Kontaktlose Energieversorgung mobiler Geräte durch induktive Nahfeldkopplung

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Die kontaktlose Energieübertragung hat Dank ihrer Vorteile ein weites Anwendungsspektrum und wird seit Jahrzehnten mit Erfolg eingesetzt. Sie kann einerseits zur Steigerung des Kom-forts eingesetzt werden oder ermöglicht vollkommen neue Anwendungen. Dieser Artikel be-schreibt die physikalischen Grundlagen und die technischen Grenzen dieser Technologie. Es wird erklärt, warum heute die kontaktlose Energieübertragung nur auf kurze Distanzen effi-zient und sicher genutzt werden kann. Die Kombination von Leistungselektronik und digitaler Signalverarbeitung steigert dabei nicht nur die Energieeffizienz sondern ermöglicht auch die Bereitstellung einer stabilisierten Spannungsversorgung für das zu betreibende Gerät. Die physikalische Grundlage für die kontaktlose Energieübertragung im Nahfeldbereich ist entweder die kapazitive oder die induktive Kopplung. Die Ausgangsbedingungen für die kapazitive Energie-übertragung sind wegen des großen Unterschiedes zwischen Permeabilitäts-und Dielektrizi-tätskonstante wesentlich ungünstiger. Die bei kapazitiver Kopplung benötigten Treiberspannungen und Frequenzen führen bereits bei der Übertragung vergleichsweise niedriger Leistungen zu hohen Verlusten. Demgegenüber sind die zu überwindenden technischen Schwierigkeiten bei induktiver Kopplung weitaus geringer mit der Folge, dass induktive Energieübertragungssysteme deutlich effi-zienter sind.

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In vielen Steuerungs-, Regelungs-, Überwachungs- und Abrechnungsprozessen muss eine Messgröße übermittelt werden, ohne dass ein Kabel zwischen der Auswerteelektronik und ihren zugehörigen Messwertaufnehmern gelegt werden kann oder soll. In diesen Fällen werden energieautarke, drahtlose Sensorsysteme (Funksensoren, engl. Transponder) eingesetzt, die von ihren Lesegeräten (engl. Reader) über eine Funkverbindung ausgelesen werden. In diesem Beitrag werden die unterschiedlichen Funktionsprinzipien funkauslesbarer Sensoren erläutert.
Chronic diseases like diabetes mellitus often require a permanent monitoring of vital signs. Especially the use of telemedicine will increase the quality of life for affected patients. Therefore, novel systems are necessary which are able to permanently detect and provide health status information. But these systems must not control patient's life and should work autonomously. For this purpose, intelligent medical implants are well qualified. This work describes a system for wireless power supply and communication with medical implant applications. Monitoring vital signs will create a big amount of data. Therefore, high data rates are necessary provided by high operating frequencies which in turn lead to electromagnetic far-field conditions. In this case, high attenuation losses due to the permittivity of the human body εr have to be considered. Hence, high frequencies are not suitable for the transfer of energy into the human body. The presented concept is based on two different frequencies for power supply and data transmission. An independent development of both blocks is thereby possible. The power supply operates at a frequency of 13.56 MHz, using inductive coupling. Consequently, the human body does not affect the energy transfer. In contrast, the data transmission is operated at a frequency of the medical implant communication service (MICS) band. The elaborated system consists of a power supply unit, a data transmission unit, and a control unit. The implementation of the power supply and data transmission as well as associated theoretical basics are presented. Performed measurements demonstrate that the realized system is qualified for the use on human beings.
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Conductive (wired) charging, where the user has to plug or unplug a cable, dominates the concepts discussed for electric vehicles up to now. Apart from the reduced range of the electric vehicle, frequent charging and especially short charging times make this plugging and unplugging appear impractical. In contrast, inductive (wireless) energy transfer makes it possible to charge without user intervention. This article attempts to answer questions on whether inductive energy transfer can already be used to charge electric vehicles and where this represents an economically attractive solution for users. To do so, first the charging technologies are presented and contrasted. It is also possible to compare the two charging technologies economically based on a cost analysis. It can be shown that no widespread use of the inductive technology is to be expected for the time being from an economic point of view due to its significant extra costs. Under certain conditions, however, there is a limited field of application as a niche technology in certain commercial areas, such as taxis, for example.
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