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Modeling of Electronic Devices using Near Field Sources

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Modeling of Electronic Devices using Near Field Sources Miniaturization of electronic devices, rising of operating frequencies, rising

of complexity and reductions in the levels of operating voltages increase the

risk of malfunctions due to the interaction between subcomponents.

Consequently, there is a great demand for the detailed analysis of

electromagnetic interference (EMI) sources, which is necessary for the

design of reliable systems.

In EMI applications, the main focus is on localization of EMI sources. One

of the common approaches is measurement of electromagnetic fields

around active devices. The near field scanner system is able to measure the

vector electromagnetic field as a function of spatial coordinates and

frequency. The measured data might be used to determine field distribution

outside scanning volume as well as for reconstruction of electric currents

and charges inside device under test (DUT).

Voltage coupled from the ECU in the car represented as Near Field Source

is calculated and compared with results of fullwave MoM solution.

Problem Definition Consider the problem, where coupling of fields from electronic control unit

(ECU) to cable inside the car is investigated (see Fig.1).

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Modeling of Electronic Devices using Near Field Sources

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Fig. 1. Models of ECU and cable, located inside the car

Investigation of complex source radiation can be performed in the following

way. Using near field scanner, ECU can be investigated in laboratory and

fields on some surfaces above the ECU can be measured. Then, closed

surface around ECU is chosen and equivalent electric and magnetic

currents, producing the same fields as detected by scanner should be

calculated. These equivalent currents must be used as surface near fields in

EMC Studio, which will give possibility to investigate coupling into

surrounding cables. It should be noted, that Near Field Source calculation

does not take into account backward interaction between source and

passive system.

Let’s consider details of the example, shown in Fig.1.

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50 50

ECU - dimensions 8cm x 10cm, height above metal 8cm

Computational Model

Far-end Termination

Near-end Termination

50 Ohm 50 Ohm

50 Ohm1V 50 Ohm

Fig. 2. Details of Models

In order to perform investigation we can simulate process of obtaining of

fields on the surface, surrounding ECU. Lets calculate these fields in the

absence of surrounding 3D car body. Model of ECU as simplified PCB

shown in the Fig. 2 is placed above the PEC ground and fields are

calculated on some surrounding surface (Fig.3).

Near field area

Height above ground 8cm

ECU

Fig. 3. ECU model

The ECU model detailed parameters:

Dimensions of near field area: 4cm x 20cm x 22cm

PCB is located at 8-cm height above ground. This corresponds to

location in car

Field observation area must be closed and all triangles should be

oriented in one direction for correct power balance

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Modeling of Electronic Devices using Near Field Sources

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Field values are demonstrated in the Fig. 4. Magnetic field distribution is

shown in the Fig.5.

Y component

X componentZ component

Fig. 4. Electric field distribution for 30 MHz

Y component

X component Z component

Fig. 5. Magnetic field distribution for 30 MHz

When calculated, near field source is placed inside the car (see Fig. 5).

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Modeling of Electronic Devices using Near Field Sources

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Near Field Source

Total Electric Field 30 MHz

Computational model

Fig. 6. Near field source placed in the car

Voltage coupled to Far-end termination is shown in Fig. 6. The numerical

results were gather using direct solution and with usage of near field source.

Far-end termination Near-end

termination

50 100 150 200-160

-140

-120

-100

-80

-60

Near Field SourceDirect Solution

Volta

ge [d

BV]

Frequency[MHz]

Computational model

Fig. 7. Comparison of Near Field Source and direct solution

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Conclusions Near Field Source solution based on Equivalence Principle is

implemented in EMC Studio

Results of application example show that Near Field Source solution is in

very good agreement with fullwave solution

Near Field Source in MoM solver can be effectively used for complex

PCB emission modeling in complete car environment