**3. Antenna input impedance characterization**

The miniaturized high-Q loop antenna impedance is highly dependant on the close environment of this antenna. Due to the unpredictable near field tissues properties, its thickness variation or patient's position change, the antenna impedance can vary introducing some quite variable losses due to mis-adaptation. To address this problem, it can be advantageous to design a tunable matching network to improve the adaptation where the variability range of the network should be able to match the variation range of the antenna impedance to the optimal impedance of the front-end radio. Therefore, there is a first need that consists in the characterization of the variability in the antenna input impedance in order to decide of the matching topology. In so far as the approach is the same whatever the chosen frequency, we decide to focus our work considering the MICS frequency band.

#### **3.1 Human body modeling**

Generally, antenna impedance is characterized in homogeneous lossy dispersive fluids which simulate the average human body electrical properties. As impedance characterization requires to know the electromagnetic field behaviour in near antenna area, only reduced volume of these lossy materials is modelled. But, to accurately take into account the near field pacemaker antenna behaviour, different human tissues close to the implant have to be also considered. This will be done by using heterogeneous model with limited dimensions as multi-layered structures or as existing accurate human model of electromagnetic simulation tool.

#### **3.1.1 Homogeneous model**

The pacemaker implant is plunged in a dispersive and lossy liquid material with frequency dependent electrical properties. In order to characterize antenna pacemaker impedance in the 402-405 MHz MICS frequency band, the 450 MHz body tissue equivalent liquid is used. The target electrical parameters of this fluid (conductivity σ and real part of permittivity εr') are provided by the FCC [23], as given in Table 1.


Table 1. Body simulating liquid electrical properties at 450 MHz

In the electromagnetic simulation tool based on Finite-Integration Time-Domain (FITD) method (CST Microwave Studio) [24], the homogeneous liquid model is represented by a parallelepiped (15cm×11cm×3.4cm). The rectangular homogeneous block dimensions and the pacemaker inside it as illustrated in Fig. 6 (a) are optimized for the heterogeneous model. For the experimental setup in Fig. 6 (b), the pacemaker is plunged into a rectangular plastic recipient filled with homogeneous liquid and which dimensions are the same than the simulated one.

link by reducing the power losses due to impedance mismatch of the body affected small

The miniaturized high-Q loop antenna impedance is highly dependant on the close environment of this antenna. Due to the unpredictable near field tissues properties, its thickness variation or patient's position change, the antenna impedance can vary introducing some quite variable losses due to mis-adaptation. To address this problem, it can be advantageous to design a tunable matching network to improve the adaptation where the variability range of the network should be able to match the variation range of the antenna impedance to the optimal impedance of the front-end radio. Therefore, there is a first need that consists in the characterization of the variability in the antenna input impedance in order to decide of the matching topology. In so far as the approach is the same whatever the chosen frequency, we decide to focus our work considering the MICS

Generally, antenna impedance is characterized in homogeneous lossy dispersive fluids which simulate the average human body electrical properties. As impedance characterization requires to know the electromagnetic field behaviour in near antenna area, only reduced volume of these lossy materials is modelled. But, to accurately take into account the near field pacemaker antenna behaviour, different human tissues close to the implant have to be also considered. This will be done by using heterogeneous model with limited dimensions as multi-layered structures or as existing accurate human model of

The pacemaker implant is plunged in a dispersive and lossy liquid material with frequency dependent electrical properties. In order to characterize antenna pacemaker impedance in the 402-405 MHz MICS frequency band, the 450 MHz body tissue equivalent liquid is used. The target electrical parameters of this fluid (conductivity σ and real part of permittivity εr')

Target values 56.7 0.94 Measured values 56.2 0.95

In the electromagnetic simulation tool based on Finite-Integration Time-Domain (FITD) method (CST Microwave Studio) [24], the homogeneous liquid model is represented by a parallelepiped (15cm×11cm×3.4cm). The rectangular homogeneous block dimensions and the pacemaker inside it as illustrated in Fig. 6 (a) are optimized for the heterogeneous model. For the experimental setup in Fig. 6 (b), the pacemaker is plunged into a rectangular plastic recipient filled with homogeneous liquid and which dimensions are the same than

Permittivity (εr') Conductivity (σ, S/m)

**3. Antenna input impedance characterization** 

antenna.

frequency band.

**3.1 Human body modeling** 

electromagnetic simulation tool.

are provided by the FCC [23], as given in Table 1.

Table 1. Body simulating liquid electrical properties at 450 MHz

**3.1.1 Homogeneous model** 

the simulated one.

Fig. 6. Homogeneous model (a) simulated configuration (b) experimental set-up
