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Since it was firstly reported (Iddan, Meron, Glukhovsky & Swain, 2000), Wireless capsule endoscope (WCE) had become increasingly attractive for imaging examination of the small intestine in a noninvasive manner without discomfort and necessity for sedation (Glukhovsky, 2003; Delvaux & Gay, 2008; Pasha, 2009). Moreover, it can be used for tissue sample and biopsy or treatment (Sang, Yo & Seung, 2005; Kyoung-chul, Jinhoon, Doyoung & Dong-il, 2005). Meanwhile, Yamamoto & Kita (2005) and Roberts-Thomson, Singh, Teo, Nguyen & Lidums (2010) pointed out that WCE would be led to innovations in the future. However, the signal is easily interfered by other radio-frequency devices and attenuated by the human tissue during transferring. In order to enhance the anti-interference ability, Kim & Nooshabadi (2010) designed a tunable all-digital CMOS chip; Woo et al. (2010) designed a high-speed receiver; the author optimized transceiver mode with channel changing (Zhao & Peng, 2007; Zhao & Hou, 2009). Although these methods can enhance the ability of RF communication for transferring data to a certain extent, the characteristic of an antenna must be studied in depth to ensure the data reliably transfer.
Because of the high-water tissue, the absorption of electromagnetic wave increases with frequency. At higher frequency, the increased spacing between an antenna and the body counteracts losses in tissues. Therefore, it may be puzzling to select a reasonable frequency. Wang, Timothy & Cumming (2007) estimated that lower frequency had a better signal-to-noise ratio, but the signal was coupled with a much smaller. Scanlon et al. (2000, 2001) pointed out that body-worn antenna suffered from reduced efficiency, radiation pattern fragmentation, and variation impedance in feed point due to electromagnetic absorption in tissue. Despite with much higher tissue losses at 2.45 GHz, antenna performs surprisingly well in this band. Chirwa et al. (2002, 2003a, 2003b) studied two representative antennas for an ingested medical device, and indicated that the maximum radiation occurred between 450 MHz and 900 MHz. However, they only researched the radiation at the frequency range from 150 MHz to 1.2 GHz. Chan, Meng, Wu & Wang (2005) estimated attenuation at the four ISM bands from 100 MHz to 6 GHz with a simplified experimental model. The result showed that 915 MHz and 2.45 GHz were good choices for the wireless link. And, there were many prototypes of WCE used the frequency of 2.45 GHz (Chiu & Chen, 2005; Han, Chi & Wang, 2006; Xie, Li, Chen, Li & Wang, 2006; Zhao, Hou, Wang & Peng, 2010).