Tapped surface acoustic wave delay line

• US 4,088,969 A
• Filed: 04/19/1977
• Issued: 05/09/1978
• Est. Priority Date: 04/19/1977
• Status: Expired due to Term

• Current Assignee: the united states of america as represented by the secretary of the navy
• Original Assignee: the united states of america as represented by the secretary of the navy
• Inventors: Giallorenzi, Thomas G., Weller, Joseph F., Crowley, James D.
• Primary Examiner(s): Smith, Alfred E.
• Assistant Examiner(s): Nussbaum, Marvin
• Application Number:
  US05/788,874
• Time in Patent Office: 385 Days
• Field of Search: 333/30 R, 333/72, 333/71, 333/70 T, 330/5.5, 310/313, 331/107 A, 364/819, 364/821, 364/836, 364/860, 350/161 P, 350/161 S, 350/161 W
• US Class Current: 333/153
• CPC Class Codes: G10K 11/36 Devices for manipulating acoustic surface waves electro-acoustic amplifiers H03F13/00; networks comprising electro-acoustic elements H03H9/00
• CPC Class Codes: H03F 13/00 Amplifiers using amplifying element consisting of two mechanically- or acoustically-coupled transducers, e.g. telephone-microphone amplifier
• CPC Class Codes: H03H 9/423 with adjustable delay time

Abstract

A tapped surface acoustic wave (SAW) delay line with time-resolved outputssing piezoelectric leaky wave coupling and bulk wave amplification, and having low loss characteristics. A solid piezoelectric semiconductor is placed adjacent to a solid piezoelectric substrate. A pulsed rf input signal is applied to interdigital transducers (IDT) on the substrate. The applied signal launches a SAW in the substrate in a direction parallel to the interface between the substrate and the piezoelectric semiconductor solid. Upon reaching the interface, the SAW is piezoelectrically leaky-wave coupled across an air gap to a bulk acoustic wave in the piezoelectric semiconductor. Reflections of the bulk wave occur at both surfaces of the piezoelectric semiconductor, and piezoelectrically couples back across the air gap to excite a SAW on the piezoelectric substrate. The resultant rf output includes the normal delayed SAW pulse and additional delayed and time-resolved pulses. The amplitude of the bulk wave may be increased using bulk wave amplification.

Claims

1. A delay line comprising:

a piezoelectric acoustically elastic substrate having a substantially planar surface with a first velocity of elastic wave propagation;

a first electroacoustic transducer mounted on said surface for transforming electromagnetic energy into a surface acoustic wave and propagating said surface acoustic wave in a given direction along said surface;

a second electroacoustic transducer mounted on said surface and spaced from said first transducer in said given direction, for receiving acoustic waves and transforming them into electromagnetic energy;

a piezoelectric element having substantially planar and parallel, first and second opposed surfaces, the first surface being placed near the surface of said substrate but separated therefrom by an air gap which is less than the wavelength of said surface acoustic wave, said element being located between said transducers and having a second-velocity of bulk acoustic wave propagation which is less than said first velocity of surface acoustic wave propagation, any surface acoustic wave generated by said first transducer along the surface of said substrate exciting a bulk wave in said element by means of piezoelectric leaky-wave coupling, said bulk wave propagating within said element and being reflected from the second to the first surface where it piezoelectrically leaky-wave couples back to the substrate to excite a second surface acoustic wave delayed with respect to the first surface acoustic wave.

2. The delay line of claim 1, wherein said piezoelectric element is fabricated from piezoelectric semiconductor material.

3. The delay line of claim 1, further including spacer means placed between said element and substrate to form the air gap.

4. The delay line of claim 1, wherein said first electroacoustic transducer applies pulsed electromagnetic energy to the substrate.

5. The delay line of claim 1, wherein said piezoelectric substrate is cut in a predetermined direction to facilitate piezoelectric coupling and aid in obtaining phase-matching between said acoustic surface waves and said excited bulk waves in the piezoelectric element.

6. The delay line of claim 1, further including a thin metal coating on a predetermined portion of the lower surface of the piezoelectric element to short electric fields of acoustic surface waves generate on the substrate.

7. The delay line of claim 3, further including means for applying an electric field across the piezoelectric semiconductor causing current carriers in said piezoelectric element to flow substantially in said given direction at a velocity slightly greater than said second velocity so as to amplify the bulk waves travelling in said piezoelectric semiconductor.

8. The delay line of claim 7, wherein said first electroacoustic transducer applies pulsed electromagnetic energy to the substrate.

9. The delay line of claim 7, wherein said piezoelectric substrate is cut in a predetermined direction to facilitate piezoelectric coupling and aid in obtaining phase-matching between said acoustic surface waves and said excited bulk waves.

10. The delay line of claim 7, further including a thin metal coating on a predetermined portion of the lower surface of the piezoelectric element to short electric fields of acoustic surface saves generated on the substrate.

11. An acoustic delay line amplifier, comprising:

a piezoelectric substrate cut in a predetermined direction having an optically polished, substantially planar longitudinal upper surface;

means for generating surface acoustic waves on said surface;

said waves propagating at a first velocity in a given direction;

a piezoelectric semiconductor element disposed substantially parallel and adjacent to said pieszoelectric substrate, separated therefrom by an air gap, said semiconductor element having a c-axis oriented in a predetermined direction to the planar surface of said substrate, and a second velocity of propagation for bulk waves which is less than said first velocity;

said semiconductor element being oriented such that bulk waves are excited by said surface acoustic waves in such a direction and at such a phase velocity as to obtain phasematching of said surface acoustic and bulk waves;

spacer means disposed between said substrate and said piezoelectric semiconductor element to separate them and form said air gap of predetermined, substantially uniform spacing which is less than the acoustic wavelength of said surface acoustic wave, such waves propagating along the planar surface of said substrate exciting bulk waves in said semiconductor element by means of piezoelectric leaky-wave coupling through said air gap, said bulk waves having a travelling electric field within said semiconductor element;

means for applying a pulsed electric field across the piezoelectric semiconductor element causing charge carriers in said piezoelectric element to flow substantially in said given direction at a velocity slightly greater than said second velocity to amplify the bulk waves travelling in said piezoelectric semiconductor; and

means for extracting surface acoustic waves from said substrate, separated from said means for generating said surface acoustic waves in the longitudinal direction.

12. The delay line amplifier of claim 11, further including a thin metal coating on a predetermined portion of the lower surface of the piezoelectric semiconductor element to short electric fields of surface acoustic waves generated on the substrate.