Transcript - ePrints Soton

Joint Academic Research Programme for Defence
Microfluidic devices for structural health monitoring: Part 1
A.
1
Cranny ,
N.
1
Harris ,
A.
1
Lewis ,
S.
2
Neodo ,
M.
2
Nie ,
K.
3
Stokes ,
J.
2
Wharton
and R.
2
Wood
1School
of Electronics and Computer Science, University of Southampton, Southampton, Hampshire, SO17 1BJ, UK
2nCATS, School of Engineering Sciences, University of Southampton, Southampton, Hampshire, SO17 1BJ, UK
3Defence Science and Technology Laboratory, Porton Down, Salisbury, Wiltshire, SP4 0JQ, UK
Overview
Microfluidics
Dstl and EPSRC have jointly funded a 3-year project at the University of Southampton to develop corrosion detection
and monitoring systems for land, marine and aerospace structures under grant number EP/F004362/1.
The onset or extent or corrosion in a structure can be
determined by monitoring changes in the concentrations of
specific metal cations in the immediate environment
surrounding the structure. A number of sensor technologies can
be used to detect these corrosion products, but few (if any) can
detect all of them simultaneously over a range of different and
potentially hostile environments.
By combining microfluidics with new, emerging sensor technologies, this project aims to develop in-situ systems that
not only detect the onset of structural corrosion, but can also assess its state and apply appropriate remediation to
inhibit its progress. The principle is illustrated in the schematic shown below.
Knowledgebase
Microprocessor
Monitored
structure
Remediation
system
For example
Fluid
sampler
Instrumentation
and HV control
Sensors
Calibration
solutions
Non-return valve
Fluidic systems
Pump
Electronic systems
Pump
control
Buffer
reservoir
Schematic showing the basic units of a microfluidic corrosion detection and monitoring
system for use in spot measurement or (semi-)permanent installation.
The project is overseen by a steering committee that is comprised of manufacturers and other interested parties that
are representative of the defence industry, namely:
● Dstl
● Rolls Royce Marine
● GKN Aerostructures
● Lloyd’s Register
A second theme to this research programme is the investigation of how corrosion processes are initiated and evolve
in a number of commonly used structural metals, alloys and composites, with particular emphasis on crevice
corrosion. This will help in the formulation of scientific models to describe these processes and also help in the
development of new remediation strategies.
From the science and fabrication technologies developed
here, we ultimately hope to see these microfluidic sensor
monitoring systems integrated within critical structures
during manufacture, as illustrated by the concept of the
‘smart’ pipeline gasket shown to the right.
Cu
C
A
Microfluidic ion separator: Gold electrodes patterned on to a
glass wafer. A = Electric field generation electrodes.
B = Zeta potential modification electrode. C = Contactless
conductivity detectors. D = Electrochemical sensor.
Microfluidic ion separator: Separation channel and sample
injection channel buried within an insulated PDMS layer.
2+
2.2
Detector Response
2.0
Dissemination
http://mdfshm.ecs.soton.ac.uk
B
2.4
● Extend platform life
● Aid scheduling of maintenance cycles
● Augment existing corrosion science knowledge
For more information, visit:
C
A
Once sufficient separation is achieved between the ion species
with the greatest electrophoretic mobility and the remaining ion
groups, this species is isolated and transported to the
measurement zone for identification and quantification before
being extracted to waste.
Such systems will:
To date, results from this project have been presented at 3
national conferences, 5 international conferences (Australia,
China, France and USA) and published in 12 peer reviewed
proceedings and journals.
A
Our approach is to do this by shuffling the ions back and forth
along the channel, thus effectively increasing the travel
distance, by alternating the direction of the electroosmotic flow
(EOF): a cohesive flow that transports all particles irrespective
of their charge. This is achieved by varying the zeta potential
along the channel walls.
The whole process is then repeated for the second most mobile
species, then the third most, and so on. The decision as to
when to reverse the EOF direction and isolate species is made
by using contactless conductivity detectors at each end of the
channel that monitor the arrival times of ion groups. Hence, the
entire process operates as a closed loop control system
requiring minimum intervention.
Objectives
D
Our strategy is to separate and isolate groups of corrosion
products from fluids sampled at a monitored structure and pass
them on to appropriate sensor systems for quantification. A
novel microfluidic ion separator using capillary electrophoresis
(CE) is being developed for this purpose.
In capillary electrophoresis, ions are separated in an electric
field due to differences in their electrical mobilities. In standard
CE, this separation is achieved as ions move along a capillary of
typically 1 m in length. The challenge with miniaturisation is to
achieve the same objective along a channel of considerably
shorter length.
Microfluidic ion separator
A
PDMS layer
1.8
Micro-channel
1.6
-
SU8 insulation
Cl
Glass wafer
1.4
Solution
reservoir
1.2
1.0
The ‘smart’ gasket – example of the integration of
microfluidics and sensor systems within a structure.
0.8
0
100
200
300
400
500
600
700
800
900
1000
Elapsed Time (s)
Example electropherogram demonstrating separation
of CuCl2 in deionised water.
Microfluidic ion separator: Cross section and detail showing
position of buried separation channel in PDMS layer.