超薄防护性网布和防水透气膜的声学建模【PPT版】
Presented by Dr.Jason McIntosh and Mr. Dest Zhao
On mesh Generations/Meshdeveloped trend
Purposeof acoustic materials
Protect audio components from foreignmaterial
solidmaterials (dust, dirt, debris, rocks, fingers, etc.) liquids(water, ear wax, oils, etc.)
Dampen acoustic modes
mode frequently detract from a desirable “flat” frequency
response resistive damping of the materials are commonly used to dampen these modes
Allow sound to pass through
most designs try to achieve an “acoustically transparent” condition
however there are times when the complex reactance can be used to enhance the acoustical behavior
Acoustic Impedance
Thin acoustic materials are characterizedby their acoustical impedance
If dP has units of Pa, and V has units of m/s,then Z will have units of MKS Rayls
If V has units of m3/s (volume velocity or U), then Z willhave units of Acoustic Ohms
Effects of Material Motion
An acoustic wave can pass through thematerial in one of two ways
Ro: Characterization as a simple resistor
Viscous shearing of the flow aroundfibers result in energy loss expressed as a resistance to the flow.
ZPM : Plate and Membrane Behavior
Plates: when a plate is deformed, the restoring force comes from its internalstructure
Membranes: when a membrane is deformed, the restoringforce comes from the tension T placed onto themembrane
Plateand Membrane Behavior
A material typically has either “plate”or “membrane” behavior, however it’s possible for it to have both, hence theimpedance through the material will be called
ZPM =impedance of Plate and/or Membrane
These modes have no net air displacementand so do not contribute to the impedance.
Effectsof Material Motion
Ares model for circular membrane showing ZPM
Anti Resonances
Circular Mode shape
Nodal line moves inward as frequency increases.
Just below Fo, the– and + volumetric displacements are equal and the net displacement is 0.
“Anti Resonances”
Effects of Material Motion
Mathematically these two paths arerepresented as a parallel combination of the viscous resistance through thefibers (Ro), and the impedance of theplate/membrane behavior of the material (ZPM).
The net material impedance (ZMAT) is
ZMAT = Ro || ZPM
Zmat= Ro || Zpm
The parallel impedance
ZMAT = Ro || ZPM
Has the property that
|ZMAT| £ |Ro|
and
|ZMAT| £ |ZPM|
Modeling in Ares – Circular shapes
Modeling in Ares – Rectangular shapes
Experimental Measurements vs Model
Mesh
Comparison between measured and simulatedreal and imaginary acoustic impedance of Acoustex 080 in a typical speakerconfiguration (left) and in an extreme configuration (right) in order tohighlight plate/membrane contribution in the acoustic impedance
Experimental Measurements vs Model
Membrane
Acoustic impedance of a “genericmembrane” measured and simulated with a typical area for MEMS protectionapplication. (left) Real and imaginary acoustic impedance. (right) Magnitude in dB.
Experimental Measurements vs Model
Hybrid material
Acoustic impedance of H68T02 (woven meshwith “leaky membrane” attached) measured and simulated with a typical area forMEMS protection application. (left) Real and imaginary acoustic impedance.(right) Magnitude in dB
Conclusions
Material motion is important indetermining the acoustical behavior of thin materials
Resonances and “Anti-resonances” dominatethe behavior of the material
Resonances are controlled by internal damping
“Leaky” resistive paths through thematerial can be used to control the “anti-resonances”
Ares “FEA” material elements model theseeffects with good correlation to experiments
