Poisson's ratio

A material property: the ratio of transverse strain to axial strain. Most acoustic materials have a Poisson's ratio between 0.29 and 0.34. [No units]

An isotropic material like aluminum will have only one Poisson's ratio. An orthotropic material like titanium will have three Poisson's ratios.

Poisson's ratio is relatively unaffected by temperature.

Poisson's ratio affects resonator tuning and uniformity. A material with a low Poisson's ratio will have low Poisson coupling and will therefore give superior resonator uniformity, all other things being equal.