Human in Car Exposed to Fields from Car-Mounted VHF Antenna

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In this example a model of the human body is seated in the driver's seat of a small car and exposed to fields radiating from a 172 MHz source transmitting from a short monopole on the rear fender of the car. The SAR in the body and the electric fields radiating from the antenna are displayed. The human model is a repositioned Visible Human mesh from Varipose in 3 mm resolution. The car model is from a CAD file and for simplicity all surfaces of the car are assumed to be metallic and perfectly conducting. 

The CAD file of the car and the repositioned body mesh are shown in Figure 1. The car is then meshed in a one centimeter grid with Remcom’s XACT Accurate Cell Technology meshing feature applied. The body data is in a 3 mm local grid and the tissue parameters are set using a Cole-Cole tissue model. The resulting meshed geometry is shown in Figure 2. The whip antenna at the rear of the car is modified slightly to make a 172 MHz quarter-wave monopole. This frequency falls within the band often used by car-based radio transmitters used by emergency responders and other operators.

Following the simulation the electric fields are plotted in two planes. For all figures the input power to the antenna has been adjusted to 1 W. In Figure 3, the fields are plotted in the XZ plane of the antenna which extends from the front to the back of the car. In Figure 4, the fields in a plane that passes through both the antenna and the center of the head of the driver are shown with the display of the person and vehicle disabled. This plane is not aligned with the coordinate axes and is a feature available only in Version 7 and higher of XFdtd. 

Figure 1: The CAD model of the car with the repositioned human.

Figure 2: The XF mesh of the repositioned human in the car with XACT meshing applied.

Figure 3: The electric field radiated from the monopole in the plane aligned with with the front-to-back axis of the car.

The 1 gram averaged SAR in the human from the exposure to the fields of the antenna are computed as well. In Figure 5 the 1g averaged Specific Absorption Rate (SAR) through a cross section of the brain is shown. In Figure 6 the 1g averaged SAR is shown through a cross-sectional slice of the human. A line plot of the SAR distribution may also be made as in shown in Figure 7 where the 1g averaged SAR is plotted on a vertical line from the seat to the top of the driver's head.

Figure 4: The electric field is plotted in a plane that intersects both the monopole and the center of the driver's head.

Figure 5: The 1g averaged SAR plotted in a slice of the driver's head.