A multiband compact low-profile planar antenna based on multiple resonant stubs is proposed and studied. By utilizing two pairs of stubs embedded on a defected ground, the reflection coefficient less than −10 dB can be achieved with broadband characteristic for applications of wireless local area network (WLAN) and worldwide interoperability for microwave access (WiMAX). Meanwhile, a pair of inserted slots on both sides of a curve slot is applied to the antenna design, which decreases the cross polarization. A multiband antenna is fabricated and measured to verify the design. The antenna is compact with operation frequencies for WLAN (2.45/5.2/5.8 GHz) and WiMAX (2.8/3.8/5.5 GHz) applications. The measured peak gains are 5.5, 4.4, 0.0, and 5.6 dBi at 2.45, 2.8, 3.8, and 5.5 GHz, respectively.

Designing novel multifunctional materials at the nanoscale is vitally important for flexible electronics. Here, we have uncovered a twodimensional metal dichalcogenide PbS 2 with intriguing negative Poisson ratio behavior and favorable optical and photocatalytic water splitting properties. The calculations indicate that the Poisson ratio of the PbS 2 monolayer is −0.061 along both x and y lattice directions, which is attributed to its unique tetrahedral motif and the ligand field of the local PbS 4 units in the PbS 2 monolayer. The electronic band structures show that the narrow band gap (1.59 eV) of the PbS 2 monolayer could be effectively modulated by strain engineering. Most importantly, the strain-induced tunability of optical absorbance and suitable band edge alignment make the PbS 2 monolayer a promising catalyst for photocatalytic water splitting, which is further confirmed by the reaction free energies. These findings offer an effective avenue for the design and synthesis of a novel optoelectronic functional material.

We perform a first-principles study and identify two intriguing ferromagnets, hollow-Fe8N (H-Fe8N) and bridge-Fe8N (B-Fe8N) monolayers, by extensive structural searches. Both H-Fe8N and B-Fe8N nanosheets are buckled triangular lattices with a similar motif, but they are distinguishable by the positions of N atoms. The magnetic and electronic properties show that H-Fe8N is a low-spin ferromagnet; in contrast, B-Fe8N is a high-spin ferromagnet, which originates from the 3d orbital splitting of the Fe atom due to the low/high symmetric crystal field. Surprisingly, two stable Fe8N monolayers can be transferred to each other by N atom diffusion from the bridge position to the hollow position with the migration energy barrier of 1.5 eV. The energy barrier is affected by introduced Fe defects and rare earth metal dopants. These findings introduce a new tactic to regulate the 2D Fe-nitride monolayers at the atomic scale.

In this article, a compact and high-efficiency loop rectenna with matching network elimination for wireless sensor applications at 2.45 GHz is presented. The proposed hollowed-out square loop antenna is designed and directly provides a conjugate matching to a compact voltage-doubler rectifier. The loop rectenna can harvest microwave power without increasing the total size or affecting the performance of a wireless sensor. The experiment results show that the peak microwave-to-dc conversion efficiency of 74% is obtained at 2.45 GHz when the input power is 18 dBm. The dimension of rectenna is 30 × 30 × 1 mm 3 and only with a weight of 0.58 g, which successfully realizes a high power-weight-ratio (PWR). Hence, the proposed rectenna can provide a convenient and practical charging solution for wireless sensors in various applications.