Detailed modeling of the human body in motion to investigate the electromagnetic influence of fields in a realistic environment

Different postures of the human body

Bioelectromagnetics as an interdisciplinary science that investigates the interaction between the biological systems and the electromagnetic fields offers new and important opportunities for development of medical devices for diagnosis and therapeutic purposes. This science is very attractive and interesting nowadays and it is a vital part of everyday life because it is related to the use of all electromagnetic devices. Additionally, wireless communication devices such as mobile phones, which are integral part of the modern telecommunications, attract high interest in the electromagnetic fields investigation. During the development of the electromagnetic devices it is very important to understand the field distribution inside the human body, since direct measurement of the electromagnetic field inside the tissues and organs of the living organisms is almost impossible. As a result of the rapid development of the computer science, simulations on the human body models can be performed to predict the electromagnetic radiation effects and the macroscopic effects such as heating and specific absorption rate (SAR) distribution.
With the fast development of the computer graphics and medical technique, accurate computational human body models such as voxel human body models were developed. These models have very large application in the simulations of realistic electromagnetic problems. One limitation of the models stated above is their posture in lying position. This is a problem when some specific electromagnetic scenarios should be investigated, for example the impact of the lightning on the driver when the car is stroked. Here the human model should be placed in a sitting position.
Within the last three years, a software application called BodyFlex was developed in order to allow the deformation of the voxel human model HUGO in positions that are common for the human in everyday life. This program can import, show, deform, posture and export a voxel model by combination of the free form deformation and the marching cubes algorithms.

Recent Results

Fingers' separation hexahedrons and FFD lattice sets

The first enhancement of the BodyFlex application is a geometrical algorithm for finger separation, needed because the skin layer between the fingers is missing in the original HUGO model. The algorithm is based on creation of hexahedrons from planes built based on the fingers’ joints positions. These hexahedrons form then the basis for the construction of the control lattices for the fingers.
The movement of the fingers is performed by deforming the FFD control lattice sets in which the fingers are embedded. These lattice sets are rotated with respect to the global coordinate system and aligned with the fingers’ orientations, in order to allow the proper movement of each particular finger’s part. The lattice sets for the other body parts, except for the wrists and the fingers are aligned with the global coordinate system. The movement of the fingers is controlled by 5 FFD control lattice sets for the thumb and 7 FFD control lattice sets for each of the rest fingers. Each of the lattice sets has 3 layers and a total of 27 points.

SAR distribution at 0.9 GHz

One of the electromagnetic applications in which the fingers’ movement of a voxel based human model has a significant meaning is the measurement of the specific absorption rate (SAR) when a model is exposed to a radio frequency electromagnetic field produced by a mobile phone. The SAR is defined as a measure of the rate at which energy is absorbed by a body exposed to a radio frequency electromagnetic field. In order to analyze the SAR distribution in the human head, three simulation scenarios were performed with the commercial software CST MICROWAVE STUDIO: 1) the mobile phone alone is placed near the head, 2) the hand is placed behind the mobile phone and 3) the mobile phone is actually held in the hand.
Next figure shows the SAR distribution at 0.9 GHz in the three scenarios. It can be noticed that there is slight difference between the areas of the SAR distribution in the head when there is no hand in the simulation and when the hand is placed behind the mobile phone. However, in the case when the mobile phone is held in the hand it can be noticed that the area of SAR distribution in the head is significantly smaller compared to the two previous cases. Additionally, by analyzing the SAR distribution inside the head, it can be noticed that the maximal area appears also in the case when the hand is not present in the simulation, while the smallest area of SAR distribution and the lowest SAR values appear in the case when the mobile phone is held in the hand. By analyzing the scenarios with the hand, it can be noticed that the maximal SAR value in HUGO’s head decreases in case when the mobile phone is held in the hand. In this case, a large part of the energy is absorbed by the hand. Although the SAR values which appear in the hand are high, they are below limits prescribed in the standards, which are fixed to 4 W/kg. For the head, the maximal allowed SAR value in Europe is 1.6 W/kg and in America it is 2.0W/kg.

Key Research Area

Bioelectromagnetics, Electromagnetic simulations, Human body movement

Contact

Marija Nikolovski
M.Sc.

Address:

Dolivostraße 15

D-64293 Darmstadt

Germany

Phone:

+49 6151 16 - 24385

Fax:

+49 6151 16 - 24404

Office:

S4|10-206

Email:

vuchkovikj (at) gsc.tu...

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