Radio frequency identification (RFID) is a technology enabling a contactless exchange of data. This technology\r\nfeatures the possibility to wirelessly transfer power to the transponder (opponent). HF-RFID is used in mobile devices\r\nlike smart phones and shows potential for applications like payment, identification, etc. Unfortunately, the needed\r\nfunctionality increases the battery drain of the device. As a countermeasure, power-management techniques are\r\nimplemented. However, these techniques commonly do not consider the whole system, which also consists of the\r\ncommunication to the transponder, to prevent wasting energy. One cross-system technique of reducing the wasted\r\nenergy is magnetic field strength scaling, which regulates the power transfer to the transponder. This article shows\r\nthree investigations made, regarding field strength scaling to prevent this wastage of energy. The results of one\r\ninvestigation, how to use field strength scaling at card detection phase in form of the PTF-Determinator method, is\r\ndescribed in detail. This method determines the Power Transfer Function (PTF) during run-time and scales the\r\nprovided power accordingly to save energy. As a case study the PTF-Determinator is integrated in an application to\r\nread digital business cards. The resulting power consumption and timing has been evaluated by simulation and\r\nmeasurement of a development platform for mobile phones. Furthermore, the impact of field strength scaling to the\r\nenergy consumption of a state of the art NFC-enhanced smart phone has been analyzed. The results of the case study\r\nshows that up to 26% less transmission energy (energy drain of NFC) is needed, if field strength scaling is applied\r\n(proofen by measurement). According to this result a smart phone�s battery drain (energy drain of the whole system)\r\ncan be decreased by up to 13% by using field strength scaling for this case study.
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