VBA Macro for construction of an EM 3D

VBA Macro for construction of an EM 3D model of a tyre and part of the vehicle

Guillermo Vietti, Gianluca Dassano, Mario OreficeLACE, Politecnico di Torino, Turin, Italy.

[email protected]

Darmstadt, Germany. 19‐21 April 2010. 1

Work partially funded by Regione Piemontein the frame of the contract RIJ09N

Contents:

1. Goals2. Geometry and main parts of the structure3. Description of the parts of the script4. Main features 5. Some examples of outcomes representation and uses6. Conclusions


Goals:Study of the EM propagation channel (from a Sensor Node inside the tyres to the TX / RX device mounted on the vehicle), in two different frequency bands.Analyis of the effects of different:

types of tyre,angular positions of tyre, steering wheel angles,weights of vehicle,air pressure,types of ground.

Estimation of attenuation introduced by all mechanical obstacles between these two radio devices. Evaluation of the multipath effect in the signals received by both devices.Plot of the near/far field pattern in this complex and large structure at different configurations.


1.Inner Liner - part of a tyre consisting of one or severalplies of rubberized cord fixed on bead rings. 2.Breaker - inner part of a tyre which consisting ofrubberized plies of steel or textile cord and located betweentread and carcass, designated for load impact softeningwhile driving. 3.Tread - outer rubber part of a tyre with molded pattern, which provides adhesion to the road and prevents carcassdamages. 4.Cap ply (breaker ply) - protective ply located betweensteel breaker and tread, provides breaker protection frommechanical damages and prevents rubber separation. 5.Bead - hard part of a pneumatic tyre case which providesits fixing on a wheel rim. 6.Side wall - outer rubber.

Brief description of main tyre elements(explode animated view)

All metallic elements are simulated with PEC material in order to simplify

the calculation4Darmstadt, Germany. 19‐21 April 2010.

We have developed a Visual Basic (VBA) script thatcontrols all CST STUDIO SUITETM tools to design allmechanical elements in the space around the tyre in a vehicle in a full parametric way.

5Darmstadt, Germany. 19‐21 April 2010.

Main script parts1. Definition of all parameters of the geometry (definition of

variables): lengths, widths, thickness, radius, and of all materials like dielectric and magnetic relative constants, losses.

2. Definition of variable/s of iterative cycle (for instance: the angular position of sensor inside of tyre, variable from 0 to 360° to know the EM propagation in each situation).

3. Setting of all units of the project (mm, GHz, s).

4. Setting the background material (Vacuum).


5. Definition of structure :– Definition of all materials, choosing the dielectric and magnetic

properties given by the tire maker.– Design of the skeleton of the tyre extruding the radial closed curves.

These curves reflect the deformation of the tire due to vehicle weight and the air pressure inside. With a “loft operation” of two consecutive curves a solid shape is created, adding all angular shapes we will create a complete solid object named sidewall.

– Insertion of the tread with the same technique.– Insertion of metallic belts inside the tire rubber. All steel cords in carcass

and breaker are simulated with a continuous metallic cylindrical shape after verifying the similar EM behavior in the work frequency bands.

– Insertion of the fully inner liner inside the tire.– Trim of fully inner liner shape with a vacuum object.– Creation of the rim.– Switch from global coordinates placed in the center of tyre to local

coordinates in the radial location inside the tyre under the belt. – Creation of SN box with the antennas using the local coordinate system.– Reactivation of global coordinate system in the center of tyre.– Design of all radial closed curves that will create the fender shape with

many “loft operations” between two consecutive planar curves. – Design with many cylindrical and angular objects of the shape of a

simplified disc brake.– Design of a very simplified suspension.


6. Setting of frequency range for the simulation

7. Definition of two discrete ports using two picked point in each antenna extremes of sensor, and setting of input impedance of these port.

8. Definition of the boundary conditions. All boundary planes around the structure are set to “open” to simulate the open space except the ground plane; it will be set like an electric plane (Etan=0) or a conducting wall to take into account the losses of the real ground.

9. Definition of many 3D electric field monitors at each frequency of interest with an iterative cycle.

10. Definition of many electric field probes in all coordinated directions in planned positions.

11. Set all mesh properties, enabling the subgridding tool and fixing a dense local mesh in the main SN, in order to take into account small details of these elements, which with an sparse general mesh can be ignored .


6. Updating of mesh.

7. Setting the transient solver parameters.

8. Starting of simulation.

9. Reading magnitudes and phases for each defined probe and saving these like .txt file.

10. Reading the electric field monitors for each frequency and saving these tridimensional complex vectors like .txt file.

11. Save the project with a name that identifies the value of cycleparameter .

12. Restarting the parametric cycle routine.



Script capable of changing the tyre deformation due to the vehicle weight and internal air pressure changing the value of one variable in the script definition

Perspective view Left view Front view


It is very easy to change the tire orientation changing the value of the variable defined to control the steering wheel angle in the

script sentence

Bottom view


Perspective view

In a similar way, it is easy to modify the suspension load changing the value of variable defined in order to control the distance from tyre to fender

Perspective view Front view


Some examples of the outcomes obtained with this script.Different types of representations


Example 1: Comparison between the sensor inside the tire and in the free space

Sensor inside the tire Sensor in the free space

Perspective view(Sensor detail)


|E(x,y,z)| at 4.5 GHz in the main coordinates planes (Sensor in the free space)


|E(x,y,z)| at 4.5 GHz in the main coordinates planes (Sensor inside the tyre)


|E(x,y,z)| at 4.5 GHz in the boundary planes (Sensor in the free space)


|E(x,y,z)| at 4.5 GHz in main coordinates planes (Sensor inside the tyre)


EM model Size 1Width: 243 mm

High: 649.7 mm

Size 2Width: 291 mm(Scaled 120 %)High: 649.7 mm

Dipole oriented along the axis of rotation

Dipole oriented perpendicular to the axis of rotation

Example 2: Comparison between two widths of the tyre with a dipole inside, two orientations


E-field average magnitude at 2.4 GHz on y=0 cut plane (clamp to range Min:0 , Max:1000 V/m)

Size 1: Width: 243 mm High: 649.7 mm

Size 2:Width: 291 mm (Scaled 120 %)High: 649.7 mm




E-field average magnitude at 2.4 GHz on z=0 cut plane(clamp to range Min:0 , Max:1000 V/m)






E-field average magnitude at 2.4 GHz on x=131 cut plane(clamp to range Min:0 , Max:100 V/m)






E-field average magnitude at 2.4 GHz on x=151 cut plane(clamp to range Min:0 , Max:40 V/m)






Example 3: Study of received signal outside of the tire in different positions for different azimuthal position of the source (SN). Probes situation (orientation along X, Y, Z axis)

Perspective view Left view Front view

θ = -90, -45, 0, 45, 90d=15 cm

θ = -90, -45, 0, 45, 90


Probe Positions.Numbers.

Front view.

θ = -90, -45, 0, 45, 90

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Excitation signal in the port (4.5 GHz carrier)


Probes for SN Angular position θ = 0°, Signals vs. time

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Example 4: Electric field magnitude animated pattern at 4.5 GHz in different cut planes


Example 5: Comparison with a real car model at 2.4 GHz


Example 6: Comparison with measurementsTotal Field level measured on a plane at 20 cm from tyre side.

With tyre Without tyre

SN SN

Tyre edge Tyre edge


Conclusions:

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This program allows to analyze a complex and large structure iteratively eliminating the need to rebuild the geometry for different mechanical and electrical conditions reducing strongly the computing time. The possibilty of automatically saving the main outcomes like text file for each cycle of simulation permits at the end of the overall simulation to elaborate easily these data with other softwares as MatLab, Microsoft Excel, ecc.It is very easy define many field monitors and probes at different locations to find the optimal position of radio devices.This VBA script allows to non expert CST users to change and to optimize the complex structure and save the outcomes in text format.

It is possible to choose the degree of accuracy of the representation of the geometry, in order to minimize the meshing load.

Darmstadt, Germany. 19‐21 April 2010.

Thank you for you attention.


Documents

VBA Macro for construction of an EM 3D