System For Deflecting Magnetic Waves Utilizing A Ferrimagnetic Plate

Abstract

The present invention relates to a device for deflecting magnetic waves. According to the invention, there is provided a system comprising a plate of ferrimagnetic material polarized by a magnetic field H, wherein magnetic waves are excited. An arrangement constituted by a serpentine wire conductor lying on an insulating plate, periodically modulates the magnetic polarizing field in a zone underlying said arrangement, the latter induces a diffraction grating disposed in such a way that the magnetic waves arrive on it at the BRAGG angle. A controllable current source 6 supplies the wire conductor.

Description

The present invention relates to a device utilizing diffraction by a grating in order to deflect magnetic waves propagating through a ferrimagnetic material; which pertains to the class of spin wave low loss dielectric materials preferably having high Q properties for both spin waves and acoustic energy. Suitable material can be an yttrium iron garnet or one of the well known ferrite materials.

A device of this kind can be used, for example, as microwave switch, but also for deflecting elastic waves. This deflection of elastic waves, which in particular facilitates the design of equipment in which a zone under investigation has to be scanned by a microwave ultrasonic beam, is something which hitherto has only been achieved at the expense of considerable difficulty.

One solution consists in propagating an elastic wave through a gyromagnetic material which is magnetically polarized along a given axis. If the direction of this polarization axis is modified in relation to the direction of the incident elastic wave, the latter will be deflected and move away from the magnetic axis at an angle which is a function of the angle between the direction of the incident wave and the direction of the magnetic field. However, this solution has the drawback that it results in wide divergence in the deflected beam.

The object of the present invention is to overcome this drawback in particular.

According to the invention, there is provided a system for switching under the control of an electrical signal the direction of propagation of magnetic waves, said system comprising a plate of ferrimagnetic material having an upper face, inductor means for creating within said plate a magnetic field substantially parallel to said upper face, means for exciting within said plate a beam of magnetic waves travelling along a direction substantially perpendicular to said magnetic field, means positioned above said upper face for scattering said beam under the control of said electrical signal, first collecting means coupled to said plate for receiving said beam, and second collecting means coupled to said plate for receiving the scattered portion of said beam ; said scattering means comprising a planar conducting loop including a plurality of parallel and equidistant rectilinear portions building up a diffraction grating, and a source for energizing said loop under the control of said electrical signal ; said diffraction grating being at an angle with said beam substantially equal to the BRAGG angle.

For a better understanding of the invention and to show how the same may be carried into effect, reference will be made to the ensuing description and the following drawings among which :

FIG. 1 illustrates a diagram of a first embodiment of the device in accordance with the invention ;

FIG. 2 is a diagram, partially in section, of a variant embodiment of the device in accordance with the invention ; and

FIG. 3 illustrates an explanatory graph.

FIG. 1 illustrates a device in accordance with the invention, used for microwave switching and comprising a wave transmission medium in the form of a substrate 1, for example an yttrium-aluminum garnet, upon which there is disposed a plate 2 of yttrium-iron garnet. The device in accordance with the invention furthermore comprises a microwave input 3 associated with an interdigitated line 4, for coupling the microwave electromagnetic input energy with the magnetic waves which develop in the plate 2 (the latter being magnetically polarized by a uniform external magnetic field H) and propagate in the direction 40 perpendicularly to the field H which is supplied from inductor means 11.

The arrangement for deflecting the magnetic waves comprises a grating 50 constituted by a conductive metallized deposit upon an insulating layer 5 of very small thickness. This layer is arranged upon the surface of the plate 2 and is displaceable and alignable thereon. A current source 6, with a control input 60, is connected to the ends of the metallized deposit 50.

A first microwave output 7 associated with an interdigitated line 70 identical to line 4, is arranged to provide coupling with the magnetic waves which are transmitted undeflected in the direction 40.

A second microwave output 8 associated with an interdigitated line 80, is arranged to provide coupling with the deflected magnetic waves.

The mode of operation is as follows :

The interdigitated line 4, as those skilled in the art will appreciate, is arranged so that coupling can take place there between the applied microwave energy and the spin system in the plate 2. The spin waves excited in the zone in which the line 4 is located, propagate in the direction 40 perpendicular to the magnetic field H.

In the case of the magnetic waves, the phase velocity and therefore the refractive index of the yttrium-iron garnet of the plate 2, depend by definition upon the wave number k in precisely the same manner as for an electromagnetic wave in a propagating medium.

It is also well known that in a ferrimagnetic material such as the garnet of the plate 2, the wave number of the propagating magnetic waves, depends upon the strength of the internal magnetic field and therefore upon the applied external field.

In accordance with the invention, the value of this field is periodically modulated in order to create within plate 2 the equivalent of a grating by spacial modulation of the refractive index of the material.

This result is achieved here with the help of the conductive grating 50, of constant pitch d, through which a constant current I is circulated. The layers 5 and 2 being of small thickness, it is reasonable to assume that the magnetic field created by the grating 50 modulates the magnetic field existing inside the plate 2, in a periodic and substantially uniform manner. The magnetic waves are then deflected by this grating in the same manner in which a light beam is deflected by a grating formed inside an elastic medium through which ultrasonic waves are propagating.

In order to obtain correct scattering and maximum diffracted energy, the magnetic waves must arrive at the grating at the BRAGG angle of incidence. The plate 5 is therefore disposed in such fashion that the grating 50 makes an angle .THETA. with the direction 40, such that :

sin .THETA. .congruent. (.lambda./2 d)

.lambda. being the wavelength of the magnetic waves in the zone in question.

For example, if the wavelengths range between 1 mm and 1 .mu., a deflection 2 .THETA. on the part of the magnetic waves, of around 6.degree. will be obtained for a pitch varying between 10 mm and 10 .mu..

Thus, by means of the control input 60 associated with the source 6, it is possible to allow the current I to flow and thus deflect the microwave energy to the output 8, or to cut off the current I which results in the undeflected transmission of the energy to the output 7, the interdigitated lines 70 and 80 being arranged in the same way as the line 4.

If the magnetic polarizing field varies inside the plate 2, the result is a spatial variation in the wavelength .lambda., and this can be taken into account by producing a variable-pitch grating 50.

FIG. 2 illustrates a possible variant embodiment of the device in accordance with the invention, enabling the deflection of elastic waves. Reference numbers which are the same as those used in FIG. 1, refer to the same elements. The plate 2 of the yttrium -iron garnet terminates in the zone where the magnetic waves have converted to substantially pure elastic waves. Following this layer there are formed with the elastic substrate 1, two ultrasonic wave guides 9 and 10 which pick up and transmit the deflected and undeflected elastic waves respectively.

The mode of operation is as follows, again, considering FIG. 3.

The external magnetic field applied to the plate 2 is not constant in the direction of propagation 40 perpendicular to H, but, as indicated in FIG. 3, it decreases commencing from a transverse section B of the plate 3. This being so, in the region between the sections A and B, where the magnetic field is substantially constant and equal to H.sub.1, magnetic waves propagate and it is in this region that the plate 5 is arranged.

Between the sections B and C, the magnetic waves convert progressively into magneto-elastic waves and then into substantially pure elastic waves. These elastic waves resulting from the deflected or undeflected magnetic waves, are picked up respectively by the ultrasonic wave guides 9 and 10 which are constituted, for example, by a layer of material having a lower modulus of rigidity than the substrate 1. Wave guides of this kind are described, for example in the report entitled "Microsound components; circuits and applications" by E. Stern (Oct. 30, 1968) M.I.T. Lexington (Massachusetts).

By utilizing similar devices in series, ultrasonic scanning of a zone which is to be explored by an ultrasonic pencil can be achieved.

Self-evidently, the invention is in no way limited to the embodiments described here.

Claims

What I claim is:

1. A system for switching under the control of an electrical signal the direction of propagation of magnetic waves, said system comprising a plate of spin wave ferrimagnetic material having an upper face, inductor means for creating within said plate a magnetic field substantially parallel to said upper face, means for exciting within said plate a beam of magnetic waves travelling along a direction substantially perpendicular to said magnetic field, scattering means positioned above said upper face for receiving said beam ; said scattering means splitting the energy of said beam under the control of said electrical signal into a transmitted portion and a scattered portion ; first collecting means coupled to said plate for receiving the transmitted portion of said beam, and second collecting means coupled to said plate for receiving the scattered portion of said beam ; said scattering means comprising a planar conducting loop parallel to said upper face, and including a plurality of parallel and equidistant rectilinear portions building up a diffraction grating, and a source for energizing said loop under the control of said electrical signal ; said diffraction grating being at an angle with said beam substantially equal to arc sin .mu./2d ; where .mu. is the wavelength of said magnetic waves, and d the pitch of said diffraction grating.

2. System as claimed in claim 1, wherein said conducting loop is deposited on an insulating layer carried on said upper face.

3. System as claimed in claim 1, wherein said source is a current source having a control input for receiving said electrical signal.

4. System as claimed in claim 1, wherein said means for exciting comprises an interdigitated line deposited on said upper face and a microwave connector for feeding said line with microwave electro/magnetic energy.

5. System as claimed in claim 1, wherein said magnetic field is a uniform magnetic field ; each of said collecting means comprising an interdigitated line deposited on said upper face and a microwave connector receiving the microwave electro/magnetic energy supplied from said line.

6. System as claimed in claim 1, wherein said magnetic field has a magnitude substantially constant between said means for exciting and said scattering means and a decreasing magnitude beyond said scattering means ; each of said collecting means being an ultrasonic waveguide coupled to the remote edge of a region of said plate where said magnetic waves are substantially converted into pure elastic waves of ultrasonic frequency.