# Harvesting Sound Energy from Piezoelectric

Discussion in 'The Projects Forum' started by aimanj, Mar 4, 2011.

1. ### aimanj Thread Starter New Member

Mar 4, 2011
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0
Hi all.

My group is doing a project that is basically trying to harvest noise and convert it to electrical output. We actually have designed a tube to amplify the sound, and at the end of the tube we will put a piezoelectric material to convert the received sound to electrical output. We want at least our device will lit on a common LED.Well, more deflection to piezoelectric material means more energy output but noise doesnt provide much deflection to the piezoelectric.

We already measured the voltage output from the piezo and we only acquired around 30mV which is very small. The LED to be used would require at least 1.5V, but now we only have 30mV. So, we got to design a circuit which is capable of increase the voltage to at least 2V and send it to the LED.Since we have very low power voltage, how can we increase the voltage? What kind of electrical component that can be used to increase it? Is there anyway to increase it to 2V so that can be used to lit on 1.5V LED?

I really need your help.Any suggestion is appreciated.

2. ### beenthere Retired Moderator

Apr 20, 2004
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Try looking at the spec sheet on the piezo device and see how much power can be produced. That will give you a feel for what is possible.

Your LED not only requires 1.5 volts to bias it into operation, but several milliamps of current to make it glow enough to see. That is on the order of 7.5 milliwatts, which is the amount of power you have to be able to get out of the piezo.

You can always arrange arrays of the piezo sensors to aid in voltage (series) and current (parallel) to give the needed output level, but that may not be within your budget.

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3. ### wayneh Expert

Sep 9, 2010
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4. ### Kermit2 AAC Fanatic!

Feb 5, 2010
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Piezo is capable of creating very high voltage. You need to harvest an energy source that suits the harvesting method. IMPACT energy would be more appropriate.

Actual speakers with cone and magnet would be a more appropriate input device for capturing sound. Use passive design tech to increase gain of the sound before presenting it to the speaker.

Also, piezo devices are being tried in various schemes to capture the energy of human foot traffic and street automotive traffic, so figuring out other 'high instantaneous energy density' activities and ways to capture them is the logical path to follow with those devices.

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5. ### aimanj Thread Starter New Member

Mar 4, 2011
13
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We already tried to use 2 piezoelectric PFCB-W24 from this manufacturer:

and we only gained maximum 70mV from both piezos.

We know more piezos means more output, but we dont want to use so many piezos in our project. Since the piezo generates AC voltage, we need to use a rectifier to convert it to DC form. I learnt that a silicon rectifier has a voltage drop around 0.7V and we only have 70mV. Do you think is there anything to increase the voltage output to at least 1V? I was wondering about this components but Im not sure about this? Can you comment on this alternatives:

1) Using AC transformer. Is there any transformer that I can find to increase very low power voltage about 100 times larger?

2) Voltage multiplier. I think it is like many diodes arranged in several bridges to increase the voltage. Does it increase voltage?

3) Germanium Diode. Silicon diode has 0.7V voltage drop, but germanium diode has only 0.3V. But still our 70mV still cant go through the 0.3V. I also dont really understand how to choose the right silicon diode to be used.

Thanks for your comment.

6. ### aimanj Thread Starter New Member

Mar 4, 2011
13
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How does the speaker with magnet will capture more sound? Can you explain a little bit how it works? What do you mean by the passive design tech? SOrry Im too noob but Im curious.

7. ### aimanj Thread Starter New Member

Mar 4, 2011
13
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I looked at this device before.This device harvest the energy from piezo, but you piezo generates AC voltage. I gotta to convert it to DC form first to be stored in this device. Well, to convert it to DC, we need to use a rectifier which has 0.7V voltage drop. But we only have 30mV from the piezo. That is why we need to increase the voltage output by electronic mean (not by Mechanical mean like using more piezo or press more).

8. ### wayneh Expert

Sep 9, 2010
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Either of these might work, but I believe the transformer approach will more efficiently transfer the power, with less loss. I've never used a voltage multiplier circuit but my understanding is that they're not very efficient. You'll need a very high turns ratio. A power transformer designed to output 3v (to substitute for 2 AAs) from a wall wart would give you 40:1, and would at least be easy to find.

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9. ### Audioguru New Member

Dec 20, 2007
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You need a very sensitive transducer (maybe a huge, rare and expensive piezo panel) and an earthquake to light a little LED.

There is a very rare IC available somewhere that takes the high voltage but extremely low current from a floor made from huge piezo panels to make hardly any electricity when hundreds of people jump on it.

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10. ### bribri Member

Feb 20, 2011
133
5
a nine-volt battery would be a good start...
...unless that defeats the point?

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11. ### wayneh Expert

Sep 9, 2010
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What part of " Random AC or DC inputs accepted" (2nd bullet from the linked blurb) do you not understand?

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12. ### Audioguru New Member

Dec 20, 2007
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An energy harvesting system using a fortune worth of piezo transducers all over a floor where hundreds of people or animals are jumping might make a good charger for a cheap little 9V rechargeable battery that can power a small light for half an hour at night.

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13. ### wayneh Expert

Sep 9, 2010
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No argument. But I believe the OP only needs an example, not really a practical machine. The difference between academia and the rest of the world.

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14. ### Audioguru New Member

Dec 20, 2007
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Why do teachers teach about stupid stuff?

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15. ### bribri Member

Feb 20, 2011
133
5
no i meant why not use a 9 volt battery and amplify the piezo and light the light. but that's why i ask if i'm missing the point because the other comments are about passive electronics.

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16. ### Audioguru New Member

Dec 20, 2007
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Little school kids do not understand (because their teachers do not teach anything?) that a battery has energy that is used up by an amplifier.
The battery must be replaced in a few minutes or in a few hours.
So you are harvesting nothing but battery expenses.

Wouldn't it be wonderful if there was an amplifier that magically used no power supply??
Then you could feed some of its output back into its input and make power.
Then you can use some of the "free" power and sell some.

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17. ### wayneh Expert

Sep 9, 2010
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Teaching "far out" concepts and innovative thinking has its place, and can help capture student attention, but it needs to be tempered with practicality. Understanding the gap between what IS and what COULD be can position one for seeing innovation when it comes along. "Chance favors the prepared mind."

Maybe the point of the exercise is to teach these students how difficult such things really are.

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18. ### bribri Member

Feb 20, 2011
133
5
i thought they just wanted to see the sound. ergo, they'd have to amplify it. i mean lighting a led isn't exactly 'harvesting' either. maybe they could save some time and just use a water-wheel or a bike dynamo to power a transistor or something.

yes an opaque and sealed, perfectly circular tube will feedback and make its own power. only minor problem is you can't get any power in or out of it.

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19. ### aimanj Thread Starter New Member

Mar 4, 2011
13
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Yeah.I understand that more deflection means more output. But my project is not about using mechanical movement to deflect the piezo transducer. We are trying to use sound instead of mechanical mean to deflect the piezo. That is why the output from the piezo is low. Since it is very low, I gotta increase or step up the voltage somehow so that it can go through a rectifier and be stored in a capacitor.Note that a rectifier has voltage drop of 0.7V.

20. ### aimanj Thread Starter New Member

Mar 4, 2011
13
0
Becoz they dont wanna lose their jobs.