def impedance_miki_model(f, sigma):
    """
    impedance_miki_model(f, sigma)
    Caculate the surface impedance according to Miki Model.
    Parameters
    ----------
    f : 1-D array of frequencies in [Hz].
    sigma : double flow resistivity in [Ns/m^4].
    Returns
    -------
    Zs : 1-D array of normalized ground impedance, Zs/rhoc.
    """
    Zs = (
        1
        + 5.51 * (1000 * f / sigma) ** (-0.632)
        - 8.42j * (1000 * f / sigma) ** (-0.632)
    )

    return Zs