Post-mortem: MRI disables every iOS device in facility
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The processor in a modern, high volume device typically has its main clock driven by what's known as a MEMS oscillator. These are barely visible mechanical systems that resonate at some designed frequency, and include packaging to convert this resonance into a useful electrical clock signal. These devices are extraordinarily cheap ways to produce a steady clock, but they have a number of drawbacks. Most relevant, in order for these types of devices to function properly, the mechanical resonator must be inside a tiny hermetically sealed chamber with either a controlled gas inside or a vacuum, as the gas composition in the chamber can affect the output frequency.
For both cost and physics reasons, these hermetic seals are not perfect, and are somewhat commonly permeable to small atomic gasses such as helium.
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For this specific case, Apple devices probably share a common family of MEMS resonator to reduce manufacturing costs. This clock likely leaks in helium rich atmospheres, pushing the output frequency outside of the bounds that the main processors are designed to handle, rendering them non-functional. If left idle long enough, the devices may begin to function again, but depending on the concentration of helium which leaked in, this could take anywhere from weeks to years to occur in natural atmosphere and temperatures.
[0] https://www.reddit.com/r/sysadmin/comments/9mk2o7/mri_disabl...
At risk of provoking a standard flame war...
They had mentioned that Android phones are unaffected, but don't those generally use even more "economical" manufacturing?
The comment is looking to explain why all the Apple devices failed; they were all affected by the same sensitivity to helium.
Android devices tend to use a multitude of different parts to each other, so while some may have been affected you wouldn’t expect them all to fail in sync like the Apple devices did.
>>There were also a lot of Android phones in the facility at the time, none of which were impacted.
Somehow, all these commodity vendors all used designs that were resilient against helium.
Not that this is necessarily 'Not Invented Here' syndrome for Apple, as I think they may have compelling reasons to design and procure a bespoke component, the benefit of using something off the shelf is that it is battle tested by other people. You get a component tested not just on your use cases and failure modes, but everyone else's, so that if your needs or environment changes it's more likely for the component to keep working.
I would also love to know more about how the enclosures used affects helium sensitivity; is helium pervasive enough that it gets everywhere anyway, or can some phone bodies etc keep it out.
Also, if there was enough helium to contaminate the entire atmosphere, was there not a pretty significant chance of an asphyxiation hazard?
Besides, an MRI's liquid helium tanks are big, but not that big to cause trouble if they leak over a period of a couple of hours in a ventilated room.
Any clues why such an environment doesn't make Android phones behave in such a way?
If it wasn't dangerous one could try the same with hydrogen. If the post is correct it should have a similar effect (if the device doesn't explode during the test).
Since the crystal is literally vibrating inside the metal can it's packaged in, the atmosphere around the crystal influences the natural frequency. Helium will make it vibrate it faster, since it presents less air resistance to the crystal.
A bit of googling seems to indicate most smart phones have a crystal oscillator. But, Android would have the advantage of manufacturer diversity...so lots of different types of crystal oscillators, perhaps some that are sealed better than the iphone ones, or quartz vs silicon, etc.
This does sort of illustrate an issue with the iphone tech monoculture. Lots of devices with similar components, and similar versions of software. Find something that adversely affects them, and you can disrupt a lot of people. It's probably hard to find something similar for Android since the hardware and even software varies a lot.
"How effective is the hermetic seal of MEMS oscillators??
One of the key elements enabling extremely stable MEMS resonators is SiTime’s EpiSeal™ process which hermetically seals the resonators during wafer processing, eliminating any need for hermetically sealed ceramic packaging. SiTime’s EpiSeal resonator is impervious to the highest concentration elements in the atmosphere, nitrogen and oxygen, and therefore acts as a perfect seal. Previous generations of EpiSeal resonators may have been impacted by large concentrations of small-molecule gas. Newer EpiSeal resonators are impervious to all small-molecule gases. Please contact SiTime in case you are planning to use a SiTime device in large concentrations of small-molecule gas, so that we can recommend an appropriate, immune part."