In this paper, we propose a design methodology for waveguide applicators to maximize microwave power deposition into human tissues. The optimized applicators can be used in the experimental studies of the biological effects of exposure to electromagnetic radiation in the frequency range from 6 GHz to 100 GHz. The design methodology relies on the provision of reflectionless matching of a dissipative waveguide load, achieved by employing a matching network based on a quarter-wave transformer prototype. The prototype is synthesized by knowledge of the voltage standing wave ratio (VSWR) evaluated in the unmatched loaded waveguide. A key difference from the conventional synthesis procedure is that in our design approach, the characteristic impedance of the first transformer section is given, and we have to not only determine the characteristic impedances of the remaining sections, but also establish the output load. A solution of this synthesis problem and the process of converting the transformer prototype into a waveguide structure are described. The physical structure can be implemented according to provided sample models of waveguide WR137 applicators employing symmetric inductive or capacitive posts. The matched waveguide applicators are easy to manufacture, and according to the results from computational simulations, they demonstrate superior performance compared to the unmatched waveguides. Limitations of our designs (narrow bandwidth, dependence on the type of tissues encountered, limited potential for miniaturization) are discussed.
2. Asan, N. B., E. Hassan, J. Velander, S. R. M. Shah, D. Noreland, T. J. Blokhius, E. Wadbro, M. Berggren, T. Voigt, and R. August, "Characterization of the fat channel for intra-body communication at R-band frequencies," Sensors (Basel), Vol. 18, No. 9, article 2752, Sep. 2018.
3. Bertin, E., N. Crespi, T. Magedanz, and Eds., Shaping Future 6G Networks. Needs, Impacts, and Technologies, Wiley, Hoboken, NJ, 2022.
4. Cohn, S. B., "Design of simple broad-band wave-guide-to-coaxial-line junctions," Proc. IRE, Vol. 35, No. 9, 920-926, Sep. 1947.
5. Dakhov, V. M., V. A. Katrich, and M. V. Nesterenko, "Compact radiator for microwave hyperthermia," Microwave & Telecommunication Technology (CriMiCo2008), 18th Int. Crimean Conf., 860-861, Sevastopol, Crimea, Ukraine, Sep. 08-12, 2008.
6. Dicke, R. H., "General microwave circuit theorems," Principles of Microwave Circuits, 130-161, Montgomery, C. G., R. H. Dicke, and E. M. Purcell, Eds., McGraw-Hill, New York, NY, 1948.
7. Dishal, M., "Alignment and adjustment of synchronously tuned multiple-resonant-circuit filters," Proc. IRE, Vol. 39, No. 11, 1148-1455, Nov. 1951.
8. Eskelinen, H. and P. Eskelinen, Microwave Component Mechanics, Artech House, Boston, MA, 2003.
9. Gajda, G. B., E. Lemay, and J. Paradis, "Model of steady-state temperature rise in multilayer tissues due to narrow-beam millimeter-wave radiofrequency field exposure," Health Phys., Vol. 117, No. 3, 254-266, Mar. 2019.
10. Gupta, R. and S. Singh, "Development and analysis of a microwave direct contact water-loaded box-horn applicator for therapeutic heating of bio-medium," Progress In Electromagnetics Research, Vol. 62, 217-235, 2006.
11. International Commission on Non-Ionizing Radiation Protection (ICNIRP), "Guidelines for limiting exposure to electromagnetic fields (100 kHz to 300 GHz)," Health Phys., Vol. 118, No. 5, 483-524, May 2020.
12. Kantor, G. and D. M. Witters, "The performance of a new 915-MHz direct contact applicator with reduced leakage," J. Microw. Power, Vol. 18, No. 2, 133-142, Jun. 1983.
13. Keshavarz, S., R. Keshavarz, and A. Abdipour, "Compact active duplexer based on CSRR and interdigital loaded microstrip coupled lines for LTE application," Progress In Electromagnetics Research C, Vol. 109, 27-37, 2021.
14. Khan, S. R., S. K. Pavuluri, G. Cummins, and M. P. Y. Desmulliez, "Wireless power transfer techniques for implantable medical devices: A review," Sensors (Basel), Vol. 20, No. 12, article 3487.
15. Lakhtakia, A. and T. G. Mackay, "Meet the metamaterials," Opt. Photonics News, Vol. 18, No. 1, 32-39, Jan. 2007.
16. Lee, Y. and K. Hwang, "Skin thickness of Korean adults," Surg. Radiol. Anat., Vol. 24, No. 3-4, 183-189, Aug.-Sep. 2002.
17. Lemay, E., G. B. Gajda, G. W. McGarr, M. Zhuk, and J. Paradis, "Analysis of ICNIRP 2020 basic restrictions for localized radiofrequency exposure in the frequency range above 6 GHz," Health Phys., Vol. 123, No. 3, 179-196, Sep. 2022.
18. Levy, R., "Tables of element values for the distributed low-pass prototype filter," IEEE Trans. Microw. Theory Techn., Vol. 13, No. 5, 514-536, Sep. 1965.
19. Levy, R., "A generalized design technique for practical distributed reciprocal ladder networks," IEEE Trans. Microw. Theory Techn., Vol. 21, No. 8, 519-526, Aug. 1973.
20. Levy, R. and L. W. Hendrick, "Analysis and synthesis of in-line coaxial-to-waveguide adapters," 2002 IEEE MTT-S Int. Microw. Symp. Dig., 809-811, Seattle, WA, USA, Jun. 02-07, 2002.
21. Lind, L. F., "Synthesis of equally terminated low-pass lumped and distributed filters of even order," IEEE Trans. Microw. Theory Techn., Vol. 17, No. 1, 43-45, Jan. 1969.
22. Matthaei, G. L., L. Young, and E. M. T. Jones, Microwave Filters, Impedance-Matching Networks, and Coupling Structures, Artech House, Norwood, MA, 1980.
23. Mehdizadeh, M., "Microwave/RF applicators and probes for material heating, sensing and plasma generation," A Design Guide, 2nd Edition, Elsevier, Oxford, UK, 2010.
24. Ness, J. B., "A unified approach to the design, measurement, and tuning of coupled resonator filters," IEEE Trans. Microw. Theory Techn., Vol. 46, No. 4, 343-351, Apr. 1998.
25. Pokharel, R. K., A. Barakat, S. Alshhawy, K. Yoshitomi, and C. Sarris, "Wireless power transfer system rigid to tissue characteristics using metamaterial inspired geometry for biomedical implant applications," Sci. Rep., Vol. 11, article 5868, Mar. 12, 2021.
26. Rappaport, C., "Synthesis of optimum microwave antenna applicators for use in treating deep localized tumors," Progress In Electromagnetics Research, Vol. 1, 175-240, 1989.
27. Riblet, H. J., "General synthesis of quarter-wave impedance transformers," IRE Trans. Microw. Theory Techn., Vol. 5, No. 1, 36-43, Jan. 1957.
28. Sasaki, K., K. Wake, and S. Watanabe, "Measurement of the dielectric properties of the epidermis and dermis at frequencies from 0.5 GHz to 110 GHz," Phys. Med. Biol., Vol. 59, No. 16, 4739-4747, Aug. 21, 2014.
29. Sasaki, K., M. Mizuno, K. Wake, and S. Watanabe, "Monte Carlo simulations of skin exposure to electromagnetic field from 10 GHz to 1 THz," Phys. Med. Biol., Vol. 62, No. 17, 6993-7010, Aug. 09, 2017.
30. Stutzman, W. L. and G. A. Thiele, Antenna Theory and Design, 3rd Ed., Wiley, 2013.
31. Uher, J., J. Bornemann, and U. Rosenberg, Microwave Components for Antenna Feed Systems: Theory and CAD, Artech House, Norwood, MA, 1993.
32. Vrba, D., D. Rodrigues, J. Vrba, and P. R. Stauffer, "Metamaterial antenna arrays for improved uniformity of microwave hyperthermia treatments," Progress In Electromagnetics Research, Vol. 156, 1-12, 2016.
33. Wang, Q. and J. Bornemann, "Synthesis and design of direct-coupled rectangular waveguide filters with arbitrary inverter sequence," 2014 16th Int. Symp. Antenna Technol. Appl. Electromagnetics (ANTEM), 1-6, Victoria, BC, Canada, Jul. 13-16, 2014.
34. Wang, Y., F. Qi, Z. Liu, P. Liu, W. Li, H. Wu, and W. Ning, "A wideband method to enhance the terahertz prenetration in human skin based on a 3D printed dielectric rod waveguide," IEEE Trans. Terahertz Sci. Technol., Vol. 9, No. 2, 155-164, Mar. 2019.
35. Weiβfloch, A., "Anwendung des Transformationssatzes uber verlustlose Vierpole auf die Hintereinanderschaltung von Vierpolen," Hochfrequenztechn. u. Elektroakust., Vol. 61, No. 1, 19-28, Jan. 1943.
36. Weissfloch, A., Schaltungstheorie und Messtechnik des Dezimeter -und Zentimeter-Wellengebietes, Birkhauser, Basel, Switzerland, 1954.
37. Young, L., "The quarter-wave transformer prototype circuit," IRE Trans. Microw. Theory Techn., Vol. 8, No. 5, 483-489, Sep. 1960.
38. Yu, M. and Y. Wang, "Synthesis and beyond," IEEE Microw. Mag., Vol. 12, No. 6, 63-76, Oct. 2011.
39. Zoughi, R., Microwave Non-Destructive Testing and Evaluation, Kluwer, London, UK, 2000.