Compression accelerometer utilizing a lithium niobate piezoelectric crystal

Abstract

The transducer of this invention utilizes an annular lithium niobate crystal operated in the compression mode with the sensitive axis of the crystal arranged at an angle of about -51.4° to the Z, or optical, axis of the crystal in the first and third quadrants of the Y-Z plane of the crystal. This accelerometer has high efficiency and operates effectively over a wide range of temperatures, including high temperatures above 1000° F.

The invention claimed is: 
     
       1. In a transducer of the compression type in which an electrical signal is developed across two flat parallel faces of a piezoelectric element in response to the relative motion of two mechanical members adapted to move relatively to each other in response to forces parallel to an axis perpendicular to such faces, said element being mounted between said two mechanical members, and in which means are provided for conducting such electrical signal to a utilization device responsive thereto, the improvement wherein said piezoelectric element comprises a lithium niobate crystal having its Z-axis at an angle of about -51.4° ± 10° to an axis normal to said parallel faces. 
     
     
       2. A transducer defined in claim 1 comprising an accelerometer wherein said element is of cylindrical configuration and in which one of said two members constitutes an inertial member supported by said element from the other of said two members and wherein said electrical signal is developed in response to the acceleration of an object that is secured to the other of said two members. 
     
     
       3. An accelerometer as defined in claim 2 wherein one of said members has a base provided with a base surface attachable to the surface of said accelerating object, said base surface being in a plane parallel to said flat parallel surfaces of said element. 
     
     
       4. An accelerometer as defined in claim 3 wherein communication is provided between said crystal and an oxygen containing atmosphere and providing a cover member cooperating with one of said two members for enclosing said crystal. 
     
     
       5. An accelerometer as defined in claim 2 comprising at least two annular piezoelectric elements mounted on a post secured to said base and having their sensitive axes anti-parallel with the outer surfaces thereof electrically connected together and having a common electrode between adjacent surfaces. 
     
     
       6. A transducer as defined in claim 1 in which said element has a central hole therein and a post extends through said element, said two members being composed of metal. 
     
     
       7. In a transducer of the compression type in which an electrical signal is developed across two flat parallel faces of a piezoelectric element in response to the relative motion of two mechanical members adapted to move relatively to each other in a direction perpendicular to such faces, which element is mounted between said two mechanical members, and in which means are provided for conducting such electrical signal to a utilization device responsive thereto, the improvement wherein said piezoelectric element comprises a lithium niobate crystal containing impurities, said crystal having a Z axis rotated θ° ± 10° from an axis normal to said parallel faces, the angle θ being the counterclockwise angle through which the Z-axis is rotated about the X axis such that the d 34  piezoelectric coefficient is equal to zero. 
     
     
       8. A transducer as defined in claim 7 wherein the angle θ is equal to about  .Badd..[.51.4°.]..Baddend. .Iadd.-51.4°.Iaddend.. .Iadd. 9. In a piezoelectric device including at least one transducer element comprising a piezoelectric crystal, the improvement according to which said piezoelectric crystal is cut from a larger crystal of lithium niobate, said crystal having a crystal orientation selected from the following:   (yxl) +38.6° (±1°), (zxtl) +60° (±1°)/+51.4° (±1°),     or a symmetrical equivalent thereof. .Iaddend..Iadd. 10. The improvement according to claim 9 in which   said cut crystal, has a (yxl) +38.6° (±1°) orientation or a symmetrical equivalent thereof. .Iaddend. .Iadd. 11. The invention according to claim 9 in which said cut crystal, has a (zxtl) +60° (±1°)/+51.4° (±1°) orientation or a symmetrical equivalent thereof. .Iaddend..Iadd. 12. In an accelerometer wherein a piezoelectric crystal is operatively associated in a compressional relationship with an inertial member, the improvement according to which said piezoelectric crystal is cut from a larger crystal of lithium niobate, said cut crystal, having a crystal orientation selected from the following:   (yxl) +38.6° (±1°) and (zxtl) +60° (±1°)/+51.4° (±1°),     or a symmetrical equivalent thereof. .Iaddend..Iadd. 13. The improvement according to claim 12 in which said cut crystal, has a (yxl) +38.6° (±1°) orientation or a symmetrical equivalent thereof. .Iaddend..Iadd. 14. The improvement according to claim 12 in which said cut crystal, has a (zxtl) +60° (±1°)/+51.4° (±1°) orientation or a symmetrical equivalent thereof. .Iaddend. .Iadd. 15. A single crystal of lithium niobate having a crystal orientation selected from the following:     (yxl) +38.6° (±1°), and (zxtl) +60° (±1°)/+51.4° (±1°). .Iaddend. .Iadd. 16. The single crystal plate of claim 15 having a (yxl) +38.6° (±1°) orientation. .Iaddend..Iadd.17. The single crystal plate of claim 15 having a (zxtl) +60° (±1°)/+51.4° (±1°) orientation. .Iaddend..Iadd. 18. In an accelerometer wherein a piezoelectric crystal is operatively associated in a compressional relationship with an inertial member, the improvement according to which said piezoelectric crystal is cut from a larger crystal of lithium niobate, said cut crystal, having a crystal orientation selected from the following:       (yxl) +38.6° (±1°) and (zxtl) +60° (±1°)/51.4° (±1°),     or a symmetrical equivalent thereof. .Iaddend. .Iadd. 19. In a piezoelectric device including at least one transducer element comprising a piezoelectric crystal operatively associated with means for compressing said crystal and electrodes for detecting resultant electrical fields developed in the direction of compression, the improvement according to which said piezoelectric crystal is cut from a larger crystal of lithium niobate, said cut crystal having a crystal orientation of (zxl) -51.4° (±10°). .Iaddend. .Iadd. 20. In an accelerometer wherein a piezoelectric crystal is operatively associated in a compressional relationship with an inertial member, the improvement according to which said piezoelectric crystal is cut from a larger crystal of lithium niobate, said cut crystal, having a crystal orientation of (zxl) -51.4° (±10°). .Iaddend.