# Atmospheric pressure on a MEMS microphone...

#### Externet

Joined Nov 29, 2005
2,022
Hi. Splitting hairs here...
On both sides of the backing plate (shown dotted/perforated) , air pressure is the same, as it is a vented element in a MEMS microphone.

But on both styles of construction shown/linked below, there is a chamber with no venting to ambient (The one not having the sound hole).

----> https://www.researchgate.net/profil...wire-bonding-Top-sound-port-in-lid-Bottom.png

Does it mean that on board of an aircraft, pressure dropping at altitude, the diaphragm can deform into rupture and leave the pilot with no microphone ?

#### #12

Joined Nov 30, 2010
18,224
Ask the manufacturer. This could be as simple as a misinterpretation by the person who made the drawing, or by you.
Where did you get the information that there is no way to equalize the pressures across time periods between 1 second and 100 seconds?

#### GopherT

Joined Nov 23, 2012
8,009
Hi. Splitting hairs here...
On both sides of the backing plate (shown dotted/perforated) , air pressure is the same, as it is a vented element in a MEMS microphone.

But on both styles of construction shown/linked below, there is a chamber with no venting to ambient (The one not having the sound hole).

----> https://www.researchgate.net/profil...wire-bonding-Top-sound-port-in-lid-Bottom.png

Does it mean that on board of an aircraft, pressure dropping at altitude, the diaphragm can deform into rupture and leave the pilot with no microphone ?

Rupture a sealed container under tension because of low atmospheric pressure (vacuum) on the exterior? How much pressure difference to you expect when you get to altitude? Hint, Max is 14.7psi. Not much. How thick do you think the Apollo space capsule was? Also a 14.7 psi delta.

#### #12

Joined Nov 30, 2010
18,224
Hint, Max is 14.7psi.
I can easily imagine that a diaphragm designed for the tiny amount of energy in air born sound could pre-stress enough to wreck the sensitivity.
What I don't expect is a hermetically sealed container.

#### crutschow

Joined Mar 14, 2008
32,043
How thick do you think the Apollo space capsule was? Also a 14.7 psi delta.
Not much?
Just for fun, calculate the total pressure on the face of an old 35" TV CRT (say 21" x 28").

#### #12

Joined Nov 30, 2010
18,224
How thick do you think the Apollo space capsule was? Also a 14.7 psi delta.
Except for the time spent at several Mach numbers while in significant atmosphere.
Just for fun, calculate the total pressure on the face of an old 35" TV CRT (say 21" x 28").
I think @Hypatia's Protege has recent experience with that.
(8643.6 pounds of pressure)

#### Hypatia's Protege

Joined Mar 1, 2015
3,226
I think @Hypatia's Protege has recent experience with that.
As a matter of fact I've yet an 85 gallon 'hazmat' drum full-up with shards as a 'memento'

With abashed regards
HP

#12

#### #12

Joined Nov 30, 2010
18,224
I've yet an 85 gallon 'hazmat' drum full-up with shards as a 'memento'
I do feel bad for those poor CRTs.

#### Hypatia's Protege

Joined Mar 1, 2015
3,226
How thick do you think the Apollo space capsule was? Also a 14.7 psi delta.
As I understand it, the LEM's bulkheads were fabricated of little more than heavy foil
Heaven spare me the asperities suffered by Federal employees!

Best regards
HP

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#### Hypatia's Protege

Joined Mar 1, 2015
3,226
I do feel bad for those poor CRTs.
As do I Still... No point crying over spilled phosphor

Best regards
HP

#12

#### #12

Joined Nov 30, 2010
18,224
Heaven spare me the asperities suffered by Federal employees!
One of the astronauts said something like, "Eight million pounds of thrust from the lowest bidder."

#### GopherT

Joined Nov 23, 2012
8,009
Not much?
Just for fun, calculate the total pressure on the face of an old 35" TV CRT (say 21" x 28").
Your example is the exact opposite of what is happening in the microphone

The point is, thin materials / foils are much better at.
- containing pressure while placed in vacuum (MEMs microphone case), vs,
- maintaining structural integrity while evacuated and subjected to 1 atmosphere of pressure.

below why your example (compression) is not a 1:1 comparison of tension forces.
A rail car of chlorine is rated for 8 atmospheres and actually rupture at about 25atmospheres.

The problem is, one atmosphere of reverse pressure from atmospheric (a la CRT) causes this.

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#### GopherT

Joined Nov 23, 2012
8,009
Except for the time spent at several Mach numbers while in significant atmosphere.

I think @Hypatia's Protege has recent experience with that.
(8643.6 pounds of pressure)
The Apollo lunar lander was extremely thin and light weight. Always pressurized internally and subjected to operating in a vacuum.

You are correct about the re-entry module - which orbited the moon while the other two guys strolled around there. That one was heavier / stronger and had to withstand the re-entry and splashdown forces.

#### JohnInTX

Joined Jun 26, 2012
4,719
Does it mean that on board of an aircraft, pressure dropping at altitude, the diaphragm can deform into rupture and leave the pilot with no microphone ?
Traditional aircraft microphones have the element open to the atmosphere on both sides of the diaphragm. Besides taking care of any venting problems they achieve a degree of noise-cancelling since the ambient cockpit racket is present on both sides of the diaphragm. The mic is positioned close to the pilots mouth so his speech goes into one side of the mic. The noise is common-mode, the speech is differential for the audio signal.

#### WBahn

Joined Mar 31, 2012
28,475
Rupture a sealed container under tension because of low atmospheric pressure (vacuum) on the exterior? How much pressure difference to you expect when you get to altitude? Hint, Max is 14.7psi. Not much. How thick do you think the Apollo space capsule was? Also a 14.7 psi delta.
When did it have a 14.7 psi delta?

During ascent the cabin pressure was dropped until it was at about 5 psi.

Besides, the issue here isn't so much rupturing the microphone, as making it so stiff due to differential pressure that it can't function as a microphone transducer. When the Apollo spacesuits had much over 4 psi differential they became very stiff and difficult to work in.

#### Externet

Joined Nov 29, 2005
2,022

#### JohnInTX

Joined Jun 26, 2012
4,719
The cargo compartments are pressurized too, FWIW

#### WBahn

Joined Mar 31, 2012
28,475
The cargo compartments are pressurized too, FWIW
Which the pets in carriers certainly appreciate!

#### #12

Joined Nov 30, 2010
18,224
How thick do you think the Apollo space capsule was?
As I understand it, the LEM's bulkheads were fabricated of little more than heavy foil
The Apollo lunar lander was extremely thin and light weight.
I did read the, "space capsule" as the stronger container of astronauts. Sorry if I misinterpreted.

#### GopherT

Joined Nov 23, 2012
8,009
When did it have a 14.7 psi delta?

During ascent the cabin pressure was dropped until it was at about 5 psi.

Besides, the issue here isn't so much rupturing the microphone, as making it so stiff due to differential pressure that it can't function as a microphone transducer. When the Apollo spacesuits had much over 4 psi differential they became very stiff and difficult to work in.
It was never 14.7 but, if one had to pull a worst case scenario out of ones ass for a first guess, one atmosphere would be all that is possible as the I orphaned goes from sea level to a very high altitude. ill let the pilots tell me what the pressure delta is to normal flight levels - but even 14psi is easily contained in a small capsule of amost any structural material.

Now that the OP's theory (concern) that the capsule is/isn't vented to the rest of the universe has been addressed by @JohnInTX and others, the question is moot.