# Medium

Medium defines a dispersionless material by relative permittivity and electric conductivity.

This object corresponds to tidy3d.Medium (opens new window).

# Name

name: Optional unique name for the medium.

# Type

type: Medium model used by this material entry.

  • Options: Medium

# Color

color: Display color used for the medium in the GUI.

  • Type: color
  • Default: automatically assigned by the GUI

# General Properties

Use Permittivity or Refractive index to choose how the dispersionless medium is defined in the GUI.

# Permittivity

permittivity: Relative permittivity of the medium.

  • Type: float number
  • Unit: unitless
  • Constraint: greater than or equal to 1
  • Default: 1

conductivity: Electric conductivity. The imaginary part of the complex permittivity at angular frequency ω\omega is defined by σω\frac{\sigma}{\omega}.

  • Type: float number
  • Unit: S/um
  • Constraint: greater than or equal to 0
  • Default: 0

# Refractive Index

n: Real part of the refractive index used to define the medium.

  • Type: float number
  • Constraint: greater than or equal to 1

k: Imaginary part of the refractive index used to define material loss.

  • Type: float number
  • Constraint: greater than or equal to 0

freq: Frequency at which the refractive index values are evaluated.

  • Type: float number
  • Unit: Hz, kHz, MHz, GHz, THz, or other available frequency unit

The refractive-index form corresponds to constructing the medium from n, k, and freq.

# Convert To

loss_tangent: Convert the material to a loss-tangent representation.

The converted material is shown as Pole Residue, with fitting controls for eps_real, loss_tangent, frequency_range, and max_num_poles.

WARNING

After conversion, the GUI changes the type to Pole Residue with no option to revert automatically.

# Advanced

set_from_global_frequency: Toggle whether the frequency range is set from the Global Settings frequency range.

  • Options:
    • True: Use the global frequency range and disable manual frequency range inputs.
    • False: Manually set frequency_range.

frequency_range: Optional range of validity for the medium.

  • Type: two float numbers
  • Unit: Hz, kHz, MHz, GHz, THz, or other available frequency unit
  • Default: None

allow_gain: Toggle whether the medium is allowed to be active.

  • Options: True/False
  • Default: False

WARNING

Gain media can make simulations unstable and may cause divergence. Use allow_gain only when an active medium is intended.

← Pole Residue →