Biomedical Engineering Reference
In-Depth Information
Fig. 6.21 a The quartz crystal microbalance (QCM) sensor [
29
], b scheme of a flow cell for
piezoelectric crystals (the oscillator circuit and frequency counter)
sensor. It is also known as a BAW device, which is made of a polymer-coated
resonating quartz disc, vibrating at a characteristic frequency (10-30 MHz).
As the volatile molecules adsorbed to the polymer surface, it increases mass of
the disc, and thus it reduces the resonance frequency. The decrease is inversely
proportional to mass of odorant adsorbed. Changes in temperature, humidity, and
flow conditions can affect sensor sensitivity. The sensor selectivity is dictated by
the thickness of the coatings. Sensor surface is coated by a sensitive material,
which is used to enable detection of the measurand in the environment. For
conversion of the measurand quantity to an electrical signal, an appropriate
electronic circuit is required. QCM sensor is a very good sensitive detector of mass
changes.
The basic working principle of the QCM sensor is represented in Fig.
6.21
.In
the surrounding space of a QCM sensor, analytes are present and it is interacting
with the sensitive coating material on the sensor surface. During the interaction,
analyte molecules are absorbed into the sensitive coating material, i.e., polymer.
The mass change on the sensor surface is occurred due to the adsorption of the
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