Note: Descriptions are shown in the official language in which they were submitted.
i767
-1- 26775-~5
This invention relates to a high frequency attenuation
cable and to a high frequency attenuation cable harness.
High frequency attenuation cables are well known. In
general, such cables include an absorption medium which filters
out high frequency energy which could otherwise interfere with
the operation of the cable. The effectiveness with which the
high frequency energy is filtered out is referred to as the high
frequency attenuation. The greater the attenuation, the higher
the effectiveness.
Various attempts have been made to improve the high
frequency attenuation of these cables. In this regard, see for
example, Mayer, USP 4,301,428; Martin, USP 4J347~487; Cornelius
et al., USP 4,486,721; and Cornelius et al., USP 4,499,438.
These references generally disclose a cable construction
in which a conductor is surrounded, in order, by a high frequency
energy attenuation medium, a dielectric, and an electrically con-
ductive shielding means. In the Cornelius et al. application,
the relative positions of the high frequency energy attenuation
medium and the dielectric are reversed.
~0 While the high frequency attenuation cables described
in the above references have improved high frequency atte-
~,r; ~
--2--
nuation above 100 megahertz (MHz), the attenuation in the
range of 10 to 100 MHz is somewhat less than that desired
for certain applications. This invention provides a high
frequency attenuation cable having improved high frequency
attenuation in the 10-100 MHz range.
One aspect of this invention comprises a high frequency
attenuation cable comprising a core comprising at least one
conductor, each said conductor being surrounded by a layer
of high dielectric constant material having a dielectric
constant greater than about 4 when measured at 10 MHz and a
volume resistivity of at least about 1013 ohm-cm; and a
layer of high frequency absorption medium. The high
dielectric constant material preferably also has a tensile
strength of at least about 4,000 pounds per square inch
(psi). Additional layers of the absorption medium and/or
the high dielectric material and/or a second dielectric
material may also be present.
It should be understood that the core is that portion of
the cable which is surrounded by the electrically conductive
shield and any outer or protective jacketing.
I have discovered that the use of a high dielectric
constant material surprisingly and unexpectedly improves the
high frequency attenuation in the frequency range of 10 to
100 MHz.
Figure 1 is a cut-away side view of one embodiment of
a cable construction according to the invention~
~5~7~7
--3--
Figure 2 is a cut-away side view of another embodiment
of a cable construction according to the invention.
Figure 3 is a cross-sectional view of one embodiment
of a cable harness according to the invention.
Figure 4 is a cross-sectional view of another embodi-
~ent of a cable harness according to the invention.
Figures 5 and 6 are graphs of attenuation versus
frequency for cable constructions according to the inven-
tion compared ~o cable constructions according to the prior
art.
Referring to the figures in more detail, and par-
ticularly referring to Figure 1, there is disclosed a high
frequency attenuation cable 2. The cable comprises a core
which, in turn, comprises conductor 4, a layer of high fre-
quency absorption medium 6 surrounding the conductor, and a
layer of high dielectric constant material 8 surrounding the
high frequency absorption medium.
It is to be understood that the cable may further
comprise additional layers of absorption medium, high
dielectric constant material, a second dielectric material
and the like. Further the cable generally also is provided
with an electrically conductive shield and a protective
outer jacket.
As will become more apparent hereafter~ the use of a
layer of high dielectric constant material accordin~ to the
;7~7
,~,
invention markedly increases the high frequency attenuation
of the cable in the frequency range of 10 to 100 MHz.
The term "high dielectric constant material" is used
herein to mean a material has a dielectric constant (~)
greater than about 4 when measured at 10 MHz. Further, the
material has a volume resistivity of at least about 1013
ohm-cm. The high dielectric constant material preferably
also has a tensile strength greater than about 4,000 psi. A
preferred high dielectric constant material is polyvinyli-
dene fluoride. The term polyvinylidene fluoride is used
herein to mean polymers of vinylidene fluoride. The homopo-
lymer is preferred. Polyvinylidene fluoride is commercially
available under the trademark Kynar from Pennwalt
Corporation, Philadelphia, PA.
In typical prior art high frequency attenuation cable
construction there generally is a conductor surrounded by a
high frequency absorption medium which is in turn surrounded
by a dielectric material such as polyethylene or TEFZEL~
(TEFZEL is a copolymer of ethylene and tetrafluoroethylene
and is a product of E.I. duPont de Nemours, Wilmington,
DE). Both polyethylene and TEFZEL are materials having low
dielectric constants (~ of about 2-3). As mentioned above
prior art cables exhibit lower high frequency attenuation in
the frequency range of 10-100 MHz than is desirable for cer-
tain uses.
The high frequency absorption medium such as the well-
known lossy materials disclosed in the Cornelius et al.
i5~67
-5- 26775-45
references serves to allow the passage of low frequency energy
but absorbs the high frequency energy. Lossy materials are also
disclosed in Mayer, USP 3,309,633 and USP 3,191,132. A preferred
lossy material for the present invention is ferrite-loaded poly-
mer, for example, ferrite-loaded VITONR A (VITON A is a copoly-
mer of vinylidene fluoride and hexafluoropropylene and is a
product of E.I. Du Pont de Nemours, Wilmington, DE).
In Figure 2 there is disclosed a second embodiment of
the invention. As shown in the figure, there is a high frequency
attenuation cable 2'. The cable comprises a conductor 4, a
layer of high dielectric constant material 9 surrounding the con-
ductor, a layer of high frequency absorption medium 6 surrounding
the layer 9 of high dielectric constant material, and an addi-
tional layer of dielectric material 8 surrounding the layer of
high frequency absorption medium. The dielectric material of the
additional layer can be a high dielectric constant material, as
defined herein, or a second dielectric material, e.g. one having
a lower dielectric constant, e.g. below about 3.
It has been found that when high dielectric constant
material is located both inside and outside of the high frequency
absorption medium that similar results are obtained as when a
layer of high dielectric constant material having a thickness
equal to the total thickness of the two layers is located only
outside of the absorption medium.
~2~6~
--6--
Another embodiment of the high frequency attenuation
cable (not shown) comprises a conductor, a layer of high
dielectric constant material surrounding the conductor, and
a high frequency absorption medium surrounding the layer of
high dielectric material. It is believed that this cable
construction will also lead to improved high frequency atte-
nuation in the 10 to 100 megahertz range, as was the case
with the previous embodiments.
Thus, it is now apparent that the high dielectric
material, preferably polyvinylidene fluoride, can be
located either inside of the high frequency absorption
medium or outside of the high frequency absorption medium
or both inside and outside of the high frequency absorption
medium. Further, a layer of dielectric material having a
dielectric constant less than about 3 can be included in the
construction, preferably as an outermost layer.
The additional layer of dielectric material can be
selected to provide desired electrical and/or mechanical
properties. For example, for maximum attenuation, it is
believed that the additional layer should be of a high
dielectric constant material, e.g. polyvinylidene fluoride.
In certain situations it may be desirable to optimize the
overall capacitance of the cable making it as low as
possible while still maintaining good attenuation. In such
a situation a material having a lower dielectric constant,
e.g. polyethylene or TEFZEL, can be used. In other instan-
ces the selection of the additional layer of dielectric
material is made to provide good mechanical properties. For
ii7~7
example good solvent resistance, toughness, abrasion
resistance, cut through resistance and the like may lead to
the selection of a particular dielectric material even if
optimum electrical performance is not achieved. Suitable
dielectric materials under these criteria include polyethy-
lene, polyvinyl chloride, TEFZEL, polyesters, polyamides,
polyamide-imides, polyether-esters, and the like also poly-
meric blends. The high dielectric constant material and the
second dielectric material, if present, can include various
additives such as stabilizers, pigments, flame retardants,
processing aids and the like.
The cable constructions may further comprise an
electrically conductive shielding means surrounding the core
and an outer jacket surrounding the shielding means.
It has been found that the use of a high dielectric
constant material, as defined above, leads to significantly
improved performance~ It has also been found that reducing
the wall thickness of the high dielectric constant material
will also lead to enhanced performance. Thus, in a pre-
ferred embodiment of this invention, a relatively thin layer
of high dielectric constant material is used. While the
reason for the improved performance is not fully understood,
it is believed to be due to the increased capacitance bet-
ween the absorptive material and the conductor when the high
dielectric constant material is positioned therebet~een or
between the absorptive medium and the electrically conduc-
tive shield when the high dielectric material is positioned
outside of the absorptive medium. The capacitance is
i767
--8--
further increased if the layer of the high dielectric
constant material is relatively thin.
Further disclosed according to the invention, as
illustrated in Figures 3 and 4, are high frequency atte-
nuation cable harnesses. Each of the cable harnesses
comprises a plurality of cables with each cable having a
core as described above. Thus~ in general the core will
comprise a conductor, a high frequency absorption medium
surrounding the conductor and at least one layer of high
dielectric constant material, preferably polyvinylidene
fluoride. The only difference between the various cores
will be the location of the high dielectric constant
material w~ich may be inside or outside, or both inside and
outside of the high frequency absorption medium.
Figure 3 illustrates one embodiment of a cable harness
20 having a plurality of cables 22 in which, in each core
there is a conductor 24 surrounded by a high frequency
absorption medium 26 which in turn is surrounded by a layer
of high dielectric constant material 28.
Similarly, in Figure 4, each cable 42 of cable harness
40 has a core having at least one conductor 44 surrounded
by a high frequency absorption medium 46 which is in turn
surrounded by a layer of high dielectric constant material
48.
The main distinguishing feature between the construc-
tions in Figures 3 and 4 is how the individual cables are
~57Ç~
shielded. Thus, in Figure 3 each cable comprises electri-
cally conductive shielding means 30 surrounding each of the
cores and an outer jacket 32 surrounding each of the
electrically conductive shielding means. The construction
in Figure 3 may further comprise protective outer jacketing
34 surrounding the plurality of cables.
Returning to Figure 4, the cable harness 40 comprises
gross electrically conductive shielding means 50 surrounding
the plurality of cables and protective outer jacketing 52
surrounding the shielding means.
As stated above, the high frequency absorption medium
may be any of the well-known lossy materials. However the
preferred lossy material is ferrite-loaded polymer and more
preferably ferrite-loaded VITON.
The advantages of the invention will become more
apparent a~ter reference to the following examples.
Two samples were prepared each by extruding a first
layer (about 15 mils thick) of high frequency absorption
medium tabout 5 mils thick) onto a stranded conductor 40
mils in diameter and then a second layer (about 5 mils
thick) of dielectric material. Each core was surrounded by
metallic braid for shielding and then surrounded by outer
jacketing. The only difference between the sa~ples was that
in one sample the dielectric material was TEFZEL (low
~L~55'7~7
--10--
dielectric constant material) and in the other sample the
insulation layer was KYNAR, polyvinylidene fluoride (high
dielectric constant material). Each sample was surrounded
by a metallic braid and the insertion loss was measured.
The results are illustrated in Figure 5.
As can be seen, the cable construction having the
KYNAR insulation layer (Sample 2) is far superior over the
entire frequency range to the cable construction having the
TEFZEL insulation layer (Sample 1). Most importantly, in
the critical range of 10 to 100 MHz the attenuation has
been dramatically improved.
Example II
Two other samples were similarly prepared. Both of the
samples in general had a conductor surrounded by a layer of
lossy material which in these samples consisted of 30 volume
percent of ferrite in VITON. The cable constructions
further comprised a layer of insulative dielectric material
surrounded by electrically conductive shielding means and
finally surrounded by outer jacketing. The results are
illustrated in Figure 6.
The only difference between the samples was that
Sample 1 had KYNAR (high dielectric constant material) insu-
lation and the other sample (Sample 2) had polyethylene (low
dielectric constant material) insulation. As can be seen in
Figure 6 the sample having the KYNAR is far superior over
the entire frequency range to the sample having the
~2~iiS7Çii7
--11--
polyethylene insulation. And again most importantly, in the
critical range of 10 to 100 MHz, the attenuation of the
sample having KYNAR insulation is markedly improved over the
sample having the polyethylene insulation.
In view of the above results it can be appreciated
that by using an insulation layer of high dielectric
constant material, preferably polyvinylidene fluoride
(commercially available as KYNAR) that the attenuation of
the cable construction in the frequency range of 10 to 100
MHz is surprisingly and unexpectedly improved over the prior
art cable constructions using polyethylene, TEFZEL, or other
similar insulation materials.
Example III
A sample was prepared by extruding a first layer of
polyvinylidene fluoride having a wall thickness of 3 mils
onto a stranded, tin plated 20 AWG copper conductor. Onto
this was extruded a 4 mil layer of ferrite filled VITON A as
described in Examples I and II. A third layer consisting of
an ethylene tetrafluoroethylene copolymer (ETFE) with a wall
thickness of 4 mils wa5 then extruded on top of the first
two layers. The sample was then surrounded with a metallic
braid, and the insertion loss was measured. The results
were as follows:
~2Si~7Çi7
-12-
FrequencyInsertion Loss
10 MHz 0.2 dB/ft
100 MHz 2.8 dB/ft
500 MHz 18.0 dB/ft
1000 MHz 41.7 dB/ft
While the invention has been described herein in accor-
dance with certain preferred embodiments thereof, many modi-
fications and changes will be apparent to those skilled in
the art. Accordingly, it is intended by the appended claims
to covsr all such modifications and changes as fall within
the true spirit and scope of the invention.
