###### Abstract  
In this work, the optimum homogeneous phantom size for an equivalent whole-body electromagnetic (EM) modeling is calculated. This will enable the simple characterization of plane wave EM attenuation and far-field link budgets in Active Medical Implant (AMI) applications in the core region of the body for Industrial, Scientific, Medical and MedRadio frequency bands. A computational analysis is done to determine the optimum size in which a minimum phantom size reliably represents a whole-body situation for the corresponding frequency of operation, saving computer and laboratory resources. After the definition of a converge criterion, the computed minimum phantom size for subcutaneous applications, 0-10 mm insertion depth, is 355 \(\times\) 160 \(\times\) 255 mm3 for 402 MHz and 868 MHz and a cube with a side of 100 mm and 50 mm for 2.45 GHz and 5.8 GHz, respectively. For deep AMI applications, 10-50 mm insertion depth, the dimensions are 355 \(\times\) 260 \(\times\) 255 mm3 for 402 MHz and 868 MHz, and a cube with a side of 200 mm and 150 mm for 2.45 GHz and 5.8 GHz, respectively. A significant reduction in both computational and manufacturing resources for phantom development is thereby achieved. The verification of the model is performed by field measurements in phantoms made by aqueous solutions with sugar. electromagnetic propagation in absorbing media; biomedical applications of electromagnetic radiation; biomedical computing; biomedical measurements; implantable biomedical devices 2021 29 June 2021  
link with wirelessly operated implanted medical devices (AMI) for improving the quality of life of patients [2]. In this respect, Transparency Market Research (TMR) estimates that the global implantable medical devices market will expand at a 4.6% compound annual growth rate (CAGR) between 2019 and 2027 [8]. In this context, human bodies are modeled by EM phantoms. A phantom is a physical or numerical model with the same electrical characteristics as the human body to accurately reproduce the effect of the body on electromagnetic radiation and vice versa. These models can be classified according to different criteria: (1) nature (physical and numerical/computer models) (2) composition (homogeneous and heterogeneous) and (3) geometry (planar, spherical, cylindrical and more realistic models based on MRI images). The right choice among them depends on the accuracy required by the application. The physical phantoms are classified as solid-dry, semi-solid and liquid phantoms. Whenever possible, the latter is the most convenient approach, as a very reasonable trade-off between complexity and accuracy is achieved. Liquid phantoms are selected in this paper, as they allow the movement of an antenna-probe inside them to monitor the electromagnetic dosimetry. Moreover, they have been extensively employed as testbeds for standard mobile phone compliance with widespread acceptance [9; 10]. The impact of their inherent homogeneous nature has been extensively reported in [11; 12]. When employed to characterize implanted antennas [13], they may be enough to test their performance and potentially simplify the measurement setup [14]. The slight detuning experimented by an implanted antenna in a homogeneous phantom [15] may well be made up by the simplicity of the model, avoiding unnecessary calculations. This is particularly true when the target is not the design of the implanted antenna but field measurements. The liquid is usually water plus several additional elements in order to control the permittivity and conductivity of the liquid. There are different liquid tissue models using sugar, salt, oil-in-water emulsions or non-ionic surfuntcants. Most common recipes add sugar for low frequencies and Diacetin, Di-ethylene Glycol Butyl Ether (DGBE, sometimes abbreviated \"Glycol\") or Ethoxylated p-tert-octyphenol (Triton(r) X-100) for higher frequencies (above 1 GHz) in order to control the permittivity [10; 16]. Several manufacturers also provide off-the-shelf tissue-simulating liquids [17; 18].