Home / Examples / Piezoelectric Analysis [Rayleigh] / Example 12: Acoustic Impedance

Example 12: Acoustic Impedance

General

Acoustic impedance is set in the model of Example 2 to take into account the air resistance.
The effect of the acoustic impedance is examined.

Results will vary depending on Femtet version and the PC environment.

Analysis Space

Item	Settings
Analysis Space	3D
Model Unit	mm

Analysis Conditions

Item	Settings
Solver	Piezoelectric Analysis [Rayleigh]
Analysis Type	Harmonic Analysis
Options	N/A
Output Setting	Select [Impedance]

The harmonic analysis tab is set up as follows.

Tab

Setting Item

Settings

Harmonic analysis

Frequency

Minimum: 4.75×103 [Hz]

Maximum: 4.90×103 [Hz]

Sweep Type

Select [Linear Step by Division Number].

Division: 50

Model, Body Attributes and Materials - same as the example 2

Boundary Conditions

Boundary Condition Name/Topology	Tab	Boundary Condition Type	Settings
Outer Boundary Condition	Mechanical	Acoustic Impedance	50 [Pa*s/m]
earth/Face	Electric	Electric Wall	Electric Potential Specified: Electric Potential 0 [V]
earth/Face	Mechanical	Acoustic Impedance	50 [Pa*s/m]
hot/Face	Electric	Electric Wall	Electric Potential Specified: Electric Potential 1 [V]
hot/Face	Mechanical	Acoustic Impedance	50 [Pa*s/m]

All boundary conditions are set with the acoustic impedance so that the acoustic impedance is set around the model entirely.

In the project file, the values of acoustic impedance are all set at 50 [Pa・s/m] for the model, [12_Harmonic analysis_50].

For the model, [12_Harmonic analysis_409], the values of acoustic impedance are all set at 409 [Pa・s/m].

For the model, [12_Harmonic analysis_0], the values of acoustic impedance are all set at 0 [Pa・s/m].

Results

The frequency responses of impedance obtained by the analysis with three acoustic impedances are compared. As the acoustic impedance becomes larger, the response at the resonant point becomes smoother.

Graph legends and corresponding acoustic impedances are as follows.

[12_Harmonic analysis_50.s1p]: 50 [Pa・s/m]

[12_Harmonic analysis_409.s1p]: 409 [Pa・s/m]

[12_Harmonic analysis_0.s1p]: 0 [Pa・s/m]

409 [Pa・s/m] is the specific acoustic impedance of the air.

The frequency response of impedance can be plotted from an S(Y) parameters graph.
To add impedance characteristics on the same graph, drag and drop the file with extension s1p from a result folder.