To assess the compliance of an ingested wireless device (IWD) with related international safety guidelines, a team of researchers used the finitedifference- time-domain (FDTD) method for two realistic body models in an electromagnetic (EM) simulator. Both biological effects and the IWD's signal intensity were studied by Lisheng Xu from China's Northeastern University together with Max Q.H. Meng, Hongliang Ren, and Yawen Chan from the Chinese University of Hong Kong.
To detail the radiation characteristics of an IWD in the small intestine, the researchers designed four capsule antennas corresponding to 430 and 800 MHz and 1.2 and 2.54 GHz. The FDTD method was applied to analyze the EM interference of the IWD with the human body. The temperature rise resulting from the specific absorption rate (SAR) deposition was calculated using a bio-heat equation. To analyze the SAR and temperature rise in the realistic human models, the XFDTD software from Remcom was used. The SAR and temperature rise value were normalized to the input power of 25 mW for RF source.
The team carried out simulation studies in 21 scenarios. For each of the two human models, the IWD was placed at seven positions with three orientations. The results indicated that the radiation intensity outside of the human body decreased as the operation frequency rose. Among all of the simulated scenarios created by the researchers, the maxima of the averaged 1-g and averaged 10-g SARs can reach 3.71 W/kg and 1.37 W/ kg at the input power of 25 mW. See "Radiation Characteristics of Ingestible Wireless Devices in Human Intestine Following Radio Frequency Exposure at 430, 800, 1200, and 2400 MHz," IEEE Transactions On Antennas And Propagation, August 2009, p. 2418.