U.S. patent number 3,776,361 [Application Number 05/241,602] was granted by the patent office on 1973-12-04 for acoustic lens.
This patent grant is currently assigned to The United States of America as represented by the Secretary of the Navy. Invention is credited to Albert L. Rolle.
United States Patent |
3,776,361 |
Rolle |
December 4, 1973 |
ACOUSTIC LENS
Abstract
An acoustical lens doublet of the type particularly useful for
focusing sc energy on the energy converter array of an
electroacoustical transducer having image resolution powers that
are substantially unaffected by varying temperatures and pressures
ambient thereto is disclosed. Included therein is a rearward shell
containing a low density polyethylene acoustically clear forward
wall-hemispherical lens combination. A forward shell is
telescopically mounted on the front end of said rearward shell,
with the forward end of said forward shell having a thin low
density polyethylene acoustically clear window located therein. An
interface fluid, preferably consisting of a predetermined quantity
of m-chloroanoline (ClC.sub.6 H.sub.4 NH.sub.2), is located under a
predetermined pressure within a chamber effected between the
forward ends of said rearward and forward shells, as a result of
the telescopic relationship thereof.
Inventors: |
Rolle; Albert L. (Panama City,
FL) |
Assignee: |
The United States of America as
represented by the Secretary of the Navy (Washington,
DC)
|
Family
ID: |
22911372 |
Appl.
No.: |
05/241,602 |
Filed: |
April 6, 1972 |
Current U.S.
Class: |
367/150; 181/176;
367/171 |
Current CPC
Class: |
G10K
11/30 (20130101) |
Current International
Class: |
G10K
11/30 (20060101); G10K 11/00 (20060101); G01v
001/16 () |
Field of
Search: |
;340/8L,8M,8S,8R
;181/.5A |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Borchelt; Benjamin A.
Assistant Examiner: Doramus; J. V.
Claims
What is claimed is:
1. An acoustical lens, comprising in combination:
a first open-ended cylinder;
a first acoustically clear wall integrally connected to one of the
open ends of said first open-ended cylinder;
an aperture centrally located within and through said first
acoustically clear wall;
a second acoustically clear wall, having a convexley curved
configuration, integrally connected to said first acoustically
clear wall around the periphery of said apertures;
a second cylinder telescopically mounted in a fluid tight manner on
and extending from that end of said first cylinder which is
connected to said first acoustically clear wall;
a third acoustically clear wall, having a first predetermined
thickness near the periphery thereof and a second predetermined
thickness that is less than said first predetermined thickness
which forms a substantially circular acoustically clear window near
the center thereof, integrally connected to the periphery of the
extended end of said second cylinder in such manner as to be
spatially disposed from said first acoustically clear wall and the
larger curved surface of the aforesaid convexley curved second
acoustically clear wall, thereby effecting a closed chamber
therebetween; and
an interface fluid, having an index of refraction that varies in an
inverse proportion with that of water over a predetermined range of
temperatures, disposed within said closed chamber.
2. The device of claim 1 whrein said first, second, and third
acoustically clear walls consist of a low density polyethylene
material.
3. The device of claim 1 wherein said first acoustically clear wall
has thickness of the order of 0.070 inches.
4. The device of claim 1 wherein said second acoustically clear
wall, having a convexley curved configuration, integrally connected
to said first acoustically clear wall around the periphery of said
aperture comprises a hemispherical acoustical lens.
5. The device of claim 1, wherein said second acoustically clear
wall having a convexley curved configuration, integrally connected
to said first acoustically clear wall around the periphery of said
aperture comprises a low density polyethylene acoustical lens
having a thickness of the order of 0.070 inches and a radius of
curvature of such dimension as to refract acoustical energy passing
therethrough and focus it at a spot having a predetermined focal
length therefrom.
6. The device of claim 1, wherein said third acoustically clear
wall, having a first predetermined thickness near the periphery
thereof and a second predetermined thickness that is less than said
first predetermined thickness which forms a substantially circular
acoustically clear window near the center thereof, integrally
connected to the periphery of the extended one of said second
cylinder in such manner as to be spatially disposed from said first
acoustically clear wall and the larger curved surface of the
aforesaid convexley curved second acoustically clear wall, thereby
effecting a closed chamber therebetween, comprises an acoustical
lens with the window portion thereof having a thickness of the
order of 0.025 inches.
7. The device of claim 1, wherein said interface fluid, having an
index of refraction that varies in an inverse proportion with that
of water over a predetermined range of temperatures, disposed
within said closed chamber comprises ClC.sub.6 H.sub.4
NH.sub.2.
8. The invention of claim 1, further characterized by:
a groove extending around the inner surface periphery of said
second cylinder; and
a resilient O-ring located in said groove in such manner as to be
urged thereagainst and against the outer surface of said first
cylinder, so as to thereby effect a fluid-tight seal
therebetween.
9. The invention of claim 1, further characterized by:
a threaded filler hole extending through the longitudinal wall of
said second cylinder; and
a threaded plug screwed into the aforesaid filler hole.
10. The invention of claim 1, further characterized by a fourth
acoustically clear wall connected to the end of said first cylinder
that is opposite said first and second acoustically clear walls in
such manner as to effect another closed chamber therebetween within
said first cylinder.
11. The invention of claim 10, further characterized by an
acoustical energy conducting and refracting fluid disposed within
said another closed chamber.
12. The device of claim 11, wherein said acoustical energy
conducting fluid disposed within said another closed chamber
comprises a fluid having predetermined sound velocity-temperature
characteristics.
13. The invention of claim 1, further characterized by:
a first flange connected to the outside diameter of said first
cylinder at the end thereof opposite said first and second
acoustically clear walls;
a first plurality of bolt holes extending through and around said
first flange, the axes of which are parallel to each other and to
the longitudinal axis of said first cylinder;
a second flange connected to the outside diameter of said second
cylinder at the end thereof opposite said third acoustically clear
wall; and
a second plurality of bolt holes of like number as said first
plurality of bolt holes extending through and around said second
flange, the axes of which are parallel to each other and the
longitudinal axis of said second cylinder, and the axes of which
are respectively in alignment with the axes of the aforesaid first
plurality of bolt holes.
14. The invention of claim 13, further characterized by means
respectively extending through said first and second pluralities of
bolt holes for the securing of said first and second flanges in a
fixed relationship together.
15. The invention of claim 13, further characterized by means
respectively extending through said first and second pluralities of
bolt holes for securing said first and second flanges in fixed
relationship together and to the housing of an electroacoustical
transducer.
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
therefore.
FIELD OF THE INVENTION
The present invention relates, in general, to lens and lens
systems, and, in particular, it is an athermal acoustic refractor
that may be advantageously combined with an array of
electroacoustical energy converter devices for the focusing of
acoustical images thereon or therefrom. In even greater
particularity, but not by way of limitation, it is an improved,
reversible, temperature and salinity compensated, compound,
ultrasonic, electroacoustical transducer lens that is eminently
suitable for being incorporated in both active and passive sonar
systems, in sonic echo-search-ranging systems, and in any other
devices or systems requiring the accurate focusing of acoustical
energy under ambient environmental conditions of varying
temperature and/or salinity.
DESCRIPTION OF THE PRIOR ART
Heretofore, numerous electroacoustical transducers have
incorporated various and sundry acoustic lenses, in order to effect
more accurate focusing of sonic energy therein. For many practical
purposes, such lenses have been quite satisfactory; however, in the
event that environmental medium ambient thereto varies in
temperature, the index of refraction thereof is changed, thereby,
in turn, effecting a change in the focal lengths thereof. Of
course, such changes in focal length ordinarily change the focus of
such prior art transducers enough to cause unwanted acoustical
image aberrations to occur therein.
In the past, the adverse effects of changing temperatures on the
index of refraction of an acoustical lens was compensated by
adjusting the distance between the lens and the electroacoustic
energy converter elements, so that the refracted acoustic images
would be properly in focus therein. Unfortunately, if such lens is
employed to form several acoustic beams over a significantly large
field of view, a change in focal length also necessitates a change
in the curvature of the transducer's energy converter array at the
image plane. Because it is exceedingly difficult to accurately
control lens focal lengths and image plane curvatures, using such
procedures is usually impractical.
Another means for compensating an acoustical lens for changing
temperature is to change the composition of the lens itself, so as
to correct the index of refraction thereof and, thus, adjust the
focus thereof. Again, for most practical purposes, so doing is too
difficult and time consuming to be effective, at least within most
practical time limits.
In addition, acoustic lenses have been made of materials that
inherently change the index of refraction thereof in compensating
proportion to the temperature change to which they are exposed, and
again, for many practical purposes, such lenses have proven to be
quite satisfactory. But, to date, for some purposes--say, for
example, during deep sea sonar operations--the temperature
compensation effected thereby is not sufficient or is not
sufficiently proportional to the actual temperature gradients
encountered to be as accurate as desired. Hence, in many instances,
they leave a great deal to be desired when actually employed in
various and sundry operational circumstances.
SUMMARY OF THE INVENTION
Perhaps the perfect method and means for compensating for
temperature changes in acoustical lenses for all operational
circumstances may not be found for quite some time, if ever;
nevertheless, for many practical purposes, the temperature
compensating ultrasonic lens of the subject invention constitutes a
vast improvement over most of the prior art, in that the index of
refraction thereof varies less per degree change in temperature for
a very important and useful temperature range, due to the new and
unique inherent temperature compensation characteristics existing
therein, as will be shown more vividly subsequently. As a result,
the versatility of electroacoustical transducers incorporating such
lenses has become considerably greater than heretofore obtainable
from those of the prior art.
Briefly, the instant invention consists of a pair of cylindrical
shells that are constructed of acoustically clear material which
are assembled together in such manner that the forward one --
herein defined as being an interface shell -- is telescopically
mounted on and partially around the rearward one -- herein defined
as being a lens shell. When so assembled, a forward looking chamber
is formed between the interface and lens shells that is filled or
partially filled with an organic fluid -- herein defined as being
the interface fluid -- the change of acoustical index of refraction
of which is opposite that of the environmental medium ambient
thereto for any given identical temperature change in both thereof.
As will be described in greater detail subsequently, said interface
fluid may be supplied under pressure from an external source or a
predetermined quantity thereof may be confined therein, depending
upon the operational circumstances -- such as, for example, the
considerable ambient pressures encountered at great water depths in
an ocean.
The aforesaid lens shell of the unique interface shell -- lens
shell assembly constituting this invention is constructed to have
such a convex configuration as to cause it to inherently refract
acoustical energy in such manner as to effect the focusing thereof
at a focal point or spot located at a given radius or focal length
(f1) therefrom in the rearward direction. In contact with the
rearward face, and optionally, but preferably, filling a
predetermined space behind it, is another organic fluid -- herein
defined as being the lens fluid -- which may or may not have an
acoustical index of refraction that varies inversely with that of
the aforesaid environmental medium for any given identical
temperature in both thereof.
Because the electroacoustic energy converters of the transducer are
also either actually or effectively located in the aforementioned
lens fluid, and because they are ordinarily located along the focal
length or radius of the lens shell, the acoustical energy received
by the lens shell is focused thereon with a relatively high degree
of accuracy, regardless of the fact that the temperature ambient
thereto may be changing rapidly. Hence, the entire transducer has a
responsiveness, a resolution, and an image fidelity hitherto
unattainable by any known prior art.
It is, therefore, an object of this invention to provide an
improved acoustical lens.
Another object of this invention is to provide an acoustical lens
having improved automatic temperature compensation
characteristics.
Still another object of this invention is to provide a new and
unique system for acquiring and image-processing the acoustical
energy emanating from an underwater target object.
A further object of this invention is to provide an acoustical lens
having an acoustical index of refraction that varies only a small
amount with temperature.
Another object of this invention is to provide an acoustical lens
which is not put out of focus as a result of being transferred from
a medium having a particular sound velocity to another medium
having a different sound velocity, such as, for example, when going
from fresh water into sea water and vice versa.
Another object of this invention is to provide an improved method
and means for focusing acoustical energy.
Still another object of this invention is to provide an improved
electroacoustical transducer sonic lens that requires no focus
adjustment over a relatively large temperature range.
Still another object of this invention is to provide an
electroacoustical transducer lens with improved power transfer
characteristics and reduced internal reflections.
A further object of this invention is to provide a more versatile
method and means for focusing sonic and ultrasonic energy.
Another object of this invention is to provide an acoustic
refractor that is substantially uneffected by changes in the
temperature thereof and its ambient environment.
Another object of this invention is to provide a compound lens
having fast sound velocity propagation components.
Another object of this invention is to provide an improved sonic
and ultrasonic compound lens which exhibits small changes in focus
over relatively wide temperature ranges.
Another object of this invention is to provide improved method and
means of forming high fidelity acoustical images when incorporated
in a compatible sonar system.
Other objects and many of the attendant advantages will be readily
appreciated as the subject invention becomes better understood by
reference to the following detailed description, when considered in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a cross-sectional view of the cylindrical lens shell of
the subject acoustical lens invention;
FIG. 2 is a cross-sectional view of another species of a
cylindrical lens shell that may be incorporated in the instant
acoustical lens invention;
FIG. 3 is a cross-sectional view of the cylindrical interface shell
of the subject acoustical lens invention;
FIG. 4 is a cross-sectional view of a preferred embodiment of the
cylindrical compound lens constituting the invention, which
includes the lens shell of FIG. 1 and the interface shell of FIG. 3
combined as a unitary assembly and which, by implication, portrays
how the lens shell of FIG. 2 may be incorporated therein by the
artisan instead of the lens shell of FIG. 2, if so desired;
FIG. 5 is a schematic representation of the invention which will be
used subsequently in disclosing the theory of the operation
thereof;
FIG. 6 is a block diagram of a sonar system which may incorporate
the instant invention to an advantage; and
FIG. 7 is a graphical representation of typical index of refraction
versus temperature curves for electroacoustical transducers
operating within approximately a forty-five degree Centigrade
temperature range, both with and without the incorporation of an
M-chloroaniline (ClC.sub.6 H.sub.4 NH.sub.2) interface fluid
therein.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to FIG. 1, there is shown an acoustical lens shell 11
having a cylindrical section 12, with an open rearward end 13 and a
closed forward end wall 14. In the disclosed embodiment of forward
end wall 14, a flat wall 15 is included, and in the center of said
flat wall is an aperture 16 to which a hemispherical lens 17 is
integrally connected at substantially the maximum diameter thereof.
At this time, it would perhaps be noteworthy that said flat wall 15
and said hemispherical lens 17 are constructed of acoustically
clear material, and that the thickness and diametrical dimensions
thereof should be such as would optimize the acoustical clearness
thereof, respectively. For example, but not by way of limitation,
wall 15 and lens 17 may be constructed of low density polyethylene
having a thickness of the order of 0.070 inches, with the inside
radius of lens 17 being of the order of 0.75 inches. Of course,
although the foregoing polyethylene material and dimensions are
quite satisfactory, it should be understood that others may be used
if operational circumstances so warrant. Moreover, the entire shell
constituting lens shell 11, including forward flat wall 15 and
hemispherical lens 17, may be so designed as to be of other
plastics, rubber, metal or any other suitable acoustically clear
materials. Of course, under such circumstances, the dimensions
therefor would have to be selected, respectively, if optimum
operation is to be obtained therefrom for any predetermined
purpose. Obviously, the selection of the appropriate materials and
dimensions for lens shell 11 would be well within the purview of
one skilled in the art having the benefit of the teachings
presented herein.
At the rearward end of cylindrical lens shell 11, and preferably
integrally connected to cylindrical section 12 thereof, is a
circular flange 18 having a plurality of holes 19 extending
therethrough and disposed uniformly around it adjacent to the
periphery thereof. Said flange 18 and holes 19 are adapted to be
respectively complementary and in line with those components (not
shown) of a transducer case or housing to which flange 18 is to be
bolted, and, in addition, with other lens elements to be described
subsequently.
FIG. 2 depicts another preferred embodiment of an acoustical lens
shell 21 that may be substituted for the aforementioned lens shell
11 in the completed lens assembly, which, likewise, will be
discussed below. Shown therein is a cylindrical section 22, with a
flat, acoustically clear wall 23 located at the rearward end
thereof for the closure thereof and a closed forward end 24
effected by a flat wall 25 effectively having an aperture 26
located at the center thereof. Integrally connected to wall 25 at
the periphery of aperture 26 is a hemispherical lens 27. Like the
aforementioned acoustical lens shell 11, acoustical lens shell 21
is made of any acoustically clear material and have whatever
dimensions are suitable therefor, in order to optimize the
operation thereof for any given purpose within any given
environmental medium. Hence, the previously mentioned materials and
dimensions are quite satisfactory for the lens shell embodiment
being discussed at this time.
At the rearward end of cylindrical lens shell 21 and preferably
integrally connected to cylindrical section 22 thereof is a
circular flange 28 having a plurality of holes 19 extending
therethrough and disposed uniformly around it adjacent to the
periphery thereof. Said flange 28 and holes 29, like the aforesaid
flange 18 and holes 19 of lens embodiment 11, are so designed as to
be respectively compatible with those components (not shown) of a
transducer case or housing to which flange 18 is intended to be
bolted, and again, in addition, with other lens elements to be
described subsequently.
The foregoing structure of FIG. 2 obviously forms a closed chamber
31 which is filled with an organic sound conducting fluid 32, the
sound velocity of which is inversely proportional to the
temperature thereof and, thus, decreases with an increase in
temperature and vice versa. Although numerous conventional organic
fluids exist which have suitable characteristics for acoustic lens
purposes, it has been determined that dibromethylene (CH.sub.2
BR.sub.2), carbon tetrachloride (CCl.sub.4), chloroform
(CHCl.sub.3), methylene iodide (CH.sub.2 I.sub.2), and Halocarbon
Oil, Ser. No. 208, manufactured by the Halocarbon Products
Corporation of Hackensack, N.J., are satisfactory for such purpose,
since the velocity of sound passing therethrough is such as
facilitates the focusing thereof on an energy converter array, as
will be discussed more fully below.
For the purpose of filling chamber 31 with fluid 32, a threaded
hole 33 is located through the wall of cylinder section 22. And for
the purpose of containing fluid 32 in chamber 31, a threaded plug
34 is screwed in threaded hole 33. Because, as previously
suggested, the interface shell will be telescopically mounted on
and around lens shell 21, plug 34 should be so designed as to make
the outer end thereof at least flush with and preferably recessed
from the outer diameter cylinder section 22, when it is inserted in
hole 33.
Referring now to FIG. 3, there is shown a preferred embodiment of
an interface shell 35 which may be telescopically mounted on and
around either lens shells 11 or 21 of FIG. 1 or FIG. 2, in order to
effect the new combination of elements constituting this invention.
Disclosed therein is a cylindrical section 36 having an open
rearward end 37 and a closed forward end 38. The closure at the
forward end is, in fact, effected by a wall having a thick section
41 near the periphery thereof and a relatively thin circular
acoustical window section 42 at the center portion thereof. For
example, said thick wall section 41 may be of the order of 0.125
inches thick, and said thin acoustical window 42 may be of the
order of 0.025 inches thick. Integrally attached to the rearward
end of cylindrical section 36 is a flange 43 having a plurality of
holes 44 extending therethrough and uniformly spaced
therearound.
As will be more fully disclosed below, the inside diameter of
interface shell 35 should be such as would cause it to fit snugly
around the outer diameter of either of the lens shells 11 and 21 of
FIGS. 1 and 2, respectively, and thereby effect a fluid tight seal
therebetween. Moreover, flange 43 and holes 44 should be so
designed as to have a complementary fit and be in alignment with
flanges 18 or 28 and holes 19 or 29, respectively, when
telescopically mounted around either of lens shells 11 or 21.
Located around the inside diameter of cylindrical section 36 of
interface lens 35 is a groove 45 adapted for having a resilient
O-ring (not shown in FIG. 3) inserted therein that will, as will be
subsequently disclosed, provide further liquid or fluid seal
between the inner surface of interface shell 35 and the outer
surface of the lens shell telescopically mounted therein.
As in the shells of FIGS. 1 and 2, the walls of interface shell 35
is made of an acoustically clear material, such as, for instance, a
low density polyethylene, rubber, metal, or the like. Again, the
material selected therefor should be compatible with the material
selected for the co-acting lens shell combined therewith.
Located in the wall of the cylindrical section 36 of shell 35 is a
threaded hole 46 adapted to be used for filling the interface shell
with an organic liquid or fluid after it is assembled with its lens
shell. A threaded plug 47 is inserted in threaded hole 46 to
prevent leakage of the organic fluid or fluid therefrom.
As an alternate possibility, hole 46 of interface shell 35 may have
a pipe nipple screwed therein, which would facilitate the
connection of other suitable piping thereto, in the event the
subject lens were incorporated, for example, in a system such as
that illustrated in FIG. 6.
FIG. 4 consists of an acoustical lens assembly 51 of the
aforementioned lens shell 11 in combination with the interface
shell 35. In order to keep this disclosure as simple as possible,
only an assembly incorporating lens shell 11 has been shown;
however, it should be understood, as previously suggested, that
lens shell 21 may be substituted therefor, in the event that a
unitary, self-contained, compound, acoustical lens is desired.
Obviously, so doing would be well within the ability of the artisan
constructing and using it, inasmuch as the teachings thereof are
explicitly included herein. Furthermore, insofar, as it is
possible, in order to correlate the various and sundry elements of
the acoustical lens of FIG. 4 with identical parts of the shells
depicted in FIGS. 1 and 3, like reference numerals have been
employed for like parts. Moreover, because all of the elements of
acoustical lens 51 would readily be recognized by the artisan as
being the same as those shown in FIGS. 1 and 3, respectively, it
will only be discussed briefly from a structural standpoint, with
only those additional structural explanations made which are deemed
necessary for the teaching thereof as an assembled unit. Hence,
lens shell 11 is shown as being telescopically disposed within
interface shell 35, with the rearward surface of flange 43 of
interface lens 35 being in complementary abutment with the forward
surface of flange 18 of lens shell 11. Of course, the respective
pluralities of the aforesaid holes 44 and 19 are in alignment,
too.
The particular acoustical lens embodiment of FIG. 4 intended to be
attached to the housing of the overall electroacoustical
transducer. Because said transducer could have any of many
suitable, conventional, geometrical configurations, it is not
disclosed in detail herein. Suffice to say, however, that the
forward end thereof should be designed in such manner that it would
form a complementary connection with the rearward surface of flange
18 of lens shell 11. Thus, a transducer housing 52 likewise
contains a flange 53 at the forward end thereof which, in turn,
contains a plurality of holes 54 that are located therein in such
manner that they are in alignment with holes 19 and 44,
respectively, of flanges 18 and 43 of shells 11 and 35.
In order to secure housing 52 to acoustical lens assembly 51, a
plurality of threaded bolts 55 are inserted through the aligned
ones of holes 54, 19, and 29, and a like plurality of nuts 56 are
screwed on the forward ends thereof. Of course, any suitable
conventional means, such as, for instance, lock washers or
additional nuts, may also be used to insure that the aforesaid nuts
56 will not come loose.
In addition, although not shown, if so desired for any given
operational circumstances, appropriately designed gaskets may be
disposed between all of the foregoing mating surfaces. One
particular sealing means disposed between shells 11 and 35 is an
O-ring 57 that is located in the aforementioned groove 45 of shell
35 and, thus, is in resilient sealing contact with the outer
surface of the cylindrical section of lens shell 11. Hence, the
seals between the assembled shells of lens 51 are fluid tight,
thereby preventing the entrance of ambients fluids therein, and
also preventing the escape of any of the acoustical energy
refracting fluids therefrom.
The transducer in which acoustical lens 51 is incorporated is what
is commonly known in the art as a liquid lens transducer.
Consequently, housing 52 thereof is filled with an acoustical
energy refracting organic liquid, herewith defined as being organic
lens fluid 58. Again, as indicated previously with respect to lens
fluid 32, lens fluid 58 may be any conventional transducer lens
liquid, such as, for example, dibromethylene (CH.sub.2 Br.sub.2),
carbon tetrachloride (CCl.sub.4), chloroform CHCl.sub.3), methylene
iodide (CH.sub.2 I.sub.2), or Halocarbon oil. Because it also fills
the rearward portion of lens shell 11, and because the
piezoelectric electroacoustical energy converters (not shown) are
also flooded thereby, said lens fluid 58 likewise constitutes a
medium which transmits the sonic energy passing through lens wall
17 to said energy converters. And because fluid 58 is a sonic
energy refracting liquid, it and hemispherical lens 17 cause the
focusing of said sonic energy on the aforesaid electroacoustical
energy converters.
Another sonic refracting liquid, interface fluid 59, fills or
substantially fills the space between the forward surface of
hemispherical membrane lens 17 and the rearward surface of flat
wall 42 of interface lens 35. This fluid is preferably the organic
compound M-chloroanaline (ClC.sub.6 H.sub.4 NH.sub.2) and has an
index of refraction that is inversely proportional to that of
water. Interface fluid filling may be effected through threaded
hole 46, after which plug 47 is inserted. Interface fluid 59, like
lens fluid 58, provides a suitable medium for transmitting the
operative sonic energy received through forward window 42 to the
forward surface of acoustical hemispherical lens 17. Although the
aforementioned M-chloroanaline (ClC.sub.6 H.sub.4 NH.sub.2) is the
fluid considered to be optimum for this purpose at the present
time, other such fluids -- such as, for instance, nitrobenzoil
(C.sub.6 H.sub.5 NO.sub.2), O-kersol (C.sub.7 H.sub.8 0), and
M-nitrotoluol (C.sub.7 H.sub.7 NO.sub.2) -- would be satisfactory
for some operational situations, too.
At this time it would perhaps again be noteworthy that lens shell
21 may be substituted for lens shell 11 in lens assembly 51. In
such case, it would, of course, be independently filled with one or
more lens fluids similar to those mentioned above as lens fluid 58.
The filling thereof would be effected through hole 46, after which
plug 47 would be inserted therein. Obviously, if such arrangement
were employed, housing 52 would also have to be filled with the
same or some other suitable sonic energy transmitting fluid, so as
to transfer the operative sonic energy from flat acoustically clear
rearward wall 23 to the piezoelectric energy converter elements of
the transducer.
Perhaps at this time it would also be noteworthy that although
lenses 17 and 27 are disclosed herein as being hemispherical
lenses, it is within the contemplated scope of this invention that
they may be designed by the artisan to have whatever geometrical
configurations -- that is, sizes, radius of curvatures, thickness,
etc. -- will give whatever focal characteristics required for any
given transducer design and operational circumstances.
It is also important, of course, as previously suggested, that the
aforesaid sonic energy refracting fluid used as interface lens
fluid 59 be such that the ratio of sound velocity therein to sound
velocity of the ambient water -- and, hence, the index of
refraction -- decreases with an increase of temperature and vice
versa, so as to thereby automatically effect a compensation for the
focal distortions that would otherwise occur as a result of a
temperature variation in said environmental medium. For such
purpose, as also previously suggested, M-nitrotoluol (C.sub.7
H.sub.7 NO.sub.2) appears to be an optimum selection for interface
lens fluid 59.
Referring now to FIG. 5, there is shown, in schematic form, the
typical operation of the invention. Disclosed is an ambient
environmental fluid F.sub.1 having a sound velocity C.sub.1 within
which sonic energy rays 61, 62, and 63 are traveling in such manner
as to pass through acoustical window 64 and into interface fluid
F.sub.2 having a sound velocity C.sub.2. From interface fluid
F.sub.2, said acoustical rays pass through acoustical lens 65 and
into lens fluid F.sub.3 having a sound velocity C.sub.3. But
because of the shape of acoustical lens 65 and the ratio of sound
velocities of C.sub.2 /C.sub.3, said acoustical rays are focused at
some radial focal length (f1) on electroacoustical energy converter
array 66, the outputs of which are supplied to a sonar receiver 67.
Under such circumstances, as will be discussed more fully during
the explanation of the operation of the invention presented below,
the controlling index of refraction, .OMEGA., of such lens system,
as far as temperature is concerned, is equal to C.sub.2 /C.sub.3,
since fluid F.sub.2 is interposed between ambient environment
F.sub.1 and lens fluid F.sub.3.
FIG. 6 illustrates a representative system that will enable the
acoustical lens of FIG. 4 to be used to an advantage at various
water depths, but especially at useful ocean depths. Shown is an
electroacoustical transducer 71 containing a temperature
compensating lens 72, similar to that indicated as acoustical lens
assembly 51 in FIG. 4, the output of which is supplied to an
electroacoustical energy converter array 73, the output of which
is, in turn, connected to the input of a sonar receiver 74. A
readout 75 is calibrated and connected to the output of sonar
receiver 74 for suitable display and/or recording of the signals
received therefrom.
Lens 72, as previously indicated, is capable of having the amount
and pressure of its interface pressure controlled, so that it may,
for instance, be operated at numerous useful ocean depth pressures.
For this purpose, interface fluid 76 is supplied to a pressure
controller 77 which regulates the pressure of the interface fluid
supplied to lens 72, so that it will be continuously equalized with
the ambient environmental pressure as a result of said ambient
pressure being sensed by a pressure sensor 78. Hence, when
acoustical energy 79 emanating through sea water 81 from an
underwater target 82 is received by lens 72, the image thereof is
not distorted enough due to a change in water temperature to
adversely affect the indication thereof by readout 75.
There are obviously numerous ways in which the system of FIG. 6
could be deployed, in order to search for targets. Hence, the way
exemplified in said FIG. 6 is by means of a carrier vehicle 83,
which, of course, may be a marine vehicle, such as a boat, ship,
submarine boat or vehicle, or the like. Thus, it should be
understood that said system is disclosed merely as an example,
rather than as a limitation.
FIG. 7 graphically displays the change of index of refraction
effected upon a liquid lens electroacoustical transducer by a
change in ambient temperature, both with and without the lens
constituting this invention incorporated therein.
THEORY OF OPERATION
The index of refraction at the interface of an ultrasonic lens
determines the focal length of the lens. In the case where the
ultrasonic lens is a fluid lens having an acoustically clear
membrane container operating within water, then the index of
refraction, n, thereof is expressed by the equation:
n = C.sub.w /C.sub. f
where
C.sub.w is the velocity of sound in water, and
C.sub.f is the velocity of sound in the lens fluid.
It has been determined that the velocity of sound in water
increases with an increase in temperature, and it has also been
determined that the velocity of sound in most acoustical lens
fluids decreases with an increase in temperature. Hence, experience
has shown that only a few degrees temperature change of liquid lens
electroacoustical transducers submerged in water ordinarily causes
the index of refraction of the lens thereof to change enough to
change the focal length thereof and thereby defocus the lens. Of
cousre, such defocusing, in turn, causes acoustical image
resolution to be deleteriously effected to the extent that, for
most practical purposes, the fidelity thereof is poor. But, if
another fluid is inserted between the transducer lens fluid and the
water or other ambient medium as an interface fluid, and if said
interface fluid is so selected as to cause it to tract the sound
velocity variation with temperature of the lens fluid, the
combination thereof becomes independent of temperature -- and, to a
considerable extent, the salinity of the ambient medium, in the
event it happens to be sea water, or the like. It has been found
that M-chloroanaline (ClC.sub.6 H.sub.4 NH.sub.2) is an is an
optimum selection for the interface fluid. When it is included
within interface lens shell 35 in combination with a fluid having
appropriate sound velocity-temperature characteristics in
acoustical lens shell 11 in the lens assembly 51 of FIG. 4 and said
lens assembly 51 is made a part of an electroacoustical transducer,
the temperature compensation characteristics which result are
depicted by line 91 of FIG. 7. As may readily be seen therefrom,
the index of refraction of the total lens changes approximately
0.06 or 3.8 percent from 10.degree. to 50.degree.C. This, of
course, is a considerable improvement over the adverse index of
refraction change that would occur in a transducer not
incorporating the subject lens, the latter of which is shown to be
about 0.29 or 19 percent by line 92 in FIG. 7. As a matter of fact,
said improvement has been theoretically calculated to be about a
factor of seven -- a significant improvement, indeed.
Moreover, as may readily be seen, this invention is an acoustical
lens that is not defocused as a result of going from one
environmental medium -- such as, for example, fresh water -- having
a given acoustic velocity characteristic to another environmental
medium -- say, salt water -- having a different acoustic velocity
characteristic and vice versa.
MODE OF OPERATION
The operation of the invention will now be discussed briefly in
conjunction with all of the figures of the drawing.
Perhaps the best representation of an operational system which
could incorporate the subject invention to an advantage is depicted
in FIG. 6. Assuming an underwater target 82 has been acquired by
lens 72 of electroacoustical transducer 72, the sonic image thereof
will pass therethrough and be focused on energy converter array 73
(in the manner similar to that exemplarily portrayed in FIG. 5). Of
course, because lens 72 is similar to that shown in FIG. 4, any
temperature variation encountered thereby is compensated within it.
Thus, sonar 74 and readout 75 can properly process the image
signals impinging on array 73 to thereby effect a visual image of
the aforesaid acoustically acquired target. And, in addition, in
the event pressure compensation is required as well -- say during
great water depth operations -- the interface fluid within lens 72
may be regulated by the combination of components herewith defined
as interface fluid supply 76, pressure controller 77, and pressure
sensor 78.
As a result of very little change of the index of refraction with
change in the ambient water temperature within this invention, as
previously indicated, the fidelity of the acquired image is
considerably improved. Hence, any search-echo-ranging or other
systems incorporating the subject lens may be rapidly moved through
the water -- and especially through sea water -- in any direction
without distorting the images of targets acquired thereby for most
practical purposes. Hence, the subject lens makes a significant
contribution to the advancement of lens used in sonar and other
electroacoustical transducers.
Obviously, other embodiments and modifications of the subject
invention will readily come to the mind of one skilled in the art
having the benefit of the teachings presented in the foregoing
description and the drawing. It is, therefore, to be understood
that this invention is not to be limited thereto and that said
modifications and embodiments are intended to be included within
the scope of the appended claims.
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