Detecting tiny metallic contaminants with magnetisation

Researchers in Japan have been working to improve the detection of metallic contaminants in food.

Existing inspection methods have limitations; the X-ray radiation method cannot detect contaminants with sizes smaller than 1 mm and it cannot be applied for the inspection of foods that have lactic acid bacteria because X-ray radiation causes ionisation of such foods.

Researchers at the Department of Environmental and Life Sciences at Toyohashi Tech have developed a system to detect small metallic contaminants via magnetisation.

The detection system uses three high-Tc RF superconducting quantum interference devices (SQUIDs), which record the remnant magnetic field of a contaminant. SQUID is a high-sensitivity magnetic sensor based on the superconductivity phenomenon.

In the process, a strong magnetic field is applied to food to magnetise the metal fragments inside, and subsequently, these metals, if they are contained in the food, can be detected by sensing their magnetic fields using the SQUID sensors. The method is safe and provides a high resolution.

Professor Tanaka, whose team has developed the method, said the system permits contaminant detection in a food package with a height of 100 mm.

In experiments, the developed system was able to clearly detect a steel ball with a diameter as small as 0.3 mm. The system was robust and not affected by electromagnetic waves from nearby mobile phones or from the motion of nearby steel objects.

This study is featured in the July 2015 issue of the TUT Research e-newsletter from Toyohashi University of Technology.