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In this paper, a high efficiency and high power 165–180 GHz balanced doubler based on the planar Schottky diode is presented. To maximize the efficiency of the doubler in the target frequency band, an in-band embedded impedance optimization method (IEIOM) is adopted. The method aims to extract the conjugate value of embedded impedances of the three-dimensional electromagnetic (3D-EM) model of the diode. Compared to the method of impedance optimization at a single frequency point using Load-Pull, the proposed method not only takes account for both conversion efficiency and bandwidth but also simplifies operation process. To verify the proposed concept, the doubler was fabricated and measured, which exhibits a conversion efficiency of 13%–46% at the 165–180 GHz band under 160–200 mW input power and a 90.88 mW peak output power with a 46% efficiency was measured at 178 GHz when the input power is 198 mW. [ABSTRACT FROM AUTHOR]

A novel 3D optical method for measuring and evaluating the springback in sheet metal forming is presented and its principle, program and steps are studied. The optical method includes a measuring method and evaluation indexes. The point cloud, obtained using photogrammetry and surface scanning systems, is used as the workpiece shape after springback. The original mould is regarded as the CAD model before springback. The point cloud and CAD model are aligned in Geomagic Qualify. A cutting line for the point cloud or CAD model can be obtained at any point in any direction of their cross sections. The springback is calculated as the difference between any two corresponding key points on the two cutting lines. The evaluation index S consists of a 3D springback value w and its vectors along x , y and z directions. Feasibility of the optical method is verified by using a refrigerator door shell. [ABSTRACT FROM AUTHOR]

• Prediction of the effective thermal conductivity of the composite material. • Establishing representative numerical simulation models at multiple scales. • Heat transfer under the condition of conduction & radiation. • Effects of the porosity and fiber volume fraction on the effective thermal conductivity of the composite materials. Composite materials are widely used in the fields of aviation and space, where their thermal properties are of importance since they are often challenged by variations of environmental temperatures. However, thermal properties of composite materials under conditions of conduction & radiation (a key mode of heat transfer in space) remain elusive. In order to address this issue, in this study, numerical simulations of the glass/polyimide composite materials were conducted to determine its effective thermal conductivity under the conduction condition with and without radiation. More specifically, unit cell models of polyimide matrix, glass-fiber yarns, and the composite materials were constructed sequentially to study the effects of the porosity and the fiber volume fraction on the effective thermal conductivities of the composite materials. Simulation results revealed that 1) an increase in porosity can reduce the effective thermal conductivity of the polyimide matrix with the maximal decreasing ratio of 39.5%; 2) an increase in fiber volume fraction can increase the transverse effective thermal conductivity of the glass-fiber yarns with the maximal increasing ratio of 49.0%; 3) differences of 26.0% and 27.6% of the in-plane and out-of-plane effective thermal conductivities of the composite materials were located under the conduction condition with and without radiation. This study provided a simulation approach to investigate thermal properties of composite materials, paving ways for their applications in the fields of aviation and space. [Display omitted] [ABSTRACT FROM AUTHOR]

• A kernel separation method is proposed to compute the singular integral accurately. • Four singular integrals with different ordered kernel are computed directly with the help of the kernel separation method. • A patch subdivision scheme is developed based on the relation between the product of wave velocity, time and the distance. In the implementation of time-domain boundary element method for elasto-dynamic problems, there are two types of singularities: the wave front singularity arising when the product of wave velocity and time is equal to the distance between the source point and the field point, and the spatial singularity arising when the source point coincides with the field point. In this paper, the singularity of the first type in the integrand is eliminated by an analytical integration over time, Cauchy principal value and Hadamard finite part integral. Four types of singularities with different orders appear in the integrand after analytical time integration. In order to accurately calculate the integral, in which the integrand is piecewise continuous, the integral domain is subdivided into several patches based on the relation between the product of wave velocity and time and the distance. In singular patches, the integrands are separated into a regular part and a singular part. The regular part can be computed by traditional numerical integration method such as Gaussian integration, while the singular part can be analytically integrated. Using the proposed method, the spatial singular integrals can be calculated directly. Numerical examples using various kinds of elements are presented to verify the proposed method. [ABSTRACT FROM AUTHOR]