A low-cost, compact, and low-power metal detector has been created by a team led by Huan Li at the China Institute of Geosciences. In addition to this device is used to identify the unique magnetic fingerprints of small metallic objects, it would allow for significant reductions in the size and the energy requirements of security screening systems.  Today’s Metal Detectors Metal detectors, such as the public security systems you’re used to seeing when going into a stadium or arena, are used to detect hidden metallic objects. They use inductor coils to transmit alternating electromagnetic fields and induce eddy currents within metallic objects. These eddy currents generate secondary fields of their own, which are picked up by the coils. While the current systems are effective, they’re bulky and consume large amounts of energy.  A Possible Alternative  The new device consists of micrometer-scale sensor arrays, making it sensitive to subtle disruptions of the Earth’s magnetic field that are caused by metallic objects. It focuses on time-dependent variations in the Earth’s magnetic field. These variations are affected by the presence of nearby metal objects.  The effect gives an object its own unique magnetic, “fingerprint”, depending on factors such as the object’s shape, size, and composition. The fingerprints can be identified using a technique the team has dubbed “weak magnetic detection” (WMD) -- which is a passive detection technique that does not transmit a probe signal -- reducing energy requirements immensely. A downside to WMD has been that the fingerprints of smaller objects have been difficult to distinguish from background noise.  Where Things Can Go From Here The team has shown that the signal-to-noise ratio of WMD can be improved by using microelectromechanical systems (MEMS). The team’s metal detector integrates three sets of magnetic sensor arrays with a microcontroller, a battery, and a PC that provides a noise-suppressing data processing framework. With this setup, they’ve successfully identified the magnetic fingerprints of metal objects smaller than 50cm. They also could distinguish between multiple objects separated by under 20 cm.  Magnetic Discoveries with Apex Magnets The team hopes to improve the accuracy of their sensor arrays to detect magnetic fingerprints form even further distances and to higher resolutions. To stay up-to-date on this story and others like it, subscribe to our monthly newsletter.