AN4427 Datasheet, PDF (15/19 Pages) STMicroelectronics – Gasket design for optimal acoustic performance

AN4427
Acoustic gasket and sealing guidelines
Figure 11. Example of tablet - design and acoustic cavity
As previously stated, the acoustic simulation is performed on the geometry of the all of the
components involved. Figure 11 (b) represents the acoustic cavity to be simulated,
extracted from the entire structure depicted in Figure 11 (a). On the other hand, the acoustic
properties of the materials must be set in the simulator to provide proper simulation results.
The materials included in this simulation are those commonly adopted by the manufacturer
of the electronic device; the printed circuit consists of FR4, the gasket is soft rubber and the
cover is made of aluminum.
The COMSOL^® tool has been used to study the effect of this geometry as well as the
materials and the result is shown in the following figure.
Figure 12. Frequency response
30
AM17603v1
Resonance frequency
@ 21600 Hz
25
20
15
10
5
0
-5
100
1000
10000
(a): Frequency responce
F (Hz)
(b): Pressure @ 21600 Hz
Figure 12 (a) shows the frequency response characterized by a resonance peak around
21600 Hz; Figure 12 (b) shows how the magnitude of the pressure, expressed in dBSPL, is
distributed inside the cavity. The pressure inside the cavity is plotted at the resonance
frequency; this is the reason why the maximum is exactly on the MEMS membrane.
DocID025705 Rev 1
15/19
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