In this letter, the dispersion characteristics and energy configurations of a cylindrical partially filled waveguide or lossy multilayered rod shielded by a metallic enclosure are presented for several modes. These parameters are obtained by a numerical simulation based on the residues theory. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 30: 192–195, 2001.

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This paper describes an innovative method for the removal of heat from semiconductors power modules operating with high power losses. In linear applications, for example, losses are often so high that air cooling is inadequate and liquid cooling must be used.Traditionally, this is achieved by bolting a standard module onto a liquid -cooled heat exchanger.While more effective than air cooling, a thermal barrier still exists between the module base plate and separate heat sink and this contributes significantly to the total junction to ambient thermal resistance. To eliminate this barrier, APT Europe has engineered an integral liquid cooled (ILC) power module package, where the module base plate doubles as the liquid cooled heat exchanger's upper lid. In this way the cooling medium is in direct contact with the module base plate and there is no interface. To illustrate the dramatic improvement in performance made possible by this approach, the thermal performance of a dual 200Vy 7 m Ohm MOSFET module operating in linear mode is analysed .A detailed description of the ILC construction as well as the influence of flow rate on thermal resistancearepresented. 1-INTRODUCTIONThe major evolution taking place in today's state of the art power modules is the ever higher degree of integration, as more and more functions are incorporated, to complement and protect the power semiconductors switches inside.The never ending quest for lower costs and the continuous improvements of silicon technology results in progressively smaller chips for a given output power. The combination of smaller chips and compact packaging conducts to forever rising power density levels that bedevil the process of heat extraction. Integral liquid cooled power modules, with their vastly improved thennal transfer properties compared to either air cooled or conventionally liquid cooled packages permit full exploitation of the performance potential associated today's leading-edge power semiconductor technology. 2-THE JLC CONCEPTThe innovative forces behind this innovative packaging concept may be summarised as follows: chips and final ambient this being interpreted as the lowest possible thermal resistance, junction to ambient. This junction to ambient thermal resistance is the sum of several thermal resistance connected in series, junction to case, case to sink and sink to ambient. The aim is to " i s e the number of elements in the chain and the magnitude of each that remains. As already described the ILC concept completely eliminates the case to sink thermal resistance, a significant part of the whole in a classic design.-The base plate associated with a typical power module is necessarily of large area, to accommodate a plurality of silicon chips and other heat generating devices like resistive current shunts. When this base plate must be mounted on the matching face of a separate heat sink, either air or water cooled, both mating surfaces must be machined to very high standards of flatness and surface finish. This expensive operation must be performed...