Fig. 11
ELECTRONC PROBES (reception)
Linear sequential array probes or linear array probes.
As was explained in paper I, when a stone falls on the water, it generates waves that get
away from the falling point and as far as it goes the bigger is the wave front as is shown in
figure 12a, it also happens when the reflection of the incident ultrasonic waves generates
the echoes (mechanic waves) in the interfaces of the tissues, these echoes go toward the
probe, the point where an echo is generated is alike the spot where the stone falls in the water, so as far as the echo travels away from the generating interface, the bigger his wave
front is, so at the probe´s crystals the echo has the way shown in figure 12b, this figure
shows that the wave front arrives first at crystal 3 (t1),the crystal is pressed mechanically by
the echo strength so the crystal oscillates and produces the electric signal, which has the
waveform of the echo, and for the better understanding they are represented as electric
pulses in the figures, then the same thing will happen with crystals 2 and 4 at time (t2), and
finally the echo arrives at crystals 1 and 5 at time (t3). As in transmission there were used
five crystal to form an ultrasonic line, now the five pulses produced by the crystals must be
added to generates an electric signal which represents one echo of the reception line, that is
why all the five pulses group must be added, but for the summation action all the pulses
must arrive at the summation block at the same time, so alike in transmission the pulses
pass through a delay circuit, now the circuit delays an amount of time the pulse at t1, coming from (L3), that was generated first by the echo wave front, this amount of time delay is to
synchronize t1 to the pulses at t2 (L2 and L4), also to synchronize it to the pulses at t3, (L1
and L5) that are the last pulses generated, a smaller delay is applied to the pulses at t2, and
no delay is applied for pulses at t3, this way all the pulses arrive at the same time at the
summation block coming from crystals as seen in figure 13.