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.
|
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°). 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°).
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. 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. 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. 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°).
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.
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 d34 piezoelectric coefficient is equal to zero.
2. A transducer defined in
3. An accelerometer as defined in
4. An accelerometer as defined in
5. An accelerometer as defined in
6. A transducer as defined in
8. A transducer as defined in
10. The improvement according to
said cut crystal, has a (yxl) +38.6° (±1°) orientation or a symmetrical equivalent thereof.
11. The invention according to
13. The improvement according to
14. The improvement according to
16. The single crystal plate of
|
|||||||||||||||||||||||||||
U.S. Pat. Application Ser. No. 50,657, filed June 29, 1970.
This invention relates to transducers and more particularly to a piezoelectric accelerometer which is of high efficiency and is adapted to be operative over a wide range of temperatures, including high temperatures above 1000° F.
The transducer of this invention makes use of a rotated Z-cut lithium niobate crystal of annular construction operated in the compression mode, thus taking optimum advantage of the characteristics of piezoelectric lithium niobate crystal material to achieve high sensitivity to compression forces in a high temperature environment. This invention will be described with reference to a compression accelerometer.
It is known that lithium niobate in monocrystalline form is piezoelectric and that its piezoelectric properties are preserved at high temperatures, such as at temperatures over 1400° F., as well as at a low temperature, such as temperatures of -60° F. The sensitivity of an accelerometer employing such a material depends in part on how the crystal is cut and how it is subjected to acceleration. This invention makes use of a rotated lithium niobate crystal operated in the compression mode with the axis of maximum sensitivity at an angle of about -51.4° from the Z, or optical, axis in the first and third quadrants of the Y-Z plane of the crystal. The electrodes are located on surfaces normal to the axis of maximum sensitivity and the compression forces are applied in directions perpendicular to these surfaces. This accelerometer not only has high sensitivity at high temperatures, but is also substantially free of cross-axis sensitivity. Furthermore, by taking special precautions, an accelerometer utilizing lithium niobate is provided for operating at such high temperatures over a long period of time.
This invention is particularly useful when employed as an accelerometer. Such an accelerometer has a high resonant frequency.
Various features of this invention are described below in connection with the accompanying drawings wherein:
FIG. 1 is an elevational view, partly in cross-section, of a balanced annular accelerometer of one embodiment constructed in accordance with this invention; and
FIG. 2 is a perspective view employed to explain the invention.
Referring to FIG. 1 there is illustrated an accelerometer 8 comprising a housing formed partly by a base 10 and a case 12 providing a cylindrical hollow cavity 14 and comprising a pair of acceleration sensing elements 16 concentrically mounted around and spaced from a post 18 projecting from the base 10. An insulator, in the form of an insulating disc or platform, 11 is mounted on the base 10 in order to provide electrical insulation between sensing units 16 and the base 10. The accelerometer 8 is rigidly secured to an object 9 undergoing test. The accelerometer is designed to have an axis A--A of maximum sensitivity parallel to the axis of the post 18 and perpendicular to the base 10. The accelerometer will be described as if mounted to detect the component of acceleration along a vertical axis.
The two acceleration sensing elements 16 comprise two piezoelectric crystals that produce electrical signals proportional to the acceleration of the accelerometer 8 in directions parallel to the A--A axis. The electrical signals generated by the crystals in response to such acceleration are supplied to a utilization device 24 in the form of a charge amplifier 20 and recorder 22.
The post 18 may be formed unitary with the base 10, or it may be threadably or otherwise secured thereto and fixed thereon by brazing or the like. The casing or case 12 is firmly secured to the base by welding or the like. THe
It is thus seen that this invention provides an accelerometer which may be employed for a prolonged period at high temperatures; and when employing a lithium niobate crystal cut and used as described, the invention provides an accelerometer which is capable of use at high temperatures for prolonged periods; and in particular, provides such an accelerometer of high sensitivity. Though the accelerometer of this invention is particularly suitable for use at high temperatures, because of the fact that the crystal material possesses high electromechanical efficiency (ratio of electrical power generated to the mechanical power produced in the crystal by the acceleration), it is also advantageous to employ the accelerometers at low temperatures.
| Patent | Priority | Assignee | Title |
| 5250871, | Jun 13 1991 | Northrop Grumman Systems Corporation | Low vibration sensitivity crystal resonator arrangement |
| Patent | Priority | Assignee | Title |
| 3185869, | |||
| 3389276, | |||
| 3487238, |
| Executed on | Assignor | Assignee | Conveyance | Frame | Reel | Doc |
| Jan 16 1974 | Becton, Dickinson Electronics Company | (assignment on the face of the patent) | / | |||
| Aug 06 1987 | Becton, Dickinson and Company | ENDEVCO CORPORATION, A NJ CORP | ASSIGNMENT OF ASSIGNORS INTEREST | 004810 | /0499 |
| Date | Maintenance Fee Events |
| Date | Maintenance Schedule |
| Feb 28 1981 | 4 years fee payment window open |
| Aug 28 1981 | 6 months grace period start (w surcharge) |
| Feb 28 1982 | patent expiry (for year 4) |
| Feb 28 1984 | 2 years to revive unintentionally abandoned end. (for year 4) |
| Feb 28 1985 | 8 years fee payment window open |
| Aug 28 1985 | 6 months grace period start (w surcharge) |
| Feb 28 1986 | patent expiry (for year 8) |
| Feb 28 1988 | 2 years to revive unintentionally abandoned end. (for year 8) |
| Feb 28 1989 | 12 years fee payment window open |
| Aug 28 1989 | 6 months grace period start (w surcharge) |
| Feb 28 1990 | patent expiry (for year 12) |
| Feb 28 1992 | 2 years to revive unintentionally abandoned end. (for year 12) |