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Difference between terminal Boundary condition and Electric potential boundary condition.
Posted 24.07.2013, 09:24 GMT-4 Low-Frequency Electromagnetics, MEMS & Nanotechnology, MEMS & Piezoelectric Devices 10 Replies
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Hi,
I am modelling a free PZT patch.
I have to apply a voltage potential of 20V across the top and bottom of the PZT patch. (attaching the model)
I am doing it via two methods,
(a) applying "electric potential" boundry condition at top surface and specifying the bottom surface as ground.
(b) applying "terminal" boundry condition at top surface and specifying the bottom surface as ground.
Ultimate aim is to find admittance of piezo.
In the first method(a) I am doing it by A= I/V, where, V= line_integral(pzd.Ey) and I = surface_integral(pzd.Jy)
and in the second method (b) Admittance = pzd.Y11
However the value of admittance in two methods is not same.
Please suggest which is the right way of getting admittance and what is the difference between two boundary conditions of "terminal' and 'electric potential'
Thank you in advance.
Regards,
Naveet
I am modelling a free PZT patch.
I have to apply a voltage potential of 20V across the top and bottom of the PZT patch. (attaching the model)
I am doing it via two methods,
(a) applying "electric potential" boundry condition at top surface and specifying the bottom surface as ground.
(b) applying "terminal" boundry condition at top surface and specifying the bottom surface as ground.
Ultimate aim is to find admittance of piezo.
In the first method(a) I am doing it by A= I/V, where, V= line_integral(pzd.Ey) and I = surface_integral(pzd.Jy)
and in the second method (b) Admittance = pzd.Y11
However the value of admittance in two methods is not same.
Please suggest which is the right way of getting admittance and what is the difference between two boundary conditions of "terminal' and 'electric potential'
Thank you in advance.
Regards,
Naveet
Attachments:
10 Replies Last Post 24.07.2013, 13:22 GMT-4
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Posted:
1 decade ago
Naveet,
the way you apply it there is not really a difference between both. The terminal, however can be connected to an external circuit, which is sometimes useful in piezoelectric models.
I assume that integrating the E-field is much less accurate than the terminal admittance. And I think it is not required to integrate the E-field. Couldn't you just take the potential boundary voltage?
Cheers
Edgar
--
Edgar J. Kaiser
emPhys Physical Technology
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Posted:
1 decade ago
Hi Edgar,
Thank you very much for your quick response.
The resonating mode frequencies of free PZT (10 mm x 10 mm x 0.3 mm) are coming correct in both methods. However, I am getting very high admittance magnitude (12 S) for terminal boundary condition case, as compared to analytic value of 1 S. For Electric voltage case, the admittance value is coming 0.0036 S (which is comparatively closer to analytical result).
I have used the Rayleigh damping with Beta 3e-9 and alpha 0.
A terminal voltage of 1V is applied.
Can you please suggest anything which I am missing. I have already attached the file in my previous comment.
I have one more query posted at www.comsol.com/support/case/1331719. It would be a great help if you can suggest me something for that also.
Thank you very much.
Kind Regards,
Naveet.
Thank you very much for your quick response.
The resonating mode frequencies of free PZT (10 mm x 10 mm x 0.3 mm) are coming correct in both methods. However, I am getting very high admittance magnitude (12 S) for terminal boundary condition case, as compared to analytic value of 1 S. For Electric voltage case, the admittance value is coming 0.0036 S (which is comparatively closer to analytical result).
I have used the Rayleigh damping with Beta 3e-9 and alpha 0.
A terminal voltage of 1V is applied.
Can you please suggest anything which I am missing. I have already attached the file in my previous comment.
I have one more query posted at www.comsol.com/support/case/1331719. It would be a great help if you can suggest me something for that also.
Thank you very much.
Kind Regards,
Naveet.
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Posted:
1 decade ago
Naveet,
if I plot pzd.Y11 (the real part instead of imaginary) it shows values between 0.8 S and 2.2 S. Resonant systems are always tricky. You can play with the damping to match the experimental results. Experiment rules!
The link to the support case leads into the void. Anyway, I think I wouldn't have access to support cases other than my own.
And I should add: Your geometry is not 10 x 10 x 0.3 mm, it obviously is 10 x 1000 x 0.3 mm. In 2D planar the z-direction is normalized to 1m by default. You can change that in the Thickness tab under pzd node.
--
Edgar J. Kaiser
emPhys Physical Technology
if I plot pzd.Y11 (the real part instead of imaginary) it shows values between 0.8 S and 2.2 S. Resonant systems are always tricky. You can play with the damping to match the experimental results. Experiment rules!
The link to the support case leads into the void. Anyway, I think I wouldn't have access to support cases other than my own.
And I should add: Your geometry is not 10 x 10 x 0.3 mm, it obviously is 10 x 1000 x 0.3 mm. In 2D planar the z-direction is normalized to 1m by default. You can change that in the Thickness tab under pzd node.
--
Edgar J. Kaiser
emPhys Physical Technology
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Posted:
1 decade ago
MY OTHER POST:
I want to apply compressive load on a piezo sensor (10mmx10mmx0.3mm) and ensure that its top surface should have constant voltage all along its area.
How to ensure this constant voltage condition? Do I need to perform some mapping of nodes at the top surface or suggest something else?
Thank you in advance.
Regards,
Naveet
I want to apply compressive load on a piezo sensor (10mmx10mmx0.3mm) and ensure that its top surface should have constant voltage all along its area.
How to ensure this constant voltage condition? Do I need to perform some mapping of nodes at the top surface or suggest something else?
Thank you in advance.
Regards,
Naveet
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Posted:
1 decade ago
You can use a terminal BC
Please note, I edited my precursor post.
--
Edgar J. Kaiser
emPhys Physical Technology
Please note, I edited my precursor post.
--
Edgar J. Kaiser
emPhys Physical Technology
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Posted:
1 decade ago
You are too good...:)
Thank you soooo much...It worked.
I am getting closer results by correcting the piezo default depth,...
Thank you so much.
Regarding my other post,
Since, I am applying compression force on piezo, and would be measuring its voltage then how would 'terminal BC' be used, since that condition is used for applying a particular value of voltage (which rather I need to measure, hence is unknown to me).
Regards,
Naveet.
Thank you soooo much...It worked.
I am getting closer results by correcting the piezo default depth,...
Thank you so much.
Regarding my other post,
Since, I am applying compression force on piezo, and would be measuring its voltage then how would 'terminal BC' be used, since that condition is used for applying a particular value of voltage (which rather I need to measure, hence is unknown to me).
Regards,
Naveet.
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Posted:
1 decade ago
You can connect the terminal to a circuit, i.e. a high impedance resistor and measure the voltage at the resistor. You can find contributions about circuit physics by search on the forum.
--
Edgar J. Kaiser
emPhys Physical Technology
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Posted:
1 decade ago
Ok..I understood your solution.
But what should be the value of resistance to be used in circuit.
Also I need to find a single value of voltage between two terminal of PZT (which would be varying all along the domain of PZT, when compression load would be applied)
So I think, putting this circuit might not serve the purpose. Or else please suggest me the way to find a single value of voltage difference between top and bottom of piezo.
One solution which I thought of was the line integral of electric field along the thickness of piezo to get the voltage. But in this case the voltage needs to be constant at top and bottom.
Regards,
Naveet.
But what should be the value of resistance to be used in circuit.
Also I need to find a single value of voltage between two terminal of PZT (which would be varying all along the domain of PZT, when compression load would be applied)
So I think, putting this circuit might not serve the purpose. Or else please suggest me the way to find a single value of voltage difference between top and bottom of piezo.
One solution which I thought of was the line integral of electric field along the thickness of piezo to get the voltage. But in this case the voltage needs to be constant at top and bottom.
Regards,
Naveet.
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Posted:
1 decade ago
It exactly works as suggested. Just make sure the resistance is much higher than the piezo's impedance.
--
Edgar J. Kaiser
emPhys Physical Technology
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Posted:
1 decade ago
Thank you very much Edgar.
I will try your suggestion and will come back if any further query..
Once again lots of thanks for your helpful support.
Kind Regards,
Naveet.
I will try your suggestion and will come back if any further query..
Once again lots of thanks for your helpful support.
Kind Regards,
Naveet.