EMC Question of the Week: January 11, 2021
The semi-transparent gray or pink bags that electronic products are often shipped in are
- excellent conductors
- slightly conductive
- excellent insulators
- magnetic field shields
Answer
The correct answer is “b.” These shipping bags are designed to protect their contents from electrostatic discharge during transit and while being removed from the bag. The bag is essentially a low-frequency Faraday cage. The slight conductivity allows charge to move around on the bag causing the electric fields inside the bag to be near zero at all times. It also allows charge to be drained off the bag prior to removing the electronics.
An excellent conductor like aluminum foil would also make a great Faraday cage. However, the foil could become part of a discharge path while the card was being inserted or extracted from the bag. Foil can also short out batteries or charged capacitances on the board resulting in damage. Insulating materials provide no protection while inserting or extracting the card and can actually be the source of triboelectric charging.
Finally, is not necessary to provide magnetic field shielding for most electronic devices. Ambient magnetic fields are generally much too weak to damage electronics and there is no magnetic equivalent to electrostatic discharge (because free magnetic charge does not exist in the real world).
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