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Homework Help: 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




    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.


    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
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