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dft_energy.py
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dft_energy.py
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from __future__ import division
import unittest
import meep as mp
# compute group velocity of a waveguide mode using two different methods
# (1) ratio of Poynting flux to energy density
# (2) via MPB from get-eigenmode-coefficients
class TestDftEnergy(unittest.TestCase):
def test_dft_energy(self):
resolution = 20
cell = mp.Vector3(10, 5)
geom = [mp.Block(size=mp.Vector3(mp.inf, 1, mp.inf), material=mp.Medium(epsilon=12))]
pml = [mp.PML(1)]
fsrc = 0.15
sources = [mp.EigenModeSource(src=mp.GaussianSource(frequency=fsrc, fwidth=0.2*fsrc),
center=mp.Vector3(-3), size=mp.Vector3(y=5),
eig_band=1, eig_parity=mp.ODD_Z+mp.EVEN_Y,
eig_match_freq=True)]
sim = mp.Simulation(resolution=resolution, cell_size=cell, geometry=geom,
boundary_layers=pml, sources=sources, symmetries=[mp.Mirror(direction=mp.Y)])
flux = sim.add_flux(fsrc, 0, 1, mp.FluxRegion(center=mp.Vector3(3), size=mp.Vector3(y=5)))
energy = sim.add_energy(fsrc, 0, 1, mp.EnergyRegion(center=mp.Vector3(3), size=mp.Vector3(y=5)))
sim.run(until_after_sources=100)
res = sim.get_eigenmode_coefficients(flux, [1], eig_parity=mp.ODD_Z+mp.EVEN_Y)
mode_vg = res.vgrp[0]
poynting_flux = mp.get_fluxes(flux)[0]
e_energy = mp.get_electric_energy(energy)[0]
ratio_vg = (0.5 * poynting_flux) / e_energy
m_energy = mp.get_magnetic_energy(energy)[0]
t_energy = mp.get_total_energy(energy)[0]
self.assertAlmostEqual(m_energy + e_energy, t_energy)
self.assertAlmostEqual(ratio_vg, mode_vg, places=3)
if __name__ == '__main__':
unittest.main()