Medium: Material Properties

The medium defines the material properties through which acoustic waves propagate. It forms the second of the four core components that define every k-Wave simulation.

Key Properties

Sound Speed (sound_speed): Speed at which acoustic waves travel through the material [m/s]. Required for all simulations.

Density (density): Material density [kg/m³]. Affects impedance and reflection at interfaces.

Absorption (alpha_coeff, alpha_power): Acoustic energy loss following \(\alpha(f)=\alpha_0\,f^{y}\), with units typically dB/(MHz^:math:y·cm).

Nonlinearity (BonA): B/A parameter controlling nonlinear wave-steepening effects.

Homogeneous vs Heterogeneous

Homogeneous: Uniform properties throughout domain:

medium = kWaveMedium(sound_speed=1540)  # Soft-tissue-like medium

Heterogeneous: Spatially varying properties:

medium = kWaveMedium(sound_speed=c_map)  # c_map shape: (Nx[, Ny[, Nz]]) in m/s

Common Media

# Water (lossless)
water = kWaveMedium(sound_speed=1500, density=1000)

# Soft tissue (with absorption)
tissue = kWaveMedium(
    sound_speed=1540,
    density=1000,
    alpha_coeff=0.75,  # dB/(MHz^alpha_power·cm)
    alpha_power=1.5,   # typical for soft tissue
)

For detailed material-property databases and advanced absorption modeling, see ../fundamentals/understanding_media.