“…The O in the Co–O and Ni–O bond may originate from the surface oxidation of NiCo alloy when exposed to air. The characteristic peaks at 871.5 and 853.6 eV can be matched to the metal Ni in NiCo alloy [ 53 , 54 ]. Fig.…”
Layered double hydroxides (LDHs) have a special structure and atom composition, which are expected to be an excellent electromagnetic wave (EMW) absorber. However, it is still a problem that obtaining excellent EMW-absorbing materials from LDHs. Herein, we designed heterostructure NiCo-LDHs@ZnO nanorod and then subsequent heat treating to derive NiCo@C/ZnO composites. Finally, with the synergy of excellent dielectric loss and magnetic loss, an outstanding absorption performance could be achieved with the reflection loss of − 60.97 dB at the matching thickness of 2.3 mm, and the widest absorption bandwidth of 6.08 GHz was realized at 2.0 mm. Moreover, this research work provides a reference for the development and utilization of LDHs materials in the field of microwave absorption materials and can also provide ideas for the design of layered structural absorbers.
“…The O in the Co–O and Ni–O bond may originate from the surface oxidation of NiCo alloy when exposed to air. The characteristic peaks at 871.5 and 853.6 eV can be matched to the metal Ni in NiCo alloy [ 53 , 54 ]. Fig.…”
Layered double hydroxides (LDHs) have a special structure and atom composition, which are expected to be an excellent electromagnetic wave (EMW) absorber. However, it is still a problem that obtaining excellent EMW-absorbing materials from LDHs. Herein, we designed heterostructure NiCo-LDHs@ZnO nanorod and then subsequent heat treating to derive NiCo@C/ZnO composites. Finally, with the synergy of excellent dielectric loss and magnetic loss, an outstanding absorption performance could be achieved with the reflection loss of − 60.97 dB at the matching thickness of 2.3 mm, and the widest absorption bandwidth of 6.08 GHz was realized at 2.0 mm. Moreover, this research work provides a reference for the development and utilization of LDHs materials in the field of microwave absorption materials and can also provide ideas for the design of layered structural absorbers.
“…The conclusion is drawn that with the increase of ZnO content, the encapsulation effect of Ni/ZnO microspheres becomes worse and MA performance decreases gradually. Meanwhile, the MA performance of single Ni particles is only − 4.7 dB, so the core-shell structured Ni/ZnO composites have better MA ability than single Ni microspheres [54,55]. The effective MA < − 10 dB could be observed in the 12.3-17.2 GHz rang for the S-1 sample synthesized at 0.017 M Zn 2+ .…”
The core-shell structured Ni/ZnO mixture with excellent microwave absorbing (MA) capability was prepared through a facile solvothermal reduction technique. The crystallographic structure, morphology and MA performance of Ni/ZnO composites were measured by X-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM) and Vector network analyzer (VNA), respectively. The smooth Ni microspheres were coated by densely ZnO particles and the Ni/ZnO mixture was shown the best MA properties while the concentration of Zn 2+ was 0.017 M. When the absorption layer thickness was only 2.0 mm, the optimal reflection loss (RL) can be reached − 45.4 dB at 14.8 GHz. At this time, the value of RL < − 10 dB was found in the range of 12.6-17.2 GHz. It is demonstrated that the as-synthesized Ni/ZnO composites can be expected to be candidates for a new generation of absorbing materials.
“…4 but IM theory has never been questioned. 27,28,29 It worth noting that both |Z in (x 1 ) -1| and |Z in (x 1 ) + 1| are greater than |Z in (x 1 )| at the minimum positions of |Z in (x 1 )| in Fig. 4a because Z in (x 1 ) is near 0.…”
It is shown here that many concepts in current mainstream microwave absorption theory are used inappropriately. Reflection loss RL has been used to characterize microwave absorption from material instead of film and the results have been rationalized by impedance matching theory. The quarter-wavelength model states that the reflection of microwaves with wavelength l from a film is minimized if the thickness of the film is m l /4 where m is an odd integer. But we show here that the model is wrong because the phase effects from interfaces have been overlooked. RL is an innate property only for metal-backed film. Impedance matching theory is developed from transmission-line theory for scattering parameter s 11 but cannot be generalized to RL.
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