Fig.17
where the crystals are arrange is convex, the ultrasound image area is sectorial as the mechanic ultrasound probes as seen in figure 18.
Fig.18
Phase array probes (transmission)
Phase array probes work in some way like linear array probes do, but as is shown infigure19, these transmit lines with different amount of angle regarding the y axis to build the
shape of the sector ultrasound image, in the example of the figure 19, the probe uses
4crystals 1,2,4, and 4,the pulses that activate the crystals are delayed sequentially in
time, no signal coming from the crystal have the same delay as happen in sequential probes
(figure 8), the crystal 1 is activated first, and crystal 4 is the last, this way the four lines arrive
at the focus at same time; now let’s pay attention only to the lines 1 and 4 by now, as was
explained before, at this point all the line are added, the adding of line 1 plus line 4 generate
a new lineL1(x,y) + L4(0,y)=L1L4(x1,y1-4), L1 has components in x and y, but L4 have only
one component in y so the x components do not cancel each other as happen in figure 7
( where L1(x) and L5(-x) have opposite signs), here as L4(x) = 0, L1(x)forces the new line to
have an angle different from 00regarding the y axis, this way the new line has been steered
to the right of the center line, and this angle of deviation of the new line will be bigger or
smaller according of the angle of L1(x). Nowlet’s focusing to all the lines of figure 19,the resulting line has a deviation angle to the right on account of L1(x), L2(x) and L3(x), as they
have equal sign, their x components do not cancel, instead they add each other and