Table 2: MEXEL input description
macro?
a= O// um, left border of upper plate
b= 1811 um. right border of upper plate
steps= 36// number of steps in discretization
h= (h-aysteps// stepsize
damp= 2.5e6// damping factor
emodul= 7.22e411 kg/(um*sec"2), modulus of elasticity
.rho= 2.7e-15// kg/(umA3), density of aluminium
delta= 0.2// um, thickness of upper plate
hi= 0.4N um, distance upper plate - isolator
di= 031 urn, thickness isolator
eps0= X.854e-hN Ig*uml(V*2*sec"2), electrical field constant
epsk 3.8// relative permittivity isolator. Si02
kl= emodul * delta"2 / ( 12 * rho)// only for canvenience
k2= epsO * epsl"2 / (2 *rho * delta) // only for convenience
end
discretirations
x: steps.a,h// spatial variable to he discretked: x
u(x,t)// U is a function of z and t (timej. 1 is globally defined
end
equations
//deflection: U. excitation: w
//second order time derivative and fouth order spatial deribative on U
u.{tt)=-kI *u-(xxxx) +W
//excitation voltage from electronic circuit: v-ex
w=k2*v~exA2/((epsl*(hi-u)+dl)"2)-damp*(u~{tj)
I/ capacitance over oxide, quadratic plate considered
c-ox = epsO*eps I *(h-a)*2/di
// capacitance over air gap by spdtial integration
c-air = epFO*(h-a)*int_(a)"(h)( l/(h-u), x)
//overall capacitance
c-dmd = c-air * c-ox / (c-air + LOX)
end
constraints
//constraints for u:zero vertical displacement at x=a and x=h.
//zero gradient of bending at x=a and x=b
u(x=a)= 0
u(x=hj= 0
I/ the folloaing equations result from the formula of the first
//order, spatial derivative approximating the iero gradient
u(x=a-h)=O.l25 *(-u(x=a+Z*h) + 8 * u(x=a+h))
u(x=h+h)= 0.125(-u(x=b-2*h) + R * u(x=h-h))
u(x=a-2*h)= 0
u(x=b+?*h)= 0
end
simulator
* circuit devices and simulator commands
.TRAN
end