This demo visualizes how the dispersion relation and wave propagation in a diatomic spring-mass chain change with the mass ratio \(m_1/m_2\) and the excitation frequency \(f\).
In the dispersion relation, there is a gap between the optical and the acoustic branch known as phononic bandgap. In the bandgap frequency range, there is no real-valued wavenumber solution and the elastic wave will be drastically attenuated.
For the acoustic branch, \(m_1\) and \(m_2\) oscillate in phase. And they oscillate out of phase on the optical branch.
