Surface acoustic wave modulator using single crystal films of lithium ferrite

• US 4,177,438 A
• Filed: 07/18/1978
• Issued: 12/04/1979
• Est. Priority Date: 07/18/1978
• 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: Vittoria, Carmine
• Primary Examiner(s): Gensler, Paul L.
• Assistant Examiner(s): Nussbaum, Marvin
• Application Number:
  US05/925,726
• Time in Patent Office: 504 Days
• Field of Search: 333/193-196, 333/150-155, 333/147-148, 310/313, 310/26, 331/107 A, 330/5.5, 332/51 R, 332/51 W, 332/51 H, 332/26, 364/821-823, 365/157, 365/171, 365/172
• US Class Current: 333/152
• CPC Class Codes: H03H 9/423 with adjustable delay time
• CPC Class Codes: H03H 9/426 Magneto-elastic surface waves

Abstract

A surface acoustic wave (SAW) device formed by an unitary insulating, magostrictive ferrite, slab whose easy axis of magnetization is initially (prior to the application of a d.c. magnetic biasing field) perpendicular to the direction of SAW-wave propagation. For example, the easy axis of magnetization in a single-crystal lithium ferrite slab is the <111> axis. Therfore this axis is aligned perpendicular to the SAW wave propagation direction and parallel to the edges of the SAW device. Application of a dc magnetic field swings the magnetic moments such that they will be parallel with the SAW wave propagation. Materials useful in carrying out this invention are those which have (1) an easy axis of magnetization, (2) good insulator qualities and (3) the magnetostrictive property. A dc magnetic field is applied parallel with the SAW direction or perpendicular to the easy axis of the material in order to align the magnetic moments in the direction of the SAW wave propagation. Such alignment of the magnetic moments of the material causes a delay in propagation time of the SAW wave.

Claims

1. A continuously tunable SAW device comprising:

a slab of material comprising a unitary piece of magnetostrictive, insulating crystalline material having at least one flat surface;

input transducer means mounted on said flat surface of said slab of material for propagating an acoustic wave along said flat surface of said slab of material;

output transducer means mounted on the same flat surface of said slab of material as said input transducer and spaced therefrom for receiving said acoustic wave propagated by said input transducer; and

means for applying a variable dc magnetic field in the direction of and along the propagation path of said acoustic wave for varying the propagation time of said acoustic wave between said input and output transducer means.

2. A SAW device as claimed in claim 1 wherein:

said input transducer is positioned on said flat surface such that an acoustic wave propagated thereby is perpendicular to the easy axis of magnetization of said slab of material.

3. A SAW device as claimed in claim 1 wherein:

said slab of material is lithium ferrite.

4. A SAW device as claimed in claim 3 wherein:

said slab of material is a single crystal with its <

111>

crystal axis perpendicular to the wave propagation.

5. A SAW device as claimed in claim 2 wherein:

the easy axis of magnetization of said crystalline material is its <

111>

crystal axis perpendicular to the wave propagation.

6. A SAW device as claimed in claim 5 wherein:

said slab of material has a thickness of about 20 μ

m and the transducers are separated by about 1 cm.

7. A SAW device as claimed in claim 2 wherein:

said slab crystalline material comprises a spinel and garnet ferrite.

8. A SAW device as claimed in claim 2 wherein:

said slab of crystalline material comprises a ferrite material of a hexagonal magento-plumbite (BaFe_12-2x P_x Q_x O₁₉) where P and Q are impurities whose valances add up to a positive 6.