13th International Conference on Fracture June 16–21, 2013, Beijing, China -5- the shape of the ion-sputtered film is always laterally zygomorphic, it is suitable to calculate the electric current by adding half of the voltage to half shape of the film. The definition of ac and Wc (Wc=1.9 mm) of the ion-sputtered film and the boundary condition for FEM are shown in Figure 5. The electric current of metal film was calculated by the integration of current density in analytical results, and the resistance was derived from Ohm’s law. 3.2. Wireless Communication 3.2.1 . Using RFID tag RFID (Radio Frequency Identification) is a technology that transmits information between a reader and tags attached to an object using electromagnetic induction for the purpose of identification. It is widely used as IC tag or IC card. The RFID system is well known for its benefits of low cost, simple measurement, easy configuration and so on. Since tag is powered by electromagnetic induction from the reader, tag itself does not need battery for sensing and data transmission. By using RFID tags, evaluating the fatigue damage has been realized in previous research.[5] The schematic of wireless system for measuring crack length using RFID tag is shown in Figure 6. Figure 6. Schematic of wireless system for measuring crack length using RFID tag and reader.[6] The wireless system composed of sputtered smart patch, RFID tag (RX2S, Yoshikawa RF Systems Co., Ltd.) and microprocessor (PIC12F675, Microchip Technology Inc.), in which the electrical resistance of the ion-sputtered metal film was converted to digital value and transmitted to the RFID reader (RX2100, Yoshikawa RF Systems Co., Ltd.). The RFID reader plays two roles of supplying power to RFID tag and acquiring the measured value from RFID tag by a unique protocol. 3.2.2. Using ZigBee Figure 7. Schematic of new wireless system To improve the communication distance, a new wireless device equipped with ZigBee (IEEE
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