Surface acoustic wave transducer with internal acoustic reflection

Claim 2

A surface acoustic wave transducer comprising: a piezoelectric substrate; a first comb-shaped electrode formed on one surface of the piezoelectric substrate and having a plurality of parallel strips extending at right angles to the direction in which surface acoustic waves propagate; and a second comb-shaped electrode formed on the piezoelectric substrate and having a plurality of parallel strips interdigitated with the strips of said first comb-shaped electrode, extending at right angles to the direction in which the waves propagate; the parallel strips provided in at least one of said first and second comb-shaped electrodes having each a first portion which corresponds to said first portion and which only electrically reflects the waves and a second portion which both electrically and acoustically reflects the waves, and an effective length of said second portion being weighted in a propagation direction of a surface acoustic wave in a predetermined fashion.

Claim 3

A surface acoustic wave transducer comprising: a piezoelectric substrate; a first comb-shaped electrode formed on one surface of the piezoelectric substrate and having a plurality of parallel strips extending at right angles to the direction in which surface acoustic waves propagate; and a second comb-shaped electrode formed on the piezoelectric substrate and having a plurality of parallel strips interdigitated with the strips of said first comb-shaped electrode, extending at right angles to the direction in which the waves propagate; the parallel strips provided in at least one of said first and second comb-shaped electrodes having each a first portion which only electrically reflects the waves and a second portion which corresponds to said first portion and which both electrically and acoustically reflects the waves, and an envelope of an effective length of said second portion being substantially a self-convolution of an envelope of an overlap region of said interdigitated parallel strips of said first and second comb-shaped electrodes.

Claim 4

A surface acoustic wave transducer comprising: a piezoelectric substrate; a first comb-shaped electrode formed on one surface of the piezoelectric substrate and having a plurality of parallel strips extending at right angles to the direction in which surface acoustic waves propagate; and a second comb-shaped electrode formed on the piezoelectric substrate and having a plurality of parallel strips interdigitated with the strips of said first comb-shaped electrode, extending at right angles to the direction in which the waves propagate; the parallel strips provided in at least one of said first and second comb-shaped electrodes having each a first portion which only electrically reflects the waves and a second portion which corresponds to said first portion and which both electrically and acoustically reflects the waves, and an envelope of an effective length of said second portion being substantially a self-convolution of an envelope of an overlap region of said interdigitated parallel strips of said first and second comb-shaped electrodes.

Claim 5

A surface acoustic wave transducer comprising: a piezoelectric substrate; a first comb-shaped electrode formed on one surface of the piezoelectric substrate and having a plurality of parallel strips extending at right angles to the direction in which surface acoustic waves propagate; and a second comb-shaped electrode formed on the piezoelectric substrate and having a plurality of parallel strips interdigitated with the strips of said first comb-shaped electrode in a predetermined overlap length weighting fashion for forming therein an overlap region and non-overlap region, extending at right angles to the direction in which the waves propagate; the parallel strips provided in at least one of said first and second comb-shaped electrodes having each a first portion which only electrically reflects the waves and a second portion which corresponds to said first portion and which both electrically and acoustically reflects the waves, and an envelope of an effective length of said second portion being substantially a self-convolution of an envelope of an overlap region of said interdigitated parallel strips of said first and second comb-shaped electrodes.

Claim 6

A surface acoustic wave transducer comprising: a piezoelectric substrate; a first comb-shaped electrode formed on one surface of the piezoelectric substrate and having a plurality of parallel strips extending at right angles to the direction in which surface acoustic waves propagate; and a second comb-shaped electrode formed on the piezoelectric substrate and having a plurality of parallel strips interdigitated with the strips of said first comb-shaped electrode in a predetermined overlap length weighting fashion for forming therein an overlap region and non-overlap region, extending at right angles to the direction in which the waves propagate; the parallel strips provided in at least one of said first and second comb-shaped electrodes having each a first portion which only electrically reflects the waves and a second portion which corresponds to said first portion and which both electrically and acoustically reflects the waves, and an envelope of an effective length of said second portion being substantially a self-convolution of an envelope of an overlap region of said interdigitated parallel strips of said first and second comb-shaped electrodes.

Claim 7

A surface acoustic wave transducer according to claim 2 or 3, wherein the first and second portions are provided in said first and second comb-shaped electrodes and the second portions of the strips of said first comb-shaped electrode are interdigitated with the second portions of the strips of said second comb-shaped electrode in such a manner that a width of the interdigitated electrodes vary with a predetermined envelope.

Claim 8

A surface acoustic wave transducer according to claim 4, wherein said first portions have the same width of λ/8, where λ is the wavelength of the surface acoustic waves, and are spaced apart from each other for a distance of λ/8, and each of said second portions is that portion of a strip which is about λ/16 wide, narrower than the end portions, or 3λ/16 wide, broader than the end portions.

Claim 9

A surface acoustic wave transducer according to claim 4, wherein said first portions include: (a) those portions of the strips of said first comb-shaped electrode which are located outside said diamond-shaped envelope and have the same width of about λ/8, and (b) those portions of the strips of said second comb-shaped electrode which are located outside said diamond-shaped envelope and have the same width of about 5λ/8; and said second portions include: (c) the other portions of said first comb-shaped electrode which are located inside said diamond-shaped envelope and have the same width of about λ/8, and (d) those portions of the strips of said second comb-shaped electrode which are located inside said diamond-shaped envelope and have the same width of about 5λ/8, each of these portions having a slit which extends over the entire length of the portion at right angles to the direction of propagation of the waves, and defines a strip having a width of about λ/8 and another strip having a width of about 3λ/8.

Claim 10

A surface acoustic wave transducer according to claim 4, wherein said first portions include: (a) those portions of the strips of said first comb-shaped electrode which have the same width of about λ/8, and (b) those portions of the strips of said second comb-shaped electrode which have the same width of about 5λ/8; and said second portions include: (c) the other portions of said first comb-shaped electrode which have the same width of about λ/8, and (d) those portions of the strips of said second comb-shaped electrode which have the same width of about 5λ/8 and have each a plurality of slits having the same width of λ/8, being aligned and spaced apart for a predetermined distance along a straight line at right angles to the direction of propagation of the waves, and defining a strip having a width of about λ/8 and another strip having a width of about 3λ/8.

Claim 11

A surface acoustic wave transducer according to claim 4, wherein said first portions include: (a) those portions of the strips of said first comb-shaped electrode which have the same width of about λ/8, and (b) those portions of the strips of said second comb-shaped electrode which have the same width of about λ/8; and said second portions include: (c) the other portions of said first comb-shaped electrode which have the same width of about λ/8 and each a plurality of wave-reflecting strips formed at predetermined positions, and (d) those portions of the strips of said second comb-shaped electrode which have the same width of about λ/8 and have each a plurality of wave-reflecting strips formed at predetermined positions.

Claim 12

A surface acoustic wave transducer according to claim 8, wherein each strip of said first comb-shaped electrode is interdigitated with the adjacent strip of said second comb-shaped electrode for a distance determined by a specially weighted interdigitated pattern.

Claim 13

A surface acoustic wave transducer according to claim 8, wherein said wave-reflecting strips are made of chromium.

Claim 14

A surface acoustic wave transducer according to claim 4, wherein said first portions are the strips of said first and second comb-shaped electrodes, which have the same width of about λ/8 and are spaced apart from each other for a distance of λ/8; and said second portions are a plurality of wave-reflecting strips electrically isolated from said first and second comb-shaped electrodes and arranged in columns extending at right angles to the direction of propagation of the surface acoustic waves.