Increasing Microwave Penetration Depth in the Human Body by a Complex Impedance Match of Skin Interface with a Two-Layered Medium

Increasing the radiated microwave penetration depth is the key to breaking the limitations of the action range in the lossy human body for non-invasive microwave technologies such as microwave hyperthermia, microwave imaging, and the wireless charging of implantable devices. This paper presents a method to increase the radiated microwave penetration depth in the lossy human body by matching the complex impedance of the skin surface using a two-layered medium. The proposed method avoided the impedance mismatch caused by the real impedance assumption of the skin surface for a lossy human body when using the traditional method. Therefore, the reflection loss on the skin surface could be significantly reduced, thereby increasing the penetration depth of the radiated microwave. Moreover, this method could select a suitable medium for the matched Layer 1 by adjusting the relative permittivity of the matched Layer 2, which is more practical than the single-layer-medium optimization method where the relative permittivity cannot be adjusted. The full-wave simulation results showed that the microwave penetration depth of the proposed method at an input power of 0.5 W was 21.01 mm and could significantly increase by 83.18% and 21.37% compared with those in a no-matched layer model and in a traditional 1/4 wavelength medium match method, respectively.