(July 29, 2015) In
Tanaka’s laboratory, a method is being studied in which strong magnetism is
applied to food to magnetize the metal fragments inside, so that these metals
can then be detected by sensing their magnetic fields using a high-sensitivity
sensor, or SQUID (Superconducting Quantum Interference Device)1. A functional
system of detecting contaminants with this method has already been completed,
and has shown excellent metal detection ability in food factories. The
researchers in Tanaka’s laboratory are currently working to improve the
performance of this system so that even small metal fragments can be detected.
The key to improving performance is to more effectively
differentiate between actual signals and noise. Metal fragments are not the
only sources of magnetic fields, rather space is filled with many magnetic
fields generated from different sources. For example, the Earth is a giant
magnet, and it emits geomagnetism. In addition, if electricity is flowing
nearby, a magnetic field is generated. The aforementioned high-sensitivity
sensor device requires a strong magnet to be placed close to the sensor in order
to magnetize the metal fragments.
Magnetic fields that originate from sources other than the
metal fragments are called noise. The fields of large metal fragments can be
identified over such noise, but those of smaller fragments are masked by the
noise and are thus difficult to detect. Even strongly magnetized metal
fragments will have small magnetic fields if the fragments are small in size.