If you’ve been limiting your application of circuit theory and
design to electronic devices, then it’s
time to think outside of the box. If
you have a working knowledge of
Ohm’s Law, basic R-C and L-C filters,
and operational amplifiers, then you
can model systems ranging from the
circulatory and renal systems to
rocket propulsion and fluid dynamics.
Moreover, if you’re quick at
breadboarding or — better yet —
fluent in one of the many circuit
simulation languages, then you can
experiment with dozens of what-if
scenarios within minutes.
As an example, let’s say you
want to model the cardiovascular
system. You could start from first
principles, modeling the contractility
of the heart muscle fibers and the
like, or simply use electronic
equivalents. For the heart, let’s use a
function generator set to a rate of,
say 72 pulses/minute.
For the aorta, use a relatively
large value electrolytic capacitor fed
through a resistor from the function
generator; for the peripheral
resistance, a potentiometer across
the electrolytic capacitor. For
monitoring the equivalent of blood
pressure, let’s put an analog
voltmeter across the electrolytic
capacitor.
When we apply power, the
analog voltmeter registers a peak
value that we’ll call systolic blood
pressure. The minimum value
registered on the voltmeter
corresponds to diastolic blood
pressure.
Now, let’s say we want to model
systemic hypertension. We increase
the value of the potentiometer, which
signifies an increase in peripheral
resistance. Now, the peak voltage
across the capacitor — representing
systolic blood pressure — is
increased, as is the minimum voltage
across the capacitor, representing
diastolic pressure.
Of course, you’d have to pick
the appropriate values of capacitance
and resistance to model a particular
system and disease state. Also, to get
a better idea of what’s happening
second-to-second, you’d need an
oscilloscope.
This is just one example of how
electronic circuits can be used to
rapidly model the behavior of a
variety of systems. In practice, few
people actually do modeling with
discrete components, and instead opt
to use a circuit modeling and
simulation application.
My latest favorite free circuit
simulator is “Quite Universal Circuit
Simulator” or QUCS from
SourceForge ( https://sourceforge.net
/projects/qucs). It’s probably too
advanced for someone new to circuit
simulation, but the graphical user
interface is both intuitive and easy to
use.
If you want to learn more about
modeling systems with electronic
circuits, search the Web for
“electrical equivalent model of
<domain>” — where <domain> is the
system or process you’re interested in
modeling. For example, when I
searched for “electrical equivalent
model of steel corrosion,” I found
circuit diagrams, academic papers,
and other references that detailed
the design and use of specific circuit
diagrams. Most models were based
on a simple voltage source and
groups of interconnected RC filters.
Clearly, whatever your areas of
interest, you can start modeling with
electronic circuits today. NV
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by
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Bergeron,
Editor DEVELOPING
PERSPECTIVES
Electronics: A Multipurpose
Modeling Tool
October 2017 5