U.S. patent number 3,831,137 [Application Number 05/246,092] was granted by the patent office on 1974-08-20 for acousto-optic underwater detector.
This patent grant is currently assigned to The United States of America as represented by the Secretary of the Navy. Invention is credited to Frank W. Cuomo.
United States Patent |
3,831,137 |
Cuomo |
August 20, 1974 |
ACOUSTO-OPTIC UNDERWATER DETECTOR
Abstract
A low frequency or pressure-gradient hydrophone comprising an
optical reftor experiencing displacements responsive to acoustic
waves. A beam light from a light source is carried by a first group
of fiber optics guides and is incident upon the optical reflector.
The light reflected from the reflector is carried by a second group
of fiber optics guides to a light detector. Any displacements of
the reflector due to pressure gradient due to acoustic waves
impinging on the opposite sides of the reflector are detected by
changes in intensity of reflected light from the light source.
Inventors: |
Cuomo; Frank W. (East
Providence, RI) |
Assignee: |
The United States of America as
represented by the Secretary of the Navy (Washington,
DC)
|
Family
ID: |
22929289 |
Appl.
No.: |
05/246,092 |
Filed: |
April 14, 1972 |
Current U.S.
Class: |
367/141;
250/227.11; 367/174; 73/653 |
Current CPC
Class: |
G01H
9/006 (20130101); G01V 1/186 (20130101) |
Current International
Class: |
G01H
9/00 (20060101); G01V 1/18 (20060101); G01V
1/16 (20060101); G01v 001/16 () |
Field of
Search: |
;350/96,193
;181/.5NP,.5H ;356/4,106 ;73/67.2,67.5,71.1,71.3 ;340/8,12,13
;250/227 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Borchelt; Benjamin A.
Assistant Examiner: Tudor; H. J.
Attorney, Agent or Firm: Sciascia; Richard S. McGill; Arthur
A. Lall; Prithvi C.
Claims
I claim:
1. A pressure-gradient hydrophone comprising:
a light-tight box having a first side and a second side opposite
said first side;
a cover plate attached to said second side;
a source of light secured to said box;
a light detector secured to said box;
a bifurcated fiber optics bundle comprising a first bifurcated
branch having a first multiplicity of fiber optics guides and a
second bifurcated branch having a second multiplicity of fiber
optics guides, an end of said first bifurcated branch being in
communication with said source of light and an end of second
bifurcated branch being in communication with said light detector,
said first multiplicity of fiber optics guides of said first branch
and said second multiplicity of fiber optics guides being
intermingled at the opposite ends of said first and second
bifurcated branches proximate said cover plate and passing
therethrough; and
an optical reflector having opposite sides, said reflector being
adjustably attached to the side of said cover plate distal said
bifurcated bundles, said sides being disposed to allow an incident
acoustic wave to impinge thereon;
whereby light is transmitted from said source of light through said
first bifurcated branch and reflected by said optical reflector,
intensity of light reflected by said reflector being proportional
to displacement of said reflector because of pressure gradient
across the both sides of said reflector due to said incident
acoustic wave impinging thereon, then carried by said second
bifurcated branch and detected by said detector.
2. The hydrophone of claim 1 wherein said reflector is attached to
said box by a plurality of pistons, said plurality of pistons being
secured to said optical reflector on one side thereof and to said
cover plate on said second side of said box;
3. The hydrophone of claim 2 wherein said plurality of pistons are
spring biased at ends connected to said cover plate.
4. The hydrophone of claim 3 wherein said bifurcated fiber optics
bundle is attached to said cover plate, passing therethrough, and
having its end facing said reflector.
Description
STATEMENT OF GOVERNMENT INTEREST
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
The present invention relates to underwater communication and
particularly pertains to low frequency hydrophones wherein any
displacements of an optical reflector resulting from pressure
gradient on the opposite sides of the reflector because of
impinging acoustic waves are detected by changes in intensity of
light reflected by the reflector.
Transducers used in underwater communication for detecting acoustic
waves generated by various sources usually employ piezoelectric
crystals of materials such as barium titanate, lead zirconate as
acoustic elements. However, such transducers are not very efficient
at low frequencies, e.g., a few hundred hertz, or below. This is
because of relatively high resonant frequencies of piezoelectric
crystals used and their relatively low detection efficiency at
these frequencies. Furthermore, they display omnidirectional
patterns and have sizes of 12 inches or longer in order to have
receiving responses averaging -90 decibels (abbreviated as dB) for
generating signals of 1 volt per microbar pressure of acoustic
waves. Besides, these transducers do not have a uniform low
frequency response and different piezoelectric crystals need be
used to cover low frequency region. Consequently, their
omnidirectional characteristics, relatively large size, and
inefficient operation at low frequencies impair their usefulness in
some underwater acoustic detection systems with particular
reference to torpedo applications.
SUMMARY OF THE INVENTION
The objects and advantages of the present invention are
accomplished by utilizing an acousto-optic transducer which
comprises a bifurcated fiber-optic bundle housed in a light-tight
box, a lightweight optical reflector which is flexibly attached to
the light-tight box by means of a plurality of springs, a source of
light, and a light detector. Light from the light source is carried
through the box by the first group of the bifurcated fiber optics
bundle to the reflector. The second group of the bifurcated fiber
optics bundle carries the reflected light through the box to the
light detector, the light-tight box preventing any extraneous light
from interfering. Pressure exerted by an incoming acoustic wave
displaces the optical reflector with resulting displacement of the
reflector being proportional to the pressure differential on the
opposite sides of the reflector and thus varies the intensity of
the light reflected from the reflector. By changing the springs
used for attaching the reflector to the box, it is possible to
change the resonant frequency of the detector and thus the
frequency band of the transducer for a uniform response. The
frequency response of the transducer can also be varied by using
optical reflectors of different masses.
An object of this invention is to have an acousto-optic transducer
having a uniform low frequency response.
Another object of this invention is to have an acousto-optic
transducer which has a directionality characteristic instead of
being omnidirectional .
Other objects, advantages and novel features of the invention will
become apparent from the following detailed description of the
invention when considered in conjunction with the accompanying
drawings.
DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates schematically an acousto-optic transducer of
subject invention;
FIG. 2 illustrates a partially exploded perspective view of the
transducer;
FIG. 3 illustrates a cross-sectional view of the transducer taken
along the line 3--3 of FIG. 2; and
FIG. 4 illustrates a cross sectional view of the transducer taken
along the line 4--4 of FIG. 2.
DESCRIPTION OF A PREFERRED EMBODIMENT
Referring more specifically to the drawings, FIG. 1 illustrates an
acousto-optic transducer 10 which comprises a light-tight box 12, a
bifurcated fiber optics bundle 14 having branches 16 and 18, a
light source 20, an optical detector 22, an optical reflector 24
attached to box 12 by means of spring biased pistons 26 and 28
schematically shown in FIG. 1 and in a perspective view in FIG. 2.
Bifurcated bundle comprises a multiplicity of optical fibers as
shown in FIG. 4 which is a cross sectional view of FIG. 2 along
line 4--4. The optical fibers as shown in FIG. 4 are arranged in
such a way that each transmitting fiber which transmits light from
light source 20 to the optical reflector 24 is completely
surrounded by receiving fibers which carry the light reflected by
the optical reflector 24 to detector 22 for increasing the
efficiency of the transducer. Cable 30 shown in FIG. 2 provides
power to light source 20 and detector 22.
FIG. 3 shows a cross sectional view along line 3--3 of the
transducer shown in FIG. 2. Two generally identical pistons 26 and
28 are spring biased and mounted in holes 32 and 34 respectively in
wall 36 of box 12 and cover plate 37 which is attached to box 12 by
set of screws not shown in the drawings. Piston 26 comprises a
wider section 38 fitting tightly in hole 32, a narrower section 40,
and a threaded section 42. Likewise piston 28 comprises a wider
section 44, a narrower section 46, and a threaded section 48.
Springs 50 and 52 are inserted in holes 32 and 34 respectively.
Spring 54 is slipped on section 40 of piston 26 abutting common
shoulder 56 of sections 38 and 40. Likewise spring 58 is slipped on
section 46 of piston 28 abutting common shoulder 60 of sections 44
and 46. Pistons 26 and 28 are then inserted into holes 32 and 34
respectively, the end of piston 26 abutting spring 50 and the end
of piston 28 abutting spring 52. Reflector 24 is supported by a
back plate 64 attached thereto all around except a small area 66 of
the reflector 24. Back plate 64 is attached to the threaded
sections 42 and 48 of pistons 26 and 28 respectively by means of
nuts 68, 70 and 72, 74. O rings 76 and 78 are used to protect
fibers 14 from water. The reflector 24 is light and is generally
made of materials such as glass, brass, and mylar coated with a
reflector paint. However, it should be understood any reflector
which is lightweight and having a high reflection coefficient can
be used regardless of the material from which it is made. By
adjusting the position of the back plate 64 of the optical
reflector 24 or by changing springs 50, 52, 54, and 58, it is
possible to change resonant frequency of the transducer and thereby
change frequency band for a uniform low frequency response of the
transducer. Furthermore, by using reflectors of different masses,
it is also possible to change frequency characteristics of the
transducer. Replacement of the springs and the reflectors can be
achieved without making any major modifications in the transducer.
The transducer can be either free flooding by making water flow on
both sides of the reflector 24 or by making water flow only one
side of the reflector 24 by adjusting the spacing between box 12
and reflector 24.
Thus, an optical reflector which is adjustably attached to a light
box having a bundle of fiber optics transmitters and receivers
passing therethrough is displaced by an acoustic wave resulting
from the pressure differential on the opposite sides of the
reflector. This displacement of the optical reflector causes
changes in intensity of light reflected by the optical reflector
and carried by fiber optics receivers to a light detector. Due to
flexibility in the choice of mass of the optical reflectors used,
it is possible to change low frequency response of the
transducer.
Obviously many modifications and variations of the present
invention are possible in the light of the above teachings. It is
therefore to be understood that within the scope of the appended
claims the invention may be practiced otherwise than as
specifically described.
* * * * *