This activity requires some non-expendable (reusable) items; see the Materials List for details.
Group Size: 2
Activity Dependency: None
Subject Areas: Physical Science, Science and Technology
NGSS Performance Expectations:
Partial design process
Grade Level: 9 (9 – 12) Time Required: 45 minutes Group Size: 2 Subject Areas:NGSS Performance Expectations:
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Students learn how to build simple piezoelectric generators to power LEDs. To do this, they incorporate into a circuit a piezoelectric element that converts movements they make (mechanical energy) into electrical energy, which is stored in a capacitor (short-term battery). Once enough energy is stored, they flip a switch to light up an LED. Students also learn how much (surprisingly little) energy can be converted using the current state of technology for piezoelectric materials. This engineering curriculum aligns to Next Generation Science Standards (NGSS).
Piezoelectric materials have the unique and useful property of being able to transform mechanical energy into electrical energy, and vice versa. This gives piezoelectric materials a wide range of potential applications from sensors and actuators to artificial muscles. One of the most interesting applications is in the field of energy harvesting, where piezoelectric materials are used to convert mechanical energy that is typically wasted into a source of electrical energy. However, the technology of currently available piezoelectric materials and methods is unable to produce a sufficient amount of energy, so engineers are researching how to improve piezoelectric energy harvesting devices.
Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.
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HS-PS3-1. Create a computational model to calculate the change in the energy of one component in a system when the change in energy of the other component(s) and energy flows in and out of the system are known. (Grades 9 - 12)
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Conservation of energy means that the total change of energy in any system is always equal to the total energy transferred into or out of the system.
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Energy cannot be created or destroyed, but it can be transported from one place to another and transferred between systems.
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Mathematical expressions, which quantify how the stored energy in a system depends on its configuration (e.g. relative positions of charged particles, compression of a spring) and how kinetic energy depends on mass and speed, allow the concept of conservation of energy to be used to predict and describe system behavior.
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The availability of energy limits what can occur in any system.
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Science assumes the universe is a vast single system in which basic laws are consistent.
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HS-PS3-2. Develop and use models to illustrate that energy at the macroscopic scale can be accounted for as either motions of particles or energy stored in fields. (Grades 9 - 12)
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At the macroscopic scale, energy manifests itself in multiple ways, such as in motion, sound, light, and thermal energy.
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These relationships are better understood at the microscopic scale, at which all of the different manifestations of energy can be modeled as a combination of energy associated with the motion of particles and energy associated with the configuration (relative position of the particles). In some cases the relative position energy can be thought of as stored in fields (which mediate interactions between particles). This last concept includes radiation, a phenomenon in which energy stored in fields moves across space.
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Each group needs:
To share with the entire class:
Cost note: Everything in this activity can be reused. The initial ~$20 cost per group can be continually reused for other classes. Ordering from SparkFun Electronics is the least expensive option (better than RadioShack); the company gives a 10% discount when purchasing 10 or more of any item. One exception is the switch; the RadioShack switch has been tested and shown to work, while the SparkFun one has not.
Visit [ www.teachengineering.org/activities/view/uoh_piezo_lesson01_activity1 ] to print or download.
Students should know the basics about electromechanical coupling, especially piezoelectricity and the use of piezoelectric materials for energy harvesting, as presented in the associated lesson, Piezoelectricity. No electrical or wiring background is necessary, but is helpful.
When you were little, did you ever wear shoes that would light up as you walk? (Answer: Expect some students to answer yes.) Does anyone know how those shoes work? (If students paid attention during the associated lesson, hopefully they answer yes.) This type of shoe has no batteries, so what is the power source? (Listen to student responses.) Piezoelectric materials are placed in the bottoms of the shoes, but they do not store any energy. So from where does the energy come? (Listen to student explanations.) The energy comes from you! Whenever you walk, your movements are mechanical energy and some of that mechanical energy can be converted into electrical energy by piezoelectric materials. In the case of the light-up shoes, that energy is used immediately to light-up some LEDs, which brings up an idea: What are the possibilities for storing that energy to use whenever we please?
(Start the seven-slide PowerPoint® presentation, showing students the circuit design on slide 2; this is a simplified circuit that you may wish to replace with the full circuit [Figure 1], which is provided as slide 8 for easy swapping.)
How much energy are we converting? We measure the voltage across the capacitor in our piezoelectric generators for two reasons. The first is simply to make sure it is working. The second, more important reason, is because we can use this voltage to calculate the amount of energy stored in our capacitors using the equation:
Where E is the energy stored in the capacitor, C is the capacitance and V is the voltage measured across the capacitor. When using this equation, make sure the units are correct. We want the capacitance to be in farads; if it is given in μF, simply divide by 1,000,000 to convert. We want the voltage to be in volts (V). Then, the units of energy will be joules (J) or equivalently, in watt-seconds (W-s).
To calculate how much energy is stored for each tap or press on the piezo element, measure the voltage before (V0) and the voltage after the tap (V1), and then use the following equation:
When performing these calculations, we find that very little energy is stored, generally around 0.00001 joules. As a comparison, a cell phone battery stores around 18,000 joules. Since this piezoelectric generator is so inefficient, engineers are working on two main approaches to improve its energy harvesting capabilities:
The second idea is the driving motivation for most piezoelectric energy-harvesting research work today. Some ideas include placing the materials under sidewalks and roads, or in clothing.
Before the Activity
With the Students
If using the SparkFun switch, a simple rocker switch, notice that it has two wires coming from it. Hook up this switch by following these steps:
Follow these steps if using the alligator clips with one clip and one exposed wire end:
alternating current power: (AC power) The type of power supplied by electrical outlets in homes as well as the piezoelectric element. In the piezoelectric element, a positive voltage is produced when pressed and an opposite, negative voltage when released.
capacitor: A device that stores energy, similar to a battery, but can be recharged and discharged much faster.
diode: An electrical component that only permits current to flow in one direction.
direct current power: (DC power) Power supplied by a current that only runs in one direction. This type of power is needed for the capacitor and LED.
light emitting diode: (LED) An LED does the same thing as a diode, but lights up when the current is sufficiently high.
multimeter: A device for making a variety of electrical measurements. In this activity it is used to measure DC voltage.
piezo element: The piezoelectric material that converts mechanical energy into electrical energy.
Piezoelectricity Lesson Review: Quickly review with students the material covered in the associated lesson. Ask: What is the piezoelectric effect? What causes piezoelectricity on the atomic level? What are some tested and conceptual applications? If you did not assign the lesson's Piezoelectricity Quiz, this is also a suitable place for it, or review the quiz answers with the class.
Activity Embedded Assessment
Energy Calculations Example: Cell Phone: Once you have given students the equation to calculate the amount of energy stored in a capacitor, see if they can figure out how long it will take to charge a cell phone that requires 18,000 joules of energy. These calculations are already done in the How to Build a Piezoelectric Generator Presentation, but have students give it a try before giving the answers.
Worksheet: Assign students to complete the Energy Harvesting Worksheet. Questions 1 and 2a require access to their generators. If only one multimeter is available, work through questions 1 and 2a as a class. For question 4, students brainstorm ways that they could use their piezoelectric generators that would be more efficient than just tapping it. Some examples include putting it under your shoe or under sidewalks. Review their answers to gauge their depth of comprehension.
The most common problem encountered in this activity is making sure that all components have current flowing in the correct direction. Often, if the circuit is not working, something just needs to be turned around.
If the capacitor does not appear to be storing any energy when tapping the piezo element, check that the switch is in the correct starting position. If the capacitor is charging, but flipping the switch does not drop the charge or light the LED, then not enough energy has been stored yet.
Diode Test video (shows how to test the diodes and the piezo element; no switch or capacitors in this setup; 22 seconds): https://www.youtube.com/watch?v=FOIs97xva6U
Circuit Test video (uses a RadioShack-type toggle switch; 71 seconds): https://www.youtube.com/watch?v=1Xyiz67jVSM
Additional YouTube videos of other piezoelectric generators:
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High School Lesson
PiezoelectricityStudents learn about a fascinating electromechanical coupling called piezoelectricity that is being employed and researched around the world for varied purposes, often for creative energy harvesting methods. Students explore the use of a piezoelectric generator.
High School Lesson
Keeping Our Roads SmoothStudents learn how roadways are designed and constructed, and discuss the advantages and limitations of the current roadway construction process. This lesson prepares students for the associated activity in which they act as civil engineers hired by USDOT to research through their own model experime.
Divya. Piezoelectricity: walk, jump, dance, and generate electricity! Posted August 1, 2012. Social Media/Technology, Consumer Instinct. Accessed April 29, 2014. http://www.consumerinstinct.com/piezoelectricity-walk-jump-dance-and-generate-electricity/
Browse the NGSS Engineering-aligned Physics Curriculum hub for additional Physics and Physical Science curriculum featuring Engineering.
National Science Foundation GK-12 and Research Experience for Teachers (RET) Programs, University of Houston
This digital library content was developed by the University of Houston's College of Engineering, based upon work supported by the National Science Foundation under GK-12 grant no. DGE 0840889. Any opinions, findings and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation.
Last modified: July 17, 2023
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