Biomedical Engineering Reference
In-Depth Information
Normal
Azimuth
Steering
Angle
q
Saw
w
p
L
Matching
Layers
Crystal
d
Backing
Elevation
Plane
Azimuth Plane
FIGURE 16.13
Construction of a one-dimensional array with a saw dicing up a multilayer sandwich structure
into individual elements. Here, the propagation direction is along the normal axis, pointing upward.
steered or translated mechanically. Each element, in terms of basic design, is treated as an
individual
transducer. Arrays and focusing will be discussed in more detail
in
Section 16.2.6 on diffraction.
Thetwomostcommontypesofarraysarethe linear array and the phased array. The
linear array forms an image by translating the active aperture (a certain number of ele-
ments) one element at a time along the length of the array, as shown in Figure 16.14a.
At each position of the active aperture, an acoustic line is created (i.e., a pulse-echo time
record of a selected length or scan depth). A total number of lines,
N
,isformedinthis
active elements
Scan line n
n
n+1
Scan line n+1
Sector (rotation)
(b)
Linear (translation)
(a)
FIGURE 16.14
The time sequencing used for image formation for (a) linear array format and (b) sector array
format.
