Proceedings CEEM'2009/Xi'an

Radiated EMI diagnosis and noise modeling for cellular phone *Lu Xiaoquan', ZhaoYang1

, 2,+ .Luo'Yongchao', YanWei1, Dong Yinghua', Yre Dong'

1 College of Electrical Engineering, Nanjing Normal University, China, 2100422 State Key Laboratory ofMillimeter Waves, Southeast University, Nanjing 210096

3 Jiangsu Metrology Institute of Science & Technology, Nanjing 210035

The CM and DM radiated EMI noisemechanism models of the cellular phoneand the changing tendency of the waveimpedance with the distance are describedto diagnosis the radiated EMI noise type ofthe cellular phone.

n.Principle of Radiated EMI Diagnosisand Noise Modeling

2.1 Mechanism of Radiated EMI Noise

of

(2)

(1)

The radiated magnetic fieldmagnetic dipole is characterized as

H _ IdSk3 [-1 1 1] . () -fkr-- ----+- sm e

(J 41Z"o kr j(kr)2 (kr)3

IdSk3 [-1 1] <fkrH =- --+- cosfJe

r 21Z" j(kr)2 (kr)3

E = IdSk4

f-I---1-]sinfJe- i kr

; 41rm&oL (kr) j(kr)2

The radiated electric field andmagnetic field can be calculated byperforming integral operation on the surfacecurrent distribution of radiated EMIsource[6].As matter of fact, the methodabove can not be easily implemented for thecalculation is complicated and it is difficultto acquire the surface current distribution ofthe radiated source. In this paper, theradiated source is modeled by electricdipole and magnetic dipole.

The radiated electric field of electricdipole is characterized as

H _ Idlk2 [-1 1] . () -jkr--·-+-sm e

; 41Z" j{kr) (kri

E = Idlk3 [2+_1_+_1_ ]

(J 41Z"aJ&o j(kr) (kr)2 j(kr)3

E Idlk3

[ -1 1] o -jkrr = 21Z"aJ&o (kr)2 + j(kr)3 cos e

I . Introduction

With wide use of the cellular phone, itsradiated EMI problem is becoming a hotissue. Electromagnetic absorption by theuser of the cellular phone is studied [1]

[2]. Moreover, a lot of works have been doneon radiated EMI noise mechanism. Theradiated common-mode(CM) anddifferential-mode(DM) current models areproposed.[3] Then, EMC trouble diagnosingtechniques by using near-field probemethod and their application areas areintroduced[4][5]. Besides these, the changingtendency of the wave impendence with thedistance in near-field region is presented [6].

However, the radiated EMI noisemechanism of the cellular phone is rarelymentioned. In order to solve this problem, adiagnosis plan based on near-field probemeasurement for the radiated EMI noise ofthe cellular phone is proposed in this paper.

Abstract: In this paper radiated EMIdiagnosis and noise modeling for cellularphone is proposed. With this method, theradiated EMI noise mechanism models ofthe cellular phone are introduced, andchanging tendency of the wave impedancewith the distance is described to diagnosisthe radiated EMI noise type of the cellularphone. It is shown from the experimentsthat the proposed method is a fast andefficient tool for radiated EMI diagnosisand modeling of cellular phone.Keywords: radiated EMI noise diagnosis,modeling, cellular phone

*This work is supported by Natural Science Foundation of Jiangsu Province, China (#BK2008429) and the Open ResearchFund of State Key Lab. of Millimeter Waves, China (#K200803).+ corresponding author

272

Proceedings

Where H is the magnetic field, E is theelectric field, r is the observation distance.

2.2 Radiated EMI Mechanism Modelingfor Cellular Phone

The radiated EMI noise is consist oftwo components", one is CM currentreferred to the HF ground current generatedby none-zero (30M-I G) potential betweenthe ground of the cable and referenceground point, another is the DM current,which flows through the circuit as theuseful current. The CM current will emit anelectric field through the cable in theoutside environment. Therefore the CMradiation of cellular phone will be treated asthe electric dipole according to their similarbehavior. On the other hand, the DMcurrent of the cellular phone, which willemit the electric field into the outside world,is similarly treated as the magnetic dipole.The suppressions technique to the CM andDM radiated noise are different so that it isrequired to diagnose the noise typebeforehand. The radiated mechanismmodels of the cellular phone are shown inFig.l. The maximum radiated CM filedECM,MAX and the maximum radiated DMfiled HOM,MAX can be given as

IEcM,MIlK 1= 1.256 x 10-6 f IICMIdl (3)r

IHDM ,M<n1= 2.632 x 10-14 /211DM IdS (4)r

ECM,Max are influenced by the frequency f,the wire length dl and CM current ICM.HOM,Max are changing with the frequency f,the loop area dS and the DM current 10M.

I ~ OD 01

eM eM ' ,01

model:::)V ) => z;...NI -Electric VN1

:::) dipole

p 10 M

:::)~M . ~mliii1 0 ...

agnatic ~dipole

Flg.I Radiated eM and DM models for cellularphone's mechanism diagnosis

273

CEEM'2009/Xi'an

2.3 Diagnosis Principle in Near-FieldRegion

The wave impedance is defined as[4]

Z=E/H. In the near-field region, wherekr-c-cl or r«IJ21t, the wave impedancefrom electric dipole can be derived fromequation (I) - (2) as

ZEOJ= Eo =_jI201i(~)::;_j1.8XlOlO nH, 21ir fr (5)

Wave impedance from magnetic dipoleare given as

ZHOJ = E, =j1201i(21ir)~j7.9XI0-6frO. (6)Ho A-

In the near-field region, the waveimpedance from electric dipole is inverselyproportional to the measurement distance r ,but the wave impedance from magneticdipole is proportional to the measurementdistance r. It is clearly shows that the waveimpendence decreases with the increasingdistance in CM radiation, while the waveimpendence increases as the distance goesup in DM radiation. Therefore, it isnecessary to achieve the electric field andthe magnetic field of the cellular phone inthe near-field region, and the waveimpedance of the cellular phone can becalculated. After that, the radiated EMImechanism of the cellular phone can bedetermined by the changing tendency of thewave impedance with the distanceincreases.

ill. Test Setup

The test setup of diagnosing cellularphone mechanism in near-field is show inFig. 2. A Gwinstek GSP-827 spectrumanalyzer (bandwidth 15KHz to 2.7GHz ), aR&S near-field probe(bandwidth 100kHz to2GHz) and a Sumsung SGH-658 GSMcellular phone are used in the measurement.The test setup is placed on a woodenplatform with a 80cm high from floor, andthe near-field probe is fixed to a moveablewooden bracket on the table.

Proceedings CEEM'2009/Xi'an

Fig.3 Three different regions of the cellular phonemeasured by near-field probe

Fig.2 Test setup for near-field mechanismdiagnosis of cellular phone

it proves that the CM radiation is dominatedin the near-field region for the speakerregion ofcellular phone.

4.2 Wave Impedance of Handset Region

The wave impedance of the cellularphone's earphone region from lmm to 4cmis shown in FigA (b). The wave impedanceincreases from l45n at lmm to 380n at4cm, which indicates the electromagneticfield of the cellular phone's handset regionis a low-impedance field, and the changingtendency of its wave impedance is inaccordance with the magnetic field. Thisproves that the DM radiation is dominatedin the near-field region for the handsetregion ofcellular phone.

4.3 Wave Impedance ofAntenna Region

As is shown in Fig. 4(c), the waveimpedance of cellular phone's antennaregion varies from Imm to 4cm. On onehand, the wave impedance increases fromOcm to 1.5cm, 2cm to 3cm, 3.5cm to 4cm,on the other hand, the wave impedancedecreases from 1.5cm to 2 em and from3.5cm to 4cm. It indicates that theelectromagnetic field of cellular phone'santenna region is a mixture of the electricfield and the magnetic field. Therefore, forthe antenna region of cellular phone, theCM and DM radiation exist at the sametime in the near-field region.

N . Experiment Results

For experimental verification, Theelectric field and magnetic field of threedifferent regions of the cellular phone aremeasured respectively. As shown in Fig.3,they are the speaker region, the handsetregion and the antenna region. It should bementioned that the observation distance ofthe cellular phone should be below5.33cm[6J, because the frequency of radiatedelectromagnetic field of the cellular phoneis around 900MHz. Then the waveimpedance of the three different regions arecalculated according to equation (5) and (6)and shown in FigA.

4.1 Wave Impedance of Speaker Region

FigA (a) shows wave impedance ofthecellular phone's speaker region with themeasurement distance varying from lmm to4cm. The wave impedance decreased from2600n at lmm to 377n at 4cm. It showsthat in near-field region the electromagneticfield of the cellular phone's speaker regionturns on a high-impedance performance,and the changing tendency of the waveimpedance with the increasing distancecomply with that of eclectic field. Therefore,

3000

2000

0'---'--'---'--'---'----''----'----'o 0.5 1.5 2 2.5

0b&en8tI0n d1stalCe (cm )

(a) Speaker region

274

Proceedings CEEM'2009/Xi'an

500

400

350

100

50

.....r/i....

0.5

•............

•...........

1.5 2. 2.5Obser.etion distance(cm)

.............

3.5

the near-field radiated EM! mechanism ofthe cellular phone is proposed with thenear-field probe measurement. The waveimpedance of cellular phone's differentregion are achieved with the proposedmethod, then the radiated EM! noisemechanisms of these different region areconcluded. Experiments verify that theproposed method can be utilized in radiatedEM! mechanism diagnosis of the cellularphone with the advantage of simplicity andefficiency.

(b) Handset region References

[1] O. P. Gandhi etc., "Electromagnetic absorptionin the human head and neck for mobile telephones at835 and 1900 MHz," IEEE Trans. On MIT., vol. 44,Oct. 1996.[2]Q. Balzano etc. , "Electromagnetic energyexposure of simulated users of portable cellulartelephones," IEEE Trans. Veh. Technol., vol. 44,[3]Paul, C. R. ,"A comparison of the contributions ofCM and DM currents in radiated emissions," IEEETrans. on EMC, vol.31, no.2, May 1989[4] FENG Li-min; QIAN Zhao-ming; EMC TroubleDiagnosing Techniques in Power Electronic Systembased on Near Field Probes, power electronics,VolA1, No.6, 2007[5]Baudry, D. etc. "Near-field techniques fordetecting EM! sources," International Symposiumon EMC, vol.1, Aug. 2004[6]Y. Zhao, K.Y.SEE, "Fundamental ofElectromagnetic Compatibility and Application",China Machine Press, 2007

3.50.5

350

450

400

500

~

~ 250

300

./ft. j! /I: ", / \ I

100 ••••••••(;1......... , •.•.•.•.Q........ /50 \ .•.•.•.•.0 ·· · .•.•J

(c) Antenna regionFig.4 Near-field wave impedance of cellular

phone's different region

V. Conclusion

The radiated EM! noise mechanismmodels of the cellular phone in thenear-field region are presented in this paper.At the same time, the diagnosis method for

275