US2944229A - Non-reciprocal electric coupling device - Google Patents

Description

July 5, 1960 G. DE VRIES NON-RECIPROCAL ELECTRIC COUPLING DEVICE Filed Nov. 6, 1957 .FIG.3

INVENTOR GERRIT DE VRIES AGEN 2,944,229 patent d an 5, 1960 NON-RECHRGCAL ELECTRIC COUPLING DEVICE Gerrit de Vries, Eindhoven, Netherlands, assignor to North American Phili s Company, Inc., New York, N.Y., a corporation of Delaware Filed Na. 6, 1957, Set. Nolssasos' Claims priority, application Netherlands Nov. 9, 1956 6 Claims. (Cl. 3313-24) of this kind are already known in which a body of prepolarized high-frequency magnetic material, for example of ferrite, is arranged in a wave guide in a manner such that waves in the wave guide are passed substantially unhindered in one direction and materially damped in the opposite direction. However, such devices are not usable for comparatively low frequencies, for example of the order of 500 mc./s., since 'the dimensions of wave guide would become too large for practical use.

Furthermore, a non-reciprocal electric coupling device is already known, which comprises two crossing coils, the winding surfaces of which are arranged at right angles to each other and which surround a common core of high-frequency magnetic material which is prepolarized in a direction parallel to the intersecting line of the winding surfaces. Such a coupling device is indicated in certain cases by the name of gyrator. It has previously been suggested to arrange an external resistor coupling between the input and the output of the coupling device in order to increase the transmission in one direction. This device is not particularly suitable for waves having a wavelength of the order of 50 cms., since-the resistor coupling introduces additional losses and is also difficult to adjust. I I H v The present invention mitigates this disadvantage. The non-reciprocal electric coupling device according to the invention lkewise comprises two windings crossing at right angles and surrounding a common core of high-frequency material which is prepolarized in a direction parallel to the intersecting line of the winding surfaces. In the device according to the invention, the prepolarizing field has a strength such that the high-frequency magnetic material is in magnetic resonance for a given frequency at which transmission of energy must not take place in one direction, an external purely reactive coupling being provided between the two circuits, having a value such that the resulting coupling factor inone direction is zero for thesaid frequency.

In order that the invention may be more readily carried into eliect, it will now be described more fully, by way of example, with reference to the accompanying drawing.

Fig. 1 shows two windings 1 and 2, crossing at right angles, which, if desired, may each comprise a single :turn and surround a common core 3 of high-frequency magnetic material, for example of ferrite. The core 3 is prepolarized in vertical direction by means (not shown), for example by means of an electromagnet as indicated by arrow H. One end of each winding is connected via a common impedanceZ to terminals K and K, of the coupling device, the other ends of-the windings being connected to terminals K and K The components 2 B and B of the magnetic inductance in two relatively perpendicular directions at right angles to the prepolarisation H may be expressed in the corresponding components H andH of the magnetic field by the relations:

y=| 2 x+I 1 y wherein [L1 and #2 indicate permeabilities, which are usually'complex values. The voltages V and V at the terminals K K and K K respectively, of the coupling device may be expressed in the currents I and I traversing the windings 1 and 2 by the quadripole equations:

1=( +.l: 1) 1+( 'j a) 2 2= a) 1+( +i a) 2. wherein L and L indicate the inductances of the windings 1 and 2, which are proportional to the permeability a and M indicates a magnetic coupling factor which is proportional to the permeability If Z-iwM=O, transmission of energy is not possible from the output terminals K K, to the input terminals K K since in this case the voltage V is independent of the output current I According to the invention, the prepolarising field H has a value such that the magnetic material of the core 3 is in magnetic resonance for the angular frequency w. The permeability ,u is in this case purely real and has a maximum value. The coupling factor M is in this case also real, so that the coupling impedance Z must be reactive. This aifords the advantage that the external coupling does not introduce additional loss and can readily be adjusted, which is important more particularly for comparatively high operating frequencies, since in the case of an ohmic or complex external coupling a variation in the ohmic component would also involve a variation in the reactive component, and conversely. When the input terminals K K are connected to a generator GN and the output terminals K K; to a load impedance Z the load on the generator due to the coupling device is. thus equal to Z+jwL thatis to say independent of the value of the load impedance Z The coupling factor for the transmission of energy in the direction of passage, that is to say from the input terminals K K to the output terminals K K is equal to Z+jwM,,=2fwM,,. This coupling factor is comparatively high, since the permeability to which the factor M is proportional, is maximum with ferromagnetic resonance. However, the permeability m is in this case also maximum, that is to say approximately imaginary and in absolutevalue equal to the permeability 1. so that the terms jwL and jwL which are equal when the coupling device is symmetrical, may be written in the form I The internal impedance, both of the input side and the output side of the coupling device, thus comprises the large loss component R. However, with a given choice of the output impedance Z the transmission output despite this fact is surprisingly very high and theoretically approaches as much as Experiments have revealed that in the coupling device according to the invention, the damping in the direction of passage may be of the order of only 1 db, in which eventthe dielectric losses and the like also play a part.

'ference of which is 90.

3 Assuming the output impedance Z to be G+jD, then applies:

2=( +1' z so that 1' i+( +i +i z= The energy given off by the generator GN is equal to:

. l la and the energy taken the impedance Z is equal to:

. i zi 7 so that .transmission output is equal to:

When the load impedance Zp=G+jD is additive complex with respect to the internal impedance R+jX+jY of the coupling .device, that is-to say G=R and the transmission output is equal to:

Y'fl Te Now, Y is proportional to the permeability L and R is proportional to the permeability whilst the absolute values ,of a and 1. become approximately equal when the magnetic material is in ferromagnetic resonance, so that Y is also approximately equal to R and hence the transmission output is equal to unity.

This may also be explained theoretically as follows: If one Winding only is traversed by a high-frequency alternating current, strong polarisation of the magnetic material occurs, which involves high magnetic losses. However, if Z is additive complex with respect to the internal impedance, then from the above-mentioned relationship between I and 1 and considering the circumstance that with resonance Y R, it follows that I =jL This implies, that the windings are traversed by currents, the absolute values of which are equal and the phase dif- A magnetic rotational field .is thus produced, which is oppositely directed to the precession direction of the electron spin in. the magnetic material, in other words the two currents counteract each other as to their reaction upon the precession, so that the magnetic losses are small. The effective magnetic coupling between the windings in the direction of passage is thus substantially zero, so that only the external coupling via the impedance Z is active, which does not, however, introduce losses due to the absence of a resistance component in this impedance.

A suitable embodiment of the coupling device according to the invention is shown in Figs. 2 and 3, of which Fig. 2 is a'plan view. and Fig. 3 an elevation view.

This embodiment comprises two conductors 1 and 2, crossing at right angles, which are bent around the core 3 of high frequency material and which are connected, at one end, to aconductive base 4. The other ends of the conductors 1 and ,2 are connected to the inner conductors high frequencies for which the device is intended. By

regulating the length {of conductorQ, the strength of the "external coupling 'betweenthe conductorsl and 2 may be varied 'andadjusted to a value such that the total coupling "has an apparent internal impedance of a complex value,

lquency.

between conductor 5 and conductor 6 is eliminated in one direction.

What is claimed is:

1. A non-reciprocal electric coupling device comprising a core of ferromagnetic material exhibiting gyromagnetic resonance, first and second windings positioned to substantially surround said core at mutually right angles with respect to each other, a source of oscillations, a load, means connecting one terminal of said source to one end of said first winding, means connecting one terminal of'said load to one end of said second winding, reactance coupling means, means connecting said reactance means between intermediate points on -said first and second windings and the other terminals of said source and load, and means providing a polarizing field in said core in a direction parallel to the line of intersection of the planes of said two windings, said field having a strength to cause said core to be in a state of magnetic resonance for a given frequency, said coupling means having such a value that there is substantially no electrical coupling in said device in the direction from said second winding to said first winding at said given frequency, whereas there is an electrical coupling in said device in the direction from said first to said second winding at said given frequency.

2. A coupling device as claimed in claim 1, wherein the value Z of said reactance coupling means satisfies the equation Z'jwM =0, where w is 21:- times said given frequency, and M is the magnetic coupling factor of said windings.

3. The coupling device of claim 1, in which said device and said load has a 'value which is additive complex to said complex value of internal impedance.

4. The coupling device of claim 1, in which said reactance coupling means comprises a first conductor connected between intermediate points on said first and sec- ,ond winding, and a second conductor connected between .a pointon said first conductor and said other terminals of said source.

5. The coupling device of claim '1, in which said reactance coupling means comprises an inductance.

6. A non-reciprocal electric coupling device comprising a core of ferromagnetic material exhibiting gyromagnetic resonance, a conductive base on one side of said core, first and second conductors on the .opposite side of said core and'crossing each other at right angles, one end of each of said first and second conductors being bent around said core and connected to saidbase, a third conductor joining intermediate points of said first and second conductors, a fourth conductor connected between saidbase and a point on said third conductor, and means providing a polariz'ing field insaid-core between said one and opposite sides :01? said core, said field having a strength to cause said core to be in a state of magnetic resonance for a given fre- References Cited in the file of this patent UNITED STATESPATENTS' OTHER REFERENCES Gianola et al.: Journal of Applied Physics, vol. 27, No. 5, June 1956, pages 608-609.

Tellegen: 'Philips Research Reports," vol. 3, April 1948, pages 81-101.

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