Abstract
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.
Highlights
In the past decade, invisible cloaking has become a major research topic in the field of metamaterials and has inspired enthusiastic research across multiple disciplines.[1,2,3,4,5,6,7] the outstanding theoretical performance of invisible cloaks in manipulating electromagnetic (EM) waves is critically challenged in reality by the complex material properties demanded from the general designs applying transformation optics
We recently extended the bilayer approach and demonstrated a three-dimensional magnetic cloak working from DC to 250 kHz, which covered most of the EM induction operational bands.[24]
Design of the device For an ideal SC, the flux exclusion property can be alternatively realized by a good conducting metal at dynamic frequencies by its perfect magnetic field shielding capability because of the huge condupctffiiffivffiffiiffiffitffiyffiffiffiffiffiffiffiσffi corresponding to a small penetration depth δ ( = 1=pf ms, where f is frequency and μ is permeability) and small resistive loss.[16]
Summary
Invisible cloaking has become a major research topic in the field of metamaterials and has inspired enthusiastic research across multiple disciplines.[1,2,3,4,5,6,7] the outstanding theoretical performance of invisible cloaks in manipulating electromagnetic (EM) waves is critically challenged in reality by the complex material properties demanded from the general designs applying transformation optics. In 2012, Gömöry et al.[17] and Narayama et al.[18] independently reported the first experimental demonstrations of successfully hiding objects in static magnetic fields using a bilayer approach and a traditional transformation optics design, respectively.[17,18] The efficiency of the bilayer approach proposed by the first group was quickly verified and applied to other
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