Continue to Site

# highest theoretical energy for piezo and dynamo or motor

Status
Not open for further replies.

#### jeromekang

##### Junior Member level 3
hi.. kinda need help in this matter urgent..

my adviser asks me to find out the highest energy a piezo can deliver for example with a force of 3N? the application would be in typing

the scenario would be like... if the battery (750mAh) is used by the keyboard (30mA).. the battery depletes after 30hrs.. given a typing rate ssay (40wpm).. or say the number of presses to deplete the battery (assuming continuous use).. how much can i generate with the piezo given the force of my presses is 3N? can anybody help me compute for the energy produced by the piezo? what particular piezo product can you give us an example for this theoretical problem?

also.. same theoretical problem if i am going to use a dynamo to generate energy.. how should i go about it? (not really good with motors or the theories revolving around it)

Elastic potential energy equals U=∫F(x) dx. F is force and dx is displacement, the compression of the piezo element in this case. Without displacement, no energy can be transferred.

This can be also easily derived from the unit of energy, which is Nm rather than N. Applying a constant force of 3 N along a displacement of 1 mm performs a work of 0.003 Nm respectively 3 mJ or 3mWs. It has to be multiplied by the conversion efficiency of your generator.

Elastic energy - Wikipedia, the free encyclopedia

Elastic potential energy equals U=∫F(x) dx. F is force and dx is displacement, the compression of the piezo element in this case. Without displacement, no energy can be transferred.

This can be also easily derived from the unit of energy, which is Nm rather than N. Applying a constant force of 3 N along a displacement of 1 mm performs a work of 0.003 Nm respectively 3 mJ or 3mWs. It has to be multiplied by the conversion efficiency of your generator.

Elastic energy - Wikipedia, the free encyclopedia

isn't that just the ideal for the force you exert on an object? how about if considering the property of a certain piezoelectric material or product? how can the energy from the piezo be computed in terms of number of key presses?

isn't that just the ideal for the force you exert on an object? how about if considering the property of a certain piezoelectric material or product? how can the energy from the piezo be computed in terms of number of key presses?
It in fact answered your original question. Now you apparently decided to replace it with a different one. This may be reasonable, but you should be at least able to calculate the ideal energy harvesting case. Your initial post however suggests, that you didn't yet think about the role of displacement, respectively don't understand the nature of mechanical energy. Number of key presses is of course nothing but a multiplier - once you have determined the energy of a single key press.

If you consider real piezo material, there's a basic property, the coupling factor k², which gives the fraction of applied mechancial energy, that can be converted into electrical energy for non-resonant transducers. You should refer to basic piezo literature to learn about these relations.

jeromekang

### jeromekang

Points: 2
It in fact answered your original question. Now you apparently decided to replace it with a different one. This may be reasonable, but you should be at least able to calculate the ideal energy harvesting case. Your initial post however suggests, that you didn't yet think about the role of displacement, respectively don't understand the nature of mechanical energy. Number of key presses is of course nothing but a multiplier - once you have determined the energy of a single key press.

If you consider real piezo material, there's a basic property, the coupling factor k², which gives the fraction of applied mechancial energy, that can be converted into electrical energy for non-resonant transducers. You should refer to basic piezo literature to learn about these relations.

sorry for the confusion FvM, thank you also :smile:

My very simple and idealized available energy calculation already reveals, that the intended harvesting rate can't be achieved, even with 100 % conversion efficiency. So I think, despite of the missing real piezo property calculation, it has a clear result.

Status
Not open for further replies.