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Ag and Cu have different advantages and are widely used in key fields due to their typical highly electrical and thermal conductive (HETC) properties. Laser powder bed fusion (LPBF), an innovative technology for manufacturing metallic multi-material components with high accuracy, has expanded the application of Ag–Cu in emerging high-tech fields. In this study, the multi-material sandwich structures of Ag7.5Cu/Cu10Sn/Ag7.5Cu were printed using LPBF, and the formation mechanism, interface characteristics, and molten pool behavior of the Ag7.5Cu/Cu10Sn (A/C) and Cu10Sn/Ag7.5Cu (C/A) interfaces were studied to reveal the influence of different building strategies. At the A/C interface, pre-printed Ag7.5Cu promoted Marangoni turbulence at a relatively low energy density (EA/C = 125 J/mm3). Due to the recoil pressure, the molten pool at the A/C interface transformed from a stable keyhole mode to an unstable keyhole mode. These phenomena promoted the extensive migration of elements, forming a wider diffusion zone and reduced thermal cracking. At the C/A interface, the molten pool was rationed from the conduction mode with more pores to the transition mode with fewer defects due to the high energy density (EC/A = 187.5 J/mm3). This work offers a theoretical reference for the fabrication of HETC multi-material structures via LPBF under similar conditions.

A 1-D wide-angle beam-scanning linear phased array with enhanced gain by using dielectric slab superstrate (DSS) is presented. In this scenario, the beams of array elements in the scanning plane should be wide enough and that in the orthogonal plane should be as narrow as possible. Different from the existing DSS technology, the DSS in this letter is used to satisfy the requirements of the beams in both planes. The parameters of the DSS and its position are optimized by setting the narrowest beam in the orthogonal plane as the objective function under the constraint of the specified wide beam in the scanning plane. To validate the proposed scheme, an eight-element DSS linear phased array operating at 10 GHz was designed, fabricated, and measured. Using the simple measure, the measured 3.5 dB gain enhancement in the scanning range of ±43° has been achieved with the aperture efficiency of 98%, the low profile of 1.39 wavelength, and the acceptable side-lobe levels (SLL) of better than −8.7 dB.

The poor wettability and weak interfacial bonding of diamond/copper composites are due to the incompatibility between diamond and copper which are inorganic nonmetallic and metallic material, respectively, which limit their further application in next-generation heat management materials. Coating copper and titanium on the diamond particle surface could effectively modify and improve the wettability of the diamond/copper interface via electroless plating and evaporation methods, respectively. Here, these dense and complex composites were successfully three-dimensionally printed via selective laser melting. A high thermal conductivity (TC, 336 W/mK) was produced by 3D printing 1 vol.% copper-coated diamond/copper mixed powders at an energy density of 300 J/mm3 (laser power = 180 W and scanning rate = 200 mm/s). 1 and 3 vol.% copper-coated diamond/copper composites had lower coefficients of thermal expansions and higher TCs. They also had stronger bending strengths than the corresponding titanium-coated diamond/copper composites. The interface between copper matrix and diamond reinforcement was well bonded, and there was no cracking in the 1 vol.% copper-coated diamond/copper composite sample. The optimization of the printing parameters and strategy herein is beneficial to develop new approaches for the further construction of a wider range of micro-sized diamond particles reinforced metal matrix composites.

In this paper, the exponential stability in mean square for Markovian jumping systems (MJSs) is discussed. A new dynamic model, which involves parameters uncertainties, nonlinearities, and Levy noises, is proposed. Moreover, an adaptive sliding mode controller is built to study the stability of such a complex model. First, an integral-type sliding mode surface (SMS) is established to obtain the sliding mode motion dynamics of MJSs. By the generalized Ito formula and the Lyapunov stability theory, some sufficient conditions are obtained to make sure the exponential stability in mean square for the sliding mode motion dynamics. Second, an adaptive sliding mode control law is provided to assure the reachability of the specified SMS. Furthermore, corresponding parameters of the sliding mode controller and the SMS can be got by solving the convex optimization problem. Finally, the validity of the stability results obtained is illustrated by a numerical simulation and a practical simulation.

Focused aperture (FA) antenna with phase center of its feeder moving along the focal plane or focal arc is an effective and low-cost approach for beam scanning. Dual polarization is always desired in the communication system. In this article, a dual-polarized linear array with overlapping handover of subarray (OHSA) is proposed to produce continuous displacement of virtual point source on the basis of the Huygens equivalence principle. As the feeder of an FA antenna, the proposed OHSA not only enables continuous beam scanning electronically but also reduces the profile of the antenna. To validate the proposed scheme, a dual-polarized electronic beam-scanning transmitarray antenna with the profile of $3.46\lambda _{0}$ is designed and measured. At the designed frequency 5.5 GHz, for both $x$ -and $y$ -polarizations, the measured gains are higher than 20.9 dBi, and the sidelobe levels (SLLs) are lower than −16 dB; within the bandwidth of 5.3 to 5.9 GHz and the scanning range of ±30°, the gains are higher than 16 dBi, and the SLLs are lower than −8 dB. The isolation between dual-polarizations in the broadside radiation is higher than 29 dB. The back lobe is lower than −15 dB. The measured results are in reasonable agreement with the simulated ones.

Single-sideband time-modulated phased array (STMPA) provides beam-scanning capability and eliminates some undesired sidebands. To further improve the frequency spectrum, the time modulator of the STMPA with S -step waveform for better eliminating the undesired sidebands and widening the allowable signal bandwidth without aliasing is proposed in this letter. The S -step waveform is realized by digital attenuators in time modulators. Most of sidebands are eliminated and the allowable signal bandwidth becomes 4 S times as wide as that of conventional time-modulated array (TMA). The general expressions of the sideband level (SBL) and the theoretical loss of the time modulator related to the number S of the steps are given. To experimentally verify the feasibility of the proposed design, the time modulator with four-step waveform and the corresponding four-element STMPA are fabricated and measured.

This paper reports on the sliding mode control (SMC) problem for nonlinear stochastic systems with one features: time-delays are not only varied with time but also characterized by random delays changed in line with a set of Markov chains (namely, time-delays are mode-dependent time-varying delays). Based on given systems, an integral switching surface is introduced. In particular, such a switching surface with an Ito process is given so that the traditional assumption imposed on systems is removed. And by applying the Ito formula, the linear matrix inequalities method and the lemma provided, more relaxed and indeed delay-dependent criteria for the second moment exponential stability are given. Then, the sliding mode controller is constructed to guarantee the reachability of the switching surface and the existence of the sliding mode. Finally, the validity and the application for the presented SMC method are illustrated by the DC motor system.

This article presents an enhanced single-sideband time-modulated phased array (ESTMPA) using modulating pulses with stepped waveforms. Based on the in-phase/quadrature (I/Q) complex modulation technique, this phase-only weighting array generates a scanning beam at the 1st sideband. The proposed modulating pulses realized through a reconfigurable power divider in I/Q time modulator can avoid the power loss from the switches during switch-OFF state and eliminate the maximum undesired sideband—the 5th harmonic in STMPA. As a result, it brings a power spectrum with less undesired sidebands, lower sideband level (−16.9 dB), higher harmonic efficiency (94.96%), and wider allowable signal bandwidth (eight times as wide as that of the conventional time modulated array). To experimentally verify the feasibility of the proposed design, a wideband enhanced I/Q time modulator and its corresponding eight-element ESTMPA are designed and manufactured. A detailed study on the effect of the magnitude and phase deviations in the circuit and the transition period of modulating pulse are presented. The measured results of power spectrum and radiation pattern have a good agreement with the simulated ones.

This paper presents a conformal log-periodic array covering an ultra-wideband of 2-18 GHz. It employs monopoles of different heights for the high band, top-hat monopoles for the middle band, and folded top-hat monopoles for the low band. The top hats help to achieve a low profile of the monopoles while the folding is to maintain a good input resistance at the low band. A meandering microstrip line on the bottom is used to feed the array. The proposed antenna is mounted on a conducting cylindrical surface with all the top hats conformal and aligned to the outline of the cylinder. A prototype is fabricated and tested. Measured results show that an impedance bandwidth from 2 to 18.3 GHz (9.15:1) for VSWR < 2 is obtained. Over the same band, the measured gain is better than 7.2 dBi. The antenna has a very low profile of 0.053 λL at the lowest operating frequency, which should be useful in many communication systems such as missile and airborne applications.