Acoustic surface wave devices

Abstract

Acoustic surface wave devices of a novel class characterized by the provision of coupling means comprising at least several spaced filamentary electrical conductors extending over a first region and a second region for causing acoustic surface waves propagated across the coupling means in the first region to interact with acoustic surface waves propagated across the coupling means in the second region, by means of alternating electric signals induced on the filamentary electric conductors. The regions to be coupled are preferably formed on piezoelectric material, but modified forms of the coupling means can be made operable with other materials and suitable biassing fields. The described devices include acoustic beam width changing, impedance matching, track changing and phase-sensitive switching devices; a hybrid junction device, resonator and recirculating filter devices, tapped acoustic delay lines, unidirectional transducers, acoustic surface wave reflectors and mode discriminators, electrically-controlled acoustic beam switches and directional couplers, acoustic beam splitters, and means for reducing unwanted reflections of acoustic surface waves.

I claim: 
     
       1. An acoustic surface wave device which comprises .Iadd.a single substrate having .Iaddend.at least a first track and a second track, said tracks being .Iadd.located at spaced areas of said substrate each of which areas is .Iaddend.formed of a material able to support acoustic surface waves and having first and second piezoelectric regions respectively across both said first and second tracks, means for launching surface acoustic waves along the first track, and means for receiving and detecting acoustic surface wave energy travelling along the second track, said device further comprising acoustic surface wave coupling means .Iadd.on said substrate .Iaddend.extending between said tracks and having a first part disposed across said first track and a second part disposed across said second track, said first and second parts of said coupling means comprising a plurality of spaced filamentary electrical conductors .Iadd.all of which are electrically insulated from one another and .Iaddend.each of which extends in length over the first region and thence without interruption over the second region, those parts of said filamentary conductors which extend across said first region being substantially parallel to another and being oriented substantially orthogonal to the direction of energy travel along said first track, and those parts of said filamentary conductors which extend across said second region being substantially parallel to one another and being oriented substantially orthogonal to the direction of energy travel along said second track, said coupling means being operative to transfer energy between said first and second tracks by transduction whereby energy in said first track comprising at least some of the acoustic surface wave energy traveling in the .[.travck.]. .Iadd.track .Iaddend.is intercepted and converted into electrical energy induced between said conductors by said first part of the coupling means extending across the first track, is then transferred toward said second track along the filamentary electrical conductors of the coupling means as said electrical energy is then converted back to surface acoustic wave energy and relaunched as surface acoustic surface wave energy .Iadd.traveling substantially in a single direction only .Iaddend.in the second track by said second part of the coupler means extending across the second track. 
     
     
       2. An acoustic surface wave device as claimed in claim 1, wherein the said material is a piezo-electric material. 
     
     
       3. An acoustic surface wave device as claimed in claim 1, wherein the said material is an electro-strictive material and the said coupling means also comprises means for applying a biassing electric field to the material under the filamentary conductors in the first region and in the second region. 
     
     
       4. An acoustic surface wave device as claimed in claim 1, wherein the filamentary conductors are connected to form closed loop circuits, and the coupling means also comprises means for maintaining a magnetic field orthogonal to the filamentary conductors over the first region and means for maintaining a magnetic field orthogonal to the filamentary conductors over the second region. 
     
     
       5. An acoustic surface wave device as claimed in claim 1, wherein said material is a magneto-strictive material which does not shortcircuit the said alternating electric signals, the filamentary conductors are connected to form closed loop circuits, and the coupling means also comprises means for applying a biassing magnetic field to the material in the first region and means for applying a biassing magnetic field to the material in the second region. .[.6. An acoustic surface wave device as claimed in claim 1 formed on a surface of suitable material, and the said first region and the said second region are different areas of the 
     
     
        surface..]. 7. An acoustic surface wave device as claimed in claim 1 formed on a non-piezoelectric substrate able to support acoustic surface waves, having piezo-electric material deposited to form the said first 
     
     
        region and the said second region. 8. An acoustic surface wave device as claimed in claim 1 wherein parts of the said filamentary conductors not over the first region and not over the second region are formed over a 
     
     
        material which attenuates or does not support acoustic surface waves. 9. An acoustic surface wave device as claimed in claim 1, wherein the parts of the filamentary conductors over the second region are curved so 
     
     
        as to form convergent acoustic surface waves in the second track. 10. An acoustic surface wave device as claimed in claim 1, constructed so that acoustic surface waves propagated from one half of the width of the first transducer means will reach the coupling means a quarter of a period in advance of the acoustic surface waves propagated from the other half of 
     
     
        the width of the first transducer means. 11. An acoustic surface wave device as claimed in claim 1, wherein each filamentary conductor has two substantially equal parts, of which one part is a quarter of an acoustic 
     
     
        wavelength nearer to the first transducer means than the other part. 12. An acoustic surface wave device as claimed in claim 1, also comprising a third transducer means disposed to launch acoustic surface waves in the second track towards the coupling means, and a fourth transducer means disposed to receive and detect acoustic surface waves propagated from the coupling means in the first track, constructed so that signals launched in phase with each other from the first transducer means and the third transducer means will reach the coupling means in a quadrature phase relationship, and the device will therefore act as a hybrid junction 
     
     
        circuit. 13. An acoustic surface wave device as claimed in claim 12, wherein each filamentary coupler has a quarter-wavelength step substantially at its center, effectively advancing one half of the coupling means by a quarter-wavelength in one track, relative to the other 
     
     
        half of the coupling means in the other track. 14. An acoustic surface wave device as claimed in claim 1, forming a tapped delay line, comprising a plurality of fractional coupling means extending across successive parts of the first track, and a plurality of transducer means disposed in the second track, comprising one transducer means disposed between each 
     
     
        fractional coupling means and the next fractional coupling means. 15. An acoustic surface wave device forming a tapped delay line as claimed in claim 14, having a plurality of deposits of acoustic surface wave attenuating material disposed in the second track between each transducer 
     
     
        means and the next fractional coupling means. 16. An acoustic surface wave device forming a tapped delay line as claimed in claim 14, wherein each of the fractional coupling means has its part in its second track disposed at an angle to its part in the first track, so that each fractional coupling 
     
     
        means will transfer signals into a distinct track. 17. An acoustic surface wave device comprising a plurality of coupling means as claimed in claim 1, disposed to direct acoustic surface wave signals around a circuit of acoustic surface wave tracks, and at least one additional coupling means for coupling signals in the circuit to a separate track, and an input transducer means and an output transducer means disposed in the said 
     
     
        separate track. 18. An acoustic surface wave device, as claimed in claim 1, forming a unidirectional transducer means wherein the said first region and the said second region lie in a common acoustic surface wave track and a transducer means is disposed between the first region and the second region so that signals propagated from the transducer means in opposite directions will reach the coupler means in a quadrature phase relationship 
     
     
        with each other. 19. An acoustic surface wave device as claimed in claim 
     
     
        18, wherein the filamentary conductors are U-shaped. 20. An acoustic surface wave device as claimed in claim 18, wherein each filamentary 
     
     
        conductor is a separate elongated O shape. 21. An acoustic surface wave device as claimed in claim 1, forming a reflector for acoustic surface waves, wherein the said first region and the said second region lie in a common acoustic surface wave track and the coupling means is a 3dB coupler 
     
     
        as hereinbefore defined. 22. An acoustic surface wave device forming a track changer, comprising a coupling means as claimed in claim 1 wherein the coupling means is a 3dB coupler as hereinbefore defined, and two reflectors are provided on one side of the 3DB coupler, one of the reflectors being disposed in the first track and the other being disposed 
     
     
        in the second track. 23. An acoustic surface wave device as claimed in claim 1, forming a unidirectional transducer means, wherein the filamentary conductors are separate J shapes, the said first region comprises two equal parts in a common acoustic wave track, and a transducer means is disposed between the two equal parts of the first region so that acoustic surface wave signals propagated from the transducer means in opposite directions will reach the two equal parts of 
     
     
        the first region in phase with each other. 24. An acoustic surface wave device as claimed in claim 1, forming a tapped delay line and comprising a plurality of unidrectional transducers wherein the coupling means are fractional coupling means as hereinbefore defined and the long ends of the J-shaped filamentary conductors extend over successive parts of the delay 
     
     
        line track. 25. An acoustic surface wave device as claimed in claim 1, wherein the coupling means is a 3db coupler as hereinbefore defined, a third transducer means identical to the second transducer means is provided to receive acoustic surface wave signals passed by the coupling means in the first track, the second and the third transducer means are connected to equivalent circuits, and acoustic surface wave absorbing material is deposited in the part of the second track on the opposite side 
     
     
        of the coupling means from the second and third transducer means. 26. An acoustic surface wave delay line device including a track changer as 
     
     
        claimed in claim 23 and a reflector. 27. An acoustic surface wave device, forming an amplifying track changer, as claimed in claim 1, wherein the coupling means is a 3dB coupler as hereinbefore defined, the second transducer means is a unidirectional transducer, an identical unidirectional transducer is disposed to receive acoustic surface wave signals passed by the coupling means in the first track, and the transducer means of both unidirectional transducers are connected to 
     
     
        similar negative-resistance amplifying circuits. 28. An acoustic surface wave device for use as a directional filter comprising a plurality of transducer means as claimed in claim 1, disposed to direct acoustic surface wave signals around a circuit of acoustic surface wave tracks, a plurality of additional coupling means extending over separate parts of the circuit, an input transducer means for launching acoustic surface wave signals towards one of the additional coupling means, and at least one output transducer means disposed for receiving acoustic surface wave 
     
     
        signals from one of the additional coupling means. 29. An acoustic surface wave device as claimed in claim 1 wherein there are two separate coupling means each extending over the first track and the second track, and a region of controllable acoustic velocity is formed in one of the tracks 
     
     
        between the two separate coupling means. 30. An acoustic surface wave device as claimed in claim 1 wherein successive filamentary conductors of the coupling means are of linearly decreasing length, for beam-splitting 
     
     
        antisymmetric mode signals. 31. An acoustic surface wave device as claimed in claim 1, wherein the leading filamentary conductors of the coupling means are V-shaped with angles which are successively increased towards 
     
     
        180°. 32. An acoustic surface wave device as claimed in claim 1, wherein the leading filamentary transducers of the coupling means increase 
     
     
        monotonically in length. 33. An acoustic surface wave device as claimed in claim 1, wherein the filamentary conductors of the coupling means also 
     
     
        extend over a region of controllable electrical impedance. 34. An acoustic surface wave device as claimed in claim 34; wherein the said region of controllable electrical impedance is formed of a photoconductive material. 
     
     
        5. An acoustic surface wave device as claimed in claim 1, wherein the filamentary transducers of the coupling means are electrically connected 
     
     
        to an array of field effect transistors. 36. An acoustic surface wave device as claimed in claim 1, wherein two arrays of diodes are connected to opposite ends of the filamentary transducers, thereby forming a plurality of connections each comprising two diodes connected in series by 
     
     
        a filamentary conductor of the coupling means. .Iadd.37.  An acoustic surface wave device as claimed in claim 1 wherein the filamentary conductors in said first and second regions are spaced apart by equal amounts. .Iaddend. .Iadd.38. An acoustic surface wave device as claimed in claim 1 wherein the filamentary conductors in said first and second regions are spaced apart by randomly varying amounts. .Iaddend. .Iadd.39. An acoustic surface wave device as claimed in claim 1 wherein the filamentary conductors in said first and second regions are spaced apart by regularly varying amounts..Iaddend. .Iadd.40. An acoustic surface wave device as claimed in claim 1 wherein the filamentary transducers in said first and second regions are spaced apart by monotonically varied amounts. .Iaddend. .Iadd.41. An acoustic surface wave device as claimed in claim 1 wherein said first and second tracks are formed on a flat surface of a piezo electric substrate, said means for launching surface acoustic waves along the first track comprising an input interdigital transducer for launching surface waves along the first track on said surface, said means for receiving and detecting acoustic surface wave energy traveling along the second track comprising an output interdigital transducer on said surface located to receive surface waves from said second track, said second track being separate from and parallel to said first track, said coupling means comprising a plurality of electrically separate filamentary conductors each of which is arranged with one end portion thereof orthogonally across said first track and another end portion thereof orthogonally across said second track, said conductors being spaced uniformly and parallel to one another at their said end portions. .Iaddend.