Introduction

Smart Entry System is one of most popular safety systems. Smart Entry allows driver to open the door and activate some electrical systems while being outside the vehicle. Also Smart Entry System allows driver to be identified by the car electronics and start the engine without mechanical key.

System consists of several antennas transmitting signals one to another: antennas fixed on the car body and antenna in the driver ‘remote key’. Parts of antennas are oriented to out-vehicle zone, and another part is oriented to the operation inside vehicle. Operation of the system is usually realized on two defined frequencies: low frequency 125 kHz for radiating mode, radio frequency (433 MHz or 315 MHz) for receiving mode. For the low frequency coil antenna wounded around ferrite is used. This antenna does not provide high-radiated power due to low efficiency. Thus determination of areas where radiated field level outside car is enough to be recognized by receiver is very important. Vice versa, areas inside car where field level is too low should be eliminated.

This application demonstrates modeling of Smart Entry System and radiated field analysis within EMC Studio / EMCoS Antenna VLab environment.

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Simulation Model Description

We consider modeling of antennas oriented to field radiation outside the car. In this case one of the typical antenna locations are front door handles. Calculations are performed for 20-turn coil antenna wounded around rectangular ferrite rod. Calculations of magnetic field at frequency 125 kHz in the plane surrounding car model are performed. Extension of near field area outside the car is 1.5 m from all sides. Grid step used for calculation is 10 cm.

For simulation of antenna near the car body two variants are used:

• Only antenna in driver door is activated
• Both antennas are activated

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Results

For analysis of radiated field level special option in EMC Studio / EMCoS Antenna VLab environment is used.
Typical sensitivity of receiving antenna is about 1 nT, what corresponds to H=0.79 mA/m. Defining this level in the dialog for Near Field Post-processing we obtain complete near field area colored in red and blue (red color corresponds to area above or below defined reference value, depending on selected option). Magnetic field distribution and areas characterized with magnetic field level above the receiver sensitivity limit for both simulation cases are shown below:

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