Biomedical Engineering Reference
In-Depth Information
A coating deposited onto SAW path specifically adsorbs a
target analyte and the interaction gas/coating alters the acoustic
characteristics of wave propagation by modulating the phase velocity
and/or attenuation of the wave producing changes at the output
of SAW devices. The shifts in velocity and/or attenuation are read
out by recording the phase (
passive acoustic devices
) or frequency
(
), respectively.
Various sensing effects contribute to the SAW gas response such as
mass loading, elastic loading, electrical loading, acousto-electrical
coupling. However, the gravimetric effect (mass loading) is the most
used in the piezoelectric sensors.
The LB process [113, 179] is a promising method for depositing
defect-free, molecularly ordered ultra-thin films with controlled
thickness and orientation. This technique allows fine surface
modifications in a multilayered film of CNTs with a controlled
manipulation to implement molecularly defined structures.
Nanocomposite LB films of CNTs incorporated in the host matrix of
CdA are of considerable interest for the development of nanomaterials
with enhanced properties at tailored amount of nanotube-filler
content for gas-sensing applications, at room temperature [113, 179,
180, 186,]. Figure 9.36 shows the diagram of a typical SAW sensor-
based on a SWCNT/CdA composite-coated two-port resonator and
inserted in a close loop by a low-noise RF amplifier to implement an
oscillator device with a frequency output.
oscillators
) and insertion loss (
passive acoustic devices
Figure 9.36
Schematic diagram of a microacoustic two-port resonator
sensor coated by SWCNTs 27.5 wt.% nanocomposite LB film
with an RF amplifier to implement an oscillator working at
a frequency of 315 or 433 MHz. This figure is reprinted and
adapted with permission from Elsevier [113].
