Biomedical Engineering Reference
In-Depth Information
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Figure 1.19
Particle movement for a shear-horizontal acoustic wave device and
schematic of a surface transverse sensor.
as the main transducer of imposed chemistry. The first of these is the magnetic
acoustic resonator sensor or MARS device.
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In this technology, the magnetic
direct approach is employed to instigate acoustic waves in a non-piezoelectric
substrate such as glass. In an analogous fashion to the EMPAS system
described above, a flat spiral coil, with a radiofrequency (RF) current is used in
conjunction with a permanent magnet to induce radial acoustic waves in an
aluminum film present on the surface of the glass substrate. In summary, the
metal film 'drags' the substrate into vibrational motion and a change in
behavior of imposed chemistry on the glass surface can be detected to generate
a response. Although available for a number of years this acoustic sensing
mechanism has not seen widespread use in bioanalytical chemistry, probably
because of diculties in obtaining acoustic resonance on a routine basis and the
relative ease of operation of the EMPAS device which does not require the use
of an adjunct magnet.
Finally, we mention the instigation of acoustic waves in thin rods of non-
piezoelectric material.
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In this arrangement an ultrasonic longitudinal wave is
piezoelectrically excited in a glass horn which in turn is coupled to a thin rod.
Extensional, flexural or torsional acoustic waves can be induced in the rod and
are detected by a second transducer in a delay-line configuration similar to that
mentioned above for the SAW. Although not used directly for biosensing, the
system possesses significant promise in view of the modern advances in
nanowires and nanorods alluded to above.
