July 29, 2015

The Trick of Finding Contamination

(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.

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