Korean researchers develop world's first ultra-compact 3-axis magnetic sensor to give robots a sense of touch

Robots that move as deftly as human hands and grasp objects with precision may soon be within reach. Korean researchers have developed a sensor no larger than 500 micrometers on each side that can measure magnetic fields in three directions simultaneously and detect forces applied to a robot's fingertip.

The Korea Institute of Machinery and Materials announced Tuesday that a team led by Oh Seon-jong, a principal researcher at the institute's Bio-Mechanical Systems Research Division, had developed the world's first ultra-compact three-axis magnetic sensor capable of simultaneously measuring magnetic fields along the x, y and z axes using superparamagnetic nanoparticles.

Precisely controlling the movement of robot joints and fingers requires sensors that can accurately read position and motion even in tight spaces. Conventional planar magnetic sensors can measure magnetic fields in the horizontal and front-to-back directions but struggle to detect fields entering perpendicular to the sensor surface — a significant limitation.

The research team found a solution in a "flux guide," a structure that redirects the orientation of a magnetic field. The team printed superparamagnetic nanoparticles onto a planar Hall magnetoresistance element using inkjet printing. The flux guide converts the perpendicular magnetic field into a planar direction that the sensor can measure.

Conventional flux guides have typically relied on ferromagnetic materials such as nickel or permalloy. The problem with these materials is magnetic hysteresis — residual magnetism that persists even after an external magnetic field is removed. Eliminating this effect required a separate reset circuit and complex fabrication processes such as electroplating and precision machining.

The superparamagnetic nanoparticles used by the research team lose their magnetism as soon as the external magnetic field is removed, eliminating the need for a separate reset circuit.

During the curing process, the team applied an external magnetic field to align the nanoparticles vertically. This boosted the sensor's sensitivity to z-axis magnetic fields by about three times compared with previous designs. The conversion efficiency for redirecting perpendicular magnetic fields into a measurable direction reached a maximum of 40 percent.

The sensor measures just 500 by 500 micrometers. Even when all four sensing elements operate simultaneously, power consumption remains at around 16 milliwatts — making it well suited for devices with tight space and power constraints, such as small robot joints, fingers and wearable devices.

The research team also extended the sensor's capabilities to serve as a robotic "sense of touch." By attaching an elastomer embedded with a permanent magnet on top of the sensor, the team built a multi-axis tactile sensor that can measure both pressing and shearing forces. A single sensor platform can thus read not only the movement of robot joints and hands but also the forces generated when the robot contacts an object.

The sensor is expected to find applications in robotic hands, soft robots, wearable devices, human-machine interfaces and medical devices — any field requiring precise measurement of movement and force.

"By using superparamagnetic nanoparticles, we resolved the magnetic hysteresis problem found in conventional three-axis magnetic sensors and realized an ultra-compact, low-power sensor through a simple printing process," Oh said. "We expect it to be widely used in robotics and wearables, where small, precise sensors are needed."

The study was conducted jointly by the Korea Institute of Machinery and Materials and a research team led by Professor Kim Cheol-gi of DGIST. The findings were published in the international journal Advanced Functional Materials and selected as a cover paper.