Biomedical Engineering Reference
In-Depth Information
d
n
4
t
3
n
g
|
1
d
n
3
.
Figure 1.18
Schematic of surface acoustic wave device. Rayleigh waves contain both
shear and compressional components.
that, in the liquid phase, the compressional component is heavily compromised
by attenuation effects rendering its operation untenable.
63
Historically, the result with the Rayleigh wave device has led to the use
of devices which possess shear wave components only, but that are induced
by surface launching. Examples of various devices employed via this technology
are shown in Figure 1.19. One of the earlier structures is the shear-horizontal
surface acoustic wave (SH-SAW) device, for which the particle displacement
is depicted in Figure 1.19.
85
This device was followed by surface transverse
wave (STW; see Figure 1.19)
86
and Love-wave
87
sensors. The use of
these biosensors, which all involve very similar biomolecule immobilization
strategies to those outlined above, have been reviewed by Rapp and
coworkers.
88
Finally, we note that there are also a number of structures where,
although electrodes are fabricated on the surface of a device, the complete
structure is caused to vibrate. The sensors are generally termed 'plate mode'
devices (see ref. 70).
Although many of these devices have been employed very successfully in gas
phase sensing, and exhibit relatively high frequency of operation conveying
high sensitivity, applications of the TSM as a biosensor still dwarf those of
SAWs in numbers.
1.4.2.4 Non-piezoelectric Acoustic Wave Devices
In this section we comment briefly on devices which display potential for
chemical and/or biosensing but which do not contain a piezoelectric substrate
