Magnetics Business & Technology - November/December 2019 - 4

EDITOR'S CHOICE

Magnetic Impedance Wire from Aichi Steel Used in
Experimental System for Automated Driving
Recent tests of automated passenger
buses in Japan have further validated
the development of highly sensitive
magnetic impedance sensors using
Aichi Steel's amorphous metal magnet
wire for guiding the vehicles, especially
in places where global positioning
signals are weak.
Made of FeCoSiB alloy wire with a
diameter of 20 micrometers and less,
the sensors have a sensitivity more
than 10,000 times greater than conventional magnetic sensors. The wire is amorphous
without a crystalline structure and exhibits ideal soft magnetism characteristics making it
perfectly suited for high sensitivity sensors, says Aichi. It produces the wire from the raw
material stage using its proprietary material technology. The sensor system is developed
by its business unit, Aichi Micro Intelligent Corp.
In the latest road tests, an automated driving bus equipped with the MI sensor modules
provided by Advanced Smart Mobility Co., Ltd., traveled repeatedly in a 1.4 kilometer section in Tama New Town with magnetic markers laid underground at an interval of 2 meters.
The area is hilly country rich in undulations and slopes. There are many places where
pedestrian bridges and roadside trees make the reception of GPS signals difficult.
An MI sensor module is affixed to the base of vehicles to measure the fitted vehicle's
position with high accuracy from the weak magnetic force of magnetic markers fitted along
the road and to control steering equipment so that the vehicle passes over the magnetic
markers. Going forward, Aichi plans to continue its efforts in verifying the system especially
for such conditions.
The magnetic impedance effect is an electromagnetic phenomenon where the impedance of a magnetic material changes relative to the strength of the external magnetic field
when a high frequency current or pulse current which causes a skin effect on the magnetic
material is applied. When amorphous wire is used as the magnetic material, the effect is
particularly marked.
According to Aichi, when the frequency of the pulse current applied to the amorphous wire
is increased to around 10 MHz the domain wall movement is suppressed, and the magnetization mainly occurs by the rotation of the magnetization vector. Unlike other types of
magnetic sensors with domain wall movement, MI Sensors can attain ultra-high sensitivity
with extremely low noise. The latest MI sensor achieves very high sensitivity by applying a
pulsed magnetic field equivalent
to .5 to 1GHz.
In operation, a pulse current
is passed through the amorphous wire and the reaction
relative to the external magnetic
field is detected by the pickup
coil wrapped around the wire.
Charging the amorphous wire
with a pulse of current creates a
change in impedance that varies
greatly depending on the external magnetic field as a result of
the MI effect.

Volume 18, Issue 6
Editor & Publisher
David Webster
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Dr. Stan Trout
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Support Services
Ross Webster
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Scott Webster
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Scott Webster
Administration
Marsha Grillo

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Experimental automated driving bus in Japan

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November/December 2019

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