Acoustic gasket and sealing guidelines

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removed, the higher-pressure air inside will flow out. The cavity will be left at a pressure

slightly lower than the outside, causing air to be drawn back in. This process repeats with

the magnitude of the pressure changes decreasing each time. The air in the port (the neck

of the chamber) has mass. Since it is in motion, it possesses some momentum. A longer

port would make for a larger mass, and vice-versa. The diameter of the port is related to the

mass of air and the volume of the chamber. A port that is too small in area for the chamber

volume will "choke" the flow while one that is too large in area for the chamber volume tends

to reduce the momentum of the air in the port.

Helmholtz resonance is the phenomenon of air resonance in a cavity, such as when one

blows across the top of an empty bottle. The name comes from a device created in the

1850s by Hermann Von Helmholtz, the "Helmholtz resonator", which he, the author of the

classic study of acoustic science, used to identify the various frequencies or musical pitches

present in music and other complex sounds. If the volume of the MEMS cavity is greater

than the neck, the resonator corresponds exactly to a Helmholtz resonator. More commonly

this condition is not respected since the volume of the MEMS cavity is smaller than the

entire volume created by the gasket cavity. Hence, since the equations regulating the

behavior of a stationary wave inside an acoustic cavity are complex and depend on the

mandatory.

when analyzing acoustics:

1.

The radiation problem: a vibrating structure (a speaker, for example) radiates sound

into the surrounding space. A far-away boundary condition is necessary to model the

unbounded domain.

2.

The scattering problem: an incident wave impinges on a body and creates a scattered

wave. A far-away radiation boundary condition is necessary.

3.

The sound field in an interior space (such as a room): the acoustic waves stay in a finite

volume so no radiation condition is necessary.

4.

Coupled fluid-elastic structure interaction (structural acoustics). If the radiating or

scattering structure consists of an elastic material, then one must consider the

interaction between the body and the surrounding fluid. In multiphysics coupling, the

acoustic analysis provides a load (the sound pressure) to the structural analysis, and

the structural analysis provides accelerations to the acoustic analysis.

5.

The transmission problem: the incident sound wave propagates into a body, which can

have different acoustic properties. Pressure and acceleration are continuous on the

boundary.

In the case of a microphone, the scenario considered is the sound field in an interior space.

Additionally the tool allows setting the boundary condition for every surface in order to

define the problem to simulate.

Typical boundary conditions are:

 Sound-hard boundaries. A sound-hard boundary is a boundary at which the normal

component of the acceleration is zero. This means that the normal derivative of the

pressure is zero at the boundary. This condition will be used to understand the

dependency of the sound-soft boundaries.

 Sound-soft boundaries. This means that the differential pressure vanishes at the

boundary.

 Impedance boundary conditions. The impedance boundary condition is a generalization

of the sound-hard and sound-soft boundary conditions. From a physical point of view, the