1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Electrostatic Clamps Using Dielectrics

  1. Nov 3, 2009 #1
    b]1. The problem statement, all variables and given/known data[/b]
    Electrostatic clamps are used for holding workpieces while they are being machined, for holding silicon wafers during electron beam microfabrication, etc. They comprise an insulated conducting plate maintained at a potential of several thousand volts and covered with a thin insulating sheet. The workpiece or the wafer resets on the sheet and is grounded. It is advisabled to apply a film of oil to the sheet to prevent sparking.

    One particular type operates at 300 volts and has holding power of 2 atmospheres. If the insulator is Mylar (Class-A; [tex]\epsilon_r=3.2[/tex], what is its thickness?


    2. Relevant equations

    [tex]F=-\frac{dW}{dx}[/tex]

    [tex]W=\frac{1}{2}CV^{2}[/tex]

    [tex]Q=CV[/tex]


    3. The attempt at a solution
    Can I treat this system as a parallel plate conductor with a dielectric in the center? I don't see how to extract the thickness from this.

    [tex]F==-\frac{dW}{dx}=\frac{1}{2}\frac{Q^2}{C^2}\frac{dC}{dx}=\frac{1}{2}V^2\frac{dC}{dx}[/tex]

    But the capacitance is constant [tex]C=\frac{Q}{\Delta V}[/tex] meaning F becomes zero... which does not makes sense...

    Is there another way to calculate the capacitance?
     
    Last edited: Nov 3, 2009
  2. jcsd
  3. Nov 3, 2009 #2
    I know the capacitance of a parallel plate configuration with dielectric filling the middle is [tex]C=\frac{A\epsilon_0\epsilon_r}{d}[/tex], but I also know that the grounded "plate" on top throws this off.... I'm just not sure how
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook