A Smart-Card E-paper Display System Based on RF Power Harvesting

Abstract

This study investigated technologies related to a smart-card display and its wireless charging system, where the wireless receiver in the smart card receives not only the data but also the power required for the display circuitry. The goal of this research was to achieve the required energy transfer during the extremely short reading time when a person swipes his or her smart card. This paper describes the design considerations and the analysis procedures of the transmitter and receiver pair for an electronic paper (E-paper) display. A series of magnetic simulations as well as experimental tests were conducted to investigate the various design factors. The design considerations included the shape and effect of using ferromagnetic cores, the component design for frequency tuning, the geometric arrangements, and the number of turns of the coils. A novel design for power transmission is then proposed using a ferromagnetic core to enhance its energy efficiency. In experiments the transmitter unit provided 250 mW of power to the transmitter antenna. The resultant transmission efficiency (S21) was ¡5.1 dB over a distance of 4.3 mm. Experimental results show that the smart card receives 220 mW, representing a high transmission efficiency of 88%.