An application of the multilevel DG-FDTD to the study of a medical implant antenna in different body models

Abstract

In this paper, we propose to use the multilevel DGFDTD approach to analyze the evolution of the transmission coefficient between an implanted antenna in two different simplified body models (an homogeneous one and a threelayered one) and a 0.5λ 0 dipole in free space at various distances from the body model. The effectiveness of the multilevel DGFDTD is compared to the classical DGFDTD method.Index Terms-FDTD methods, Medical Implants Communication Systems. I.INTRODUCTIONMedical implant communications systems are a growing application field in the Body Area Network context [1]. The determination of power transmission between an implanted antenna and an external antenna is a major issue that requires time consuming FDTD simulations. Indeed, due to their small size, implanted antennas usually demand a very fine description. Besides, these antennas are placed inside the human body, with high dielectric constants. Considering the size of the human body, such a precise mesh implies oversampled areas which increase the computation time. On the other hand, the external receiving antenna is much larger and stands in free space, which still enhances the problem of oversampled areas.A way to overcome this issue, is to use the principle of the DGFDTD method. As explained in [2], [3], this technique is particularly wellsuited to analyze small antennas working in a large environment. It combines a fine description of the antenna with a coarse description of its environment. It permits to study the effect of the environment on both the input impedance and the radiation pattern of the antenna. In this paper, we present an extension of the DGFDTD method, which consists in splitting the overall simulation into several classical FDTD simulations sequentially executed with an appropriate mesh in order to respect the constraints of each element.The multilevel DGFDTD method is applied here to analyze power transmission between an implanted antenna in a simplified part of a human body model and a λ0/2 dipole in free space. First, we present the configuration of the problem used to illustrate the new method. Then, the principle of the multilevel DGFDTD related to the study context is exposed. Finally, we evaluate the effectiveness of the new method in terms of computation time, compared to the original DG FDTD. The advantages of the multilevel DGFDTD are lastly used to analyze the characteristics of the implanted antenna in two kinds of simplified part of body model. II.DESCRIPTION OF THE PROBLEMThe implanted antenna configuration and its environment are presented in Fig.1. The original description of the problem can be found in [4]. We are interested in the transmission between the implanted antenna placed in a simplified hexahedral part of body model and a λ 0 /2 dipole in free space. The implanted antenna is a meanderedtype PIFA. Its ground plane is orientated so that the antenna is radiating towards the dipole. The printed element is sandwiched between substrate and superstrate dielectric layers whose permittivity is 10.2 and thick...