Acoustic wave devices
First Claim
1. In a surface acoustic wave (SAW) device including input means for generating acoustic waves, output means for delivering a signal from the device and a frequency-selective reflective array which comprises a plurality of parallel rows of individual scatterers, each scatterer forming one or more scattering centres from which acoustic waves, generated by the input means and propagated to the array, are scattered in a desired predetermined direction by Bragg reflection, the improvement consisting essentially of and in combination with the above elements:
- the scatterers being disposed such that the local spacing between scattering centres, in relation to the acoustic wavelength at the frequency at which Bragg reflection occurs in the desired direction, said Bragg reflection frequency being determined by the inter-row spacing associated with the row or rows containing those scattering centres, causes the acoustic waves scattered from the individual scattering centres at the Bragg reflection frequency to constructively interfere in the desired predetermined direction and to not constructively interfere in directions other than the desired direction.
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Accused Products
Abstract
A surface acoustic wave reflective array of the kind in which parallel rows of scatterers produce Bragg reflection of an incident wave in a wanted direction at a given frequency determined by the row spacing. The rows (4) are formed of scattering centers, eg metallized dots (11) divisible into unit structures (10) each containing a group of at least two such centers; the orientation and relative spacings (in terms of the Bragg wavelength) of the centers within each unit, relative to the direction (Z) of an incident beam, are such that the scattered waves constructively interfere in the wanted direction (X) while avoiding constructive interference in other directions. The scattering centers of each unit structure may be in the same row or in adjacent rows. The invention alleviates a disadvantage of existing reflective dot arrays, which tend additionally to produce reflections in unwanted directions.
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Citations
26 Claims
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1. In a surface acoustic wave (SAW) device including input means for generating acoustic waves, output means for delivering a signal from the device and a frequency-selective reflective array which comprises a plurality of parallel rows of individual scatterers, each scatterer forming one or more scattering centres from which acoustic waves, generated by the input means and propagated to the array, are scattered in a desired predetermined direction by Bragg reflection, the improvement consisting essentially of and in combination with the above elements:
the scatterers being disposed such that the local spacing between scattering centres, in relation to the acoustic wavelength at the frequency at which Bragg reflection occurs in the desired direction, said Bragg reflection frequency being determined by the inter-row spacing associated with the row or rows containing those scattering centres, causes the acoustic waves scattered from the individual scattering centres at the Bragg reflection frequency to constructively interfere in the desired predetermined direction and to not constructively interfere in directions other than the desired direction. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A surface acoustic wave (SAW) device, comprising:
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a substrate for propagating surface acoustic waves; an input transducer, integrated onto the substrate for generating surface acoustic waves in response to an input signal coupled to the SAW device; a frequency-selective reflective array for receiving surface acoustic waves generated by the input transducer and propagated along the substrate, and (b) Bragg reflecting them in a predetermined desired direction, the array comprising a plurality of rows of individual scatterers, each scatterer forming one or more scattering centres; the scatterers being disposed such that local spacing between scattering centres, in relation to the acoustic wavelength at the frequency at which Bragg reflection occurs in the desired direction said Bragg reflection frequency being determined by the inter-row spacing associated with the row or rows containing those scattering centres, causes the acoustic waves scattered by individual scattering centres at the Bragg reflection frequency to constructively interfere in the desired direction and to not constructively interfere in directions other than the desired direction; and an output transducer, integrated onto said substrate for (a) receiving acoustic surface waves reflected by the array and propagated by the substrate and (b) generating an output signal of the SAW device. - View Dependent Claims (15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26)
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Specification