Analysis of the Low-Frequency Ferrite Antenna. Kazuaki Abe (CASIO COMPUTER CO., LTD.), Jun-ichi Takada (Tokyo Institute of Technology)

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1 IM * (), () Analysis of the Low-Frequency Ferrite Antenna Kazuaki Abe (CASIO COMPUTER CO., LTD.), Jun-ichi Takada (Tokyo Institute of Technology) Abstract In this paper, we evaluated the characteristics of the ferrite antenna that is used to receive long wave radio of time standard. In the calculation results using the electromagnetic simulator, inductance and Q-value of ferrite antenna are well agreed with the experimental results. As sensitivity evaluation of ferrite antenna, we measured antenna factor by the replacement method. In case of metal plate existing near the ferrite antenna, eddy current losses occur in the metal and antenna sensitivity becomes worse. When the distance between antenna and metal is 1 mm, the degradation of antenna sensitivity is about 20 db. (Low-frequency, Ferrite antenna, Magnetic body, Antenna factor, Eddy current) 1. 2 () cut and try 2. (NICT) () dBV/m 1 [1] Table1 Characteristics of radio station JJY[1] Ohtakadoya-yama Hagane-yama Date service began 6/10/ /1/2001 Location Fukushima pref. Saga/Fukuoka pref. Latitude, Longitude 3722 N, E 3328 N, E Height 790 m 900 m Antenna type Omni-directional Antenna height 250 m 200 m Carrier power 50 kw 50 kw Antenna efficiency 25 % or more 45 % or more Carrier frequency 40 khz 60 khz Frequency accuracy /6

2 kHz 1 Fig.1 The shape of prototype antenna 1 L (3.1) [2]K app L L 0 (3.1) 2 No.1 No.2 WNo.3 N No.46 ML- 24D(Mn-Zn ) 3 Prototype No. Ferrite core length: Winding width: W, Number of turns: N 2 π (φ / 2) N L = K µ app W 2 Table2 Parameters of prototype antenna Core size: Winding parameters: diameter, W, N mm 0.08 mm, 11 mm, 103 turns mm 0.08 mm, 5.5 mm, 103 turns mm 0.08 mm, 11 mm, 770 turns mm 0.08 mm, 11 mm, 103 turns mm 0.08 mm, 11 mm, 103 turns mm 0.08 mm, 11 mm, 103 turns 2 3 ML24D Table3 Parameters of ferrite core ML24D Test Characteristics Value condition Initial permeability: i Saturation magnetic flux density: B s mt Residual flux density: B r mt Coercive force: H c A/m Relative loss factor: tan/ i 40 khz Curie temperature: T c > 200 Electrical resistivity: 5 m Maxwell 3D[3] (HP4194A) 25mm 35mm 3 2 AL 2 4 (1)W 1/2 L 2 app L 2 2/6

2 Fig.2 Measurement and simulation result of the antenna to core length ) 4 8000 5 Fig.5 The shape of product ferrite antenna 3 Fig.

3 2 Fig.2 Measurement and simulation result of the antenna to core length ) Fig.5 The shape of product ferrite antenna 3 Fig.3 Measurement and simulation result of the antenna to number of turns 4 Fig.4 Measurement and simulation result of the antenna to winding width (Mn-Zn 4 MT80D Table4 Parameters of ferrite core MT80D Test Characteristics Value condition Initial permeability: i Saturation magnetic flux density: B s mt Residual flux density: B r mt Coercive force: H c A/m Relative loss factor: tan/ i 40 khz Curie temperature: T c > 120 Electrical resistivity: 0.05 m 4.2 Q S/N Q 6 (pf ) R cu R fer 3 Q 6 Q=(L/R s ) 6 tan fer =(L/R fer ) R cu <<R fer (2) ωl Q = R s s 1 R tanδ cu + ωl µ i fer µ app (4.1) R cu L (tan fer / i ) app (4.1)(tan fer / i ) app 3/6

4 4 (4.1) Q 40kHz 60kHz 78 N 1053turn 3% 40kHz N=1053turn mH 18.0mHQ kHz m 60kHz (4.1) 9 (Total loss) (Core loss)(copper loss) 95kHz (Q ) 40kHz 60kHz R cu R fer L 6 Fig.6 The equivalent circuit of ferrite antenna 7 Q (f=40khz) Fig.7 Inductance and quality factor of ferrite antenna(f=40khz) = R s L 8 Q (f=60khz) Fig.8 Inductance and quality factor of ferrite antenna(f=60khz) 9 Fig.9 The relationship of core loss and cupper loss () (AF) (5.1) E AF = (5.1) V [4] M EMC ( 30MHz1GHz 40kHz 60kHz JJY 4/6

5 ) ( 10) 3m 1.27m 40kHz 60kHz 11 JJY 40kHz 60kHz 20cm 38.2kHz 55.1kHz 12 50dBV/m 38.2kHz 39.2dB/m 55.1kHz 34.4dB/m 55.1kHz 4.8dB Q 40kHz 60kHz dBV/m Receive antenna Rode & Schwarz: HFH 2-Z2 Antenna factor: 20.2dB/m Ferrite antenna with tuning condenser 10 Fig.10 Measurement of standard loop antenna 11 Fig.11 Measurement of ferrite antenna 12 Fig.12 The antenna factor of ferrite antenna , 3, 5mm SUS430 SUS m 0.60m Lock-in amp nf: NI m Rode & Schwalz test receiver Measure received voltage 1.27 m Influence of noise Separation distance = 3m EMI shield room Antenna distance = 3 m EMI shield room Built-in SG nf NI5640 Transmit antenna Kyoritsu: KBA203 Continuous wave: 40kH or 60kHz Transmit antenna Kyoritsu: KBA /6

6 38.2kHz 55.1kHz db 1mm 20dB 3 SUS304 SUS (55.1kHz) Fig.15 The sensitivity loss in case metal exists (55.1kHz) 13 Fig.13 Arrangement of a ferrite antenna and a metal plate 5 Table5 Parameters of metal plate SUS430 SUS304 Titanium Diameter 43.6 mm 40 mm 40 mm Thickness 1.0 mm 0.8 mm 0.8 mm Initial permeability Electrical resistivity 0.6 m 0.72m 0.55m Antenna Diameter Metal plate Top view Direction of arrival 5 mm Antenna Distance Metal plate Side view Thickness 14 (38.2kHz) Fig.14 The sensitivity loss in case metal exists (38.2kHz) 6. Q 50dBV/m () [1] [2] :,, 1972 [3] Maxwell 3D 3 [4] Y.yamamoto, S.Ishigani, T.Iwasaki: Evaluation of the Complex Antenna Factors of Loop Sensors for Measuring Magnetic Fields, IEICE Technical Report, EMCJ96-117, ( ) (In Japanese),, :,, EMCJ96-117, ( ) 6/6

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