EEVblog #1149 - How An Electrostatic Whiteboard Works

How an electrostatic adhesion Coulomb Force whiteboard works.
Plus teardown and measurement.

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[KerryWongBlog]

Old plotters (like the HP 7044A I did a teardown a while ago) use electrostatic to hold down paper on the plotter surface. It was from the 80's...

[maxsnts]

So... how many circuits will you kill with this thing around? :)

[danlay]

Cool idea! Might want to keep it well away from static sensitive parts tho

[StreuB]

Dave, stop apologizing about the new lab! You just moved over man. We all know it's going to take a few months for harmony to set back in. We're here for you and the content, the rest is just adder. It'll get done when it gets done. Looks great anyway!

Thank you for your efforts and great content!

[motalasuger]

How nice to get videos relating to electrostatic stuff, after searching for information about a old (~70s?) electrostatic “air cleaner” that I bought after stumbling upon it on a second hand place. It’s a bit scary with the thought of high voltages in the box, but it does give that nice ozone fresh air smell too… ;)

[Bigrignohio]

Interesting. If it gets us more tutorials then great!

[TrystansWorkbench]

The explanation starts at 2:47 Excellent.

[bjiirn]

5:09 would it work with an antistatic bag?

[hjups]

I think the word that you were looking for is "permeate" (of the electric field).
That's a pretty interesting / clever device. I am guessing that it's working by creating a bunch of dipoles in the material that you stick on the surface, which bridge the gaps. Since the electric field will sort of spread out in arcs from the edges of the two plates, it will permeate what ever object you place on it. Since every object has a dielectric constant, the permeated electric field will induce a dipole which is proportional to k*E, where k is the constant and E is the electric field. And then the distribution of charge created from the induced dipoles attract the medium to the surface, with a stronger local electric field. That also explains why paper and aluminium foil were sticking better than wax paper, having a dielectric constant of 3.5, 10.8, and 2.5, respectively. This is compared to the dielectric constant in air which is nearly 1.
It's also interesting that one of the gap pairs have an increased surface area (the wiggles) when compared to the other. That might have something to do charge distribution, and / or making sure that the reverse dipoles are smaller (since each gap will induce a dipole in the direction of the electric field).
Note that the above is just a guess, especially since it's been a while since I have taken an E&M course.

[sausage]

I thought the video Q was great Dave. I'd be more than happy with the result!

[zarboov]

I think that the terminology was good, I would say that the new configuration with the paper “as a dielectric” is a lower energy state of the system, so it takes work to separate the paper - into the higher energy state.

[andymouse]

its also used as an "electrostatic chuck" for holding wafers prior to ion implantation in semiconductor cool Applied Materials use them

[vwestlife]

Unfortunately with the glare from the clear plastic sheet, it doesn't look as good on camera as a regular whiteboard. Especially what you wrote with the green marker is hard to see.

[TheDefpom]

Swap those multiplier caps out to quadruple the value.... MORE POWER!!!

[jsleeio]

is this the kind of thing we've seen in TV shows et al for decades ... where blueprints / xray films / etc are stuck up on an illuminated wall and Important People nearby immediately notice some invariably-plot-thickening detail?

[niklaskoskinen]

How I would describe the working principle of this thing is that it produces an electric field in the air in front of it. The field flows out from the positively charged electrode and into the negatively charged one, basically forming a capacitor with the board surface and air as it's dielectric. The electric field is mostly tangential to the surface. When an insulator is added in front of the board, charges in it will be polarised, creating an electrostatic force holding it to the board. On the other hand when you placed the foil on the board, electric influence will be the main factor affecting the situation, effectively moving charges in the foil to exactly mirror the charges in the board, again pushing it into the board. This also explains why the voltage drops when the foil is placed on the board; the foil increases the capacitance of the board significantly by effectively reducing the distance between the electrodes by creating two capacitors connected in series.

[WillArtie]

9:35! Yes the current does go "through" the plates/object - as per your video about current "through" a capacitor! I dont know really - i just remembered your capacitor vid discussion... edit: oh wrote too soon - you mention it...

[jmonsted]

Now you just have to find a A0 plotter in the dumpster so you can print stuff to put on that.

[dipi]

4:30 As one who likes proper units for checking:
k_sub_e == 8.9875×10⁹ N·m²/(A·s)²
Cheers!

Edited to add: discovered on Wikipedia that the SI value of the constant is exactly 8987551787.3681764 N·m²/(A·s)².

[tomaszwota]

I immediately thought "Hair!" when you said it's an electrostatic board. And you immediately mentioned them. ;)