This dissertation is about performance improvement of
magnetometers used as a part of detection system on conventional
sea mines, which play important role in Korean defense and security.
The proposed magnetometer is verified through the modeling and
simulation process in advance. then, its performance is improved
through practically manufactured with experimentation. It shall be
applied to new underwater weapon systems. Since there is limitation
in increasing detection performance of acoustic sensors which are
commonly influenced by underwater operation environment, such as
temperature, seabed materials, etc, magnetometers are used as an
alternative solution for detection systems.
Since after the cold war Korea is still remained as a divided
nation, and still exposed to the threat of the underwater weapons
system, such as ''The sink of Cheon-an(PCC) by the attack of the
underwater weapon''. Deploying conventional mines in coastal area of
hostile region has a risk factor. Our operation ship could be exposed
to hostile surveillance systems. and our soldiers will be in danger. So,
The national defense organizations in leading countries had been
trying to develop mobile mines including CAPTOR(enCAPsulated
TORpedo) which are combined at the propulsion part of torpedoes
and warhead part of conventional mine. Our country where the threat
of the underwater weapon systems like torpedoes continues,
procurement of the new underwater weapon system like mobile mine
is essential. Considering the development trend of leading mobile mine
technology, it is necessary to upgrade conventional bi-axial magnetic
sensors to 3-axis flux-gate sensors by introducing magnetometers.
The biggest challenge in combining those two parts is that the
ferromagnetic materials in propulsion systems can severely disturb
magnetometers in main sensing component. So theoretical study is
carried to investigate the effect of magnetic induction, permanent
magnetization and magnetization induced by magnetostriction on the
magnetometer performance. The non-magnetic instrument for
magnetic field distribution measuring was made in order to measure
the magnetic field distribution about the actually manufactured
components and miniature combat ship and submarine by magnetic
modeling were made for measuring their magnetic field using
self-manufactured equipment with the moving mode. Based on these
experiments, when the magnetometer of the conventional 2-axis was
placed as the arbitrary rotation angle, the problem that is being
generated in the magnetic field measurement was proved.
Moreover, the some experiment was taken about the proposed
3-axis magnetometer. Firstly, conventionally, in the case of the used
magnetometer, because of continuous power supply in order to secure
the safety of the output characteristics, the battery capacity is the
main problem for the mine system, especially for dropping or the Fire
and Forget ones. A recently developed magnetometer proved that it
can deliver equal or better performance than conventional one, while
maintaining excellent stability and lower power consumption rate.
Meanwhile, in the case of the traditional magnetometer, because of
being comprised of the sensor of 2-axis, when it goes down to the
bottom of sea by the dropping, the difference could not help being
generated according to the bottoming positions. But, there are two
methods to measure the magnetic field for 3-axis magnetometer. The
first is that it measures the azimuth angle, the roll angle respect to
bottom and the vertical and horizontal magnetic fields can be found
with transformation of output coordinates. The second method is that
it is possible to find the magnitude of magnetic field(total magnetic
field) of the 3-axis magnetometer output, In the case of the latter, as
simulated in the second chapter of this dissertation it is irrelevant of
bottoming position and the detection capacity can be consistently
maintained. Therefore, the second method is regarded as actually
being the best. Also, the effect of the propulsion motor and actuator,
where the ferromagnetic material used in mobile-mine, on the
magnetic distortion for the magnetometer was tested.
The detecting sensors including magnetometer, are mainly
positioned in front part of a mine. Propulsion system including
electric motors and actuators is usually placed in rear part, which is
about 6 m away from the head where magnetometers are placed. In
this case, the permanent magnetic components of the electric motor 9
nT and induced component gave 4.5 nT extent effect, and it was
measured that the permanent magnetic components and induced
magnetic component gave the effect in about 0.3 nT for actuators.
Considering magnetic field component and daily varying capacity of
the earth magnetic field in the case of the permanent magnetic
components, there is no problem. And, in the case of the induced
magnetic components, in case of assuming the change in the
magnetic field by the tested object(warship or submarine) as 2,000
nTs, it did not have an effect on the response performance of main
detection sensor just about 0.4 nTs. so, there is no magnetic field
distortion by the propulsion electric motor, actuator and etc. Since it
can be predicted that small amount(some nT) of magnetic field
change by the permanent magnetic components of the rotor and
encoder can not make the magnetic distortion. However, the screw
(propeller) will be rotated by the sea current after bottoming of
mobile-mine, we will need to verify through the experiment and some
tests in sea.