electrostatic
When we comb our hair (with a plastic comb) and then bring the comb close to bits of paper, the bits get attracted to the comb. I understand this is because the comb is now electrically charged.
Why then, don't these same bits of paper get attracted to a live wire, or a terminal of a battery? Isn't the battery electrically charged?
You can't guarantee the polarity of the charge and so some form of rectification is needed to ensure that any current is passed through in the same direction irrespective of polarity. This could be achieved with two capacitors and two diodes so that you can store the energy from positively and negatively charged people on two separate capacitors.
The diodes should have an extremely low leakage to prevent charge being lost. The capacitor should also be chosen to have very low leakage for the same reasons.
I think I'd also consider having a spark-gap protection device across the input to the diodes to prevent over-voltage damage. If you use the carpet static value value below to work out the capacitance and voltage rating you should be OK: -
20 mJ = \$\dfrac{CV^2}{2}\$ and if you chose 1 uF, the voltage rating would need to be: -
\$\sqrt{\dfrac{2\times 20\times 10^{-3}}{1\times 10^{-6}}}\$ = 200 volts.
For 10 uF the voltage rating would be 63 volts
1 nF would require a voltage rating of over 6000 volts.
I was planning to have a metal plate on a wristband and the capacitor connected to this and then to ground, this I think should charge the capcitor from what I understand. Would this work?
I would consider the capacitor(s) and diode(s) to be fixed and let folk walking around discharge themselves to a plate connected via the diode(s) to the capacitor(s). It might be a good idea to issue conductive thimbles so that folk don't feel the spark that might jump to the plate. Safety should be considered and the diodes will prevent someone getting a full energy discharge if they touch the plate.
Antistatic precautions mean you should never move a device through a large potential difference.
Once you and the ESD mat are connected to ground, they are at the same 0v potential. Take hold of the bag, this bring it and its contents to 0v. Now you can open the bag and handle the devices with anything that's also at 0v. This includes fingers, or conductive things you are holding. So metal tweezers, 'antistatic' pliers that have special conductive plastic handle covers, cotton gloves (which retain enough moisture to be slightly conductive) but NOT tools with insulating handle covers or plastic gloves.
Best Answer
If you charge up a plastic comb or balloon, etc., enough to get a tiny spark, that surface charge can be on the order of a few thousand volts, due to the tiny capacitance of the object. Whereas the chemistry inside a typical battery can only create a voltage of on the order of a single volt.
The difference in electric field potentials, and thus the force they can create, is thus several orders of magnitude.