US3631534A

US3631534A - Variable inductance device

Info

Publication number: US3631534A
Application number: US855574A
Authority: US
Inventors: Eiichi Hirota; Yutaka Neichi; Minoru Sugimura
Original assignee: Matsushita Electric Industrial Co Ltd
Current assignee: Panasonic Holdings Corp
Priority date: 1969-09-05
Filing date: 1969-09-05
Publication date: 1971-12-28
Anticipated expiration: 1988-12-28
Also published as: GB1288273A; FR2063096A1; FR2063096B1

Abstract

A variable inductance device which has a magnetic core having two coils thereon, the two coils being not coupled magnetically to each other. The inductance of one of the two coils is controlled by a DC current flowing through the other of said two coils. The device has a high Q-value, and a wide range of inductance is produced by a small DC current. The device is useful in tuned circuits of various electronic instruments.

Description

United States Patent [72] Inventors Eiichi Hirota;

Yutaka Neichi; Minoru Sugirnura, all of Osaka-tu, Japan [21] Appl. No. 855,574

[22] Filed Sept. 5, 1969 [45] Patented Dec. 28, 1971 [73] Assignee Matsushita Electric Industrial Co., Ltd.

Osaka, Japan [54] VARIABLE INDUCTANCE DEVICE 6 Claims, 9 Drawing Figs.

[52] U.S. Cl 336/155, 336/184, 336/212, 336/233 [51] Int. Cl 1-101121/08 [50] Field oiSearch 336/212,

[56] References Cited UNITED STATES PATENTS 3,415,751 12/1968 Hirota et a1 252/6259 1,601,400 9/1926 Latour 1,628,398 5/1927 Casper et al 336/212 X 2,064,773 12/1936 Vogt.... 336/212 X 2,846,637 8/1958 Huge 336/155 X 2,996,695 8/1961 Dickinson 336/212 X 3,189,859 6/1965 Olsen 336/212 3,188,552 6/1965 Owen 323/48 2,932,787 4/1960 Krabbe et al. 336/155 X 2,911,586 11/1959 Zeling 336/155 OTHER REFERENCES Bozorth, Ferromagnetism, D. Van Norstrand Company, Inc., l96l,pp. 870- 871.

Primary Examiner-Thomas J. Kozma Attorney-Wenderoth, Lind & Ponack ABSTRACT: A variable inductance device which has a magnetic core having two coils thereon, the two coils being not coupled magnetically to each other. The inductance of one of the two coils is controlled by a DC current flowing through the other of said two coils. The device has a high Qvalue, and a wide range of inductance is produced by a small DC current. The device is useful in tuned circuits of various electronic instruments.

PATENTED niczamn 3353153 4 saw 1 or 2 INVENTORS EIICHI HIROTA -YUTAKA NEICHI MINORU SIGIMURA ATTORNEYS 1 VARIABLE INDUCTANCE DEVICE This invention relates to a variable inductance device, the inductance of which is controlled by means of a DC current. Such a device can be used in the tuned circuits of radio receivers and other electronic instruments, especially for tuned circuits of automatically controlled electronic instruments.

Prior art variable inductance devices controllable by DC currents have consisted of a toroidal-shaped magnetic core with two coils wound on the core. The magnetic inductance L of one of these two coils is controlled by a DC current flowing through the other of the coils. This prior art device has a low Q-value because the high-frequency coil is directly coupled to the DC current coil, and the DC current coil has a very low impedance. To correct this problem, prior art devices have a chocking coil having large inductance connected in series to the DC current coil to increase the impedance of the DC current coil. This arrangement is usually large and complex and, moreover, requires a large DC current to obtain the desired range of variable inductance.

A variable inductance device for high frequency use usually includes a magnetic core of ferrite material. The high-electrical resistivity of ferrite materials assures a high Q-value of the inductance device. But the ferrite core is also required to have a widely variable range of permeability, since a large DC current is necessary for obtaining the desired range of variable inductance. This means that the ferrite material used in the variable inductance device must have a high-initial permeability and a low-magnetic loss in high-frequency ranges. The devices must also be stable under varying environmental conditions. Therefore, ferrite materials used in the devices must have lowmagnetic hysteresis, small temperature coefficients of permeability and low decrease in permeability with time, i.e., low disaccomodation (D.A.). The disaccomodation, D.A., means a time decrease of permeability as defined in e14 of Snoeks New Development in Ferromagnetic Oxide Materials, Elsvier Publishing Co., New York, I949.

An object of the present invention is to provide a variable inductance device which requires only a low amount of DC current to obtain the desired variable range of inductance.

A further object of the present invention is to provide a variable inductance device having a high Q-value and a high stability under changing environmental conditions.

A still further object of the invention is to provide a variable inductance device comprising an improved magnetic core which consists of a novel ferrite composition suitable for the present purpose.

These objects are achieved by a novel variable inductance device according to the present invention which comprises a magnetic core having two coils thereon, said two coils not being coupled magnetically to each other, whereby the inductance of one of said two coils is controlled by a DC current flowing through the other of said two coils.

These and other objects will be apparent upon consideration of the following description taken together with the accompanying drawings, wherein:

FIG. I is a schematic diagram of a variable inductance device according to the present invention;

FIG. 2a is a perspective view of E-shaped and I-shaped magnetic bodies which are combined to form a magnetic core of one embodiment of the present invention;

FIG. 2b is a schematic diagram of a variable inductance device made of the magnetic bodies of FIG.

FIG. 3a is a perspective view of an Ishaped magnetic body and a magnetic body having a cutout therein, the said two bodies being combined to form a magnetic core of a second embodiment of the present invention;

FIG. 3b is a schematic diagram of a variable inductance device made of the magnetic bodies of FIG. 312;

FIG. 4a and 4b are magnetic cores having two windows and consisting of two magnetic bodies combined through the insertion of magnetic material having a magnetic permeability higher than that of said magnetic bodies in accordance with the present invention; and

FIGS. 5 and 6 are curves of tuned frequency versus DC current and of Q versus DC current relations which are exhibited by the present invention when used in tuned circuits.

Before proceeding with a detailed description of a variable inductance device according to the present invention, the principal construction of the inductor device will be explained with reference to FIG. 1 of the drawings wherein reference character 11 designates a magnetic core having two windows 14 and 14' formed therein. A coil 12 is wound on a portion 16 between said two windows 14 and 14'. Another coil 13 is wound on two

portions

15 and 15 formed between the core periphery and said window 14 and between the core periphery and said window 14'. It is important that the two coils l2 and 13 are not magnetically coupled to each other. The inductance of one of said two coils 12 and 13 is controlled by a DC electric current flowing through the other of said two coils l2 and 13. When DC current flows through the coil 12. magnetic fluxes d) and are induced in core portions 15 and 15', respectively. The coil winding 13 on the portion 15 is wound clockwise to the flux qb and on the portion 15 is wound counterclockwise to the flux d), and has numbers of turns N and N at

core portions

15 and 15, respectively. The coil windings l2 and 13 do not couple magnetically with each other when N=N'. Under this condition, when a high-frequency voltage is applied to coil 13, no voltage is induced in coil 12. The coil 13 has a large Q-value, regardless of the small impedance of the coil 12. Therefore, the variable inductance device according to the present invention does not need the choke coil used in prior art devices.

It has been discovered according to the present invention that the magnetic core 11 having two windows is easily constructed in the following way. Referring to FIGS. 2a and 2b, the magnetic core 11 having two windows 14 and 14' consists of an E-shaped magnetic body 17 and an I-shaped magnetic body 18 which are combined together to form said core having two

windows

14 and 14. Another arrangement is shown in FIGS. 3a and 3b, in which the magnetic core 11 consists essentially of a magnetic body 19 having a cutout 22 therein and an I-shaped magnetic body 20, the two bodies being combined to form said core having two windows 14 and 14'.

When the magnetic core 11 is formed by combining

magnetic bodies

17 and 18 or 19 and 20, the core must have no airgap at the surfaces at which

magnetic bodies

17 and 18 or 19 and 20 come into contact with each other. An airgap at these surfaces would decrease the variable range of inductance or would necessitate the use of a larger DC current for obtaining the desired variable range of inductance. It is desirable to combine the two

magnetic bodies

17 and 18 or 19 and 20 by means of an insertion 21 of magnetic material having magnetic permeability higher than that of said magnetic bodies as shown in FIGS. 4a and 4b.

The present inductance device can be used in the tuned circuit of a radio receiver. In this application the variable range of inductance must cover the range of radio-signals in a broadcast band, i.e., a range between about 500 to 1,650 kHz. The tuned frequency f is inversely proportional to the square root of inductance of the device, i.e. f QC 1/ V An inductance of an inductance device is linearly proportional to the magnetic core 11. The permeability of magnetic core 11 decreases with an increase in the DC current ln order to cover the frequency rang-e of SOUTO ITGSURHZItBe 'Lfieifthe permeability of the coil 11 must satisfy the following relations:

vp ht fl ,650 (kHz.)/500(kHz.), eon/#1350 wherein #501 and m are perrneabilities at DC currents which make the tuned frequencies of tuned circuit 500 kHz. and 1,650 kHz., respectively. The DC current necessary for the u will be defined as the maximum DC current. In other words, the maximum DC current defined herein is a DC current which is necessary for achievement of the lowest inductance in the desired variable inductance range. It has been discovered according to the present invention that the maximum DC current is lowered by using a variable inductance device according to the present invention in association with the ferrite material specified below.

The specified ferrite material is Mn-Zn-ferrite, which consists essentially of 52 to 55 mol percent of Fe O 8 to 18 mol percent of ZnO and the balance being MnO and an additive combination of 0.05 to 1 percent by weight of GeO and 0.05 to 1 percent by weight of CaO. A variable inductance device comprising this specific ferrite material not only provides a wider range of variable inductance, but also exhibits improved properties such as low loss in a high frequency use, low-magnetic hysteresis and small temperature coefficient of permeability and low disaccomodation.

The following examples are meant to be illustrative preferred embodiments of the invention, but are not meant to limit the scope thereof.

EXAMPLE 1 A mixture of 54 mol% E6 30 mol% MnO, 16 mol% ZnO and 0.1 wt. 6e0 0.4 wt.% CaO is calcined at 800 C. for 2 hours in air. The calcined powder is then molded into E- shaped and I-shaped bodies. The pressed bodies are heated to l 1 80 C. in air and maintained at that temperature for 2 hours in a N -gas atmosphere and cooled to room temperature in N gas. The obtained ferrite material has magnetic properties as listed in table I. The dimensions of the E-shaped and I-shaped bodies (FIG. 22) are listed in table II.

. TABLE I Permeability 900 Q (at 1 mHz) 50 D.A.= 100,- percent Temperature coefiicient of permeability 15 mo and mm are permeabilities at 10 sec. and 1,000 sec. after demagnetieatlon. respectively.

Da-nm. D5095 mm. D==l.80 mrn. D,=2.2 mm.

l D,=3.80 mm. D,=l.00 mm.

D =1.30 mm.

? Sintered E-shaped and I-shaped bodies are combined together to form a magnetic core on which two coils are wound as shown in FIG. 2b. The number of turns of coil 12 at portion 16 is 140 turns and the number of turns of coil 13 is 77 turns at each portion 15 and 15' of FIG. 2b. The DC current flows through the coil 12 and controls the inductance of coil I 13. The inductance of coil 13 at a DC current of 10 ma. is 1.2 mh. and decreases to 0.1 mh. at DC current of 100 ma. Characteristics of this variable inductance device are shown in table III. A tuned circuit is formed by using this variable inductance device combined with a condenser of 85 pf. The curve of tuned frequencies versus controlled DC current is given in FIG. 5. The Q-value of this circuit is also shown in 55 there]? and an two w ndows.

FIG. 5.

TABLE III wider than (l:l0) smaller than l00 ma. larger than 50 smaller than kHz.

smaller than IXIO" less than 1% the value necessary for covering the broadcast band.

weight of C210.

EXAMPLE II The magnetic bodies shown in FIG. 3a are made of a ferrite exactly the same as that of example I. The sintered bodies are combined to form a magnetic core as shown in FIG. 3b. The dimensions of the sintered bodies are listed in table IV.

TABLE IV D 'nm. D,=0.85 mm. D:=I.55 mm. D5200 mm. D -,=5.3 mrn. D =l.00 mm. D =l.55 mrn.

The number of turns of coil 12 at core portion 16 is 120 turns and the number of turns of coil 13 is 32 turns at each of the two

portions

15 and 15 of FIG. 3b. The DC current flows through the coil 12 and controls the inductance of coil 13. The inductance of coil 13 at a DC current of 10 ma. is 515 ph. and decreases to 75 ,uh. at DC current of ma. A tuned circuit is formed by using this inductance device combined with a condenser of 205 pf. The curve of tuned frequencies versus controlled DC current is given in FIG. 6. The O-curve of the circuitisals o sl1own ir FIG. 6.

We claim:

1. A variable inductance device comprising a magnetic core having two coils thereon, said two coil windings being not coupled magnetically to each other, and a source of DC current connected to one of said coils, whereby a wide range of inductance in one of said two coils is controlled by a small range of said DC current flowing through the other of said two coils, said magnetic core comprising a Mn-Zn ferrite which consists of 52 to 55 mol percent of Fe O 8 to 18 mol percent of ZnO and the balance being MnO and as an additive combination, 0.05 to 1 percent by weight of GeO and 0.05 to 1 percent by 2. A variable inductance wherein said magnetic core has two windows formed therein, and one of said two coils is wound on a portion between said two windows and the other of said two coils is wound on two portions formed between a core periphery and one of said two windows and between a core periphery and another of said two windows.

3. A variable inductance device according to claim 2 wherein said core comprises an E-shaped magnetic body and an I-shaped magnetic body combined to form said two windows.

4. A variable inductance device according to claim 2 wherein said core comprises a magnetic body having a cutout shaped magnetic body combined to form said 5. A variable inductance device according to claim 3 further comprising a magnetic material having magnetic permeability higher than that of said magnetic bodies inserted between said magnetic bodies 6. A variable inductance device according to claim 4 further comprising a magnetic material having magnetic permeability higher than that of said magnetic bodies inserted between said magnetic bodies.

device according to claim 1,

Claims

1. A variable inductance device comprising a magnetic core having two coils thereon, said two coil windings being not coupled magnetically to each other, and a source of DC current connected to one of said coils, whereby a wide range of inductance in one of said two coils is controlled by a small range of said DC current flowing through the other of said two coils, said magnetic core comprising a Mn-Zn ferrite which consists of 52 to 55 mol percent of Fe2O3, 8 to 18 mol percent of ZnO and the balance being MnO and as an additive combination, 0.05 to 1 percent by weight of GeO2 and 0.05 to 1 percent by weight of CaO.

2. A variable inductance device according to claim 1, wherein said magnetic core has two windows formed therein, and one of said two coils is wound on a portion between said two windows and the other of said two coils is wound on two portions formed between a core periphery and one of said two windows and between a core periphery and another of said two windows.

4. A variable inductance device according to claim 2 wHerein said core comprises a magnetic body having a cutout therein and an I-shaped magnetic body combined to form said two windows.

5. A variable inductance device according to claim 3 further comprising a magnetic material having magnetic permeability higher than that of said magnetic bodies inserted between said magnetic bodies.

6. A variable inductance device according to claim 4 further comprising a magnetic material having magnetic permeability higher than that of said magnetic bodies inserted between said magnetic bodies.