The thermal conductivity data provided by the manufacture are not always sufficiently accurate, and not available for newly formulated materials. However, it is crucial to obtain precise data of the thermal conductivity for low (less as 0.2 $\mathbf{W}\ \ \mathbf{m}^{-1}\ \ \mathbf{K} ^{-1})$ thermal conductivity materials where measurement errors have significant impact. There are several experimental methods to measure the thermal conductivity of insulating materials. These methods can be generally divided in two broad groups: steady-state and transient methods. In our work, we compared the results of thermal conductivity obtained by 3 different methods for the in-house formulated thermally insulating xerogel - epoxy composite adhesive. We performed the steady-state thermal conductivity measurements in vacuum chamber with low pressure of 7 10–9 mbar to suppress the conduction and convection losses. The results obtained by that method were compared with data obtained using two transient methods, a laser flash analysis (LFA) and an infrared (IR) thermography method. The LFA and IR thermography are indirect methods and require at least three independent measurements to obtain the thermal conductivity. The measurements error is larger than for the steady-state method. Additionally, to that, the IR thermography method exhibits several practical complications to realize necessary conditions of thermal transfer. That results in possible measurements errors and makes it not possible to obtain the thermal conductivity accurately. The steady-state and LFA methods can be used for the characterization of the thermal conductivity for low thermal conductivity materials such xerogel-epoxy composites.
The paradigm change from empirical lifetime models to a physics-of-failure based approach for automotive power electronics is driven by need for higher power densities. Hence, the usage of wide-bandgap semiconductor materials is necessary. This is accompanied by higher requirements on the packaging technologies, especially the die attach, in terms of electrical, thermal and mechanical properties. A die attach material meeting these demands is sintered silver which is already widely-used in automotive power electronics. In this study, passive thermal cycling experiments for different die sizes are performed and corresponding finite element simulations are used to find relative correlations.
High power wiring of power generators is an expensive affair that needs more attention. The cost of replacement after all paths are pulled and covered is high, and the defect is not always visible such as squeezing or bending but hidden. Therefore, due to the need for electrical testing, almost 80% of all tests performed in power systems are related to insulation quality testing. This is much more cost-effective than changing the wiring later. Most electrical equipment in industrial and commercial power systems uses 50 or 60 Hz AC voltage, depending on the range. So, using an AC power source to test insulation seems a logical choice. At the same time, however, isolation systems are extremely capacitive, which is one of the reasons that DC testing has found a large niche in this technology. In this paper, we present the implementation of a DC power supply adjustable between 0 and 500 V DC used for underground cable insulation testing.
This paper explores the possibility of using the power of the wind created by a car-in-motion for charging the car batteries. When a vehicle is moving even in a still atmosphere, a wind will act on a turbine mounted on the vehicle, this wind is called further relative wind. We study the possibility of using only the power of relative wind. The main disadvantage of electric and hybrid cars is the limited capacity of their storage batteries which impedes them from covering long distances. The obvious advantages of electric cars are canceled by the limited amount of energy stored in their batteries. Also, it is known that the conversion of an energy into another always comes with losses; therefore, a perpetuum mobile is not possible. We do not try to violate this principle, but we try to increase the efficiency of a wind turbine mounted on a car in motion. The wind turbine must be mounted on the vehicle chassis in a way to satisfy the aerodynamic and aesthetic criterions. So, the turbine system shall charge the car propulsion battery without creating supplementary friction. Results regarding the impact of the relative wind on the car conduct are analyzed using software named ANSYS and experimental tests and they are exposed in present paper. The base of this research is to demonstrate if the relative wind is sustainable to charge the battery in motion even for small improve.
Along with the large scale implementation of 5G networks a number of crucial technical challenges are still under development. Some of these are concerning the packaging and module developments, where the implementation of a large number of signal connections compatible with high data rates, the use of novel RF materials and finally new process approaches are the main issues to be tackled. Within the European funded project SERENA, an integration platform based on printed circuit board (PCB) embedding technology was developed. The technology enables the reduction of module size, system power consumption, design time, and complexity. At the same time improved performance and transmitted output power were achieved. In particular, by PCB embedding integrated RF electronic modules containing ICs for RF signal generation in very close proximity to the antennas were realized in a single package, thus minimizing the signal path losses. In the framework of the project, new materials suitable for the embedding of RF-components are used in combination with high gain GaN and SiGe dies. In this way a scalable System-in-Package operating at 39 GHz was ultimately implemented. In the course of the project a low and a high power module have been investigated. A functional low power module was fabricated at Fraunhofer IZM. Two process technologies had to be adopted (1) a combination of novel RF laminate and high-end prepreg materials to embed the dies into the build-up of the PCB and (2) the electrical connection of 3 µm Au contact pads by laser drilling and electroplating. Electrical test structures were fabricated in parallel to assess the electrical performance of package configuration and technology. Package interconnects and integrated patch antenna arrays were designed based on simulations with a 3D full-wave EM simulator (AnsysEM HFSS). The simulated structures were fabricated and measured using a network analyzer. The very short interconnection signal path between the passive and active elements realized in the PCB embedding technology achieve very low insertion (less than 0.4 dB) and return loss (better than 20 dB).The antennas in the package designed and fabricated using the PCB embedding technology achieved a wide bandwidth (3.1 GHz) with a peak gain of 8.8 dBi. Mutual coupling less than - 20 dB is obtained over the entire frequency range of interest between the elements of the antenna, thus making it suitable for beamforming. The approach proved to be well suited for the fabrication of 5G System-in-Package RF modules. The paper will give a detailed description of the fabrication processes and will discuss the technological approaches in depth. A brief overview of the electrical results will be given.
