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In this study, the CoCrCuFeNi high entropy alloy was diffusion bonded with the Inconel 600 superalloy at bonding temperatures ranging from 950 to 1100 °C for a bonding time of 2 h under a pressure of 20 MPa in a vacuum. The microstructure and mechanical properties of the diffusion bonded joints were investigated. The diffusion zone of the welded joint contains of two distinct zones: a coarse grain zone (on the Inconel 600 superalloy side) and the diffusion interface layer. The blocks Cr23C6phase and Cu-rich phase were formed in the diffusion interface layer at 950 °C. As the bonding temperature increased, the Cr23C6gradually disappeared and the blocks Cu-rich phase transformed into nano Cu-rich precipitate in the diffusion interlayer at 1100 °C. The hardness of the interface layer was significantly higher than that of the base metal at all temperature. When the bonding temperature increased from 950 °C to 1100 °C, the ultimate tensile strength of the welded joints increased from 521 MPa to 558 MPa, and the elongation increased from 10.3 % to 31.2%, respectively. The ultimate tensile strength reached 96 % and 82 % than that of the CoCrCuFeNi HEA and Inconel 600 base metal, and the elongation is comparable to that of the base metals. All the welded joint fracture near the diffusion interface layer. As the bonding temperature increased, the fracture mode of the joint transformed brittle to ductile. At an elevated temperature of 300 °C, the ultimate tensile strength and elongation of the welded joint are 325 MPa and 9.8 %, respectively. The welded joint exhibits a mixed fracture mode of ductile and cleavage fractures.

The carbon fiber array (CFA) cathode has been successfully utilized in slow wave high power microwave (HPM) sources as a kind of explosive emission cathode (EEC), since it has good emission uniformity, a low explosive emission threshold, and a low cathode plasma expansion velocity. In this letter, the CFA cathode is being used for the first time in a coaxial cavity gyrotrons to increase the output power. The parasitic oscillations were successfully suppressed through the delicate design of the beam tunnel and the beam collector. In the experiment, the unwanted mode competition was suppressed, and stable microwave generation was realized. At an external magnetic field of 0.55 T, a diode voltage of 300 kV and a beam current of 500 A, the coaxial gyrotron generated the designed microwave at 10.3 GHz, with a pulse width was 40 ns and an output power of about 11 MW. The experimental power efficiency was lower than the simulation results, further efforts should be made to decrease the electron velocity spread.

Benzocyclobutene (BCB) has been widely used as passivation and interlayer dielectric for sub-millimeter-wave applications and terahertz monolithic microwave integrated circuits (TMICs). In this work, the influence of BCB passivation on 100-nm InP-based high-electron-mobility transistors (HEMTs) was investigated. A set of 100-nm HEMTs with different gate recess structures were fabricated and compared. A SiO2 hard mask was adopted in the gate recess, which contributed to an improved device performance after BCB passivation. DC and RF performances were characterized before and after BCB passivation. The results show that BCB passivation in the recess region degraded InP HEMTs’ performance, and a better performance was achieved by the SiO2 hard mask. For traditional devices, of which the gate recess was exposed to silicon nitride (SiNx) and BCB passivation layers, both dc and RF performances were deteriorated drastically even though the thickness of SiNx passivation layer was increased from 20 to 50 nm. However, the SiO2 hard mask preserved the device performances to a great degree, with only degradation by increased parasitic capacitances according to the small-signal equivalent model. In addition, the threshold voltage shift after BCB passivation was suppressed by the SiO2 hard mask. Thus, a device structure suitable for BCB passivated TMIC applications is proposed and validated.

A high-reliability small-signal equivalent circuit model for indium-phosphide-based high-electron-mobility transistors (InP-based HEMTs) is proposed. A de-embedding scheme for the representative structure is utilized in this model with an electromagnetic simulation approach to consider the distributed extrinsic parasitic elements. The intrinsic part of the small-signal model is directly extracted with the Y-parameter of the intrinsic two-port network. The extraction of the parametric elements was performed under different biases and three different gate widths ( $2\times 20\,\,\mu \text{m}$ , $2\times 30\,\,\mu \text{m}$ , and $2\times 50\,\,\mu \text{m}$ ), our S-parameter predictions showed good agreement with measurements in the 1–50-GHz frequency range. The proposed model performs an electromagnetic simulation of different gate-width devices, considers the devices’ distribution and radio-frequency behavior, and avoids errors caused by traditional tests’ extraction of parasitic parameters. The proposed model solves the problem that the conventional indium phosphide-based HEMT small-signal model is limited by the device topology, making the high-frequency modeling more accurate.

The ${f}_{\text {T}}$ -doubler has higher RF power and transit frequency than that of a single device, and it can be used as a single device in RF circuit design, so an accurate model of the ${f}_{\text {T}}$ -doubler is needed to achieve a good circuit performance prediction. In this article, an electromagnetic (EM) simulation-based distributed modeling technique is applied to build a ${f}_{\text {T}}$ -doubler small signal model. A four-port distributed parasitic network characterizes the extrinsic components. The three HBTs of the intrinsic part are characterized independently and then combined to construct the intrinsic model of the ${f}_{\text {T}}$ -doubler. This article convers how the modeling theory was developed, as well as the detailed modeling procedures and experimental validation. The proposed method is verified in the frequency range of 0.1–50 GHz, and quite good fitting results are achieved, and the modeling method has a significant improvement in accuracy compared to the conventional method.

A novel cross-band frequency hopping giga- watts (GWs) class high-power microwave (HPM) oscillator is proposed in this brief, which consists of an inner Ku-band coaxial oscillator, an outer ${X}$ -band coaxial oscillator, a beam transfer channel, and an extraordinary external magnetic field system. Compared with ordinary design, the external magnetic field of this device is generated by three closely spaced solenoids. Through the adjustment of the current passing through each solenoid, two kinds of magnetic field distribution can be generated, each guides the beams into a separate frequency beam-wave interaction region. The preliminary particle-in-cell (PIC) simulation results were as follows: when the currents passing through the three solenoids were the same of 700 A, a HPM output with a frequency of 14.4 GHz, and a power of 1. 5 GW was obtained, achieving a power efficiency of 37%; when the three solenoid currents were 1800 A, 225, and 460 A, respectively, a HPM output with a frequency of 8.2 GHz and a power of 1.6 GW was obtained, achieving a power efficiency of 40%.

10,11-Dehydrocurvularin is a natural benzenediol lactone (BDL) with a 12-membered macrolide fused to a resorcinol ring produced as a secondary metabolite by many fungi. In this review, we summarized the pieces of literature regarding biosynthesis, chemical synthesis, biological activities, and assumed work mechanisms of 10,11-dehydrocurvularin, which presented a potential for agricultural and pharmaceutical uses.