Radiation Characteristic Analysis of Antenna Deeply Implanted in Human Body and Localization Sensor Array

In vivo antennas are increasingly used in human implant devices. However, the two most confusing issues, analytical solutions of radiation fields and communication frequency selection of antennas deeply implanted in human bodies, have not been studied and resolved, whereas they are both significant to antenna design, communication, and localization system construction of human implant devices. Therefore, in this article, the electromagnetic model of an antenna in a lossy multilayered cylindrical media is established, which can more accurately simulate the human environment. The analytical solutions of electric intensity, magnetic intensity, and Poynting vector are derived by solving the boundary value problem of electromagnetic fields, which have not been reported in the existing literatures. Through theoretical calculations at 433 MHz, 915 MHz, and 2.45 GHz, the radiation characteristics of the antenna in the torso are analyzed, and the important results are achieved: 1) the electromagnetic fields in human body do not attenuate monotonously with the increasing of the field point distance, and multiple extreme points appear due to the influence of the reflected wave at the interface of different human tissues; and 2) the electromagnetic field intensity at the surface of human body is the largest at 915 MHz, while the induced voltage of receiving antenna outside the body is the largest at 2.45 GHz. Finally, by experiments and simulations, the analytical solutions are verified, which can provide theoretical guidance for the in vivo antenna design, frequency selection, communication, and electromagnetic localization. A localization system for human implant devices as an antenna application example is built, and it is proven that the theoretical model proposed in this article can be used for human implant device localization.