# Measure exponential field attenuation
Propagate a forward-plane component through a medium whose attenuation
coefficient is `ln(2)` nepers per metre. Its field amplitude halves over each
metre while its propagation phase continues to rotate.
The coefficient is homogeneous over the complete problem. This recipe does not
model interfaces, spatially varying materials, or scattering.
The field remains a three-dimensional scalar free-field model without
polarization, impedance, obstacles, or diffraction. Amplitude-squared
observations are normalized proxies, not physical intensity, power, or energy.