Can a tiny sensor track movement in three directions? A nanoparticle-based design brings three-axis magnetic sensing to spaces where conventional sensors struggle.
Researchers at the Korea Institute of Machinery and Materials (KIMM) have developed a magnetic sensor that can detect magnetic fields along the x, y, and z axes. The technology is designed for applications where precise motion sensing is required in confined spaces, such as robot joints and fingertips.
A key advantage of the sensor is its ability to detect out-of-plane magnetic fields along the z-axis without requiring a separate reset circuit. Conventional planar magnetic sensors can detect fields along two directions on the sensor surface but have difficulty measuring fields perpendicular to it. The KIMM approach redirects these fields into detectable in-plane components, allowing one sensor to measure all three axes.
The sensor combines a Planar Hall Magnetoresistance (PHMR) sensor with a superparamagnetic nanoparticle flux guide (SPMFG). The researchers inkjet-printed the nanoparticles directly onto the sensor and used field-assisted curing to arrange them into vertical chain-like structures, forming a Chain MFG.
The resulting sensor has a 500 μm × 500 μm footprint and consumes about 16 mW when all four PHMR sensing elements operate simultaneously. The Chain MFG increased z-axis magnetic-field sensitivity by about three times compared with the conventional configuration and achieved a magnetic-field conversion ratio of up to 40%.
The use of superparamagnetic nanoparticles also addresses the magnetic hysteresis found in conventional flux guides made from ferromagnetic materials such as nickel or permalloy. Because the nanoparticles have negligible hysteresis and remanent magnetisation, the sensor can repeatedly measure changing magnetic fields without a separate reset circuit. Printing the nanoparticles directly onto the sensor also simplifies the fabrication process.
The same platform can be extended for tactile sensing. By placing an elastomer containing a permanent magnet above the sensor, the researchers demonstrated detection of normal force and shear forces along three axes.
The technology could therefore help robotic systems sense joint and hand movements as well as contact forces. KIMM expects the sensor platform to find applications in robotic hands, soft robots, wearable devices, human-machine interfaces, and medical devices.
