Lumped Modeling with Circuit Elements, Ch. 5, Text Ideal elements represent real physical systems. Resistor, spring, capacitor, mass, dashpot,
inductor To model a dynamic system, we must figure out how to put the elements from different domains together. Alternatives include numerical modeling of the
whole system. Lumped element modeling offers more physical insight and may be necessary for timely solutions. Example. Electrical: ResistorInductor-Capacitor (RLC) system.
C No power source, transient response depends on initial conditions
R i L B1, B2 depend on initial conditions
Example. Mechanical: Spring-MassDashpot system. x k
m No power source, transient response depends on initial conditions
b B1, B2 depend on initial conditions Equations are the same if:
1/k k b
m . I <-> x b
. x m
or C 1/C
R L L
R Goal: Simulate the entire system. Usual practice: Write all elements as electrical circuit elements.
Represent the intradomain transducers (Ch. 6) Use the powerful techniques developed for circuit analysis, linear systems (if linear), and feedback control on the whole MEMS system.
Senturia generalizes these ideas. Introduce conjugate power variables, effort, e(t), and flow, f(t). Then, generalized displacement, q(t) And generalized momentum, p(t)
e . f has units of power e . q has units of energy p . f has units of energy Variable Assignment Conventions
Senturia uses e -> V, that is, effort is linked with voltage in the electrical equivalent circuit. He explains the reasons (for example potential energy is always associated with energy storage in capacitors).
Following Senturias e -> V convention: For effort source, e is independent of f For flow source, f is
independent of e For the generalized resistor, e=e(f) or f=f(e) Linear resistor e=Rf
Electrical, V=RI Mechanical, F=bv For the generalized capacitor (potential energy):
For a linear electrical capacitor: permitivity A area G Gap
The mechanical equivalent is the linear spring. (Check in table.)
Cspring = 1/k, F=kx Generalized Inductor or inertance (kinetic energy?)
p1 Linear inertance: momentum flow
m mass v velocity p momentum momentum?
Electrical? But what is this??? ???
v Reluctance
q=Ce, e=(1/C)q, Electrical Q=CV (Fmm in example!) (Senturia, not necessary to approximate)