Wearable wireless technology has developed as an exciting topic over the last couple of years. With the extensive use of Wearable Wireless Devices (WWD) in greater proximity to the body for various wireless applications, the concern about biological effects due to the interaction of human tissues with the radiations is growing. In this research, we investigate the application of Infrared Thermography (IRT) to obtain temperature dynamics and reconstruct Specific Absorption Rate (SAR) to evaluate the exposure amenability of WWDs. A microstrip monopole antenna on a wearable substrate is used to determine the biological effects of the interaction of electromagnetic (EM) waves on the body. SAR is obtained using EM field simulations and by reconstruction from thermal measurements with the use of Bio-heat equationsfor a continuous exposure of 300 s. Validation of IRT to reconstruct SAR is demonstrated by comparison with EM computations. The maximum SAR was 32 mW/kg, for simulations and 35 mW/kg, from reconstruction after IRT experiments. The maximum temperature change in both cases was always less than 1˚C. The difference between the SAR obtained through IRT and simulation tools accounted for an average of 8.7%. Information acquired using IR temperature dynamics can yield SAR values which can assess radio frequency exposure compliance for WWD at frequencies used for modern wireless technologies, with reliability.
1. Hall, P. S. and Y. Hao, Antennas and Propagation for Body-centric Wireless Communications, 2nd Ed., Artech House, 2012.
2. Christ, A., M. C. Gosselin, M. Christopoulou, S. Kuhn, and N. Kuster, "Age-dependent tissue-specific exposure of cell phone users," Phys. Med. Biol., Vol. 55, 1767-1783, 2010. doi:10.1088/0031-9155/55/7/001
3. Brishoual, M., C. Dale, J. Wiart, and J. Citerne, "Methodology to interpolate and extrapolate SAR measurements in a volume in dosimetric experiment," IEEE Trans. Electromagn. Compat., Vol. 43, 382-389, 2001. doi:10.1109/15.942609
4. Chavannes, N., R. Tay, N. Nikoloski, and N. Kuster, "Suitability of FDTD-based TCAD tools for RF design of mobile phones," IEEE Antennas and Propagation Magazine, Vol. 45, 52-66, 2003. doi:10.1109/MAP.2003.1282180
5. Schmid, T., O. Egger, and N. Kuster, "Automated E-field scanning system for dosimetric assessments," IEEE Transactions on Microwave Theory and Techniques, Vol. 44, 105-113, 1996. doi:10.1109/22.481392
6. Institute of Electrical and Electronics Engineers Recommended practice for determining the peak spatial-average SAR in the human head from wireless communications devices: Measurement techniques, IEEE Standard 1528-2013, 2013.
7. Wu, T., T. S. Rappaport, and C. M. Collins, "The human body and millimeter-wave wireless communication systems: Interactions and implications," 2015 IEEE International Conference on Communications (ICC), 2423-2429, IEEE, 2015. doi:10.1109/ICC.2015.7248688
8. Chou, C. K. and J. A. D'Andrea, "Reviews of effects of RF fields on various aspects of human health: Introduction," Bioelectromagnetics, Vol. 24.S6, 2003.
9. Tuovinen, T., M. Berg, K. Y. Yazdandoost, and J. Linatti, "On the evaluation of biological effects of wearable antennas on contact with dispersive medium in terms of SAR and bio-heat by using FIT technique," ISMICT, 149-153, Tokyo, Mar. 2013.
10. Thotahewa, K. M., J. M. Redouté, and M. R. Yuce, "SAR, SA, and temperature variation in the human head caused by IR-UWB implants operating at 4 GHz," IEEE Transactions on Microwave Theory and Techniques, Vol. 61, No. 5, 2161-2169, 2013. doi:10.1109/TMTT.2013.2250515
11. Zhadobov, M., N. Chahat, R. Sauleau, C. Le Quement, and Y. Le Drean, "Millimeter-wave interactions with the human body: State of knowledge and recent advances," International Journal of Microwave and Wireless Technologies, Vol. 3, No. 2, 237-247, 2011. doi:10.1017/S1759078711000122
12. Wu, T., T. S. Rappaport, and C. M. Collin, "Safe for generations to come: Considerations of safety for millimeter waves in wireless communications," IEEE Microwave Magazine, Vol. 16, No. 2, 65-84, 2015. doi:10.1109/MMM.2014.2377587
13. Sankaralingam, 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. doi:10.2528/PIERB10032705
14. Florence, E. S., M. Kanagasabai, and G. N. M. Alsath, "An investigation of a wearable antenna using human body modelling," Applied Computational Electromagnetics Society Journal, Vol. 29, No. 10, 2014.
15. Alon, L., G. Y. Cho, X. Yang, D. K. Sodickson, and C. M. Deniz, "A method for safety testing of radiofrequency/microwave-emitting devices using MRI," Magnetic Resonance in Medicine, Vol. 74, No. 5, 1397-1405, 2015. doi:10.1002/mrm.25521
16. Alon, L., D. K. Sodickson, and C. M. Deniz, "Heat equation inversion framework for average SAR calculation from magnetic resonance thermal imaging," Bioelectromagnetics, Vol. 37, No. 7, 493-503, 2016. doi:10.1002/bem.21996
17. Karthik, V. and T. Rama Rao, "Thermal distribution based investigations on electromagnetic interactions with the human body for wearable wireless devices," Progress In Electromagnetics Research M, Vol. 50, 141-150, 2016. doi:10.2528/PIERM16071703
18. Gabriel, C., S. Gabriely, and E. Corthout, "The dielectric properties of biological tissues: I. Literature survey," Phys. Med. Biol., Vol. 41, 2231-2249, 1996. doi:10.1088/0031-9155/41/11/001
19. Italian National Research Council, Institute for Applied Physics, homepage on Dielectric properties of body tissues, [Online]. Available: http://niremf.ifac.cnr.it.
20. Tuovinen, T., M. Berg, K. Y. Yazdandoost, and J. Linatti, "Ultra wideband loop antenna on contact with human body tissues," IET Microwave and Antennas Propagation, Vol. 7, No. 7, 588-596, 2013. doi:10.1049/iet-map.2012.0082
21. Garg, R., P. Bhartia, I. Bahl, and A. Ittipiboon, Microstrip Antenna Design Handbook, Artech House, 2001.
22. Allen, S. G., et al., "ICNIRP guidelines for limiting to time varying electric, magnetic, and electromagneticfields (upto 300 GHz)," Health Physics, Vol. 74, No. 4, 494-522, 1998.
23. IEEE Standard for Safety Levels with Respect to Human Exposure to the Radio Frequency Electromagnetic Fields 3 kHz to 300 GHz, IEEE Std. C95.1, 2005.
24. Kritikos, H. N., P. Herman, and Schwan, "Potential temperature rise induced by electromagnetic-field in brain tissues," IEEE Trans. on Biomedical Engineering, Vol. 26, No. 1, 29-34, 1979. doi:10.1109/TBME.1979.326493
25. Karthik, V. and T. Rama Rao, "Investigations on SAR and thermal effects of a body wearable microstrip antenna," Wireless Personal Communications, 1-17, 2017, DOI: 10.1007/s11277-017-4059-9.