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J.L. Aroyan et at.
to, and about 1.0cm medial to, the center of the left MLDB complex. Also,
three maxima of the inverse (8, <1» = (10°,0°) pattern (not pictured here)
occurred against the skull down within the right nasal plug. Generally,
however, the foci not lying against the skull appeared below the right
MLDB.
The far-field emission pattern at 75 kHz for the skull and soft tissue model
is illustrated in Figure 10.9. The distribution was computed for a point
source at the 75-kHz inverse simulation foci of maximum potential energy
density shown in Figures lO.8c and d. Note that addition of the soft tissues
has narrowed the skull-only emission pattern. The melon (in combination
with other soft tissues of the forehead) collimates much of the energy projected to the side and upward by the skull alone. The increased directivity
index indicates a significant contribution by the melon to the formation of
narrow biosonar beams.
3.3 Skull, Air Sacs, and Soft Tissue Simulations
The air sac model illustrated in Figure 10.3 was added to the skull and soft
tissue model to form the skull, air sacs, and soft tissue model. This combined
model constitutes a fairly complete representation of the dolphin's forehead tissues, although the air sac model was conservative (see Section 2.2).
The results of this model are therefore of special interest.
Figures 1O.lOa and b illustrate the 10% isosurface level of the maximum
PSR potential energy density Wpolential (viewed from above and from
the right, respectively) for an inverse (8, <1» = (5°,0°) skull, air sacs, and
soft tissue simulation at 75 kHz. Energy collimation is clearly occurring in
the melon, with strong channeling in both the vertical and horizontal
directions back through a region passing approximately 0.7 cm ventral to
the right MLDB complex. Again, this channeling is most pronounced
within the posterior throat of the melon. Note that the anterior melon
also appears to be functioning as a lensing element (note the curvature of
the anterior energy fronts in Figure 1O.10a). Except for slightly sharper
maxima, parasagittal PSR slices of the energy density in this model look
very similar to the results pictured in Figure 10.8 for the skull and soft tissue
model.
The focal maxima locations are plotted in Figures 10.lOc and d (as viewed
from the right and the front, respectively) for inverse (8, <1» = (5°,0°) simulations at frequencies of 25, 50, 75, and 100 kHz in the skull, air sacs, and
soft tissue model. Again, the maxima up against the skull is shown when it
exists and the soft tissue position of highest potential energy density for
each frequency. Note that all of the foci occur on the right side of the nasal
passages, not on the left, and that they have become fairly well grouped
along the guide channel of the posterior melon, which passes roughly
0.7 cm below the right MLDB. Besides the 8 = 5° maxima shown in Figure
10.14, focal positions were also determined for vertical return angles of 15°,
J.L. Aroyan et at.
to, and about 1.0cm medial to, the center of the left MLDB complex. Also,
three maxima of the inverse (8, <1» = (10°,0°) pattern (not pictured here)
occurred against the skull down within the right nasal plug. Generally,
however, the foci not lying against the skull appeared below the right
MLDB.
The far-field emission pattern at 75 kHz for the skull and soft tissue model
is illustrated in Figure 10.9. The distribution was computed for a point
source at the 75-kHz inverse simulation foci of maximum potential energy
density shown in Figures lO.8c and d. Note that addition of the soft tissues
has narrowed the skull-only emission pattern. The melon (in combination
with other soft tissues of the forehead) collimates much of the energy projected to the side and upward by the skull alone. The increased directivity
index indicates a significant contribution by the melon to the formation of
narrow biosonar beams.
3.3 Skull, Air Sacs, and Soft Tissue Simulations
The air sac model illustrated in Figure 10.3 was added to the skull and soft
tissue model to form the skull, air sacs, and soft tissue model. This combined
model constitutes a fairly complete representation of the dolphin's forehead tissues, although the air sac model was conservative (see Section 2.2).
The results of this model are therefore of special interest.
Figures 1O.lOa and b illustrate the 10% isosurface level of the maximum
PSR potential energy density Wpolential (viewed from above and from
the right, respectively) for an inverse (8, <1» = (5°,0°) skull, air sacs, and
soft tissue simulation at 75 kHz. Energy collimation is clearly occurring in
the melon, with strong channeling in both the vertical and horizontal
directions back through a region passing approximately 0.7 cm ventral to
the right MLDB complex. Again, this channeling is most pronounced
within the posterior throat of the melon. Note that the anterior melon
also appears to be functioning as a lensing element (note the curvature of
the anterior energy fronts in Figure 1O.10a). Except for slightly sharper
maxima, parasagittal PSR slices of the energy density in this model look
very similar to the results pictured in Figure 10.8 for the skull and soft tissue
model.
The focal maxima locations are plotted in Figures 10.lOc and d (as viewed
from the right and the front, respectively) for inverse (8, <1» = (5°,0°) simulations at frequencies of 25, 50, 75, and 100 kHz in the skull, air sacs, and
soft tissue model. Again, the maxima up against the skull is shown when it
exists and the soft tissue position of highest potential energy density for
each frequency. Note that all of the foci occur on the right side of the nasal
passages, not on the left, and that they have become fairly well grouped
along the guide channel of the posterior melon, which passes roughly
0.7 cm below the right MLDB. Besides the 8 = 5° maxima shown in Figure
10.14, focal positions were also determined for vertical return angles of 15°,