Question

Explain daiatomic lattice behaves as which fillter and why

Answer 1

A diatomic lattice can be considered as a linear chain of equal masses connected with a spring. Waves propagate in this lattice if their frequency is lower than

$$\omega_0=1\sqrt{k/m}.$$

Higher frequencies lead to amplitude decrease (evanescent waves). Frequencies between 0 and $\omega_0$ is referred to as a pass-band.