U.S. patent application number 10/094513 was filed with the patent office on 2003-09-11 for emi shielded module.
Invention is credited to Bluband, Zakh, Czyscon, Joe, Loeffelholz, Todd, McClellan, Terry, Podell, Allen.
Application Number | 20030168235 10/094513 |
Document ID | / |
Family ID | 27788122 |
Filed Date | 2003-09-11 |
United States Patent
Application |
20030168235 |
Kind Code |
A1 |
Loeffelholz, Todd ; et
al. |
September 11, 2003 |
EMI shielded module
Abstract
A module for containing a circuit is provided that attenuates
emitted signals without the use of a cover. The module includes a
housing and a receptacle. The housing has a front having a certain
thickness and the receptacle is accessible from the front of the
housing. The receptacle is shaped to receive a circuit component
and forms a waveguide.
Inventors: |
Loeffelholz, Todd;
(Minnetonka, MN) ; Bluband, Zakh; (Minnetonka,
MN) ; Czyscon, Joe; (Plymouth, MN) ;
McClellan, Terry; (Maple Grove, MN) ; Podell,
Allen; (Palo Alto, MN) |
Correspondence
Address: |
MERCHANT & GOULD PC
P.O. BOX 2903
MINNEAPOLIS
MN
55402-0903
US
|
Family ID: |
27788122 |
Appl. No.: |
10/094513 |
Filed: |
March 7, 2002 |
Current U.S.
Class: |
174/53 |
Current CPC
Class: |
H05K 1/0237 20130101;
H01R 13/447 20130101; H05K 1/141 20130101; H05K 9/0062
20130101 |
Class at
Publication: |
174/53 |
International
Class: |
H01H 009/02 |
Claims
What is claimed is:
1. A module for containing a circuit, the module comprising: a
housing having a front having a certain thickness; and a receptacle
accessible from the front of the housing, the receptacle shaped to
receive a circuit component wherein the receptacle forms a
waveguide.
2. A module according to claim 1 further comprising a plurality of
receptacles accessible from the front of the housing wherein each
receptacle is shaped to receive an individual circuit component and
each receptacle forms a waveguide.
3. A module according to claim 1 wherein the receptacle has the
shape of a rectangular chamber.
4. A module according to claim 1 wherein the front of the housing
is recessed in a region surrounding the receptacle.
5. A module according to claim 4 further comprising a cover shaped
to fit within the recess wherein the cover extends over the
receptacle.
6. A module according to claim 5 further comprising a means for
attaching the cover to the front wall of the housing.
7. A module according to claim 5 further comprising a snapping barb
for securing the cover to the front of the housing.
8. A module according to claim 1 wherein the circuit component is a
removable plug, the module further comprising: a circuit board
located in the interior of the housing wherein the circuit board
has a conductive pathway on a first side of the circuit board and a
second conductive pathway on a second surface of the circuit board
opposite the first surface; and a plug connector mounted on the
circuit board for receiving the plug, wherein the plug has a first
terminal and a second terminal extending from a back portion of the
plug so that the first and second terminals are exposed in the back
portion wherein the plug fits in the receptacle and is received in
the plug connector and the first terminal is electrically coupled
to the first conductive pathway on the first surface of the circuit
board and the second terminal is electrically coupled to the second
conductive pathway on the second surface of the circuit board.
9. A module according to claim 8 wherein the plug includes a third
terminal located between the first and second terminals wherein the
third terminal extends into the circuit board.
10. A module according to claim 9 wherein the circuit board is a
layered circuit board and has a ground plane located in a center
layer, wherein the third terminal of the plug contacts the ground
plane layer of the circuit board.
11. A module according to claim 1 wherein the thickness of the
front of the housing ranges from about 0.2 to about 0.8 inches.
12. A module according to claim 11 wherein the thickness is about
0.25 inches.
13. A module according to claim 11 wherein the thickness is about
0.75 inches.
14. A module according to claim 8 wherein the plug has a plastic
housing and circuitry located in the plastic housing near the back
portion of the plug so that when the plug is inserted in the
receptacle and received by the plug connector, the circuitry is
located in an interior of the housing.
15. A module according to claim 1 wherein the housing is made of a
conductive material.
16. A module according to claim 5 wherein the cover is made of a
nonconductive material.
17. A module according to claim 5 wherein the cover when placed in
the recessed opening of the front obstructs access to the
receptacle.
18. A module according to claim 14 wherein the circuitry includes
an attenuator circuit.
19. A module according to claim 8 further comprising a plurality of
coax connectors secured to a back of the housing; and a plurality
of connection locations on the circuit board wherein the coax
connectors are coupled to the connection locations.
20. A module according to claim 19 wherein the circuit board
includes a plurality of circuit components interconnected with one
another and with the connection locations through a plurality of
circuit paths wherein the plurality of circuit components includes
splitter components for receiving a main signal from one of the
connection locations and dividing the main signal into a plurality
of branch signals delivered along the circuit paths to individual
reaming ones of the connection locations.
21. A module according to claim 19 wherein the circuit board
includes a plurality of circuit components interconnected with one
another and with the connection locations through a plurality of
circuit paths wherein the plurality of circuit components includes
combiner components for receiving a plurality of branch signals
from individual ones of the connection locations and combining the
branch signals into a main signal delivered along the circuit paths
to a remaining one of the connection locations.
22. A module according to claim 5 wherein the module has an
emission rating of greater than 100 dB down from a carrier signal
when the cover is removed.
23. A module according to claim 1 wherein the housing is made of
conductive material and the waveguide is formed by the thickness of
the housing.
24. A module for containing a circuit, the module comprising: a
housing having a front having a certain thickness; and a receptacle
accessible from a surface of the housing, the receptacle shaped to
receive a circuit component wherein the receptacle forms a
waveguide.
Description
Background of the Invention
[0001] In the telecommunications industry and more particularly in
the video transmission industry, signals (e.g., 5 MHz to 1 GHz) are
carried over coax conductors from a headend to customers. At the
headend of the systems, numerous signals are manipulated to achieve
a wide variety of functions and objectives. For example, signals
carried on numerous coax cables may be combined onto a single coax
conductor. Similarly, a signal on a main coax conductor may be
divided into a plurality of signals carried on branch coax
conductors.
[0002] In addition to combining, splitting, diverting or adding
signals, the headend will also include a module for modifying
signals. For example, in order to adequately tune the system, it
may be desirable to provide attenuators or the like to attenuate a
signal to a desired level. Further, as a broadband RF signal is
carried over a length of cable, the high frequency range of the
signal may be attenuated more than a low frequency range of the
signal. As a result, equalizers are utilized to modify the signal
to have a level intensity throughout its frequency range.
[0003] Frequently, tuning is accomplished through the use of
plug-in devices (e.g., attenuators or equalizers). Exemplary
systems including plug-in devices are disclosed in U.S. Pat. No.
6,289,210 which is hereby incorporated by reference.
[0004] Typically, a module such as a combiner has receptacles
mounted on a printed circuit board. Terminals of a plug extend into
a receptacle and are electrically coupled to the circuit board by
electrical components that are all located on the same side of the
circuit board. In particular, electrical components communicate
with the receptacle and electrically couple terminals of a plug to
the proper layer of the circuit board using vias, for example, if
necessary. This style of mounting increases the amount of signal
radiating around the electrical components causing cross talk in
adjacent circuits. Also, because the leads of the electrical
components are inductive, special circuit designs are used to
compensate.
[0005] It is desirable to improve the amount of isolation between
adjacent ports on a module. In addition, it is desirable to reduce
parasitics that reduce loss of a specific port and increase
insertion loss.
[0006] It is important to provide electromagnetic shielding to
modules that house electrical components. For example, in a
combiner module, a plurality of attenuator plugs that house
circuitry are inserted in one side of the module. For example, a
plurality of attenuator plugs may be inserted in receptacles of the
housing. Once the plugs are inserted, a conductive cover is placed
over the plug and receptacles to shield the circuit board from the
outside environment and vice versa. When the cover is removed for
maintenance, for example, the module radiates signals into the
outside environment about 60 dB down from the carrier. Such
radiation interferes with the operation of the headend. Sometimes,
it is possible that the cover is not replaced after the repair is
completed. Other times the repairs may take hours to perform while
the cover must remain off.
[0007] It is desirable to provide a module in which such emissions
are at least 100 dB down from the carrier so that the possibility
of interference is reduced. In addition, it is desirable to provide
a module with improved shielding.
SUMMARY OF THE INVENTION
[0008] According to a first aspect of the invention, there is
provided a module for containing a circuit. The module includes a
housing and a receptacle. The housing has a front having a certain
thickness and the receptacle is accessible from the front of the
housing. The receptacle is shaped to receive a circuit component
and forms a waveguide.
[0009] According to a second aspect of the invention, there is
provided a module for containing a circuit. The module includes a
housing and a receptacle. The housing has a front having a certain
thickness and the receptacle is accessible from a surface of the
housing. The receptacle is shaped to receive a circuit component
forms a waveguide.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a perspective view of an eight port RF combiner
module 10 according to a preferred embodiment of the present
invention with a top plate removed.
[0011] FIG. 2 schematically depicts an exemplary circuit diagram
for one plug 30 the combiner of FIG. 1.
[0012] FIG. 3 is a perspective view of the eight port RF module 10
shown in FIG. 1 with the top plate removed.
[0013] FIG. 4 is a perspective view of the module shown in FIG. 1
with one of the covers affixed to the front wall of the housing and
the other cover removed therefrom.
[0014] FIG. 5 is an exploded view of the module shown in FIG.
1.
[0015] FIG. 6 is an exploded view of a portion of the circuit
board, plug connector and plugs according to a preferred embodiment
of the present invention.
[0016] FIG. 7 is a top view of the module shown in FIG. 1.
[0017] FIG. 8 is a cross-sectional view of the module shown in FIG.
7 taken along lines 8-8.
[0018] FIG. 9 is an enlarged view of a portion of the cross-section
shown in FIG. 8.
[0019] FIG. 10 is a side view of a module according to another
preferred embodiment of the present invention.
[0020] FIG. 11 is a front view of the module shown in FIG. 10.
[0021] FIG. 12 is a cross-sectional view of a portion of a
receptacle according to a preferred embodiment of the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE PRESENT
INVENTION
[0022] Referring now to the drawing figures in which identical
elements are numbered identically throughout, a description of the
preferred embodiments of the present invention will now be
provided.
[0023] It will be appreciated that the disclosed RF components are
merely examples of the type of equipment to which the various
aspects of the present invention are applicable. Thus, it will also
be appreciated that the various aspects of the present invention
are applicable to types of RF components other than those
specifically shown. Further, the present invention has general
applicability in the telecommunications field, and is not limited
to RF applications.
[0024] FIG. 1 is a perspective view of an eight port RF combiner
module 10 according to a preferred embodiment of the present
invention with a top plate removed. The module 10 includes a
housing 12. The housing 12 includes a front 16 and a back 18
opposite the front 16. The front and back 16, 18 are joined by a
pair of sides 20 and 22. While the front and back are illustrated
as being parallel to one another, they may be at an angle with
respect to one another. In one preferred embodiment, major side 24
of the housing 12 is open and major side 26 is closed by a plate
formed as an integral member of the rest of the housing 12 which
can not be removed from the housing 12 and major side 24 is
enclosed by a removable plate 28 secured to the housing 12 by
fasteners (e.g., bolts or screws). Alternatively, major side 26 may
be open as well and enclosed by a removable plate like major side
24.
[0025] The housing 12 is adapted for at least partially enclosing
radio frequency circuitry (e.g., splitter circuitry, combiner
circuitry, etc.). While the circuitry could have any number of
known configurations, preferably the circuitry is provided on a
circuit board 32 sized to be mounted within the housing 12. The
module 10 includes a at least one receptacle but preferably a
plurality of receptacles 14 for each containing a plug 30 that is
accessible from the front of the housing. While accessibility from
the front of the module 10 is described as a preferred embodiment,
if the plug 30 is to be accessed from the back, the bottom, top or
sides of the module, the preferred embodiments of the present
invention may be employed respectively in the back, the bottom, top
or sides of the module 10 and the present invention is not limited
to access only through the front of the module. The receptacle 14
which will be described in detail hereinafter may be formed by a
combination of a cutout extending through the front 16 of the
housing 12 and plug connectors 36-1, 36-2. Alternatively, the
receptacles 14 may be formed by a plug connector having a built-in
waveguide as will be described in detail hereinafter. Other
combinations can be appreciated in providing a waveguide to shield
EMI wherein the removable plug is accessed other than by the front
of the module 10.
[0026] In one embodiment of the present invention, the front 16 of
the housing 12 has a thickness, t, that creates a waveguide that
provides a desired amount of attenuation for signal emitted from
the housing 12. Preferably, the thickness ranges from about 0.2
inches to about 0.8 inches. More preferably, the thickness is about
0.25 inches and most preferably the thickness is about 0.75 inches.
In a preferred embodiment, eight receptacles 14 are located in the
housing 12. Each receptacle 14 is sized to receive a plug 30
therein. Each plug has a plastic housing which contains circuitry
such as an attenuator circuit, equalizer circuit of other similar
circuit. Terminals 29 (see FIG. 5) are exposed in a rear portion of
the plug for electrically coupling the plug to circuitry located on
the circuit board 32. Mounted at one edge of the circuit board 32
are plug connectors 36-1 and 36-2 as will be described in detail
hereinafter with respect to FIG. 6. Four plugs 30 are received in
one plug connector 36-1 and the remaining plugs 30 are received in
the other plug connector 36-2. It will be appreciated that one plug
connector may be provided to receive all of the plugs or that
individual plug connectors may be provided for each plug or any
combination of the above configurations. The phrase "plug
connector" will be understood to include devices or arrangements
adapted for receiving or otherwise providing electrical connections
between the terminals of the plugs and the circuit board on which
it is mounted. In the preferred embodiments, the plug connectors
are adapted for providing electrical connections with multi-pin RF
circuitry plugs such as equalizer plugs or attenuator plugs.
[0027] When the circuit board 32 is mounted within the housing 12,
the attenuator plugs 30 can be accessed from the front 16 of the
housing 12 without the use of tools. The housing 12 may also
include covers 40 that are secured to the front 16 of the housing
12 so as to cover the receptacles 14 as can be seen in FIG. 4. The
cover 40 may be secured by snapping barbs 15, for example. By
removing the cover 40 from the housing 12, the attenuator plugs 30
can be accessed. As will be described in detail herein after,
unlike known systems that require conductive covers for EMI
shielding, the module 10 according to the preferred embodiments of
the present invention does not require such shielding. Covers 40
may be provided for aesthetic purposes or to prevent unauthorized
access to the plugs, however, the covers 40 may be formed out of a
nonconductive material such as plastic which provides a cost
savings.
[0028] With reference to FIG. 3, the module 10 further includes a
plurality of connectors 42-0 to 42-8 mounted at the back 18 of the
housing 12. While the connectors 42-0 to 42-8 can have any number
of configurations for receiving a signal, the connectors are
preferably 75 ohm coaxial connectors such as BNC type connectors or
F type connectors. The connectors 42-0 to 42-8 are preferably
connected to a rear edge of the circuit board 32 by conventional
techniques such as card edge connectors. Additionally, grounded
shields of the connectors 42-0 to 42-8 are preferably in electrical
contact with the housing 12. Monitor ports 41 are electrically
connected to the circuit board 32, and are adapted to be mounted at
the front 16 of the housing 12.
[0029] FIG. 2 schematically depicts an exemplary circuit diagram
for one plug 30 of the combiner of FIG. 1. In a preferred
embodiment, the plug 30 houses an attenuator circuit. As shown in
FIG. 2, the combiner includes a first two-to-one combiner 44-1
preferably in the form of a transformer electrically connected to
plug connector 36-1. The first combiner 44-1 and a second combiner
(not shown) are electrically connected to a fifth two-to-one
combiner 44-5. The fifth two-to-one combiner 44-5 and a sixth
two-to-one combiner (not shown) are electrically connected to a
seventh two-to-one combiner 44-7. The seventh two-to-one combiner
44-7 is electrically connected to a directional coupler 46. The
directional coupler 46 is electrically connected to coaxial
connector 42-0 as well as monitor port 41 as is well known to those
of ordinary skill in the art.
[0030] While the configuration of FIG. 2 has been described as an
eight to one coupler, it will be appreciated that the same
configuration could also be used as an eight-to-one splitter with
monitor capabilities by slightly modifying the configuration of the
directional coupler 46. In other words, it will be understood by
those of skill in the art that the transformers 44-1 to 44-7 can be
used as splitters as well as combiners.
[0031] Referring to FIG. 2, the plug connector 36-1 includes a
dielectric housing 300 only a portion of which is illustrated that
can be mounted at the edge of the circuit board as will be
described in detail with reference to FIG. 6. Two through-contacts
302 (i.e., IN and OUT contacts) are mounted within the housing 300.
One of the through-contacts 302 is electrically connected to the
combiner 44-1, and the other through-contact 302 is electrically
connected to the coaxial connector 42-1. A conductive bypass-path
304 is used to provide an electrical connection between the two
through-contacts 302. The bypass-path 304 includes contact regions
306 positioned adjacent to each of the through-contacts 302. The
base member connector 36-1 also includes a ground contact 305
positioned between the two trough-contacts 302. The ground contact
305 is electrically connected to ground.
[0032] While the through-contacts 302 and the ground contact 305
could have a variety of different configurations, the contacts 302
and 304 are depicted in FIG. 2 as resilient, conductive springs.
The through-contacts 302 are preferably biased toward the contact
regions 306 of the bypass-pathway 304 such that when no plug is
inserted in the housing 300, the through-contacts 302 engage their
respective contact regions 306 (i.e., the through-contacts
"normally" engage the contact regions). The engagement between the
through-contacts 302 and the contact regions 306 causes the
bypass-pathway circuit 304 to be closed such that signals can be
routed through the plug connector 36-1 even in the absence of a
plug. Each plug 30 has three exposed terminals 308,310 that will be
electrically coupled to the circuit board. It will be appreciated
that contacts 302, 305, and terminals 308 and 310 may not all be
located in the same plane.
[0033] As can be seen in FIG. 3, the front 16 of the housing 12 has
a longitudinal axis L that extends from one of the pair of sides 20
to the other sidewall 22. The receptacles 14 in the front 16 of the
housing 12 also each have a longitudinal axis 1. As can be seen in
FIG. 3, for example, the longitudinal axis 1 of each receptacle 14
is an angle .alpha. with respect to the longitudinal axis L of the
front 16. In a preferred embodiment, the angle may range from about
.+-.10 degrees to about .+-.80 degrees. In a preferred embodiment,
the angle is about .+-.45 degrees. Because of this angle, the IN
and OUT terminals of each plug 30 will straddle the circuit board
32. So the IN terminal will make contact with a first side of the
circuit board and the OUT terminal will make contact with a second,
opposite side of the circuit board as will be described with
respect to FIG. 8. Thus, unlike a mounting which was previously
described where all terminals are located on one side of the
circuit board, by angling the receptacles, there is no need for
using vias, for example, to bring a terminal into electrical
contact with the proper layer of the circuit board. Because the IN
and OUT terminals are located on opposite sides of the circuit
board, isolation between ports is improved. In addition, parasitics
and insertion loss are reduced and return loss of a specific port
is increased.
[0034] Also, by placing the receptacles 14 at an angle, the density
of plugs 30 can be increased because less space is used.
[0035] The front 16 of the housing 12 has a thickness (t)
preferably ranging from about 0.2 inches to about 0.8 inches. The
receptacles extend through the front 16 and create a waveguide 31
that helps reduce the signals emitted from the module. In addition,
because the front 16 is thicker than known systems, the circuit
board 32 located in the interior of the housing 12 is pushed
further away from the front 16 of the housing 12. Due to the
combination of the spacing and the thick, waveguide-shaped
receptacles 14, the module 10 does not need any additional EMI
shielding over the receptacles 14 and yet the module still radiates
signals that are reduced to better than 100 dB down from the
carrier. In modules that do use a conductive cover for shielding,
when the cover is removed, signals that are only 60 dB down from
the carrier are emitted which cause interference at the headend.
Thus, the plugs 30 are readily accessible and can be replaced
without the use of tools and the amount of signal emitting into the
headend is not significantly changed. In addition, because the
plugs 30 are longer in length in order to reach the plug
connectors, the circuitry located inside the plastic housing of the
plug is located near the exposed terminals of the plug. When the
plug 30 is inserted in the plug connector, the circuitry in the
plug is now located inside the module 10 instead of exterior
thereto. This also provides improved performance.
[0036] The region 33 surrounding the receptacles may be recessed as
shown to allow a cover to be placed over the receptacles 14. While
not necessary for shielding purposes, such a cover may be desirable
for aesthetic reasons. In addition, a cover may be desirable to
prevent access to the plugs. Because the cover is not needed for
purposes of shielding, it may be made out of a nonconductive
material thereby resulting in cost savings from known systems.
[0037] FIG. 4 is a perspective view of the module shown in FIG. 1
with one of the covers 40 affixed to the front 16 of the housing 12
and the other cover 40 removed. The covers 40 may be provided with
snapping barbs 15 to fasten the covers 40 to the front 16 of the
housing 12. To remove a cover 40 from the front 16, opposite sides
of the cover may be squeezed to disengage the snapping barbs from
the recessed area in the front 16.
[0038] FIG. 5 is an exploded view of the module shown in FIG. 1. It
can be appreciated in FIG. 5 that a majority of the circuit board
is pushed back away from the front 16.
[0039] FIG. 6 is an exploded view of a portion of the circuit
board, plug connector and plugs according to a preferred embodiment
of the present invention. The plug connector 36-1 has a groove 37
extending along a back wall of the plug connector 36-1. A front
edge of the circuit board 32 fits into the groove. Each plug 30 has
three exposed terminals in a rear portion of the plug. Partially
located in the plug connector 36-1 are three sockets 39, one for
each of the plugs terminals. The sockets 39 are only partially
inserted in the plug connector, the remaining portion is exposed so
that it may make electrical contact with appropriate layers on the
circuit board 32 as will be described in detail hereinafter. The
circuit board 32 has a plurality of layers. On a first side 43 the
board will have conductive traces and circuitry such as
transformers (none of which are illustrated). Likewise, a second
side opposite the first side 43 also will have conductive traces
and circuitry. Located along the front edge of the circuit board
are a plurality of recesses 44. Recesses 44 expose a conductive
trace 45 located in the center of the board. This conductive trace
45 is held at ground. When the sockets 39, plug connectors 36-1,2
and circuit board 32 are assembled, the middle socket is located in
a recess 44 and the exposed portion of the socket is soldered to
trace 45. The other two terminals adjacent the middle one extend
through their respective sockets and one terminal will lie on a top
surface of the circuit board and the other terminal will lie on a
bottom surface of the circuit board.
[0040] FIG. 7 is a top view of the module shown in FIG. 1. FIG. 8
is a cross-sectional view of the module shown in FIG. 7 taken along
lines 8-8. In the cross section, all of the parts are assembled.
FIG. 9 is an enlarged view of a portion of the cross-section shown
in FIG. 8 showing the arrangement of the plug connector 36-1, plug
30 and circuit board 32. The middle terminal 33 slides inside the
middle socket which is electrically coupled to the ground trace
located in the center of the circuit board. One of the other two
terminals 35 is shown contacting the bottom surface of the circuit
board and the other terminal is not shown but contacts the top
surface of the circuit board.
[0041] FIG. 10 is a side view of a module 100 according to another
preferred embodiment of the present invention. Some internal
structures of the module 100 are shown in dashed lines. Not all of
the internal structures of the module 100 have been illustrated. In
addition, no external structure such as mounting flanges or
connectors has been illustrated for purposes of clarity. In this
preferred embodiment, a housing 112 preferably made of conductive
material houses a circuit board 132. In this preferred embodiment,
the circuit board has been rotated 90 degrees from the preferred
embodiments already discussed. Located in the front 116 of the
housing 112 are a plurality of receptacles 114 sized to receive
plugs 130. The receptacles 114 are formed in the housing which is
made of conductive material and thus the receptacles form
waveguides that attenuate emissions. FIG. 11 is a front view of the
module 100 shown in FIG. 10.
[0042] FIG. 12 is a cross-sectional view of a portion of a
receptacle according to a preferred embodiment of the present
invention. Instead of making the front of the housing thicker to
create the waveguide, the plug connector itself may be provided
with its own individual waveguide. As seen in FIG. 12, the plug
connector forms a receptacle to receive a plug and has a front
portion 200 and a rear portion 202. The front portion 200 is made
of conductive material whereas the rear portion 202 is made of
nonconductive material. The front portion 200 of the plug connector
thus form the waveguide.
[0043] The above specification, examples and data provide a
complete description of the manufacture and use of the composition
of the invention. Since many embodiments of the invention can be
made without departing from the spirit and scope of the invention,
the invention resides in the claims hereinafter appended.
* * * * *