Residential Piezoelectric Energy Sources

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Technical Overview
Piezoelectric materials exhibit the unique property known as the piezoelectric effect. When these materials are subjected to a compressive or tensile stress, an electric field is generated across the material, creating a voltage gradient and a subsequent current flow. This effect stems from the asymmetric nature of their unit cell when a stress is applied. As seen in Figure 1, the unit cell contains a small positively charges particle in the center. When a stress is applied this particle becomes shifted in one direction which creates a charge distribution, and subsequent electric field.


Application to Residential
There are several ways to incorporate piezoelectric technology into a residential setting. The first would be to use small piezoelectric sources in the place of batteries. These piezoelectric sources could be used to power sensors throughout the house so that the batteries would never need to be changed. Another application was one proposed by Dr. Rob Clark and Dr. Henri Gavin. Their idea was to use piezoelectric materials to cancel out vibrations in certain household appliances.


Simulation Results
In my physics 171L class for my final project I modeled a circuit I found in a book in the simulation program PSpice. The circuit used a piezoelectric transducer as the voltage source which than fed into an op amp. The purpose of the circuit was to provide a voltage gain of 100. Our simulation results proved that the op amp did in fact multiply the voltage from the piezo-transducer by a factor of 100. Unfortunately, in the program we could not find an actual piezo-transducer so we had to model it with an ideal voltage source with an estimated equivalent Thevenin resistance


Future Direction
The next step would be to team up with Dr. Gavin and work with the energy harvesting setup he has. Once you understood the fundamentals of it, you could model some of your own circuits on a simulation program. Right now the most likely simulation to use would be Ansys.

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Residential Piezoelectric Energy Sources details


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Abstract
The DELTA Smart House is going to have a large number of sensors and microelectronic devices located throughout the house. These devices will need a clean, reliable source of energy that won’t need constant maintenance. The goal of this project is to utilize piezoelectric energy sources to provide power to certain applications in the house. Initially the plan was to create an energy scavenging floor that used piezoelectric transducers to harvest wasted energy in the foot strike of a human being. In consideration of the high cost and minimal power output of these piezo-sources, it seems more feasible to create small, localized energy sources rather than one large unified system. This idea has lead to several potential applications. The first is to combine a piezoelectric power source with sensors such that there would be no need to ever change the batteries in these sensors. The next application is to use piezoelectric cable throughout the floors of the house as a means of tracking. The final application is to combine piezoelectrics with a device to eliminate vibrations in household appliances.



Technical Overview

Piezoelectric materials exhibit the unique property known as the piezoelectric effect. When these materials are subjected to a compressive or tensile stress, an electric field is generated across the material, creating a voltage gradient and a subsequent current flow. This effect stems from the asymmetric nature of their unit cell when a stress is applied. As seen in Figure 1, the unit cell contains a small positively charges particle in the center.



Existing Technologies
There are several companies and research institutes throughout the world who are focusing on finding useful applications for piezoelectric energy sources. Several years ago a project was done at MIT entitled, “Energy Scavenging with Shoe-Mounted Piezoelectrics.” In this project the researchers lined the bottom of a shoe with piezoelectric transducers and saw what kind of power they got out of it. They eventually attached an RF-transmitter to the shoe that was powered by the piezoelectrics. The two materials they used were polyvinylidene fluoride (PVDF) and lead zirconate titanate (PZT). Their initial results were that the PVDF material produced 1.3 mW per foot strike and the PZT produced around 8.4 mW. They went back and tried numerous other approaches but they were confined to working with the limitation of a shoe.



Application to Residential

There are several ways to incorporate piezoelectric technology into a residential setting. The first would be to use small piezoelectric sources in the place of batteries. These piezoelectric sources could be used to power sensors throughout the house so that the batteries would never need to be changed. Another application was one proposed by Dr. Rob Clark and Dr. Henri Gavin. Their idea was to use piezoelectric materials to cancel out vibrations in certain household appliances. They envisioned a device that could autonomously adapt the amount of dampening based on the magnitude of the vibrations.



Cost Analysis

Buying a piezoelectric transducer can be quite expensive. Two different suppliers I looked at were Face International Corp. and Active Control eXperts. Their piezo-transducers sold for about $100 and $200 respectively. Buying piezoelectric cable is much cheaper. One supplier in the UK, Ormal Electronics Ltd., gave a quote of £2.75 per meter for purchases of more than 2000 meters. Another supplier in the US, Measurement Specialties Inc., sells piezo-cable for $8.00/m for more than 1000 m. Even if we were to use piezo-cable to line the house at 4” apart, the cost would still exceed $30,000.