Page 290 - Semiconductor For Micro- and Nanotechnology An Introduction For Engineers

Inhomogeneities
2
2
∂ u
∂ u
3
3
ρ---------- = C ---------- +
11
2
2
∂t ∂x 3
(7.112c)
2
2
2
2
 ∂ u ∂ u   ∂ u ∂ u 
3
1
2
3
( C 12 + C ) ----------------- + ----------------- + C  ---------- + ----------
44 
44
2
 ∂x ∂x 1 ∂x ∂x 2  ∂x 2 1 ∂x 
3
3
2
The surface of a material can be used to serve as a mechanical wave
guide, and work in much the same way as optical wave guides do. Four
geometrical configurations, shown in Figure 7.14, characterize the very
a) b)
x x
y y
z z
c)
d)
x y x
y
z z

Figure 7.14. Four basic planar surface acoustic waveguide configurations and their
wave types. a) Thin mechanical plate: Lamb waves. b) Thin film on top of an elastic half-
space: Love waves. c) Mechanical homogeneous beam: Flexural waves. d) Homogeneous
elastic half space: Raleigh waves.

Semiconductors for Micro and Nanosystem Technology 287