Search

The H-plane coupled multi-input multi-output (MIMO) rectangular microstrip patch antenna (MPA) array is investigated. To ensure compact size as well as good radiation performance, the excited MPA is designed to operate in the single fundamental TM01 mode. On the other hand, due to the near-field coupling effect, the TM01 mode and the adjacent TM11 mode are simultaneously excited in the coupled MPA. The superposed field of the two coupled modes forms a null-field region at the position of feeding probe, generating an intrinsic coupling dip with low $\vert \text{S}_{21}\vert $ above the resonance frequency of TM01 mode. To make use of this intrinsic coupling dip, the decoupling band is moved downward to overlap with the impedance passband by simply truncating two rectangular corners from the rectangular MPA. A self-decoupled convex MPA array is thus achieved without requiring any additional decoupling structure. This self-decoupling method is also applicable to the E-plane coupled MPA array, and more importantly, it is extendable to a large-scale planar MIMO array, showing great universality. For validation, a $2\times2$ MPA array is simulated, fabricated, and measured. A 4% usable bandwidth with $\vert \text{S}_{ii}\vert < -10$ dB and $\vert \text{S}_{ij}\vert < -20$ dB is achieved, and the maximum isolation is over 50 dB.

Ce2Fe14B compound has a great potential to serve as a novel permanent magnet alternative thanks to the abundant and inexpensive rare-earth element (cerium), while its low magnetocrystalline anisotropy and energy product severely restrict its applications. In this work, a novel strategy combining melt-spinning and electron-beam exposure (EBE) aiming for fabricating high-performance Ce-Fe-B magnetic materials is reported to solve the above-mentioned problem. Remarkably, this strategy facilitates developing a suitable grain boundary configuration without using any additional heavy rare-earth element. Under the optimal EBE condition, the maximum energy product ((BH)max) of pure Ce-Fe-B alloy is 6.5 MGOe, about four times higher than that obtained after conventional rapid thermal processing method for the same precursor. The enhanced intergranular magnetostatic coupling effect in the EBE sample is validated by mapping the first-order-reversal-curve (FORC) diagrams. The in-situobservation of magnetic domain wall motion for Ce-Fe-B alloy using Lorentz transmission electron microscopy reveals that the boundary layers are very effective in pinning the motion of domain walls, leading to the increased coercivity under EBE, and this pinning effect is further verified by micromagnetic simulations. Our results suggest that CeFeB materials using EBE could be a promising candidate after further processing, which could fill the performance “gap” between hexaferrite and Nd-Fe-B-based magnets.

The Ce-substituted (Nd1−xCex)12.2Fe81.6B6.2(x = 0.0, 0.2, 0.4, 0.6) nanocrystalline ribbons were prepared by annealing amorphous ribbons from melt spinning. It is found that all ribbons are in a multiphase state consisting of α-Fe phase, Nd(Ce)-rich phases and RE2Fe14B (RE = Nd, Ce) phases. However, the coercivity of all annealed ribbons can reach a considerably high value without doping any heavy rare earth or other coercivity enhanced elements. A strong intergranular exchange coupling appears in these nanocrystalline ribbons. The Nd12.2Fe81.6B6.2ribbons with multiphase have a coercivity of about 11.3 kOe, and the coercivity decreases slightly with increasing Ce content. A coercivity of 7.5 kOe can be obtained when 60 at% of Nd is replaced by Ce (x = 0.6) due to the grain refinement and the strong intergranular exchange coupling. This provides a practical approach of fabricating high coercivity Ce-substituted Nd-Fe-B materials.

In this work, we report the tuning effect of the Si substitution on the magnetic and high frequency electromagnetic properties of R2Fe17compounds and their paraffin composites. It is found that the introduction of Si can remarkably improve the magnetic and electromagnetic properties of the R2Fe17compounds, making the R2Fe17–xSix-paraffin composites excellent microwave absorption materials (MAMs). By introducing the Si element, their saturation magnetizations decrease slightly, while much higher Curie temperatures are obtained. Furthermore, better impedance match is reached due to the decrease of the high-frequency permittivity ε′ by about 40%–50%, which finally enhances the performance of the microwave absorption. The peak frequency (fRL) of the reflection loss (RL) curve moves toward high frequency domain and the qualified bandwidth (QB, RL ≤ −10 dB) increases remarkably. The maximum QB of 3.3 GHz (12.0–15.3 GHz) is obtained for the Sm1.5Y0.5Fe15Si2-paraffin composite (d = 1.0 mm) and the maximum RLof −53.6 dB is achieved for Nd2Fe15Si2-paraffin composite (d = 2.2 mm), both surpassing most of the reported MAMs. Additionally, a distinguished dielectric microwave absorption peak is observed, which further increases the QB in these composites.