Presently, wireless capsule endoscopy (WCE) is the sole technology for inspecting the human gastrointestinal (GI) tract for diseases painlessly and in a non-invasive way. For the further development of WCE, the main concern is the development of a high-speed telemetry system that is capable of transmitting high-resolution images at a higher frame rate, which is also a concern in the use of conventional endoscopy. A vital task for such a high-speed telemetry system is to be able to determine the path loss and how it varies in a radio channel in order to calculate the proper link budget. The hostile nature of the human body's channel and the complex anatomical structure of the GI tract cause remarkable variations in path loss at different frequencies of the system as well as at capsule locations that have high impacts on the calculation of the link budget. This paper presents the path loss and its variation in terms of system frequency and location of the capsule. Along with the guideline about the optimum system frequency for WCE, we present the difference between the maximum and minimum path loss at different anatomical regions, which is the most important information in the link-margin setup for highly efficient telemetry systems in next-generation capsules. In order to investigate the path loss in the body's channel, a heterogeneous human body model was used, which is more comparable to the human body than a homogenous model. The finite integration technique (FIT) in Computer Simulation Technology's (CST's) Microwave Studio was used in the simulation. The path loss was analyzed in the frequency range of 100 MHz to 2450 MHz. The path loss was found to be saliently lower at frequencies below 900 MHz. The smallest loss was found around the frequency of 450 MHz, where the variation of path loss throughout the GI tract was 29 dB, with a minimum of -9 dB and a maximum of -38 dB. However, at 900 MHz, this variation was observed to be 38 dB, with a minimum of -10 dB and a maximum of -48 dB. For most positions of the capsule, the path loss increased rapidly after 900 MHz, reaching its peak at frequencies in the range of 1800 MHz to 2100 MHz. During examination of the lower esophageal region, the maximum peak observed was -84 dB at a frequency of 1760 MHz. The path loss was comparatively higher during examination of anatomically-complex regions, such as the upper intestine and the lower esophagus as compared to the less complex stomach and upper esophagus areas.
2. Yu, M., "M2ATM capsule endoscopy: A breakthrough diagnostic tool for small intestine imaging ," Gastroenterology Nursing, Vol. 25, No. 1, 24-27, Feb. 2002.
3. Pan, G. and L. Wang, "Swallowable wireless capsule endoscopy: Progress and technical challenges," Gastroenterology Research and Practice, Vol. 2012, 1-9, 2011.
4. Theilmann, P., M. A. Tassoudji, E. H. Teague, D. F. Kimball, and P. M. Asbeck, "Computationally efficient model for UWB signal attenuation due to propagation in tissue for biomedical implants," Progress In Electromagnetics Research B, Vol. 38, 1-22, 2012.
5. Chen, Z. and Y.-P. Zhang, "Effects of antennas and propagation channels on synchronization performance of a pulse-based ultra-wideband radio system," Progress In Electromagnetics Research, Vol. 115, 95-112, 2011.
6. Phaebua, K., C. Phongcharoenpanich, M. Krairiksh, and T. Lertwiriyaprapa, "Path-loss prediction of radio wave propagation in an orchard by using modified UTD method," Progress In Electromagnetics Research, Vol. 128, 347-363, 2012.
7. Anang, K. A., P. B. Rapajic, R. Wu, L. Bello, and T. I. Eneh, "Cellular system information capacity change at higher frequencies due to propagation loss and system parameters," Progress In Electromagnetics Research B, Vol. 44, 191-221, 2012.
8. Anang, K. A., P. B. Rapajic, L. Bello, and R. Wu, "Sensitivity of cellular wireless network performance to system & propagation parameters at carrier frequencies greater than 2 GHz," Progress In Electromagnetics Research B, Vol. 40, 31-54, 2012.
9. Van Laethem, B., F. Quitin, F. Bellens, C. Oestges, and P. de Doncker, "Correlation for multi-frequency propagaton in urban environments," Progress In Electromagnetics Research Letters, Vol. 29, 151-156, 2012.
10. Vidal, N., S. Curto, J. M. Lopez-Villegas, J. Sieiro, and F. M. Ramos, "Detuning study of implantable antennas inside the human body," Progress In Electromagnetics Research, Vol. 124, 265-283, 2012.
11. Gao, Y., Y. Zheng, S. Diao, W. Toh, C. Ang, M. Je, and C. Heng, "Low-power ultrawideband wireless telemetry transceiver for medical sensor applications ," IEEE Transactions on Biomedical Engineering, Vol. 58, No. 3, 768-772, Mar. 2011.
12. Diao, S., Y. Zheng, Y. Gao, C. Heng, and M. Je, "A 7.2mW 15 Mbps ASK CMOS transmitter for ingestible capsule endoscopy," 2010 IEEE Asia Pacific Conference on Circuits and Systems (APCCAS), 512-515, 2010.
13. Chi, B., J. Yao, S. Han, X. Xie, G. Li, and Z. Wang, "Low-power, high-data-rate wireless endoscopy transceiver," Microelectronics Journal, Vol. 38, 1070-1081, 2007.
14. Kim, K., S. Yun, S. Lee, S. Nam, Y. Yoon, and C. Cheon, "A design of a high-speed and high-e±ciency capsule endoscopy system," IEEE Transactions on Biomedical Engineering, Vol. 59, No. 4, 1005-1011, Apr. 2012.
15. Izdebski, P. M., H. Rajagopalan, and Y. Rahmat-Samii, "Conformal ingestible capsule antenna: A novel chandelier meandered design," IEEE Transactions on Antennas and Propagation, Vol. 57, No. 4, 900-909, Apr. 2009.
16. Zulkefli, M. S., F. Malek, M. H. Mat, S. H. Ronald, and M. F. Jamlos, "A compact peanut-shaped printed antenna for bio-telemetric tablet system," 2012 International Conference on Biomedical Engineering (ICoBE), 454-457, Feb. 27-28, 2012.
17. Gabriel, C., S. Gabriel, and E. Corthout, "The dielectric properties of biological tissues: I. Literature survey," Physics in Medicine and Biology, Vol. 41, 2231-2249, 1996.
18. Gabriel, S., R. W. Lau, and C. Gabriel, "The dielectric properties of biological tissues: II. Measurements in the frequency range of 10 Hz to 20 GHz," Physics in Medicine and Biology, Vol. 41, 2251-2269, 1996.
19. Gabriely, S., R. W. Lau, and C. Gabriel, "The dielectric properties of biological tissues: III. Parametric models for the dielectric spectrum of tissues," Physics in Medicine and Biology, Vol. 41, 2271-2293, 1996.
20. Ibrani, M., L. Ahma, E. Hamiti, and J. Haxhibeqiri, "Derivation of electromagnetic properties of child biological tissues at radio frequencies," Progress In Electromagnetics Research Letters, Vol. 25, 87-100, 2011.
21. Peyman, A., "Dielectric properties of tissues; variation with age and their relevance in exposure of children to electromagnetic fields; state of knowledge," Progress in Biophysics and Molecular Biology, Vol. 107, 434-438, 2011.
22. Chirwa, L. C., P. A. Hammond, S. Roy, and D. R. S. Cumming, "Electromagnetic radiation from ingested sources in the human intestine between 150MHz and 1.2 GHz," IEEE Transactions on Biomedical Engineering, Vol. 50, No. 4, 484-492, Apr. 2003.
23. Jung, J. H., S. W. Kim, Y. S. Kim, and S. Y. Kim, "Electromagnetic propagation from the intestine-ingested source in the human body model," IEEE Transactions on Antennas and Propagation, Vol. 58, No. 5, 1683-1688, May 2010.
24. Vaccari, A., A. Cala' Lesina, L. Cristoforetti, and R. Pontalti, "Parallel implementation of a 3D subgridding FDTD algorithm for large simulations," Progress In Electromagnetics Research, Vol. 120, 263-292, 2011.
25. Guo, X.-M., Q.-X. Guo, W. Zhao, and W.-H. Yu, "Parallel FDTD simulation using NUMA acceleration technique," Progress In Electromagnetics Research Letters, Vol. 28, 1-8, 2012.
26. Abbasi, Q. H., A. Sani, A. Alomainy, and Y. Hao, "Numerical characterization and modeling of subject-specific ultrawide-band body-centric radio channels and systems for healthcare applications," IEEE Transactions on Information Technology in Biomedicine, Vol. 16, No. 2, 221-227, Mar. 2012.
27. Takizawa, K., H. Hagiwara, and K. Hamaguchi, Path-loss estimation of wireless channels in capsule endoscopy from X-ray CT images, 33rd Annual International Conference of the IEEE EMBS Boston, 2242-2245, Massachusetts, USA, Aug. 30-Sep. 3, .
28. Stoa, S., R. Chavez-Santiago, and I. Balasingham, "An ultra wideband communication channel model for the human abdominal region," 2010 IEEE Globecom Workshops (GC Wkshps), 246-250, Dec. 6-10, 2010.
29. Katircioglu, O., H. Isel, O. Ceylan, F. Taraktas, and H. B. Yagci, "Comparing ray tracing, free space path loss and logarithmic distance path loss models in success of indoor localization with RSSI," 2011 19th Telecommunications Forum (TELFOR), 313-316, Nov. 22-24, 2011.
30. Pozer, D. M., Microwave Engineering, 3rd Ed., John Wiley & Sons, 2005.
31. Hall, P. S. and Y. Hao, Antennas and Propagation for Body-centricwireless Communications, Artech House, 2006.
32. Iero, D. A. M., T. Isernia, A. F. Morabito, I. Catapano, and L. Crocco, "Optimal constrained field focusing for hyperthermia cancer therapy: A feasibility assessment on realistic phantoms," Progress In Electromagnetics Research, Vol. 102, 125-141, 2010.
33. Mohsin, S. A., "Concentration of the specific absorption rate around deep brain stimulation electrodes during MRI," Progress In Electromagnetics Research, Vol. 121, 469-484, 2011.
34. Zhang, M. and A. Alden, "Calculation of whole-body SAR from a 100MHz dipole antenna," Progress In Electromagnetics Research, Vol. 119, 133-153, 2011.
35. Kong, L.-Y., J. Wang, and W.-Y. Yin, "A novel dielectric conformal FDTD method for computing SAR distribution of the human body in a metallic cabin illuminated by an intentional electromagnetic pulse (IEMP)," Progress In Electromagnetics Research, Vol. 126, 355-373, 2012.
36. Ronald, S. H., M. F. B. A. Malek, S. I. Syed Hassan, E. M. Cheng, M. H. Mat, M. S. Zulkefli, and S. F. Maharimi, "Designing asian-sized hand model for SAR determination at GSM900/1800: Simulation part," Progress In Electromagnetics Research, Vol. 129, 439-467, 2012.
37. Vrbova, B. and J. Vrba, "Microwave thermotherapy in cancer treatment: Evaluation of homogeneity of SAR distribution," Progress In Electromagnetics Research, Vol. 129, 181-195, 2012.
38. Gemio, J., J. Parron, and J. Soler, "Human body effects on implantable antennas for ISM bands applications: Models comparison and propagation losses study," Progress In Electromagnetics Research, Vol. 110, 437-452, 2010.
39. Online Document AboutHUGO Human Body Model, available: www.sonnetsoftware.com/pdf/cst/human body and radiator.pdf-d radiator.pdf.
40. Gjonaj, E., M. Bartsch, M. Clemens, S. Schupp, and T. Weiland, "High-resolution human anatomy models for advanced electromagnetic field computations," IEEE Transactions on Magnetics , Vol. 38, No. 2, 357-360, Mar. 2002.
41. CST User Interface for Hugo Human Body Model, [online] available: http://www.cst.com/Content/Applications/Article/HUGO+Human+Body+Model.
42. Klemm, M. and G. Troester, "EM energy absorption in the human body tissues due to UWB antennas," Progress In Electromagnetics Research, Vol. 62, 261-280, 2006.
43. Moglie, F., V. Mariani Primiani, and A. P. Pastore, "Modeling of the human exposure inside a random plane wave field," Progress In Electromagnetics Research B, Vol. 29, 251-267, 2011.
44. Ott, H. W., Electromagnetic Compatibility Engineering, John Wiley & Sons, Inc., Hoboken, New Jersey, 2009.
45. Data sheet, Federal Communication Commission, [online], www.fcc.gov/fcc-bin/dielec.sh-09/2002.
46. Iqbal, M. N., M. F. B. A. Malek, S. H. Ronald, M. S. Bin Mezan, K. M. Juni, and R. Chat, "A study of the EMC performance of a graded-impedance, microwave, rice-husk absorber," Progress In Electromagnetics Research, Vol. 131, 19-44, 2012.
47. Vidal, N., S. Curto, J. M. Lopez-Villegas, J. Sieiro, and F. M. Ramos, "Detuning study of implantable antennas inside the human body," Progress In Electromagnetics Research, Vol. 124, 265-283, 2012.
48. Malek, M. F. B. A., E. M. Cheng, O. Nadiah, H. Nornikman, M. Ahmed, M. Z. A. Abd Aziz, A. R. Osman, P. J. Soh, A. A. H. Azremi, A. Hasnain, and M. N. Taib, "Rubber tire dust-rice husk pyramidal microwave absorber," Progress In Electromagnetics Research, Vol. 117, 449-477, 2011.
49. Pues, H., Y. Arien, F. Demming-Janssen, and J. Dauwen, Numerical evaluation of absorber reflectivity in an artificial waveguide, 2009 20th International Zurich Symposium on Electromagnetic Compatibility, 409-412, Jan. 12-16, 2009.
50. Nornikman, H., M. F. B. A. Malek, P. J. Soh, A. A. H. Azremi, F. H. Wee, and A. Hasnain, "Parametric study of the pyramidal microwave absorber using rice husk," Progress In Electromagnetics Research, Vol. 104, 145-166, 2010.
51. Alomainy, A. and Y. Hao, "Modeling and characterization of biotelemetric radio channel from ingested implants considering organ contents," IEEE Transactions on Antennas and Propagation, Vol. 57, No. 4, 999-1005, Apr. 2009.