Electronics > Projects, Designs, and Technical Stuff
CPLD erase from Airport X-ray scanners
EEEnthusiast:
I can minimize the impact in one direction. that the best which can be done..
David Hess:
--- Quote from: Psi on February 03, 2020, 10:02:34 am ---
--- Quote from: David Hess on February 03, 2020, 04:46:39 am ---Maybe someone left the package in the x-ray machine for an extended inspection?
--- End quote ---
About 12 years ago I was contracted to write a small report into the safety of consumer electronics going through airport xrays.
The airport staff wanted some factual data/evidence when dealing with customers who insisted the xray machine had damaged their device or data.
For the first test I put a hard disk, a floppy disk and USB drive through the machine 5 times and checksum'ed them before/after to confirm data integrity.
Then i sat them on the xray window inside the tunnel with the conveyor off but xrays forced on. They were in the xray beam continuously for a time that equaled around 9000 cycles through the machine normally. They still all checksum'ed correctly.
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Multilevel Flash memory with a low retention time is what would fail first and it was neither as common nor as sensitive 12 years ago. I would not expect magnetic media or drives to be affected at all. NOR Flash and EPROM are relatively insensitive but they can be erased by x-rays eventually just like UVEPROMs.
--- Quote from: texaspyro on February 04, 2020, 05:10:28 am ---There is a company (can't recall who) that makes a line of precision voltage reference chips that use the charge in a floating gate to set the voltage. They have a report on how x-rays affect the voltage. Also saw some independent tests. I seem to remember the results said the technology was not all that precision.
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That was Xicor purchased by Intersil in 2004.
Advanced Linear Devices also uses floating gate technology in analog applications.
ejeffrey:
--- Quote from: EEEnthusiast on February 04, 2020, 05:58:33 am ---Based on the inputs, it looks like an aluminum heat sink over the CPLD may be the cheapest solution for the problem. They are easy to buy and install..
Not sure of Zinc sheets, will check if they are available online.
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One of those tin plated steel EMI cans may be better than an aluminum heat sink depending on the relative thickness. And as that intersil appnote listed above suggests copper ground planes on the PCB side helps a lot.
Basically, x-rays come out of the source in an energy spectrum. X-rays are efficiently stopped by materials that have ionization transitions comparable to the xray energy. The bigger the atomic number, the higher energy the innermost electrons ionization energy and the higher total absorption cross section for lower energy x-rays. You mostly only care about the xrays that will be absorbed by silicon (Z=14) or other elements inside your chip -- higher energy xrays will just go right through with little fuss. Aluminum (Z=13) is only marginally effective at stopping the x-ray energies that you care about. Iron (Z=26), copper (Z=29) and tin (Z=50) are going to be much more effective even if they are substantially thinner.
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