Acoustic surface wave filter

Claim 2

In a selective transmission device having a medium propagative of surface and bulk acoustic waves, an input transducer disposed on a surface of said medium and responsive to an input signal for launching desired surface waves along a selected path in said surface and also productive of undesired bulk waves traveling in the body of said medium along a predetermined path and an output transducer disposed on said surface of said medium responsive to said surface waves for developing an output signal while also being capable of responding to bulk waves by developing spurious signals, the improvement comprising: diverting means included in said device for modifying the direction of said selected path to enable response of said output transducer to said surface waves while substantially reducing response of said output transducer to said bulk waves; and means disposed in said selected path beyond said divertIng means for dissipating surface waves.

Claim 3

A device as defined in claim 1 in which said diverting means includes a reflector disposed on said surface in said path selected for reflecting to said output transducer surface waves received from said input transducer.

Claim 4

A device as defined in claim 2 in which said output transducer has a greater width across said selected path than that of said input transducer.

Claim 5

A device as defined in claim 2 in which said input and output transducers have substantially the same width across said selected path.

Claim 6

A device as defined in claim 2 in which each one of said input and output transducers is disposed at least partially in the portion of said selected path between said reflector and the other.

Claim 7

A device as defined in claim 2 in which each one of said input and output transducers is disposed in a portion of said selected path exclusive of that of the other.

Claim 8

In a selective transmission device having a medium propagative of surface and bulk acoustic waves, an input transducer disposed on a surface of said medium and responsive to an input signal for launching desired surface waves along a selected path in said surface and also productive of undesired bulk waves traveling in the body of said medium along a predetermined path and an output transducer disposed on said surface of said medium responsive to said surface waves for developing an output signal while also being capable of responding to bulk waves by developing spurious signals, the improvement comprising: diverting means, including a pair of reflectors successively disposed on said surface in said selected path with the first of said reflectors reflecting to the second waves received from said input transducer and the second of said reflectors reflecting to said output transducer waves received from the first, for modifying the direction of said selected path relative to said predetermined path to enable response of said output transducer to said surface waves while substantially reducing response of said output transducer to said bulk waves.

Claim 9

In a selective transmission device having a medium propagative of surface and bulk acoustic waves, an input transducer disposed on a surface of said medium and responsive to an input signal for launching desired surface waves along a selected path in said surface and also productive of undesired bulk waves traveling in the body of said medium along a predetermined path and an output transducer disposed on said surface of said medium responsive to said surface waves for developing an output signal while also being capable of responding to bulk waves by developing spurious signals, the improvement comprising: diverting means, including a pair of reflectors successively disposed on said surface in said selected path with the first of said reflectors reflecting to the second waves received from said input transducer and the second of said reflectors reflecting to said output transducer waves received from the first, for modifying the direction of said selected path relative to said predetermined path to enable response of said output transducer to said surface waves while substantially reducing response of said output transducer to said bulk waves.

Claim 10

A device as defined in claim 7 in which said reflectors are each disposed at an angle of 45* to said selected path and at a right angle with respect to each other.

Claim 11

A device as defined in claim 7 in which said medium is anisotropically piezoelectric, and in which both said input and output transducers are oriented in a direction effecting substantially maximum transducer coupling factor.

Claim 12

In a selective transmission device having a medium propagative of surface and bulk acoustic waves, an input transducer disposed on a surface of said medium and responsive to an input signal for launching desired surface waves along a selected path in said surface and also productive of undesired bulk waves traveling in the body of said medium along a predetermined path and an output transducer disposed on said surface of said medium responsive to said surface waves for developing an output signal while also being capable of responding to bulk waves by developing spurious signals, the improvement comprising: diverting means included in said device for modifying the direction of one of said paths relative to the other in an amount effecting presentation of said bulk waves to said output transducer with at least substantially an effective 2 pi total range of phase variation.

Claim 13

In a selective transmission device having a medium propagative of surface and bulk acoustic waves, an input transducer disposed on a surface of said medium and responsive to an input signal for launching desired surface waves along a selected path in said surface and also productive of undesired bulk waves traveling in the body of said medium along a predetermined path and an output transducer disposed on said surface of said medium responsive to said surface waves for developing an output signal while also being capable of responding to bulk waves by developing spurious signals, the improvement comprising: diverting means included in said device for modifying the direction of one of said paths relative to the other in an amount effecting presentation of said bulk waves to said output transducer with at least substantially an effective 2 pi total range of phase variation.

Claim 14

A device as defined in claim 10 in which said medium is anisotropically piezoelectric, and in which the orientation of both said input and output transducers is selected, relative to an orientation effecting maximum transducer response at a desired center frequency, such that deviation in orientation effects like variation in center frequency in both of said transducers.

Claim 15

A device as defined in claim 11 in which the orientation of said transducers is selected in satisfaction of the relationship: d2Vs/dP2 0 where Vs is the surface-wave velocity and P Is the direction of propagation.

Claim 16

In a selective transmission device having a medium propagative of surface and bulk acoustic waves, an input transducer disposed on a surface of said medium and responsive to an input signal for launching desired surface waves along a selected path in said surface and also productive of undesired bulk waves traveling in the body of said medium along a predetermined path and an output transducer disposed on said surface of said medium responsive to said surface waves for developing an output signal while also being capable of responding to bulk waves by developing spurious signals, the improvement comprising: diverting means, including a material disposed on said surface in said selected path between said input and output transducer, for modifying the velocity of propagation of said surface waves unequally across the width of said selected path, said output transducer being oriented relative to the concomitant change in direction of said selected path in a manner to exhibit substantially maximum response to said surface waves and also being oriented to exhibit substantially minimum response to said bulk waves.

Claim 17

In a selective transmission device having a medium propagative of surface and bulk acoustic waves, an input transducer disposed on a surface of said medium and responsive to an input signal for launching desired surface waves along a selected path in said surface and also productive of undesired bulk waves traveling in the body of said medium along a predetermined path and an output transducer disposed on said surface of said medium responsive to said surface waves for developing an output signal while also being capable of responding to bulk waves by developing spurious signals, the improvement comprising: diverting means, including a material disposed on said surface in said selected path between said input and output transducer, for modifying the velocity of propagation of said surface waves unequally across the width of said selected path, said output transducer being oriented relative to the concomitant change in direction of said selected path in a manner to exhibit substantially maximum response to said surface waves and also being oriented to exhibit substantially minimum response to said bulk waves.

Claim 18

A device as defined in claim 13 in which said material is affixed to said surface and has a length along said selected path that changes across said width.

Claim 19

A device as defined in claim 13 in which said diverting means tilts said selected path by an angle Alpha , in which said output transducer is oriented relative to the tilted path to exhibit substantially maximum response to said surface waves at a desired center frequency, and in which said output transducer also is oriented relative to said bulk waves in substantial satisfaction of the relationship: W Alpha n lambda . where W is the wavefront width of said surface waves, n is an integer other than zero, and lambda is the apparent wavelength at the surface for the bulk waves.

Claim 20

A device as defined in claim 13 in which said material effectively is of right-triangular shape, having a base parallel to and facing said input transducer and a hypotenuse facing said output transducer and defining an angle with respect to said input transducer satisfying the relationship: sin gamma /sin ( gamma + Alpha ) Vsm/Vs, where gamma is the angle between said selected path initiating from said input transducer and a normal to said hypotenuse, Alpha is the angle by which said output transducer is tilted from a normal to said selected path initiating from said input transducer, Vsm is the velocity of surface-wave propagation in the portion of said medium underlying said material and Vs is the velocity of surface wave propagation in portions of said medium free of said material.

Claim 21

A device as defined in claim 13 in which said material effectively is of triangular shape, having a first interface facing said input transducer and defining an angle with respect thereto in accordance with the relationship: sin psi /sin sigma Vs/Vsm, where psi is the angle between the propagation vector of the surface waves initiating from said input transducer and a normal to said first interface, sigma is the angle between that same normal and the surface-wave propagation vector following said first interface, Vsm is the surface-wave velocity in the portion of said medium underlying said material and Vs is the surface-wave velocity in in portions of said medium free of said material; said material having a second interface facing said output transducer and defining an angle thereto in accordance with the relationship sin delta /sin epsilon Vsm/Vs, where delta is the angle between the normal to said second interface and the surface-wave propagation vector approaching said second interface and epsilon is the angle between the last-mentioned normal and the surface-wave propagation vector following said second inTerface.

Claim 22

A device as defined in claim 17 wherein said first and second interfaces together effect bending of said surface-wave propagation vector by an amount ( psi - sigma ) + ( epsilon -delta ), and in which said output transducer is tilted by said amount relative to said input transducer.

Claim 23

In a selective transmission device having a medium propagative of surface and bulk acoustic waves, an input transducer disposed on a surface ef said medium and responsive to an input signal for launching desired surface waves along a selected path in said surface and also productive of undesired bulk waves traveling in the body of said medium along a predetermined path and an output transducer disposed on said surface of said medium responsive to said surface waves for developing an output signal while also being capable of responding to bulk waves by developing spurious signals, the improvement comprising: diverting means, including an element disposed in said predetermined path, for modifying the direction of propagation of said bulk waves by an amount substantially inhibiting response by said output transducer thereto.

Claim 24

In a selective transmission device having a medium propagative of surface and bulk acoustic waves, an input transducer disposed on a surface ef said medium and responsive to an input signal for launching desired surface waves along a selected path in said surface and also productive of undesired bulk waves traveling in the body of said medium along a predetermined path and an output transducer disposed on said surface of said medium responsive to said surface waves for developing an output signal while also being capable of responding to bulk waves by developing spurious signals, the improvement comprising: diverting means, including an element disposed in said predetermined path, for modifying the direction of propagation of said bulk waves by an amount substantially inhibiting response by said output transducer thereto.

Claim 25

A device as defined in claim 17 in which said element is a face of said medium opposite said surface and defining a finite angle relative thereto.

Claim 26

A device as defined in claim 18 in which said angle is defined in a plane normal to said selected path and its value theta at least approximately satisfies the relationship: (W theta / lambda o)tan phi n/2, where W is the wavefront width across said selected path, lambda o is the wavelength of maximum response exhibited by said transducers, n is any integer other than zero and phi is the angle between said selected and predetermined paths.