Biomedical Engineering Reference
In-Depth Information
(
A
)
(
B
)
SU-8 nanocomposite NMC's response to TNT vapours
14 ppb
30 ppb
46 ppb
0
TNT introduced
-20
110
(
B
)
N
2
OFF
TNT ON
TNT ON
105
100
95
90
85
80
75
0
-40
TNT OFF
TNT OFF
N
2
ON
N
2
ON
Reversibility of the sensor
0 0
Time (seconds)
600
800
1000
-60
0
30
60
Time [seconds]
90
Figure 9.23
(A) Response of a 4-MBA coated polymer nanocomposite microcantilever to
dif erent concentrations of TNT vapour in nitrogen. Inset: Response of these devices for
alternate cycles of TNT and Nitrogen (B) Explosive detector prototype developed at IIT
Bombay based on a piezo-resistive polymer nanocomposite cantilever platform [27].
contacts. h e microcantilevers were kept inside a PTFE gas l ow cell [27].
h e reference and measurement devices connected in bridge circuit were
connected to a standard signal conditioning circuit for continuous moni-
toring of the microcantilever response.
Nitrogen purging was performed before starting the explosive vapour
exposure experiment. h is helped in bringing down the humidity levels.
A calibrated vapour generator containing TNT source was used. Gas l ow
of 30 SCCM was maintained using a mass l ow controller (MFC). h e
calibrated vapour generator was capable of delivering TNT vapours with
concentrations < 10 ppb. Microcantilever response for alternating cycles
of TNT (~30 ppb) and nitrogen for three minutes and i ve minutes respec-
tively was recorded as shown in i gure 9.23 (A)[26]. It can be observed
that the polymer nanocomposite cantilever sensor is reusable even at er
multiple exposure cycles. h e responses of these microcantilevers to dif-
ferent concentrations of TNT vapours were also recorded. h e output volt-
age was found to increase with increase in concentration (i gure 9.23(A)).
Considering the noise levels, these devices should be able to detect TNT
vapours down to a few ppb (~ 6 ppb) concentrations with an approximate
sensitivity value of 1 mV/ppb [27]. h e hand-held explosive detector pro-
totypes developed based on these polymer nanomechanical cantilever sen-
sor platform is shown in i gure 9.23(B). h ese detectors could detect TNT
and RDX in normal ambient.
h e analysis presented here for the explosive vapour exposure experiments
conducted in controlled environment. However, the experiments conducted
