The key unit of most of the reported sensors is a SAW oscillator (shown in Figure 1),
which consists of a periphery circuit, a SAW detector and a sensitive film deposited on the detector
surface. The sensitive film can strongly absorb a certain kind of gasses and almost dose not absorb
other gasses; therefore we can obtain the content of the gas by measuring the change in oscillation
frequency. The emphasis of this kind of sensor is to coat a sensitive film with high selectivity and high
adsorption capacity. Such a SAW sensor or sensor matrix can only perceive one or several kind of
gases; thus they are applicable to measure the content of some special gases [6–9]. In many areas, such
as environmental monitoring, food security, explosive detection, there is a strong need for sensors
which have a wide detecting range to monitor volatile organic or semi-volatile organic compounds
(VOCs or SVOCs) [10–12]. To satisfy the demand, another kind of SAW sensor [13–17] was reported,
in which a gas separation apparatus such as a gas chromatography (GC) column is set in front of the
detector to separate and identify the tested multi-component gas. A multi-component gas can be
separated and identified by their characteristic retention time in the GC column; thus SAW-GC sensors
are available to detect VOCs and SVOCs in a wide range.