midterm review Flashcards
the forces between the plates are all _____ and tend to _____ with capacitor size
attractive, incease
the effective k of a cantilever is more sensitive to which? thickness b, width a, or length L
L and b, because only linearly depends on a
The fringing field is independent of ___
displacement
What are we “trying to do in electrostatic actuators”?
increase capatnce C
for electrostatic comb drives, what dC/dx?
thicker, closer and more fingers, makes stronger forces.
dC/dx changes a lot with what in electrostatic comb drives?
h and g^-beta
what is the mater with making finger in comb drives closer? why want to do this?
We want them closer to increase the force, but putting things close introduces bending forces.
how do we control charge in electrostatic actuators?
we have a grounding plate
levitation is generallay :desirable or undesirable?
undesirable. we can avoid it by alternating the charges, and by putting a crounding layer.
WHat is the pull in voltage?
the voltage after which (larger values) will lead to snapping of the actuator. Vp is when the mechanical spring force can no longer conter the electrostatic force and the plates snap together. the static equation for equilibrum Fnet=Fmech+Felectrostatic=0 is not satisfied.
What is pull in voltage weakly and strongly a function of?
weakly a function of A area and k spring constant, but strongly of gap d.
What is xp?
the pull in displacement, which is 1/3 of d
The beauty of harmonic excitation, the phase shift between the displacement, velocity, and acceleration is ___. and the frequency does or does not change?
90 degrees not change
harmonic system is stable if and only if ….
both real and imaginary parts are negative
when are both the real and imaginary parts of the roots to equation of motion negative ?
when the coefficients have the same sign, m, c, k
