Page 404 - Microsensors, MEMS and Smart Devices - Gardner Varadhan and Awadelkarim

384 IDT MICROSENSORS

device. The sensor is modeled using Mason's equivalent circuit concept. For the effective
numerical calculation of the gyroscope output, a cross-field equivalent circuit model was
chosen because then Coriolis force can be directly related to input force on the SAW
sensor model.
Various SAW devices have been modeled using COM theory. The application of
coupled-mode theory on SAW devices for given geometry and material data is well
documented by Cross and Schmidt (1977), Haus and Wright (1980), and Campbell (1998).
Figures 13.20 and 13.21 show a modeling example of an IDT—IDT pair and a two-port
SAW resonator, respectively. Different complex layouts of SAW devices can be modeled
by adding more transfer functions at appropriate locations.
Figure 13.21 presents the two-port resonator represented in terms of its component
matrices. The G matrix represents SAW reflectors, T matrix represents the relation
"W IK

a, , a 3 b 3
it t

~w t

Figure 13.20 Schematic representation of an IDT-IDT pair

Input Output

Reflectors Reflectors

Input IDT Output IDT

Figure 13.21 Schematic matrix representation of a two-port SAW resonator