Biomedical Engineering Reference
In-Depth Information
A miniaturized gas ionization sensor with raw aligned MWCNT
film as anode was developed by Modi
. [148]. Figure 9.10 shows
sensor diagram. It consists of MWCNT film anode, Al plate cathode
and a 150
et al
m thick glass insulator between them. Vertically aligned
MWCNT film was prepared by CVD on SiO
µ
substrate with tip
2
µ
diameter in the range of 25-30 nm and 30
m in length.
During operation, the individual MWCNTs create very high
nonlinear electric fields near the tips. This results in the formation
of a
or conduction filament of highly ionized gas. The
breakdown voltage provides a
corona
chemical fingerprint
to each gas under
test of NH
, He, Ar, and Air by indicating the potential for
the identification in a gas mixture, as shown in Fig. 9.11a. Moreover,
the discharge current of each gas showed almost linear relationship
with the gas concentration (see Fig. 9.11b), but the breakdown
voltage was rarely affected by the concentration. This was explained
by the fact that the discharge current is dominated by the number
of molecules per unit volume and the breakdown voltage depends
mainly on the intensity of electric field and the bonding energy of the
gas molecules.
, CO
, N
, O
3
2
2
2
Figure 9.11
(a) I-V curves for NH
, He, Ar, and Air, showing
distinct breakdown voltages; ammonia displays the highest
breakdown voltage, and helium the lowest. (b) Discharge
current at breakdown as a function of gas concentration. The
discharge current varies logarithmically with concentration.
Reprinted with permission from
, CO
, N
, O
3
2
2
2
Nature
[148].
Penza
. [153] demonstrated the integration of the raw HiPco
SWCNTs onto two different transducers such as the quartz crystal
microbalance (QCM) and standard silica optical fiber (SOF) sensor
et al
