Thin wire

A wire or rod whose diameter is small compared to the length of a pressure wave in the wire at a given frequency. The diameter is considered small if the wave speed is not affected by transverse motion due to Poisson coupling.

Note: the wire's cross-sectional area is assumed to be constant along its length.

For common resonator materials (aluminum, titanium, steel) whose wave speeds are approximately 5000 m/sec and whose Poisson's ratios are about 0.3, the error in wave speed or wavelength will be less than 0.1% if the rod diameter is less than 10% of the thin-wire half-wavelength (e.g., a diameter of less than about 13 mm at 20 kHz).

Also see —
Inverse Mori equation
Mori equation
Rayleigh equation
Thin-wire wave speed