import pyfar as pf
import numpy as np
frequencies = np.linspace(20, 20e3, 1000)
omega = 2*np.pi*frequencies
wavenumber = omega/pf.constants.reference_speed_of_sound
length = 30e-3
kl = pf.FrequencyData(wavenumber*length, frequencies)
cross_section = np.pi*(3.5e-3)**2
Z0 = pf.constants.reference_air_impedance/cross_section
T = pf.TransmissionMatrix.create_transmission_line(kl, Z0)
ax = pf.plot.freq(T.input_impedance(np.inf))
ax.set_ylim(100, 200)