Laboratory Study of Rock Deformation and Fracture - Ultra and Extremely Low Frequency Electromagnetic Fields - page 332

Fig. 9.1 A schematic
arrangement of laboratory
experiment devoted to the
shock polarization effect.
Adapted from Mineev and
Ivanov ( 1976 )

SW

3

R 1

R

2

1

4

Fig. 9.2 A typical
oscillogram of the
polarization current caused by
the shock loading of NaCl
monocrystals. Adapted from
Mineev and Ivanov ( 1976 )

U , V

3,2

t , m s

0

0,5 1,5

1,0

-3,2

electromotive force (EMF) or a jump of electric potential most likely occurs at the
shock front. The measured parameter is the voltage drop at the load resistance, R 1 .
The polarization current is directly proportional to the area, S, of the electrode.
Therefore, the area of the protective ring, S 1 , and the load resistance, R 1 , are chosen
so that S 1 R 1 D SR. In this case, the voltage drop at the resistances R and R 1 are
equal. Under this arrangement the influence of lateral effects is avoided. The areas
used were S 1 D S D 1-3 cm 2 , the thickness of the sample was l D 0.1-3 cm, and
R 1 D R D 92 Ohm are chosen to ensure the condition of a short-circuit. The latter
means that the circuit relaxation time t r l=V s where V s is the velocity of SW
propagation.
A typical oscillogram of the polarization current is depicted in Fig. 9.2 .The
current results from shock loading of monocrystal NaCl with a pressure magnitude
of 10 GPa (Mineev and Ivanov 1976 ). The vertical axis corresponds to the voltage