A team at KIST Europe in Saarbrücken and Delft University of Technology has published a proof-of-concept sensor in Communications Engineering, a Nature Portfolio journal. The chip is a centimetre square and weighs under 0.3 g: A liquid crystal with an embedded mesh of nickel wires, sandwiched between crossed polarising films. An alternating magnetic field heats the mesh, the liquid crystal flips from its ordered nematic phase to a disordered one, and the chip visibly darkens. It needs no battery, no electronics and no light source beyond ambient daylight, and the change reverses in about ten seconds.
The reported sensitivity is approximately 6 millitesla at a frequency of 125 kilohertz, and the experiments ran at 125 kilohertz with field amplitudes up to 30 millitesla. Those are strong fields at a low frequency, so the chip is pitched as an overexposure warning for people and equipment near powerful sources rather than as a meter for background radiofrequency fields from phones or masts. The authors name ultra-low-power wearables, mobile platforms and electronic warfare systems as the intended applications.
Quotes
"Such passive, non-electronic, and small-scale sensor systems could enable applications such as lightweight wearable devices to protect individuals or equipment at risk of overexposure, as well as low-cost indicators on devices that may emit hazardous radiation when malfunctioning."
"The hybrid LC chip is designed to exhibit an optical response to external radio-frequency fields without the need for electronic components or an external power supply, relying solely on ambient light."
"Both theoretical and experimental results demonstrate that the sensor exhibits a field sensitivity of approximately 6 mT at a radiation frequency of 125 kHz, with a response time on the order of (milli-)seconds."
"When exposed to an external radiofrequency field with intensities exceeding 6 mT, the embedded ferromagnetic mesh within the hybrid LC matrix responds via magnetothermal effects."
"Experiments conducted at 125 kHz with field amplitudes up to 30 mT demonstrated a response time as fast as 30 ms upon induction heating, with the LC phase transition propagating generally from the exterior toward the interior."
"The combination of extreme simplicity, ultra-small scale, lightweightness, passive operation, independence from electronics, and robust visual readout makes this sensor a promising candidate for applications in ultra-low-power wearable technologies, mobile platforms, and electronic warfare systems."
Location
📍 Germany
Electronics-free, ultra-low-power, wearable sensor chip for high-frequency electromagnetic field detection
Mohizin A, Abelmann L, Sung B (2026) Communications Engineering Journal Level 0ⓘ
