires to the spring holders and stoppers. This will keep them out of the way of the impact rods.

Assemble the Unit and Test It.

Put the top plate back on. Connect the output wires to a multi-meter and test the unit. Make sure it slides smoothly and that the wires are not in the way of the impact rods.

Build a Load Circuit.

This can be anything, though LEDs are a quick and satisfying load and demonstration of piezoelectric energy harvesting. The load circuit used in this project included 12 LEDs wired in parallel. One of the most important pieces of the load circuit is a full-wave bridge rectifier. A full-wave bridge rectifier flips the negative voltage spike and makes it a positive spike. This will be needed if capacitors are a part of the load circuit. The output power is also doubled when using a full-wave bridge rectifier. A half-wave bridge rectifier would also work, but the power would be half of what a full-wave would provide. Additionally, depending on what the load circuit involves, capacitors could be used for storage or voltage regulation, and linear regulators could be useful for voltage regulation.

**Depending on what you want to do, you may find step 13 in Angelo's Instructable quite helpful. He discusses hooking the generator up to a battery to store and later use the produced energy.

File Downloads and Resources

To request project files, do one of the following:

Download directly (below)
- Write-up
- Circuit diagram
Post a comment on this Instructable with your email address
Send a direct message to me on Instructables

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I STRONGLY encourage questions and comments, so PLEASE feel free to contact me. I usually respond within a day or two!

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Project Files
File Descriptions:
Piezo_bottomplate_3D.dwg - Base plate in 3D. File has layers.
Piezo_plates_CNC.dwg - Base plate and top plate for CNC router (2D)
Piezo_plates_CNC.dxf - Plates for CNC in DXF file type
Presentation.pptx - Powerpoint presentation
Impact_rod.stl - Impact rods (18 printed on 3D printer)
Stoppers_holders_base.dwg - Stoppers and spring holders (base) (CAD file)
Stoppers_holders_base.stl - Stoppers and spring holders (base) (3D printer)
Stoppers_holders_top.dwg - Stoppers and spring holders for top (CAD file)
Stoppers_holders_top.stl - Stoppers and spring holders for top (Printer file)

Resources and Research Files
File descriptions:
PyzoFlex.pdf - PyzoFlex - Printed Piezoelectric Pressure Sensing Foil
Images SI Inc.pdf - Piezo Film Sensors - Technical Manual (Images SI Inc.)
MIT.pdf - MIT-Modeling and Design of a MEMS Piezoelectric Vibration Energy Harvester
JR-EAST.pdf - JR-EAST Piezo Floor
APC.pdf - APC International, Ltd. - First Steps Towards Piezoaction
Piezoelectricity wiki.pdf - Wikipedia page on Piezoelectricity

Other
For questions, comments, resources, or any other inquiries, please feel free to post comments or send direct messages on Instructables.

**If anything from this Instructable or any of the attached files is used, please credit references accordingly. Thank you and enjoy!**

Downloads

Schematic.pdf

Write-up.pdf