Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
1999-12-02
2001-12-11
Aftergut, Jeff H. (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S169000, C156S173000, C250S271000
Reexamination Certificate
active
06328837
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention refers generally to an acceleration sensor and more specifically to a high performance fiber optic interferometric acceleration sensor.
2. Description of the Related Art
An accelerometer is typically viewed as a mass-spring transducer housed in a sensor case with the sensor case attached to a moving part whose motion is inferred from the relative motion between the mass and the sensor case. The relative displacement of the mass being directly proportional to the acceleration of the case and therefore the moving part.
One type of accelerometer is a piezoelectric based electronic accelerometer. However, it tends to suffer from several major drawbacks when faced with the continuing stricter demands of the industry. Most higher performance piezoelectric accelerometers require power at the sensor head. Also, multiplexing of a large number of sensors is not only cumbersome but tends to occur at significant increase in weight and volume of an accelerometer array.
Another type is the interferometric fiber optic accelerometers based on linear and nonlinear transduction mechanism, circular flexible disks, rubber mandrels and liquid-filled-mandrels. Some of these fiber optic accelerometers have displayed very high acceleration sensitivity (up to 10
4
radians/g), but tend to utilize a sensor design which is impracticable for many applications. For instance, sensors with a very high acceleration sensitivity typically tend to have a seismic mass greater than 500 grams which seriously limits the frequency range in which the device may be operated as an accelerometer and are so bulky that their weight and size renders them useless in many applications. Other fiber optic accelerometers suffer either from high cross-axis sensitivity or low resonant frequency or require an ac dither signal and tend to be bulky (>10 kg) and expensive. For many applications, the fiber optic sensor is expected to have a flat frequency response up to several kHz (i.e., the device must have high resonant frequency), high sensitivity, be immune to extraneous measurands (e.g., dynamic pressure), be lightweight and easily configurable in an array (i.e., easy multiplexing).
SUMMARY OF THE INVENTION
The object of this invention is to provide an accelerometer that is highly immune to dynamic pressure signals and having excellent directivity that may be produced cheaper than those currently in use.
Another objective is to produce an accelerometer that is immune to electromagnetic interference and is of a light weight.
Another objective is to produce an accelerometer that may be easily multiplexed to provide for large arrays of accelerometers.
These and other objectives are accomplished utilizing an interferometric fiber optic accelerometer mounted on a circular flexural disk. The accelerometer is viewed as a mass-spring transducer housed in a sensor case. The sensor case is attached to a moving part whose motion is inferred from the relative motion between the mass and the sensor case. In this invention, a flexural disk is housed in a sensor case which is accelerated in a direction normal to the plate surface. The plate undergoes displacement resulting in strains on the plate surface. A coil of optical fiber, made to be part of an optical interferometer, is attached to the flexural disk, the strain from the disk is transferred to the fiber thus changing the path length of the fiber interferometer. The interferometer output in demodulated providing the acceleration response.
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patent: 4978413 (1990-12-01), Schotter
patent: 5317929 (1994-06-01), Brown et al.
patent: 5328512 (1994-07-01), Steelman et al.
patent: 5364489 (1994-11-01), Bailey et al.
patent: 5369485 (1994-11-01), Hofler et al.
Dandridge Anthony
Danver Bruce
Tveten Alan
Vohra Sandeep T.
Aftergut Jeff H.
Karasek John J.
Mills John G.
The United States of America as represented by the Secretary of
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