MaterialGrid with same material type is not working

[ramji28]

Dear Meep community,

I was trying to build a metasurface layer with the MaterialGrid class. The layer consists of two mediums. I calculated the absorption spectrum of the metasurface built with and without MaterialGrid. If the two mediums which make up the layer are of different material types (LorentzianSusceptibility and frequency-independent isotropic ε), then the absorption spectrum with and without the Material grid matches. However, if the two mediums are mediums of the same material type (LorentzianSusceptibility), then the absorption spectrum with and without the MaterialGrid does not match (see the plots below). Can someone help me with this issue?
Thank you in advance.

eps_inf = 1.1
num_lorentzians = 2
E_susceptibilities = []
ps = [37.0880, 0.0000, 0.0483, 0.0000, 8.9469, 5.8681]
for n in range(num_lorentzians):
    mymaterial_freq = ps[3 * n + 1]
    mymaterial_gamma = ps[3 * n + 2]
    if mymaterial_freq == 0:
        mymaterial_sigma = ps[3 * n + 0]
        E_susceptibilities.append(mp.DrudeSusceptibility(frequency=1.0, gamma=mymaterial_gamma, sigma=mymaterial_sigma))
    else:
        mymaterial_sigma = ps[3 * n + 0] / mymaterial_freq**2
        E_susceptibilities.append(
            mp.LorentzianSusceptibility(
                frequency=mymaterial_freq,
                gamma=mymaterial_gamma,
                sigma=mymaterial_sigma,
            )
        )

Medium1 = mp.Medium(epsilon=eps_inf, E_susceptibilities=E_susceptibilities)

Medium2 = mp.Medium(index=1)

w0 = np.array([1390])  # in cm^-1
sqrt_s = np.array([185.42])  # in cm^-1
gamma = np.array([20])  # in cm^-1
e_inf = 1  # epsilon infinity


w0_um = 1e4/np.array(w0)  # convert to um
gamma_um = 1e4/(np.array(gamma))  # convert to um   
s = np.square(sqrt_s)  # in cm^-2
sigma = (s/np.square(w0))  # unitless

f_n = 1/(w0_um)  # convert to frequency
f_gamma = 1/(gamma_um)  # convert to frequency

susc = [mp.LorentzianSusceptibility(frequency=f_n[0], gamma=f_gamma[0], sigma=sigma[0]),]
            
Medium3 = mp.Medium(epsilon=e_inf, E_susceptibilities=susc)`

[smartalecH]

Are you passing the dispersive materials via the extra_materials parameter in your Simulation constructor? Meep can't pull dispersive materials from MaterialGrids directly.

Edit: hmm looks like you are.