Page 395 - Microsensors, MEMS and Smart Devices - Gardner Varadhan and Awadelkarim
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APPLICATIONS 375
Antenna
Figure 13.14 Calibration of the remote reading system
400
40 60 80
Temperature (°C)
Figure 13.15 Phase shift difference versus temperature (after jump correction) of a SAW-IDT
microsensor
13.4.3 Pressure Sensor
The SAW-based pressure sensors use the strain principle described in Section 13.4,1. To
illustrate this principle, let us consider a circular quartz membrane with thickness h. The
deflection of the plate, w, under uniformly distributed pressure (P) is assumed to be
smaller than h/5. The differential equation describing the elastic behaviour of the middle
plane of a thin plate is obtained from the elementary theory of plates
p
(13.45)
D
where D is the stiffness of the plate with piezoelectric properties of quartz. In the case
of simply supported edge, the deflection w is given by
