Module 1: Membrane Type of Acoustic Metamaterials

Lesson Summary

Common Membranes:
- Diaphragm on loudspeaker
- Drum vellum
- Ear drum
- Diaphragm of microphone

Two types of membrane:
Limp - sustain transverse loading using in-plain normal tension (membranes).
Stiff - sustain transverse loading using shear stresses and bending moment (panels).

The Unit Cell Type 1, is a membrane clamped inside a subwavelength waveguide and subjected to a plane wave front.

The Unit Cell Type 2, is a membrane with a mass attached to the center, clamped inside a subwavelength waveguide and subjected to a plane wave front.
External Response Parameters
External pressure applied on membrane
External Tension applied on membrane
Internal Response Parameters
Membrane density
Membrane thickness
Attached mass density
Attached mass location
Membrane Type AMM manipulate sounds using the principle of negative effective density - These are know as Negative density metamaterials.

Thin and elastic membranes that are nearly acoustically transparent, become perfect sound wave blockers in a wide frequency region of negative effective density due to the resultant wave not propagating spatially in a negative density region.
The region of negative effective density depends on:
Surface density of the membrane
Thickness of the membrane
Tension applied to the membrane
Young's Modulus
Poisson's Ratio
Mass value attached to membrane