Room-temperature broadband quasistatic magnetic cloak

In the past decade, invisible cloaks have experienced rapid research development in the metamaterial community driven by their revolutionary practical potentials. Among them, magnetic cloaks, which are able to conceal metallic or magnetic objects from electromagnetic induction detection, have attracted a great amount of attention. However, applications of these reported devices are limited by their low-temperature environment requirement because of the involvement of superconductors to acquire the perfect diamagnetic response. In this work, we remove this temperature hurdle by fully taking the diamagnetic features of usual metals and demonstrate a three-dimensional room temperature quasistatic magnetic cloak using a ferromagnetic metallic bilayer structure. Experimentally, our device exhibits a prominent cloaking effect in a wide frequency range from 5 to 250 kHz with a maximum field disturbance ratio <0.5%. The practical potential is verified through a commercial handheld metal probe working at 25 kHz. Our results unambiguously show that an invisible cloak may be realized in the low-frequency region for scenarios where screening an external magnetic field without disturbance is specifically demanded. Devices that manipulate electromagnetic fields to hide metal objects from detection can now operate at room temperature. Recent designs for ‘bilayer’ magnetic cloaks use hollow spheres with superconducting inner shells and ferromagnetic outer coatings that work together to prevent magnetic fields from reaching objects inside. However, these cloaks require liquid-nitrogen temperatures to function. Yungui Ma from Zhejiang University in China and colleagues report a way to avoid such impractical, frigid conditions by replacing the superconducting shell with one made from copper. The team's simulations revealed this metal can similarly deflect magnetic waves when driven with an alternating current at kilohertz frequencies. Optimizing the copper thickness enabled production of a working broadband prototype that rendered small pieces of metal invisible to commercial probes at ambient conditions. In this work, the authors reported a three-dimensional room temperature quasistatic magnetic cloak using a ferromagnetic metallic bilayer structure by showing prominent cloaking effect in a wide frequency range from 5 to 250 kHz. The practical potential was also verified through a commercial handheld metal probe working at 25 kHz.