## 4 Human Body Models
### Type of the Human Body Models
#### 4.1.1 Simulation Based Human Body Models  
Near-field provides a strong coupling effect with the surrounding lossy media; as a result, the presence of a human body may affect the performance of a wearable device. An appropriate selection of the human body model is essential to accurately predict the interaction between the wearable device and the body. In the literature, various human body models have been shown and measured. In the numerical simulations, one may use a simple layered model of the body [223], like the one shown in Figure 17. These types of models, although they do not have the anatomical details of the body, are an effective tool for fast simulations and often are accurate enough for small devices. The advantage of a layered model is the fast simulation time that makes it possible to run optimisations for the best performance [224]. It is expected that after the simple simulations, a more realistic body model or an experimental study will follow to ensure the accuracy of the results. A good review of body phantoms used for the simulations and experimental validations in WBAN systems is presented in [225]. Multiple dielectric values of the biological tissues of the human body are briefly explained in [226].  
Figure 17: Layered model of the human body tissues used in the literature [227].  
Many factors, including application, computation time, and resource constraints, influence the choice of body models. It is usual to choose a theoretical or canonical phantom in the early stages of a design system for the following two reasons: to save time and computational resources. A more complex assessment phase will require realistic and voxel phantoms. Therefore, the simulation tools that use an accurate body phantom should not be underestimated. Another fact to consider is that fluctuations in the electrical properties of the body tissues may lead to changes in performance. This dependency on the body model and the type of phantom employed calls for a design that provides good isolation from the body and is not significantly affected by the body's dielectric properties [241]. Some phantom models and existing animal tissues employed in the literature are depicted in Table 6. In the literature, simple geometrical shapes are utilised to evaluate the antenna performance in human body models. For example, rectangular cuboids are commonly used phantom models because they are simple and planar [242]. Cylindrical [243] and spherical phantoms [244] are often used to model the arm [245], neck [246], head [247], or eyeball [248]. In [249], ellipsoid shapes are used to represent the trunk. In [250], semi-spherical phantoms represented the breast models and were used to model hyperthermia treatment devices. In [251], canonical forms were used to model the entire human body. In [252], different geometries were used to model different parts of a pregnant female body. Various important factors in the design of wearable sensor antennas include the shape of the phantom models, the distance between the phantom surface and the sensor, the orientation of the sensor to the body surface, the frequency bandwidth, temperature, and tissue.