# How to use bempp if the surface has dielectric and perfect conducted parts
**URL:** https://bempp.discourse.group/t/how-to-use-bempp-if-the-surface-has-dielectric-and-perfect-conducted-parts/53
**Category:** Applications
**Created:** [10 December 2020 18:13 UTC](https://bempp.discourse.group/t/how-to-use-bempp-if-the-surface-has-dielectric-and-perfect-conducted-parts/53 "2020-12-10T18:13:55Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@Mix](https://bempp.discourse.group/u/Mix)
#### Post date: [10 December 2020 18:13 UTC](https://bempp.discourse.group/t/how-to-use-bempp-if-the-surface-has-dielectric-and-perfect-conducted-parts/53/1 "2020-12-10T18:13:55Z")
Hello everyone!
I saw the example when bem++ is used for two dielectric spheres. But if I have the perfectly conducted sphere and it has a layer of dielectric, how to solve this in bem++? Could you please help and provide the example?
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### Author:  [@timo](https://bempp.discourse.group/u/timo)
#### Post date: [17 December 2020 13:50 UTC](https://bempp.discourse.group/t/how-to-use-bempp-if-the-surface-has-dielectric-and-perfect-conducted-parts/53/2 "2020-12-17T13:50:46Z")
Hi, you can define different boundary parts in your spaces and your grid functions. The Laplace mixed-Neumann Dirichlet Notebook has examples for how to do this. This will allow you to define problems, where the boundary condition changes across the boundary.
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### Author:  [@massdm](https://bempp.discourse.group/u/massdm)
#### Post date: [15 May 2025 09:21 UTC](https://bempp.discourse.group/t/how-to-use-bempp-if-the-surface-has-dielectric-and-perfect-conducted-parts/53/3 "2025-05-15T09:21:08Z")
Hello.
The Laplace mixed-Neumann Dirichlet Notebook assumes boundary conditions of the two kinds:
1. def dirichlet\_data(x, n, domain\_index, res):
2. def neumann\_data(x, n, domain\_index, res):
Meanwhile a Neumann boundary condition on the boundary between two dielectrics is quite different: \epsilon\_1 E\_1 = \epsilon\_2 E\_2