Communications – electrical: acoustic wave systems and devices – Signal transducers – Underwater type
Reexamination Certificate
1996-08-26
2001-05-08
Lobo, Ian J. (Department: 3662)
Communications, electrical: acoustic wave systems and devices
Signal transducers
Underwater type
C073S655000
Reexamination Certificate
active
06229762
ABSTRACT:
STATEMENT OF GOVERNMENT RIGHTS
The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates generally to acoustic sensors and, more particularly, to fiber optic acoustic sensors for monitoring a point in space remote from the sensor. Such monitoring is achieved by the provision of acoustic sensor for a point in space a compact and economical sensor for measuring low acoustic energy and spatially localized processes.
2. Brief Description of Related Art
Methods of measuring localized acoustic energy signals are known. For example, parabolic reflectors have been used to focus acoustic input signals on a single acoustic sensor located at the focal point of the parabolic reflector. However, parabolic reflectors receive all acoustic energy signals originating from a particular direction rather than from only a desired point of interest. Thus, unwanted noise is measured and other acoustic techniques may be required to detect and isolate the desired acoustic signals. Moreover, for a parabolic sensor to localize an acoustic signal in three dimensions the sensor must be moved so that the acoustic signals originating from a point of interest may be detected and measured from more than one location.
An array of acoustic sensors arranged in a beamformed planar array may also be used to isolate a desired acoustic process originating from a point in space by adding the desired signal in phase. However, to detect signals at reasonably high frequencies a uniform sensing surface requires a large number of sensors. Such an arrangement is limited by cost, weight and space requirements. Additionally, beamformed arrays introduce electromagnetic noise and are sensitive to electromagnetic noise. Such electromagnetic noise may originate, for example, from x-ray machines or magnetic based medical diagnostic equipment.
Thus, there is a need for a compact, economical acoustic sensor that is capable of isolating and measuring acoustic energy signals originating from a point of interest, whether that point be in air, water or a human or animal body.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide an acoustic sensor capable of detecting and isolating acoustic energy signals originating from a point in space remote from the sensor.
It is a further object of the present invention to provide an acoustic sensor suitable for monitoring point in space acoustic signals originating in either air or water.
It is still a further object of the present invention to provide an acoustic sensor suitable for monitoring point in space acoustic signals originating in a human or animal body.
It is yet another object of the present invention to provide a fiber optic sensor for measuring low acoustic energy signals originating from a point in space remote from the sensor that is capable of canceling vibration and other noise associated with movement of the sensor and with location of the sensor relative to sources of thermal or electromagnetic interference.
Other objects and advantages of the present invention will become apparent to those skilled in the art upon a reading of the following detailed description taken in conjunction with the drawings and the claims supported thereby.
In accordance with the present invention, an improved acoustic sensor for detecting acoustic energy originating from a point in space is provided. The sensor includes a base structure having a concave surface formed thereon, and means for detecting acoustic energy. The detecting means includes acoustic sensing means mounted on the concave surface to form an acoustically sensitive surface and means for processing output signals from the sensing means. The concave surface has a focal point associated therewith that corresponds to the point in space from which acoustic measurements are desired. The detecting means may further include a reference means for providing an acoustic reference signal to the processing means, and means for transmitting coherent light to the acoustic sensing means and the reference means.
In a preferred embodiment of the present invention, the acoustic sensing means comprises a sensing cable including a light transmitting optical fiber core encased within an acoustically sensitive jacket and a soft silicone buffer layer surrounding the optical fiber core between the optical fiber core and the acoustically sensitive jacket. The buffer layer of the sensing cable is bonded to both the optical fiber core and the acoustically sensitive jacket resulting in the acoustically sensitive jacket being bonded to the optical fiber core. The reference means comprises a reference cable including a light transmitting optical fiber core encased within a protective jacket and a soft silicone buffer layer surrounding the optical fiber core between the optical fiber core and the protective jacket wherein the protective jacket is not bonded to the optical fiber core. The means for processing output signals is an electro-optical unit receiving transmitted light from the acoustic sensing means and the reference means and suitable for determining a phase shift differences between transmitted light received from the acoustic sensing means and the reference means.
In a more preferred embodiment, the sensing and reference cables are configured as a collocated pair configured in a coil on the concave surface wherein the concave surface is a partial sphere. The sensing and reference cables are encased within an acoustically transparent material, either independently or as a pair. The coiled collocated pairing forms the acoustically sensitive surface mounted on the concave surface of the base structure.
In a further embodiment of the present invention, a fiber-optic sensor for measuring acoustic signals originating from a point remote from the sensor is provided. The sensor includes: a base forming a three-dimensionally curved concave surface having a focal point associated therewith; means, having optical characteristics that vary when subjected to acoustic impingement, for sensing acoustic energy; means, having optical characteristics that are insulated from acoustic impingement, for sensing vibration signals; the means for sensing acoustic energy and the means for sensing vibration signals configured to form a continuous acoustically sensitive layer on at least a portion of the concave surface; means for providing coherent light to the means for sensing acoustic energy and the means for sensing vibration signals; and means for processing output from the means for sensing acoustic energy and the means for sensing vibration signals. The fiber-optic sensor provides a low vibration noise acoustic signal that originates from the focal point. The means for sensing acoustic energy comprises a fiber-optic core having an acoustically sensitive jacket continuously bonded thereto and is wound in a spiral pattern on the concave surface. The means for detecting vibration signals comprises a fiber-optic core having a jacket that is not bonded thereto and is wound in a spiral pattern on the concave surface.
In the above embodiments, the sensor may include means for locating the focal point of the concave surface. The locating means includes three or more light sources distributed peripherally about the base. Each of the light sources projects light such that the projected light intersects at the focal point producing a visual indication of the focal point.
A preferred application of the present invention is to measure acoustic signals originating in a human or animal body. When used for such an application, the sensor includes means, juxtapositioned between the body and the acoustically sensitive surface, for substantially matching the acoustic impedance of the body. The acoustic impedance matching means preferably comprise a flexible container containing a fluid having an acoustic impedance substantially corresp
Chandler Larry S.
Fisher Stanley A.
Forrest John
Lobo Ian J.
Shuster Jacob
The United States of America as represented by the Secretary of
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