3500 IEEE TRANSACTIONS ON MAGNETICS, VOL. 32, NO. 5, SEPTEMBER 1996

L STUDY ATION OF PARAMET IC MAGNETIC REPRO

Koiclii Karasawa Nagano National College of Teclinology, 71G Tokiiina, Nagano 381, Japan

Yorim o t o Ta nno Niigata Institute of Technology, 1719 Fii.jiliaslii, Kashiwazaki 945-11, Japan

and Kiyoliito Yamsrsawa Sliinshu University, Faculty of Engineering, 500 Wakasato, Nagano 380, Japan

Abstract - The mechanism of a parametric mag- netic reproducing head is explained and the ex- perimental results are reported. The head is fab- ricated with an additional inductive pickup coil to verify the flux in the magnetic circuit. It is excited by the oscillation current under the sinu- soidal magnetization condition and the oscillation voltage is obtained by differentiating the magnetic flux. The incremental permeability and the loss of the B-H loop are measured and compared as a function of DC biased current for one set of os- cillation parameters. The reproduction conditioiis that the slope of the R H loop is steep and the loss is low are presumed.

I. INTRODUCTION

Tlie parametric niagnct,ic reproducing head is a fliix rcsponsctype head. Therefore tlie amplitude of the out,- put voltage is indepentlcnt of a signal frequency [l]. The sensitivity of the head is expected to be higher than that of any other type head. The mechanism of the reproduc- ing process of this head Iias been modeled by using an :ipproxiinate solution of a non-linear Mathieu's equation under simple assumptions 121. To analyze the operation txperimcntally, we propose to use tlie B-I1 loop of the head corc in the paramctric oscillation.

In order to measure the flux dcnsity B of the head core, ~ v c developed n prototype head with an additional coil for tlctwting tlie induced voltage. The B-H loop in the os- cillation is obtainccl by integrating the oscillation voltage. The loss and tlie incremental permeability calculated by the B-I1 loops clarify the mrchanism of the parametric reproduction.

11. PROTOTYPE PARAMETRIC MAGNETIC REPRODUCING HEAD

Fig. 1 shows the configuration of the prototype pnrn- mctric magnetic reprodncing Iicad [ 3 ] . As a conventional liratl lias two coils, tlie head lias three coils (Coil 0, Coil D, Coil I) in order to compare the parametric oscillnt,ion voltage with thc induccd voltage. Coil 0 is uscd for the oscillation, Coil R for DC biasing, and Coil I for detection of the induced voltage 21;. The number of turns for oscil- lation No, for biasing Nb and for detection Ni are 1000,

1000 and 10 respectively. The parametric oscillation volt- age vu occurs when the voltage TJ shown by the followi11g qiiation is applied to varactor diodes

v = r/, i- I/,si122.rrfet, (1)

whcre I[,, Ife and fe are t,he DC?eversed voltage, tlic3 exciting voltage, ,and the exciting frequency, respcctively. Thc oscillation voltage is measured by tlic output of the differential amplifier. The frcquency is f e / 2 . The DC l i - asctl current I b is applied in order that the inductance of the head is changed by the signal field. In the oscilla- tion, tile inductance of tlie liead core is cliangcd by the signal ficltl from the recorded media and the parnmctric oscillation voltage is modiilatcd in amplitude. Tlie repro- tliicctl ontpnt voltage ti, is obtained at tlie output of thc dcmotlulator.

11 I. EXPERlhll?NTAL REsuurs

Fig. 2 shows the waveforms of (a) a parametric oscil- lation current io, (b) the oscillation voltage ti,, and (c) the induced voltage z ~ ? with the conditions of fe = XkTIz, IT, = 2 . N , V, = 1.7V and J b = 3.3inA. From Pigs. 2(b) and (c), the waveforms are similar and tlie ratio of thc amplitude of TJ, to 2ri is aboiit 87.5: 1. Fig. 3 sliows powcr spwtra of (a) io, (b) 21, and (c) vi . Figs. 2(a) antl 3(a) reveal that the oscillation cnrrent is approximately sinii- soitlal and has only the oscillation frequency component of f e / 2 , and that the varactor-diodcnetwoik opcratm as a constant-current source.

Figs. 3(b) and 3(c) show that a, and T J ~ contain the finitlament al f e / 2 antl the harmonic components. Tlic

-0 V"

4,

Manusct ipt received March 4, 1996. Fig. 1. Prototype paramctric magnetic reproducing litatl.

0018-9464/96$05 00 0 1996 IEEE

3501

4

10pddiv

2

F

cs' E - 0

-2

-4

(a)usinp, io and vu)

Fig. 2. Waveforins: (a) io (O.hA/div), (b) v, (lV/cliv), and (c) vi (2OinV/cliv).

2 -

- 20.00 .- !? f 9 - -20.00

0,

$ & -60.00

-10 0 10 Frequency [kHz] II, [A/ml

(b)ueing I, and vi

- 20.00 Fig. 4. n-11 loops: (a) using io and ti,, (b) using io antl u 8 t ' j .

-20.00 2 c g -60.00 voliagc ratios are also as s a m e as i,he d i o No i,o N,,

and t lie oscillation voltage is obtaincd by tlini.reni,ial iiig 0 50 100 N0q5. The waveforms of ;I, antl v,, howevei., iiiclude tlic

Frequency [kHz1 harmonics. So, we iisc the following approximation

999

(2) At - 20.00 SN

-20.00 b $ g -60.00

B~ or ~3, M - v,, (b) v, n=O

wlicrc Bj or Bo is thc flux dcnsity when vi or v, is sub- stitmtcd for I fn in (2). Also, At is the sampling i,imc (= O.I/is), S is the avcrnge cross-sectional area of tlic corc' (=2.8miii2), Ifn. is the peak voltage at tlie n-tli, and A' is ttic winclings of N, or N,.

Fig. 4 shows the n-11 loops: (a) using io and vu, (1)) using io and vi. Tlic total cncrgy F'h exhaustccl at, the iv l iok~ head is given by

3

loo 0 50

Frequency [Id121

(c) vi

Pr, = ( S e / 2 ) S b I , ( 3 ) Fig. 3. Poiver spectra: (a) io, (b) v, and ( c ) vi.

where 1 is the average length of the magictic path (==25.!Iiniiii), and ~ ' 1 ~ is the mea of the loop.

In the oscillation, l)ot,h the DC-biased field /ZI, tint1 tlie osci11:it ion magnetic f i c M 11, arc appliccl.

For tlic peak-to-peak fliix density AD and niagiict ic f i c M AI1 of the D-11 loop, tlic iiicreiiiental pclnicabilii1y

3502

lin\V] /LA

Fig. 4(a) Fig. 4(b) 22.3 2’2.1

2‘10.0 246.0 I ’ I

(4)

Taking account for the ratio of No to N, as 87.5:1, Ph and / / A for the B-I1 loops of Figs. 4(a) mid (b) are cal- ctilntcd as shown in Table I. It is found from Table I that tlie B-H loops in Figs. 4(a) and 4(b) are same and tlie J3-11 loop of the liead core in the oscillation is obtained by integrating the oscillation voltage without tlie intlticc<l voltage.

Nest, we discuss the mcclianism of the parametric re- production by using p~ and Ph of the B-I1 loops. Fig. 5 s11ows the parametric oscillation voltage V, versus the DC biased current I b with tlie conditions of fe = 37kHz, V, = 2.1V, and V, = 1.7V. The DC biased current region (2.25 5 10) is dividcd into three regions, Region I (2.25 5 1, < 3.0), Region I1 (3.0 5 Ib 5 4.0), and Region 111 (4.0 < I b ) , as shown in Fig. 5. In Region IT, the filled marks ( 0 ) are

w bo Y I

E 8

= 2 6 z L

3 4 .d u +

E 0 - - $ 2 e E o cr, 2 3 4 5 6

W

DC biased current I b (mA)

Fig. 5. The parametric oscillation voltage versus tlic DC biased current.

t,he bias points at which tlie signal is reproduccd from the niedia. In Regions I and TIT, however, the reproduction is impossible.

To clarify the reason, we measured the DC biased cur- rent dependence of / i ~ arid Ph with the conditions of fe = 37kHz, \f, = 2.4V and I f , = 1.7V. Figs. G and 7 sltom /ca v ~ r s u s 1, and PIL veimis I,, respectively. Fig. G rewcals that tlie slope I / L A / [ ~ ~ is 55 in Regions I and 11, and 5 in TIT. Fig. 7 shows that t.he loss PI& in Region I is more than 150[mW], while in Regions I and TI less tlian 30[1iiIV]. \!’e giiess that tlie slope I / c a / f b l must be steep and the loss must be small in order to reproduce the signal from i,lie recorded media.

IV. CONCLUSIONS

Tlie incclianism of the reprodiicing process of tlie para- metric magnetic reproducing head was discussecl. In i hc

320

300

280

260

240

220

d 3-

Fig. 0. Tlie increincntal permeability / L A versus the TIC biased current 1b.

300

- 200 ti L-.l

n” 100

Cr * I I I

0

Fig. 7. The total energy Ph versus the DC b i n d current I b .

paranietric oscillation, tlie head core is excited by tlie os- cillat ion magnetic field under the sinusoidal conditions.

By comparing Ph and /la of tlie B-€1 loops in the para- metric oscillation, it was forintl that the reproduction oc- rim iindcr a steep slope of the 13-13 loop and the low loss.

ACKNOWLEDGEMENTS

The authors with to thank Mr. Tukslda of SI-IINANO KENS131 CO., LTD., and hfr. Yamaguchi of TECIIRECO CO., JTD., for the fabrication of the prototype parametric magnetic reproducing head.

REFERENCES

I<. Karasawa, Y. Tanno and T. Mikoshibai “ShoIt-‘l’ii~ic Rcproduct.ion Charact.crist,ics of The Parametric Mag- nct,ic Tape Recordw,” E1ectron.i~~ arid Com,m.unicabions in, Japan,, Part 3, vol. 78, No. 8 , pp. 29-38, 1995. Y . T a n n o and S . Tsomki: “Analysis of t.lie para~rict ik magnet.ic sensor,” IBICE, vol. J71-C, No. 1, pp. 130- 137, 1988 K . Karasawa, Y. Tanno and K. Yamasawa: “A S‘I‘UDV OF A NEW PARAMETRIC MAGNETIC REPRODUC ING HEAD,” IEBR T“. Magn., vol. 31, No. 6, pp. 2678-2680, 1995.