**2.2 Transceiver design constraints and limitations**

Medical devices require ultra low power, high performance transceiver. The design considerations of such transceivers are subjected to strong technical challenges which basic requirements [22] are as follows:


In such medical microsystem, over specify the system consumes more energy, reduces the battery lifetime and is therefore not mandatory to improve the limited communication range. Longer range implies the design of an automatic power optimized system. Thus, the integration of an automatic antenna tuning unit should contribute to improve the budget

An Efficient Adaptive Antenna-Impedance

**3.1.2 Heterogeneous model** 

behaviour.

model.

Tuning Unit Designed for Wireless Pacemaker Telemetry 229

(a)

(b)

The implantable device is inserted in three heterogeneous models: the heterogeneous human model named Hugo which is the simulation tool human model [24], a multi-layered structure and a simple experimental setup made to validate simulated heterogeneous models, the "human + hand" model. Compared to previous homogeneous model, the main advantage of these heterogeneous models is the ability to carefully model all human tissues in near antenna area to accurately take into account the near field pacemaker antenna

The pacemaker device is implanted in the pectoral of Hugo, in a limited volume sample of 11.2 x 6.4 x 11.6 cm3 (Fig. 7 (a)). The voxel size of the human body model is the minimal voxel size of the simulation tool, i.e. 1 mm3. The whole body phantom contains 44 different tissues, whose real part of permittivity (εr') and conductivity (σ) are taken from [24] at 450 MHz. The chosen limited sample obviously includes fewer tissues than the complete body

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

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