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> Figure 22. Electrical signal of a microcrack in freshwater columnar ice
Figure 21. Signal recovery system used to detect emissions
Figure 26. Amplitude of electric potential ϕ on the surface of he ice sample measured in the configuration shown in Figure 25
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0.01
0.00
-0.01
-0.02
-0.03
-0.04
Figure
22.
Electrical
signal
of a
microcrack
in
fresh-
water
columnar
ice
(after
Fifolt
et
al.
1993).
T
=
33
C,
σ
=
6.3
MPa.
-0.05
0
1
2
3
4
Time,
ms
0.006
0.004
0.002
0.000
-0.002
-0.004
Figure
23.
Electrical
signal
of a
large
crack
splitting
many
columns
in freshwater
colum-
-0.006
nar
ice
(after
Fifolt
et
al.
1993).
T
=
30
C,
σ
= 3.78
MPa.
-0.008
0
20
40
60
80
100
0
0
Time
(s) 0
0
0
split
electrically
pre-polarized
ice,
causing
the
appear-
1.5
ance
of
growing
or oscillating
electrical
dipoles
(see
the
theoretical
section
above).
This
mechanism
was
1.2
later
proven
in
experiments
in
which
a
strong
external
0.9
electrical
field
was
applied
to
ice
samples
with
grow-
ing
cracks
(Petrenko
1993d).
It
was
shown
that
in
this
0.6
case
the
magnitude
of
electrical
signals
from
cracks
is
proportional
to
the
external
electrical
field
E
⊥
, in
ac-
0.3
cordance
with
eq
33.
An
example
of a
signal
generated
by a microcrack in
the
presence
of an
external
electri-
0
cal
field
is
shown
in
Figure
24.
Again,
the
decay
time
2
0
3
1
of
the
signals
coincided
with
the
slow
dielectric relax-
t
(ms)
ation
time
τ
2
.
Figure
24.
Typical
electrical
signal
cap-
Electrical
polarization
of
ice,
induced
by a
stable
tured
from
a
microcrack
in
freshwater
crack,
attributable
to
the
pseudo-piezoelectric
effect,
ice
under
the
action
of an
external
elec-
tric
field
E
⊥
= 10
V/cm.
T =
10
C,
crack
was
studied
using
the
scheme
depicted
in
Figure
25 to
dimensions 2
2 cm
(after
Petrenko
determine
electrical
field
distribution
around
the
crack
1992a).
(Petrenko
1992a).
Narrow
cracks
prepared
by a
thin
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