PROJECT NET-EMC: NUMERICAL SIMULATION REPORT (CIMNE)

PROJECT NAME: NET-EMC

PROJECT NET-EMC: NUMERICAL SIMULATION REPORT (CIMNE)

CIMNE - International Center for Numerical Methods in Engineering Parque Mediterráneo de la Tecnología (PMT) c/ Esteve Terradas nº5 - Edificio C3 08860 Castelldefels (Barcelona, Spain) www.cimne.com Castelldefels (Barcelona, Spain) - March 2012

PROJECT NAME: NET-EMC

DOCUMENT HISTORY

Version Date Authors E-mail

01

23/03/2012

Xavi Roca Martí Coma Rubén Otín Javier Mora

[email protected] [email protected] [email protected] [email protected]

Eurostars Project E! 4648 NET-EMC

NET-EMC - Numerical simulation report (CIMNE) 23/03/2012

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CONTENTS

1. SCOPE

2. REFERENCES

3. TERMINOLOGY

3.1 ABBREVIATIONS

3.2 DEFINITIONS

4. FEEDING MODELS - CURRENT PROBE

5. FEEDING MODELS - COAXIAL

6. GEOMETRICAL VARIATIONS INSIDE A METALLIC BOX

7. AIRCRAFT MOCK-UP



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1. SCOPE In this report are showed the finite element simulations performed by CIMNE in the frame of the Eurostars project E! 4648 NET-EMC. The objective is to show the influence of the geometry in the distribution of the electromagnetic fields and assets the performance of analytical approaches when a canonical structure changes.

2. REFERENCES

[1] R. Otin. Regularized Maxwell equations and nodal finite elements for electromagnetic field computations in frequency domain. CIMNE M-123, ISBN: 978-84-89925-03-8, 2011. [2] Dirk Baumann, Christophe Fumeaux, Pascal Leuchtmann, Rudiger Vahldieck, Finite-Volume Time-Domain (FVTD) Method and its Application to the Analysis of Hemispherical Dielectric- Resonator Antennas. IEEE MTT-S Digest, 2003.



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3. TERMINOLOGY

3.1 ABBREVIATIONS

ERMES Electric Regularized Maxwell Equations with Singularities

FEM Finite Element Method

Mod(E) Electric field modulus

PEC Perfect Electric Conductor

PMC Perfect Magnetic Conductor

3.2 DEFINIT IONS

ERMES Finite element tool developed by CIMNE.

GiD A universal, adaptive and user-friendly graphical user interface for geometrical modelling, data input and visualisation of results for all types of numerical simulation programs (www.gidhome.com).



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4. FEEDING MODELS - CURRENT PROBE The objective of this and the next section is to see what feeding model fits better with the measured behavior of the antennas used by the UPC. Here we test the current probe feeding model.

4.1 Case 9-12: Transverse posit ion of the antennas

In this case of study the feeding model is a current probe located at the base of the antenna. A volumetric current is imposed at the base of the antenna, in the z-axis direction. A general view of the geometry is shown in Fig 4.1.

Fig 4.1. General view of the geometry and position of the antennas. It is shown half of the box.



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The dimensions of the antenna are shown in Fig 4.2.

Fig 4.2. Geometry of the antennas.

The analysis has been done only with half of the box; the other half has been replaced by a PMC condition on the symmetry plane of the box. PEC condition is applied on the other walls of the metallic box.



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Fig 4.3. FEM mesh (538911 2nd order Lagragian elements.)



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Fig 4.4. S12 for the case 9-12. ERMES results are compared with measurements.



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4.2 Case 9-13: Longitudinal posit ion of the antennas

In this case of study the feeding model is an impulse current at the base of the antenna. A volumetric current is imposed at the base of the antenna, in the z-axis direction. A general view of the geometry is shown in Fig 4.1. The differences with the case 9-12 are in the positioning of the antennas inside the box. .

Fig 4.5. General view of the geometry and positioning of the antennas. It is shown half of the box



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The dimensions of the antennas are shown in Fig 4.6.

Fig 4.6. Geometry of the antennas.

The analysis has been done only with half of the box, the other half has been replaced by a PMC condition on the symmetry plane of the box. PEC condition is applied on the other walls of the metallic box.



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Fig 4.7. FEM mesh (494713 2nd order Lagragian elements.)



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Fig 4.8. S12 for the case 9-13. ERMES results are compared with measurements



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4.3 Case 6: Non-symmetric posit ioning of the antennas

This case is similar to cases 9-12 and 9-13. The same model of antenna and feeding is used, the differences is in the positioning of the antenna which are located in the same place as the coaxials showed in the next section. The results are shown in fig. 4.9

Fig 4.9. S12 for the case 6. ERMES results are compared with measurements and the FDTD simulations performed by the UPC.



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5. FEEDING MODELS - COAXIAL

In this section we are going to test the coaxial model of ERMES. We will test different approaches to model the geometry of the coaxial and its connexion to the box. The feeding of the coaxial is done by imposing a Robin boundary condition at the base of the coaxial and assuming that only the TEM mode is propagating. First we validate the model comparing the S11 parameter of a hemispherical dielectric resonator antenna calculated by different computational methods and then we apply the same model to the box used in the previous section. The scattering parameters of the antennas inside the box were measured by the UPC.

5.1 Hemispherical dielectr ic resonator antenna.

The first case is a hemispherical dielectric-resonator antenna. The objective is to validate the coaxial model of ERMES with the results given in [2]. The geometry and dimensions are shown in Fig. 5.1. The antenna is surrounded by a dielectric hemisphere, with a permittivity of 9.5. The electric permittivity of the coaxial is 2.33.

Fig.5.1 - Dimensions of the antenna in mm



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Fig.5.2 - Dimensions of the antenna with the dielectric hemisphere and the vacuum hemisphere.

Fig.5.3 - Global mesh for the whole geometry.



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Fig.5.4 - Mesh of the singularity area of the antenna.

Fig.5.5 - Scattering parameters calculated with different tools



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5.2 Coaxial feeding: problem set-up

We tested different geometry approaches to the modeling of the coaxial, all of them located at the same place, inside a box. The main difference between cases is the geometry of the feeding port. In cases 2 to 6 the positioning of the antennas and the dimensions of the box are the same. The geometry of the box and the position of the antennas, for the cases 2 to 6, are shown in figures Fig and Fig respectively.

Fig 5.6. Dimensions of the box.



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Fig 5.7. Position of the antennas in [mm].

The condition PEC has been applied on the wall of the box. The different geometries of the feeding model and their particularities are detailed below.



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5.3 Case 2: Coaxial 50 Ohms Antenna with protruding dielectr ic

This case of study is a coaxial antenna. Dimensions and geometry are shown in Fig 5.7 and 5.8. The pink volume is dielectric material with a relative electric permittivity of 2.0.

Fig 5.7. Geometry of the antenna.



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Fig 5.8. Dimensions of the antenna.



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Fig 5.9. FEM mesh of the box with the antennas (805881 2nd order Lagrangian elements)

Fig 5.10. Detail of the mesh.



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Fig 5.11. Case 2: coaxial 50 Ohms Antenna with protruding dielectric



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5.4 Case 3: Coaxial 50 Ohms Antenna with hidden dielectr ic

This case of study is a coaxial antenna similar to the previous one but with the geometry showed in Fig. 5.12. Dimensions are shown in Fig 5.13. The pink volume is dielectric material with a relative electric permittivity of 2.0.

Fig 5.12. Geometry of the antenna.



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Fig 5.13. Dimensions of the antenna, in [mm].



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Fig 5.14. FEM mesh of the box with the antennas (912180 2nd order Lagrangian elements)




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Fig 5.16. Case 3: Coaxial 50 Ohms Antenna with hidden dielectric



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5.5 Case 4: Coaxial 24 Ohms Antenna without dielectr ic

The fourth case is an antenna without dielectric material. The geometry and dimensions are shown in Fig. 5.17.




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Fig 5.18. FEM mesh (720482 2nd order Lagragian elements).




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Fig 5.20. Case 4: Coaxial 24 Ohms Antenna without dielectric.



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5.6 Case 5: Coaxial 28 Ohms without dielectr ic.

The 5th case is also an antenna without dielectric material but with different coaxial dimensions compared with the previous one. The geometry and dimensions are shown in Fig. 5.21.




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Fig 5.22 FEM mesh (537945 2nd order Lagragian elements).

Fig 5.23 Detail of the mesh.



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Fig 5.24. Case 5: Coaxial 28 Ohms without dielectric.



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5.7 Case 7: Coaxial 50 Ohms Antenna with protruding dielectr ic encased

This case is similar to the coaxial 50 Ohms antenna with the protruding dielectric (case 2), with the difference that, now, the dielectric is surrounded by a metallic wall. Geometry and dimensions showed in Fig. 5.25.

Fig 5.25. Dimensions of the antenna for the case 7, in [mm].



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Fig 5.26 Detail of the mesh

Fig 5.27. Case 7: Coaxial 50 Ohms Antenna with protruding dielectric encased



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6. GEOMETRICAL VARIATIONS INSIDE A METALLIC BOX

In this section we are going to make small changes in the geometry to see the effect of these changes in the transmission coefficients of the antennas.

6.1 Case 5-10: Coaxial 28 Ohms without dielectr ic: 100 mm length

In this case the antenna is similar to the one used in the case 5 but with different length. The geometry and dimensions are shown in Fig 6..




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Fig 6.4. S12 ERMES results for the case 5-10.



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6.2 Case 5-05: Coaxial 28 Ohms without dielectr ic: 5 mm length

In this case the antenna is similar to the one used in case 5 but with different length. The geometry and dimensions are shown in Fig. 6.5.




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Fig 6.7. S12 ERMES results for the case 5-05.



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6.3 Comparison between Coaxial 28 Ohms without dielectr ic: di f ferent lengths

Fig 6.8. S12 calculated with ERMES for the cases of the coaxial 28 Ohms without dielectric and different antenna lengths (cases 5, 5-05 and 5-10).



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6.4 Case 5-A: Coaxial 28 Ohms without dielectr ic: 10 mm length. Rounded corners box.

This case is an antenna similar to previous cases but with the particularity that the corners of the box are rounded with a radius of 34 mm. The antenna and the ports are equivalent to 5.6 Case 5: Coaxial 28 Ohms without dielectric.

Fig 6.9. Corner rounded box.




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Fig 6.11. S12 ERMES results in case 5-A.



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6.5 Results comparison between the rounded corners' box and the standard box.

Fig 6.12. S12 for the cases of the standard box (case 5) and rounded corner box (case 5-A).



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6.6 Case 5-empty: Box without screen

Now we are going to analyze the effect on the scattering parameters of different objects located inside a metallic box. The reference box and the positioning of the antennas are showed in fig. 6.13.

First, we are going to analyze the reference box empty. It will be used as a reference to see the effects of the objects. A general view of the geometry is shown in figures 6.13 and 6.14. The analysis has been done only in a half of the box. A PMC boundary condition was applied as shown in fig. 6.15. A PEC boundary condition is applied in the walls of the box.

Fig 6.13. Positioning of the antennas.



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Fig 6.14. Geometry of the case 5-empty.

Fig. 6.15. PMC condition.



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Fig 6.16. FEM mesh (157604 2nd order Lagrangian elements).




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Fig 6.18. S12 for the case 5-empty.



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6.7 Case 5-Q: Box with rectangular hole screen

In this case we place a metallic wall with a rectangular hole in the middle of the box. The hole is centered in the wall, and its dimensions are 10 cm width x 2 cm height. A general view of the geometry is shown in Fig. 6.19.

Fig 6.19. General view of the geometry.




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Fig 6.21. S12 ERMES results of the case 5-Q.



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6.8 Case 5-R: Box with circular hole screen

In this case there is a metallic wall with a circular hole in the middle of the box. The hole is centered in the wall, and its radius is 2.523 cm, having the same area than the rectangular hole in previous case. A general view of the geometry is shown in Fig 6..





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Fig 6.24. S12 ERMES results for the case 5-R.



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6.9 Results comparison between empty box and the same box with circular and rectangular hole screens.

Fig 6.25. S12 for the empty box (case 5-empty) and the same box with circular (case 5-R) and rectangular (case 5-Q) hole screens.



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6.10 Case 5-P: Box with dielectr ic sphere

In this case there is a sphere made of a dielectric material with a relative electrical permittivity of 41.3 in the middle of the box. The radius of the sphere is 2.523 cm, having the same radius than the circular hole in case 5-R. A general view of the geometry is shown in Fig 6.





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Fig 6.28. S12 ERMES results of the case 5-P.



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6.11 Result comparison for the box with a dielectr ic sphere and the empty box

Fig 6.29. S12 for the empty box (case 5-empty) and the same box loaded with a dielectric sphere (case 5-P).



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7. AIRCRAFT MOCK-UP

The objective of this section is to see how the field pattern changes inside the aircraft mock-up when the basic geometry changes. We analyse the electric field pattern for three frequencies (f = 100MHz, 200MHz and 300 MHz) and in three different geometrical set-ups. A dipole antenna is located in the middle of the aircraft roof. We show the modulus of the normalized electric field (normalized to its maximum value, En = E/Emax) Three different geometries have been studied:

Canonical aircraft: a half of the aircraft’s fuselage without the cockpit.

Aircraft with cockpit.

Aircraft with dummies: the same geometry than the canonical aircraft adding some dummies. The antenna used in all the cases is 5 cm height and has a diameter of 0.4 cm. The feeding of the antenna is a current probe with 0.5 cm of height and 0.2 cm of diameter. The CAD geometry employed is shown in Fig. 7.1. On the external surfaces of the fuselage have been applied PEC conditions. In the symmetry plane we applied a PMC boundary. The dummies were also considered PEC.

Fig. 7.1. CAD geometry.



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Fig 7.2 - Canonical aircraft at f = 100 MHz - Mod (En).




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Fig 7.4 - Aircraft with cockpit at f = 100 MHz - Mod (En).




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Fig 7.6 - Aircraft with dummies at f = 100 MHz - Mod (En).




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Fig 7.10 - Canonical aircraft at f = 200 MHz - Mod (En)




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8. CONCLUSIONS

In this report is shown the some of the numerical simulations performed in CIMNE in the frame of the project NET-EMC.

The main conclusion is that, although ERMES is a valuable tool for solving electromagnetic problems in frequency domain with complex geometries, it can be computationally expensive if we want to solve wide frequency band problems with small geometrical details as small dipoles or wires. For these cases a time domain method (as FDTD, FVTD, etc) can be a better option.

Another important conclusion is that when we depart from the canonical geometry (adding dummies, different cockpit shapes, etc) important changes can be expected in the field pattern. This has to be taken into account when extrapolating results from our semi-analytical models to reality.

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PROJECT NET-EMC: NUMERICAL SIMULATION REPORT (CIMNE)