Aerospace & Defense Technology - August 2022 - 36

Tech Briefs
ment of biodetection technologies, and
also to interpret the experimental data/
observations for technological refinement.
The accompanying figure illustrates the
principle of impedance-based molecular
detection. The solution containing the
analytes of interest is introduced into a
microfluidic or nanofluidic environment
(a). A pair of electrodes is energized with
an AC field (characterized by a voltage and
w
~
- - - -
h
s
++ ++ +
-
Flow
AC
(a)
h
+ +
w s
Csol
-
-
Flow
(b)
frequency). The induced current is related
to the applied voltage and impedance of
the system, which in turn is dependent on
the composition of the solution (presence
or absence of target agents).
In an analogy to electrical circuit theory,
we can consider impedance in the
solution as a combination of resistance
and capacitance, with the solution acting
as a resistor (Rsol
), while the Electric
Double Layer (EDL
) at the electrode surface
and the solution in the channel act
as capacitors (CDL
and Csol
). The equivalent
electrical circuit and resistor-capacity
connection is illustrated in Figure (c).
The concentrations of analytes and electrolytes
impact the impedance in two
ways: (1) Resistivity (or resistance) of the
solution is a function of its electrical
conductivity and, hence, depends on
electrolyte and analyte concentrations;
(2) EDL
capacitance is a function of double
layer thickness (which in turn is a
function of electrolyte concentration)
and surface charges at the electrode.
Therefore, when a sample with different
ionic compositions is flowed through
the system, it changes both the EDL
capacitance and the solution resistance.
The changes are reflected in the form of
a disturbance (called " differential current " )
to the induced base current.
This work was done by Yi Wang,
Hongjun Song, Ketan Bhatt, and Kapil
Pant of CFD Research Corporation;
Monserrate C. Roman of NASA Marshal
CDL
Rsol
CDL
(c)
Principle of micro- and nano-impedance-based chemical sensors (a) Microstrip design (b) Coplanar design
(c) Equivalent circuit model
Space Flight Center; and Eric Webster,
William Diffey, and Paul Ashley for the
Army Research, Development and Engineering
Command. For more information,
download the Technical Support
Package (free white paper) at www.
aerodefensetech.com/tsp under the
DAQ, Testing & Sensors category.
ARDEC-0008
Evaluation and Test Requirements for Liquid Rocket Engines
This Standard establishes test and evaluation requirements related to the development, qualification (or
certification), and acceptance (flight production unit) of liquid propellant rocket engines and associated
propulsion systems.
Air Force Space Command, El Segundo, California
T
36
he primary objective of any test program
is to maximize the probability,
within programmatic constraints, that
the flight design will function properly
and successfully when used in actual
service for the intended application.
Flight risks are mitigated via prudent
and effective analysis and testing. While
analysis can sometimes be used in place
of test, proper analytical techniques utilize
test data as the basis for model correlations.
The combination of analysis
and test verification is used for both
qualification of the LRE design as well
as workmanship verification of each
LRE flight unit.
Certain key tenets of testing have
served the liquid propulsion test community
well as it has tried to accomplish
that objective. One particular
mobilityengineeringtech.com
" tried and true " philosophy is the
" Test-Like-You-Fly " (TLYF) approach.
TLYF means that testing should demonstrate
engine operation with flight-representative
hardware and under
flight-representative conditions,
including expected worst-case conditions.
The overall test program should
encompass and explore as much of the
operational flight envelope as possible
Aerospace & Defense Technology, August 2022
http://www.aerodefensetech.com/tsp http://www.mobilityengineeringtech.com
Aerospace & Defense Technology - August 2022

Table of Contents for the Digital Edition of Aerospace & Defense Technology - August 2022
