Ultra wideband (UWB) antenna operation close to tissue is examined by using lumped-element equivalent circuits in the present paper. The impact of tissue within the reactive near-field of the antenna is introduced in terms of efficiency, impedance and matching to 50 Ω. The parasitic components for the series- and parallel-resonant stages of the equivalent models are proposed for taking the impact of tissue into account on the antenna design. The first time the antenna impedance behaviour is presentedin terms of capacitance, inductance and resistance as a function of the radiator distance on the tissue surface for UWB antennas. The capacitance was observed to increase with the distance on the tissue surface by achieving the maximum value close to the reactive near-field boundary. The inductance has the maximum on contact the tissue, decreasing strongly with the first millimetres and remaining constant with the higher distance. The maximum value of input resistance was seen to clearly increase with the distance, having the maximum value in the first third of the studied range, descending close to the value in free space at the boundary at the end. The results are achieved by realising electromagnetic simulations for the antennas and comparing the performance with the operation of the equivalent models.
2., "IEEE standard for local and metropolitan area networks,", IEEE 802.15.6-2012 --- Part 15.6:Wireless Body Area networks, 2012.
3. Sankaranlingam, S. and B. Gupta, "Development of textile antennas for body wearable applications and investigations on their performance under bent conditions," Progress In Electromagnetics Research B,, Vol. 22, 53-71, 2010.
4. Vorobyov, A. and A. Yarovoy, "Human body impact on UWB antenna radiation," Progress In Electromagnetics Research M, Vol. 22, 259-269, 2012.
5. Kivekas, O., T. Lehtiniemi, and aP. Vainikainen, "On the general energy-absorption mechanism in the human tissue," Microw. Opt. Tech. Lett., Vol. 43, No. 3, 195-201, Nov. 2005.
6. Klemm, M. and G. Troester, "EM energy absorption in the human body tissues due to UWB antennas," antennas," Progress In Electromagnetics Research, Vol. 62, 261-280, 2006.
7. Tuovinen, T., M. Berg, K. Y. Yazdandoost, and J. Iinatti, "Ultra wideband loop antenna on contact with human body tissues," IET Proceedings --- Microwaves Antennas and Propagation, Vol. 7, No. 7, 588-596, Mar. 2013.
8. Christ, A., A. Klingenbock, T. Samaras, C. Goiceanu, and N. Kuster, "The dependence of electromagnetic far-field absorption on body tissue composition in the frequency range from 300MHz to 6 GHz," EEE Trans. Microw. Tech., Vol. 54, No. 5, 2188-2195, May 2006.
9. Tuovinen, T., T. Kumpuniemi, K. Y. Yazdandoost, M. HÄamÄalÄainen, and J. Iinatti, "Effect of the antenna-human body distance on the antenna matching in UWB WBAN applications," Proc. 7th Int. Symp. Med. Inform. Commun. Technol. (ISMICT2013), 1-5, Japan, Mar. 2013.
10. Alomainy, A., Y. Hao, and D. M. Davenport, "Parametric study of wearable antennas with varying distances from the body and di®erent on-body positions," IET Seminar on Antennas Propag. for Body-Centric Wireless Commun., 84-89, London,UK, Apr. 2007.
11. Kaivanto, E., M. Berg, E. Salonen, and P. Maagt, "Wearable circularly polarized antenna for personal satellite communication and navigation," IEEE Trans. Antennas Propag., Vol. 53, No. 124, 4490-4496, Dec. 2005.
12. Koohestani, M., N. Pires, A. K. Skrivervik, and A. A. Moreira, "Performance study of a UWB antenna in proximity to a human arm," IEEE Antennas Wireless Propag. Lett., Vol. 12, 555-558, 2013.
13. Sani, A., A. Alomainy, J. Santas, and . Hao, "Time domain characterization of ultra wideband wearable antennas and radio propagation for body-centric wireless networks in healthcare applications," Proc. Int. Summer School and Symp. Med. Dev. Biosensors (ISSS-MDBS), 129-132, Hong Kong, Jun. 2008.
14. Balanis, C. A., Antenna Theory Analysis and Design, 3rd Ed., John Wiley & Sons, 2005.
15. Stutzman, W. L. and G. A. Thiele, Antenna Theory and Design, 2nd Ed., John Wiley & Sons, 1998.
16. Wheeler, H. A., "The radiansphere around a small antenna," Proc. the Inst. Radio Eng. (IRE), 1325-1331, 1959.
17. Raisanen, A. V. and A. Lehto, Radio Engineering for Wireless Communication and Sensor Applications, Artech House, Norwood, 2003.
18. Tuovinen, T., M. Berg, and E. Salonen, "The comparative analysis of UWB antennas with complementary characteristics: A functionality in FS and applicability for the usage close to tissues," PIERS Proceedings, 134-138, Stockholm, Sweden, Aug. 12-15, 2013.
19., "Revision of Part 15 of the commission's rules regarding ultra wideband transmission systems,", FCC Notice of Proposed Rule Making, ET-Docket 98-153, FCC 02-48, 2002.
20. Oppermann, I., M. Hamalainen, and J. Iinatti, UWB Theory and Applications, John Wiley & Sons, England, 2004.
21., "Computer simulation technology microwave studio software,", Online Available: http://www.cst.com.
22. Chen, Z. N., Antennas for Portable Devices, John Wiley & Sons, 2007.
23. Tuovinen, T. and M. Berg, "Impedance dependency on planar broadband dipole dimensions: an examination with antenna equivalent circuits," Progress In Electromagnetics Research, Vol. 144, 249-260, 2014.
24. Harrington, R. F., Time-harmonic Electromagnetic Fields, McGraw-Hill, 1961.
25. Alves, T. M., B. Poussot, and J.-M. Laheurte, "Analytical propagation modeling of BAN channels based on the creeping-wave theory," IEEE Trans. Antennas Propag., Vol. 57, No. 4, 1269-1274, Apr. 2011.
26. Sanchez-Hernµandez, D. A., High Frequency Electromagnetic Dosimetry, Artech House, 2009.
27. Holopainen, J., R. Valkonen, O. Kivekas, J. Ilvonen, L. Martinez, P. Vainikainen, J. R. Kelly, and P. S. Hall, "Equivalent circuit model-based approach on the user body effect of a mobile terminal antenna," Proc. Loughborough Antennas Propag. Conf. (LAPC), 217-220, UK, 2010.
28. Barnes, F. S. and B. Greenebaum, Bioengineering and Biophysical Aspects of Electromagnetic Fields, 3rd Ed., Taylor & Francis Group, Boca Raton, 2007.
29. Gandhi, O. P., B. Q. Gao, and J. Y. Chen, "A frequency-dependent finite-difference time-domain formulation for general dispersive media," IEEE Trans. Antennas Propag., Vol. 41, No. 4, 658-665, Apr. 1993.
30. Wang, Y., J. Z. Li, and L. X. Ran, "An equivalent circuit modeling method for ultra-wideband antennas," Progress In Electromagnetics Research, Vol. 82, 433-445, 2008..
31. Ansarizadeh, M. and A. Ghorbani, "An approach to equivalent circuit modeling of rectangular microstrip antennas," Progress In Electromagnetics Research B, Vol. 8, 77-86, 2008.
32. Li, R. L., W. Terence, B. Pan, K. Lim, J. Laskar, and M. M. Tentzeris, "Equivalent-circuit analysis of a broadband printed dipole with adjusted integrated balun and an array for base station applications," IEEE Trans. Antennas Propag., Vol. 57, No. 7, 2180-2184, Jul. 2009.
33. Hamid, M. and R. Hamid, "Equivalent circuit of dipole antenna of arbitrary length," IEEE Trans. Antennas Propag., Vol. 45, No. 11, 1695-1696, Nov. 1997.
34. Holopainen, J., R. Valkonen, O. Kivekas, J. Ilvonen, and P. Vainikainen, "Broadband equivalent circuit model for capacitive coupling element-based mobile terminal antenna," IEEE Antennas Wireless Propag. Lett., Vol. 9, 716-719, 2010.
35. Liao, Y., T. H. Hubing, and D. Su, "Equivalent circuit for dipole antennas in a lossy medium," IEEE Trans. Antennas Propag., Vol. 60, No. 8, 3950-3953, Aug. 2012.
36. Tang, T. G., Q. M. Tien, and M. W. Gunn, "Equivalent circuit of a dipole antenna using frequency-independent lumped elements," IEEE Trans. Antennas Propag., Vol. 41, No. 1, 100-103, Jan. 1993.