Radio frequency identification (RFID) is a technology enabling a contactless exchange of data. Thistechnology features the possibility to wirelessly transfer power to the transponder (opponent). HF-RFID is used in mobile devices like smart phones and shows potential for applications like payment,identification, etc. Unfortunately, the needed functionality increases the battery drain of the device. Asa countermeasure, power-management techniques are implemented. However, these techniques com-monly do not consider the whole system, which also consists of the communication to the transpon-der, to prevent wasting energy. One cross-system technique of reducing the wasted energy is magneticfield strength scaling, which regulates the power transfer to the transponder. This article shows threeinvestigations made, regarding field strength scaling to prevent this wastage of energy. The resultsof one investigation, how to use field strength scaling at card detection phase in form of the PTF-Determinator method, is described in detail. This method determines the Power Transfer Function(PTF) during run-time and scales the provided power accordingly to save energy. As a case study thePTF-Determinator is integrated in an application to read digital business cards. The resulting powerconsumption and timing has been evaluated by simulation and measurement of a development plat-form for mobile phones. Furthermore, the impact of field strength scaling to the energy consumptionof a state of the art NFC-enhanced smart phone has been analyzed. The results of the case study showsthat up to 26% less transmission energy (energy drain of NFC) is needed, if field strength scaling isapplied (proofen by measurement). According to this result a smart phone's battery drain (energydrain of the whole system) can be decreased by up to 13% by using field strength scaling for this casestudy.
Electrical Engineering, Measurement and Control Technology