# Analysis of Human Body Shadowing Effect on Wireless Sensor Networks Operating in the 2.4 GHz Band
## 2 Materials and Methods
### Human Body Model for Shadowing Analysis in UTD-Based Program  
Simulations of the body shadowing effect based on the FDTD method are of limited use for the design of wireless sensor systems. The computer resources required constrain the physical size of the geometry that can surround the body model in simulations. For the 2.4 GHz frequency of interest in this study, it was possible to simulate path loss only over a distance of a few meters from the human body. This is far too small a region to model the path loss in indoor wireless sensor networks. Ray-based numerical methods are more suitable for this task [33; 34]. They can simulate the interactions of large objects even with very short waves, utilizing the resources of a typical personal computer. This motivated the author to elaborate a model of the human body that could be used for simulating the shadowing effect in software that uses ray-based methods for wireless system design. The next stages of the research utilized the Remcom XGtd(tm) program ver. 3.1.2.0 [35]. This is a general purpose electromagnetic simulation program based on the analysis of rays radiating from the source and interacting with simulated objects. The program can be used to model the propagation of electromagnetic waves in the vicinity of objects that are large in comparison to the wavelength (aircraft, vehicles, anechoic chambers, etc.). It is particularly useful for studying cases where antennas are positioned in large objects, such as vehicles or buildings. This motivated the author to use XGtd(tm) to simulate a wireless sensor network operating inside a building. The XGtd(tm) program models the physical characteristics of objects and anechoic chambers, performs the electromagnetic calculations, and then evaluates the signal propagation characteristics. It can be used to predict how the transmitters and receivers will interact with large objects, calculating the signal strength, path loss, and far zone antenna gain. Simulations in XGtd(tm) are made by shooting rays from the transmitters and propagating them through the defined geometry of the modeled object. The rays interact with the geometrical features of the objects as they make their way to the receiver. Ray interactions that are simulated include reflections from feature faces, diffractions around feature edges, and transmission through feature faces. The ray-based solvers use the uniform theory of diffraction (UTD) to evaluate the electric field along the ray path [36; 37; 38]. Accurate results are provided when the simulated object is significantly large compared to the wavelength of the propagating wave. This requirement is only partially fulfilled in the studied case of human body shadowing in the 2.4 GHz band because the wavelength is equal to 0.125 m and the body height is 1.8 m. However, the UTD method has been shown in the literature to be adequate for modeling the body shadowing effect in the 2.4 GHz band [13], albeit not taking fully into account the shape of a human body. In [25], a simplified human body model was used to simulate body shadowing in the 3.6 GHz band, demonstrating the possible applicability of the UTD method to the considered case. For typical applications, UTD-based models provide accurate predictions from approximately 100 MHz to approximately 100 GHz and the considered band is within this range. The three-dimensional propagation model applied in XGtd(tm) at each receiver location combines and evaluates the contributions from arriving ray paths to determine predicted quantities, such as electric and magnetic field strength, received power, interference measures, path loss, delay spread, direction of arrival, impulse response, electric field vs. time, electric field vs. frequency, and the power delay profile. In the case of a model that consists of transmitting and receiving antennas, the path loss is also calculated. Modeling the body shadowing effect using a ray-based program requires simplification of the human body shape.