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Katsuji Hirabayashi

Jun Inami

Nagatoshi Kuroda

Kazuyuki Umetani

Development of Electric Field Strength Estimation System and Application to EMC Design

AbstractAutomotive electronic devices have highly developed, and become complicated. However, EMC perfor-

mance, which is required by the enhancement of global EMC regulations, has grown severer every year. �erefore, we, one of manufacturers of in-vehicle electronic devices, have to develop the product to pass the EMC certi�cation of each sales target country, and have to respond to the tough requirement of EMC performance of each automotive manufacturer. As a result, we puzzle over design and countermeasures very much.

�is EMC performance is shown with the electric �eld strength of the electromagnetic wave noise produced by the product which is measured at a long distance, and these values have to be under the limit of the requirement. In addition, the electric �eld strength must be measured in radio anechoic chamber with the characteristics of shielding noise from the object excluding product so as to avoid the in�uence of noise in surrounding environment. �is measurement needs much preparation, e�ort and time.

At this time, we have created and developed the algorithm that estimates the electric �eld strength at a long distance with use of “Noise Visualization system” which can measure the electromagnetic wave noise near the printed wiring board of the product at bench. As a result, this system helps us evaluate and study the EMC performance at bench, and has greatly advanced and streamlined the development of the product. �is paper introduces the contents of development.

Development of Electric Field Strength Estimation System and Application to EMC Design

90FUJITSU TEN TECH. J. NO.42(2016)

2.1 Development of automotive electronic devices

2.2 Requirement for EMC performance and EMC problem in actual vehicle

Fig. 1 Automotive Electronic Devices

1 Introduction

2 EMC environment and evaluation in automotive electronic devices

Nowadays the term EMC is a popular word in electronics devices such as home electronics, IT devices, and automotive electronic devices.

EMC is an abbreviation of "electromagnetic compatibility". This means that the robustness of devices or systems which do not give electro-magnetic interference to anything, and functions completely without malfunction under the condi-tion of electromagnetic interference.

As EMC is quality performance regulated in many countries by law, the devices are not allowed to be sold in each country if they do not conform to both of EMC performance mentioned previously.

However, EMC performance of automotive electronic devices is easy to be worse due to high processing speed of embedded microcom-puter and increase of current consumption in the circuit etc. In addition, EMC regulation has been continuously strengthened in the world to prevent EMC problem. When we develop prod-ucts, we need to design a circuit, a Printed Cir-cuit Board (hereafter referred to as PCB) pat-tern, and structure (hereafter referred to as EMC design) based on deep consideration of EMC in order to meet this tough EMC perfor-mance.

This time we focused on "the EMC perfor-mance which doesn't give electromagnetic inter-ference" (hereafter referred to as EMC perfor-mance) among EMC performance, then we have developed a method for designing product effec-tively with "noise visualization system".

Various automotive electronic devices have rapidly developed and equipped many places of vehicle. As the number of ECU (electronic devices) installed in some luxury car reached 100, vehicle cannot function without electronic

devices. (Refer to Fig. 1) And ECU, for example, the latest navigation system which needs high-speed processing has the advanced performance comparable to the latest personal computer, and it causes increase of high frequency noise due to high-speed data processing and communication.

In addition, low frequency magnetic field noise increases by the large current due to increase of vehicle equipped with motors for electric-powered devices. Environment of automotive electronic devices changes into very severe con-dition in terms of EMC performance.

Each automotive manufacturer often requests an original EMC standard for automotive elec-tronic devices in addition to conformity require-ment for the EMC law. Such standards are more likely to be tougher than the law requirement, or to require applying an original test method.

As these requirements aim to avoid any EMC problem in vehicle, no EMC problem with the total vehicle system should be finally validated. For example, Actual vehicle equipped with com-munication systems such as AM/FM radio, digital TV, Bluetooth, wireless LAN, and mobile phone etc.

Each electronic device should not neither affect other systems nor be affected by them. Fig. 2 shows an interference situation of electromag-netic waves from electronic devices in vehicle.

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2.3 Evaluation of EMC performance and measurement equipment

3.1 Point of EMC design and present situation

3.2 Process improvement of EMC design and developmental target setting

Fig. 2 Interference Situation of Electromagnetic Wave in Vehicle

Fig. 3 Conventional EMC Design Process

3 Present Situation and Improvement of Countermeasure for EMC design

Each electronic device must be assured of con-forming to EMC standard. EMC standard is defined by the electric field strength of electro-magnetic noise produced by a target product, which is measured at a long distance, and these values are validated under the limit of require-ment for all electronic devices.

This electric field strength needs to be mea-sured in radio anechoic chamber where noise from any object except the product can be shielded.

The following two approaches for EMC design are important to satisfy EMC performance early in product development.

One is EMC front loading design prior to pro-totyping. This means to perform EMC-DR, which is DR focused on EMC, during paper design prior to prototyping, and reflect EMC design in paper design as much as possible with use of various type of EDA. We FUJITSU TEN adopt this approach proactively, because we can minimize for problems to occur at the evaluation of a proto-type.

Another is evaluation and improvement of EMC performance after prototyping, so that it takes much effort and time. We have focused on the second point and have improved it this time.

Conventional procedure of improvement for

EMC design is as shown below.①Measurement of electric field strength: Grasp

present situation based on the result of mea-surement and evaluation of EMC performance of a product in radio anechoic chamber.If any problem is found, move to procedure ②.

②Measurement of PCB noise: A PCB extracted from the product is measured by noise visual-ization system (details are described in section 4) at bench, then grasp the strength and spread of noise (hereafter referred to as noise distribu-tion)

③Study for countermeasure: Specify the areas with possible problem in the PCB circuit from the measurement result of noise distribution on the PCB and improve them.

④Measurement of electric field strength: Evalu-ate again in radio anechoic chamber the product into which the improved PCB is embedded. Thus if the result meets the required standard, process is completed.

The noise visualization system mentioned above in ② can grasp noise generated area only on PCB. Therefore it was conventionally neces-sary to repeat the above procedure from ② to ④ many times in order to improve EMC perfor-mance. Fig. 3 shows this EMC design process.

We have studied effective utilization method of the noise visualization system to improve EMC design process. Here are the good point and the poor point of conventional process.・Good point: Possible to specify the areas with possible problem by noise visualization.

・Poor point: No correlation between the mea-surement result of noise visualization system and measurement level in radio anechoic cham-ber.Based on this, we thought to be able to

greatly improve the process of "design improve-ment and confirmation evaluation", if we can evaluate and improve EMC performance all at once by estimation of electric field strength in radio anechoic chamber based on the measure-ment result of the noise visualization system. Fig. 4 shows revised EMC design process accord-ing to the above idea.

Development of Electric Field Strength Estimation System and Application to EMC Design

92FUJITSU TEN TECH. J. NO.42(2016)

5.1 Point

Fig. 4 EMC Design Process After Countermeasure

Fig. 5 Example of Noise Visualization System (1)

Fig. 6 Operation of Measurement Probe and Measurement Range

Fig. 7 Measurement Example of Noise Visualization

4 Mechanism of Noise Visualization System

5 Basic Development of System Estimating Distant Electric Field Strength

We have studied effective utilization method of the noise visualization system to improve EMC design process. Here are the good point and the poor point of conventional process.・Good point: Possible to specify the areas with possible problem by noise visualization.

・Poor point: No correlation between the mea-surement result of noise visualization system and measurement level in radio anechoic cham-ber.Based on this, we thought to be able to

greatly improve the process of "design improve-ment and confirmation evaluation", if we can evaluate and improve EMC performance all at once by estimation of electric field strength in radio anechoic chamber based on the measure-ment result of the noise visualization system. Fig. 4 shows revised EMC design process accord-ing to the above idea.

The noise visualization system is designed to measure magnetic field noise near PCB. This sys-tem equips with a measurement probe that can measure magnetic field near itself. Sweeping this probe all over PCB by servomotor enables to measure noise distribution of PCB.

As this is also able to visualize parts and pat-tern generating noise by measuring noise distri-bution, it is very useful to find the areas with pos-sible problem, and used for specifying the points that needs some kind of countermeasure. Fig. 5 shows this overall system, Fig. 6 shows operation of the measurement probe and Fig. 7 shows a measurement example.

We have studied the application method of following formula (1) which leads to the amount of radiation of the Differential Mode Noise (hereafter referred to as DMN).

This formula can approximate electric field strength Ed at the point away from this loop by r when DMN current with frequency component f flows to circuit loop with area S.

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Fig. 8 Printed Circuit Board For Basic Verification

Fig. 9 System Diagram of Electric Field Strength Measurement in Radio Anechoic Chamber

Fig. 10 Setting Situation of Printed Circuit Board for Verification

On the other hand, the noise visualization sys-tem can measure the maximum noise of PCB and spread of the noise. We have paid our attention to apply the measured maximum noise to DMN cur-rent id of formula (1), and apply noise distribution area to loop area S of formula (1).

There are some problems and issues to be solved in order to apply measurement results of noise visualization to formula (1), which are as shown below.・Issue① Accurate measurement method of maxi-mum DMN current id :

We study the method optimizing the den-sity of probe measurement to grasp maximum noise current accurately.

・Issue② Applicability of formula (1) and modifi-cation of formula as needed：

Originally, S of formula (1) means loop area of circuit pattern, however visualization mea-surement provides spread of noise.We study the method to calculate the electric

field strength when applying the noise distribu-tion area to S.

We have proceeded with the study by using basic verification PCB to solve the issues. In this verification, we made four kinds of prototype PCBs, which have different noise spreading area each to improve the accuracy. Fig. 8 shows an

example of the basic verification PCBs.

5.2 Issue to be solved when applying general formula

5.3 Basic Study

First, we have measured the generated noise from these basic verification PCBs in radio anechoic chamber, and measured the reference data of electric field strength. This measurement environment and situation are as shown in Fig. 9 to Fig. 11.

Development of Electric Field Strength Estimation System and Application to EMC Design

94FUJITSU TEN TECH. J. NO.42(2016)

Fig. 11 Measurement Situation in Radio Anechoic Chamber

Fig. 12 Result of Basic Verification (Spread of noise near clock line)

5.4 Result of Basic Study

Subsequently, pattern shapes of verification PCBs that have different area and change of noise distribution according to those size differ-ence are as shown in Fig. 12.

As noise distribution changes depending on the change of pattern shape, we confirmed that the study of issues in the previous section is fea-sible with these verification PCBs. In addition, situation of noise radiation from PCB is examined by comparing with the result by electromagnet-ic-field simulators. It is confirmed that this verifi-cation is proper.

A: Shape of PCB for verification(Verification by difference of size)

B: Measurement result of Nose Visualization System

We have proceeded with the study while cal-culating electric field strength by setting the electric field strength as a reference which is measured with verification PCB in radio anechoic chamber. The following show outline of study

result.・Issue① Accurate measurement method of maxi-mum DMN current id :

Short operation period of measurement probe is better for accurate measurement. However, amount of measurement data and measurement time increases.

We have determined the minimum opera-tion period taking a balance of data amount and measurement time based on the result of investigation of receiving sensitivity and direc-tivity of measurement probe. ・Issue② Applicability of formula (1) and modifi-cation of formula as needed：

We have not succeeded to estimate proper electric field strength by applying the noise distribution area simply to formula (1).

As the result of study, we have found better method to estimate electric field strength by applying an area of the region in which noise level is more than -6db of maximum noise level and an area of that in which it is more than -12db to formula (1) with two steps.

Formula (2) shows newly found formula for calculating electric field strength.

With application of this algorism, the differ-ence between actual measurement value of elec-tric field strength and estimated value by calcula-tion has been about ±5dB in broad frequency band. Fig. 13 shows this result.

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Fig. 13 Differences between Actual Measurement Value of Electric Field Strength and Estimated Value

by Calculation

Fig. 15 Parts mounted Image of Printed Circuit Board of In-vehicle Audio

Fig. 16 Noise Visualization Result of Printed Circuit Board of In-vehicle Audio

Fig. 17 Difference between Estimated Value of Electric Field Strength and Actual Measurement Value of ProductFig. 14 Image of In-vehicle Audio Product

6 Study of Application to Actual Product of Estimation System

6.1 Study on productActual PCB for product has complicated

structure such as multilayer structure, many parts placed, and complex pattern wiring etc.

We have applied the newly developed algo-rithm to actual product and checked the effec-tiveness and issues.

For checking in-vehicle audio product is selected.

This is a typical audio product equipped with radio tuner, CD deck, and power amplifier for speaker output. Fig. 14 shows image of this prod-uct, Fig. 15 shows image of parts mounted PCB, and Fig. 16 shows the result of noise distribution of PCB measured by the noise visualization sys-tem.

We have calculated the electric field strength by applying noise data of Fig. 16 to formula (2). Actual measurement result of this product and estimation calculated by formula (2) are as shown in Fig. 17.

There are many points where electric field strength differs in 10 dB or more in all measure-ment band, thus we have concluded the estima-tion is not accurate enough.

Development of Electric Field Strength Estimation System and Application to EMC Design

96FUJITSU TEN TECH. J. NO.42(2016)

Fig. 18 Difference between Estimated Value of Electric Field Strength and Actual Measurement Value of

Product (After countermeasure)

Fig. 19 Operation Display of Noise Visualization System

6.2 Separation of Issues and Clarification of Application Method

6.3 Addition of Estimation Function to Noise Visualization System

After analysis of factors for gap of estimated value, we have clarified the difference between basic verification PCB and product one. The result is as shown below.・There are two cables which are connected to CD deck and operation panel, and noise may be radiated from cables.

・There is a circuit board for operation panel separately from the target PCB and noise may be radiated from that portion.With shielding radiated noise except for that

from target testing board, we have estimated the electric field strength again. Fig. 18 shows the result. The difference between actual measure-ment value and estimated value of electric field strength is about ±5dB, we have confirmed the effectiveness of introduced algorithm by prevent-ing noise other than target PCB.

This estimation of electric field strength by formula (2) is good for products which have few cables or are composed of single PCB. Moreover, we have understood this is effective even for products which have cables and/or noise gener-ating portion by defining a use flow to separate the target noise from the noise caused by other factor, so that we are able to apply it to actual design.

Based on the above result, we have deter-mined to utilize it to study and countermeasure

with use flow mentioned later.

We have studied the method to use the esti-mation algorithm of electric field strength easily with formula (2).

With the idea of design improvement proce-dure, we included the developed estimation soft-ware in present operation software of the noise visualization system. And we have developed the specification of this system so as to display the electric field strength calculated on a real-time basis during measurement of the noise visualiza-tion for the efficiency of countermeasure.

Fig. 19 shows the operation display of the standard noise visualization system. After sweep-ing and measuring the predetermined PCB area by measurement probe, the noise distribution is displayed on the left side of screen and the spec-trum of designated portion is done on the right.

Fig. 20 shows the operation display of electric field strength estimation software developed this time. Spectrum of distant electric field strength that is automatically calculated is displayed on the right side while noise distribution is done on the center of screen.

We have succeeded to estimate very easily the distant electric field strength in radio anechoic chamber by using this estimation software.

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Fig. 20 Operation Display of Electric Field Strength Estimation Software

Fig. 21 Use Flow Chart Example of Electric Field Strength Estimation Software

7 Conclusion

6.4 Application Method of Estimation SystemDeveloped electric field strength estimation soft-

ware is very useful tool. But as mentioned in section 6.2, it does not work properly without separating the influence of noise from cables etc. Then we have made a use flow that can apply to actual design. Fig. 21 shows outline of this flow.

This time we have developed an algorithm, which can estimate distant electric field strength from magnetic field near PCB and exclusive soft-ware. We have already begun to operate this esti-mation system for actual design and found the effect of EMC design process improvement gradually.

In the future, we will accumulate usage know-how of this system and improve the accu-racy by proceeding with its improvement.

We also have a plan to reform and improve product design by including this flow to design process of each business department.

At the development of this system, we have succeeded to develop electric field strength esti-mation software with the cooperation of FDK CORPORATION, who developed noise visualiza-tion system (product name: Near Field Emission Scanners), and included it to the system.

We would like to take this opportunity to express our appreciation to them.

"Bluetooth® is registered trademark of Bluetooth SIG，Inc.""DSRC is registered trademark of general incor-porated foundation ITS Technology Encasement Association.""VSC is registered trademark of Toyota Motor Corporation.""VICS is registered trademark of incorporated foundation Vehicle Information and Communica-tion System Center.""ETC is registered trademark of general incorpo-rated foundation ITS Technology Enhancement Association.""Wi-Fi is trademark or registered trademark of Wi-Fi Alliance."

《Reference》(1)FDK CORPORATION ： Near Field Emission Scannershttp://www.fdk.co.jp/cyber-j/pi_anecho.html

Development of Electric Field Strength Estimation System and Application to EMC Design

98FUJITSU TEN TECH. J. NO.42(2016)

Profiles of Writers

Katsuji HIRABAYASHIEngineering Management Dept

Kazuyuki UMETANIEngineering Management Dept

Jun INAMIFujitsu Ten Technology LimitedEngineering Dept 2

Nagatoshi KURODAEngineering Management Dept