Fiber optic sensor and method for detecting shock wave pressure and mass velocity in solid media

Patent metadata

Field	Value
Publication number	US-10018646-B2
Application number	US-201414482580-A
Country	US
Kind code	B2
Filing date	Sep 10, 2014
Priority date	Nov 8, 2013
Publication date	Jul 10, 2018
Grant date	Jul 10, 2018

Abstract

A fiber optic pressure and mass velocity sensor for measuring a shock wave pressure in a solid media includes an optical fiber having a means for measuring a change in an optical path length (OPL) of the fiber when positioned in the solid media caused by the shock wave altering the physical length of the fiber and the refractive index of the fiber. The means for measuring the change in the OPL is coupled at one end to a laser and at its second end to a means for detecting the change in OPL. The sensor has a high operating bandwidth (>>10 MHz), is sufficiently rigid to withstand the force of the shock wave, has a sensitivity that can also be tailored for the application, and is immune to electromagnetic interference. Measurement can be made on materials under extreme strain conditions, and the sensor can also provide characterization of protective materials such as bullet/blast proof materials.

First claim

What is claimed as new and desired to be protected by Letters Patent of the United States is:

1. A differential displacement sensor for measuring a shock wave mass velocity in a solid media, comprising
a Michelson interferometer (MI) having an input and an output, comprising;
a first interferometric arm comprising a cleaved first optical fiber with a first end face having a first mirror surface coating thereon,
a second arm comprising a cleaved second optical fiber, an acousto-optic modulator, and a second end face having a second mirror surface coating thereon,
a coherent laser coupled to the MI input, and
a detector coupled to the MI output, and wherein
the first and second optical fibers are aligned parallel to each other and the first and second endfaces are spaced-apart axially a distance sufficient so as to register a measurable phase shift due to a differential displacement of the first and second endfaces corresponding to a rate of change of a mass displacement due to a travelling shock wave in the solid media equal to the mass velocity.

2. The differential displacement sensor of claim 1 , further comprising
a fiber optic pressure sensor for further characterizing an energy in the shock wave.

3. The differential displacement sensor of claim 1 , wherein the axial spacing between the first and second endfaces is in the range of from 1 μm to 250 μm.

4. A method of measuring a shock wave mass velocity in a solid media, comprising:
providing a first Michelson interferometer (MI) having an input and an output, comprising:
a first arm comprising a cleaved first optical fiber with a first end face having a first mirror surface coating thereon,
a second arm comprising a cleaved second optical fiber, an acousto-optic modulator, and a second end face having a second mirror surface coating thereon,
a coherent laser coupled to the MI input, and
a detector coupled to the MI output, and wherein
the first and second optical fibers are aligned parallel to each other and the first and second endfaces are spaced-apart axially a distance sufficient so as to register a measurable phase shift due to a differential displacement of the first and second endfaces corresponding to a rate of change of a mass displacement due to a travelling shock wave equal to the mass velocity;
positioning the first and second fibers in the solid media;
exposing the solid media to a shock wave; and
measuring one or more desired characteristics of the shock wave.

5. The method of claim 4 , further comprising determining the direction of the shock wave based on the measured characteristics.

6. The method of claim 4 , further comprising:
providing three sensors mounted in orthogonal axes as a three-axis velocity sensor,
reconstructing three vector components of mass velocity,
combining the three-axis velocity sensor with a fiber optic pressure sensor, and
characterizing a shock energy when the shock wavefront is nonplanar.

7. The method of claim 4 , further comprising measuring a single velocity measurement in the direction of shock propagation and pressure measurement to calculate a shock energy when the shock wavefront is planar.

8. The method of claim 4 , further comprising providing and positioning a second sensor, selected from the group consisting of Fabry-perot, fiber Bragg grating and a second MI sensor, at a first radial distance from the shock wave and positioning the first MI at a second radial distance from the shock wave different than the first radial distance, and
measuring the shock velocity by determining a difference in arrival times at the respective sensors.

9. The method of claim 8 , wherein the difference between the first and second radial distances is in the range of 5 mm to 20 mm.

Assignees

• Cranch Geoffrey A
• Grun Jacob
• Us Navy

Inventors

• Cranch Geoffrey A
• Grun Jacob

Classifications

• G01L1/00

  Measuring force or stress, in general (measuring force due to impact G01L5/00) · CPC title

• G01D5/266

  by interferometric means (G01D5/353 takes precedence) · CPC title

• G01D5/268

  using optical fibres (G01D5/28 - G01D5/38 take precedence) · CPC title

• G01P3/36 Primary

  Devices characterised by the use of optical means, e.g. using infrared, visible, or ultraviolet light (G01P3/68 takes precedence; gyrometers using the Sagnac effect, i.e. rotation-induced shifts between counter-rotating electromagnetic beams G01C19/64) · CPC title

• G01D5/35312

  using a Fabry Perot · CPC title