U.S. patent application number 13/354638 was filed with the patent office on 2012-08-09 for conformal electronic device.
Invention is credited to Yakup Bayram, John L. Volakis, Zheyu Wang, Lanlin Zhang.
Application Number | 20120199056 13/354638 |
Document ID | / |
Family ID | 46599780 |
Filed Date | 2012-08-09 |
United States Patent
Application |
20120199056 |
Kind Code |
A1 |
Bayram; Yakup ; et
al. |
August 9, 2012 |
CONFORMAL ELECTRONIC DEVICE
Abstract
A method for manufacturing a conformal electronic device
includes securing an electrically-conductive fiber to a fabric or
substrate using an assistant thread.
Inventors: |
Bayram; Yakup; (Falls
Church, VA) ; Zhang; Lanlin; (Columbus, OH) ;
Wang; Zheyu; (Columbus, OH) ; Volakis; John L.;
(Columbus, OH) |
Family ID: |
46599780 |
Appl. No.: |
13/354638 |
Filed: |
January 20, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61434479 |
Jan 20, 2011 |
|
|
|
Current U.S.
Class: |
112/475.08 ;
112/475.19 |
Current CPC
Class: |
D05D 2303/40 20130101;
D05B 23/00 20130101 |
Class at
Publication: |
112/475.08 ;
112/475.19 |
International
Class: |
D05B 19/00 20060101
D05B019/00 |
Goverment Interests
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] This invention was made with government support under Grant
FA 9550-07-1-0462 awarded by the Air Force Office of Scientific
Research (AFOSR). The government has certain rights in the
invention.
Claims
1. A method for manufacturing a conformal electronic device,
comprising: providing an electrically-conductive fiber in proximity
to a first surface of a substrate; and sewing an assistant thread
through the first surface, around the electrically
conductive-fiber, and back through the first surface to secure the
electrically-conductive fiber to the substrate.
2. The method of claim 1, wherein the substrate comprises a
silicon-based polymer.
3. The method of claim 2, wherein the silicon-based polymer is a
polysiloxane or a polysilsesquioxane.
4. The method of claim 3, wherein the polysiloxane is
polydimethylsiloxane.
5. The method of claim 2, wherein the substrate further comprises a
ceramic material dispersed in the silicon-based polymer.
6. The method of claim 5, wherein the ceramic material comprises a
titanate.
7. The method of claim 6, wherein the titanate is a rare earth
titanate.
8. The method of claim 1, wherein the electrically-conductive fiber
comprises one or more electrically-conductive threads; and wherein
each of said one or more electrically-conductive threads comprises
a core and a conductive shell.
9. The method of claim 8, wherein the conductive shell comprises a
conductive material selected from the group consisting of carbon
nanotubes and metals.
10. The method of claim 9, wherein the metal is selected from the
group consisting of silver, copper, and nickel.
11. The method of claim 8, wherein the core comprises an aramid
fiber or an oxazole.
12. The method of claim 1, wherein the sewing is performed in a
predetermined pattern using a digitized sewing machine.
13. The method of claim 1, wherein the substrate is pre-stretched
prior to sewing.
14. The method of claim 1, wherein the conformal electronic device
further comprises a fabric layer between the substrate and the
electrically-conductive fiber.
15. A method for manufacturing a conformal electronic device,
comprising: providing an electrically-conductive fiber in proximity
to a first surface of a fabric; and sewing an assistant thread
through the first surface, around the electrically
conductive-fiber, and back through the first surface to secure the
electrically-conductive fiber to the fabric to form an embroidered
fabric.
16. The method of claim 15, further comprising: securing the
embroidered fabric to a substrate.
17. The method of claim 16, wherein the substrate comprises a
silicon-based polymer matrix and a ceramic material dispersed
within the silicon-based polymer matrix.
18. The method of claim 15, wherein the electrically-conductive
fiber comprises one or more electrically-conductive threads; and
wherein each of the one or more electrically-conductive threads
comprises a core and an electrically-conductive shell.
19. The method of claim 18, wherein the electrically-conductive
shell comprises a conductive material selected from the group
consisting of carbon nanotubes and metals.
20. A method for manufacturing a conformal electronic device,
comprising: providing a predetermined digital pattern to a sewing
machine; and embroidering the pattern onto a first surface of a
substrate with an electrically-conductive fiber using an assistant
thread from the sewing machine; wherein the embroidering is
performed by (a) providing a portion of the electrically-conductive
fiber in proximity to a pattern section of the first surface of the
substrate; (b) sewing the assistant thread from a second surface of
the substrate through the first surface, around the portion of the
electrically-conductive fiber, and back through the first surface
to secure the portion of the electrically-conductive fiber to the
pattern section of the substrate; and (c) repeating elements (a)
and (b) for different portions of the electrically-conductive fiber
and different pattern sections of the first surface of the
substrate until the pattern is complete.
Description
[0001] This application claims priority to and the benefit of U.S.
Provisional Patent Application Ser. No. 61/434,479, filed Jan. 20,
2011. Ser. No. 61/434,479 is incorporated by reference herein in
its entirety.
BACKGROUND
[0003] The present disclosure relates to conformal electronic
devices and methods for manufacturing the same. It finds particular
application in conjunction with antennas, and will be described
with particular reference thereto. However, it is to be appreciated
that the present exemplary embodiment is also amenable to other
like applications.
[0004] Conformal electronic devices have recently attracted
considerable attention for various electromagnetic applications
including wearable electronic devices and antennas for unmanned
aerial vehicles. Conformal electronic devices must exhibit suitable
electrical properties and performance while also providing
mechanical conformity and flexibility. Previously known processes
for manufacturing conformal electronic devices may yield
mechanically or electrically deficient products and/or may be
complicated and difficult to reproduce.
[0005] It would be desirable to develop new fabrication methods for
manufacturing conformal electronic devices.
BRIEF DESCRIPTION
[0006] The present disclosure relates to methods for manufacturing
conformal electronic devices. The methods comprise securing
electrically-conductive fibers to a fabric or substrate using an
assistant thread.
[0007] Disclosed in embodiments is a method for manufacturing a
conformal electronic device. The method includes providing an
electrically-conductive fiber in proximity to a first surface of a
substrate; and sewing an assistant thread through the first
surface, around the electrically conductive-fiber, and back through
the first surface to secure the electrically-conductive fiber to
the substrate.
[0008] The substrate may include a silicon-based polymer. The
silicon-based polymer may be a polysiloxane or a
polysilsesquioxane. The polysiloxane may be
polydimethylsiloxane.
[0009] The substrate may further include a ceramic material
dispersed in the silicon-based polymer. The ceramic material may be
a titanate. The titanate may be a rare earth titanate.
[0010] The electrically-conductive fiber may include one or more
electrically-conductive threads. Each thread may include a core and
a conductive shell. The conductive shell includes a conductive
material. The conductive material may be selected from carbon
nanotubes and metals. The metal may be silver, copper, or nickel.
The core may include an aramid fiber or an oxazole.
[0011] The sewing may be performed in a predetermined pattern using
a digitized sewing machine.
[0012] The substrate may be pre-stretched prior to sewing.
[0013] The electronic device may further include a fabric layer
between the substrate and the electrically-conductive fiber.
[0014] Also disclosed is another method of manufacturing a
conformal electronic device. The method includes providing an
electrically-conductive fiber in proximity to a first surface of a
fabric; and sewing an assistant thread through the first surface,
around the electrically conductive-fiber, and back through the
first surface to secure the electrically-conductive fiber to the
fabric to form an embroidered fabric.
[0015] The method optionally includes securing the embroidered
fabric to a substrate. The substrate may include a silicon-based
polymer matrix and a ceramic material dispersed within the
silicon-based polymer matrix.
[0016] The electrically-conductive fiber may include one or more
electrically-conductive threads. Each thread may include a core and
an electrically-conductive shell. The shell includes a conductive
material. The conductive material may be selected from carbon
nanotubes and metals.
[0017] Further disclosed is another method for manufacturing a
conformal electronic device. The method includes providing a
predetermined digital pattern to a sewing machine; and embroidering
the pattern onto a first surface of a substrate with an
electrically-conductive fiber using an assistant thread from the
sewing machine. The embroidering is performed by (a) providing a
portion of the electrically-conductive fiber in proximity to a
pattern section of the first surface of the substrate; (b) sewing
the assistant thread from a second surface of the substrate through
the first surface, around the portion of the
electrically-conductive fiber, and back through the first surface
to secure the portion of the electrically-conductive fiber to the
pattern section of the substrate; and (c) repeating elements (a)
and (b) for different portions of the electrically-conductive fiber
and different pattern sections of the first surface of the
substrate until the pattern is complete.
[0018] These and other non-limiting aspects and/or objects of the
disclosure are more particularly described below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] The following is a brief description of the drawings, which
are presented for the purposes of illustrating the exemplary
embodiments disclosed herein and not for the purposes of limiting
the same.
[0020] FIG. 1 is a side-view of a conformal electronic device being
manufactured in accordance with an exemplary method of the present
disclosure.
[0021] FIG. 2 is a cross-sectional view of an exemplary electronic
device of the present disclosure.
[0022] FIG. 3 is a graph illustrating the dielectric constant of
composite materials including varying amounts of a ceramic
material.
DETAILED DESCRIPTION
[0023] A more complete understanding of the processes and
apparatuses disclosed herein can be obtained by reference to the
accompanying drawings. These figures are merely schematic
representations based on convenience and the ease of demonstrating
the existing art and/or the present development, and are,
therefore, not intended to indicate relative size and dimensions of
the assemblies or components thereof.
[0024] Although specific terms are used in the following
description for the sake of clarity, these terms are intended to
refer only to the particular structure of the embodiments selected
for illustration in the drawings, and are not intended to define or
limit the scope of the disclosure. In the drawings and the
following description below, it is to be understood that like
numeric designations refer to components of like function.
[0025] The modifier "about" used in connection with a quantity is
inclusive of the stated value and has the meaning dictated by the
context (for example, it includes at least the degree of error
associated with the measurement of the particular quantity). When
used with a specific value, it should also be considered as
disclosing that value. For example, the term "about 2" also
discloses the value "2" and the range "from about 2 to about 4"
also discloses the range "from 2 to 4."
[0026] The present disclosure relates to methods for manufacturing
conformal electronic devices. The methods generally include
securing an electrically-conductive fiber to a fabric or substrate
using an assistant thread.
[0027] FIG. 1 is a side perspective view of an electronic device
being manufactured with an apparatus 100 in accordance with an
exemplary embodiment of the present disclosure. An
electrically-conductive fiber 110 is fed to close proximity to a
first surface 124 of a fabric or substrate 120 from an
electrically-conductive fiber source 115. The fabric or substrate
120 is guided by a second guiding member 140 and a first guiding
member 145. An assistant thread 150 is provided through a needle
160. The needle 160 enters the second surface 122 of the substrate
120, passes through the substrate 120, and emerges through the
first surface 124. The assistant thread 150 and/or the
electrically-conductive fiber 110 are arranged such that the
assistant thread 150 surrounds a portion of the
electrically-conductive fiber 110 on a side opposite the substrate
120. As the needle 160 is brought back through the substrate 120,
the assistant thread 150 secures or couches the
electrically-conductive fiber 110 to the first surface 124 of the
substrate 120. The process may be repeated until a desired pattern
or surface conductivity is achieved.
[0028] The electrically-conductive fiber source 115 may comprise a
spool or a bobbin loaded with the electrically-conductive fiber
110. The electrically-conductive fiber 110 may have a diameter
larger than the hole in the needle 160. In some embodiments, the
diameter of the electrically-conductive fiber 110 is larger than
the diameter of the needle 160. The guiding members 140 and 145,
needle 160, and electrically-conductive fiber source 115 may be
parts of a computerized sewing machine. In some embodiments, the
sewing machine can receive a desired digital pattern and produce
the pattern on the fabric or substrate 120 with the
electrically-conductive fiber 110. The methods of the present
disclosure may also be performed manually.
[0029] FIG. 2 is a cross-sectional view of an exemplary electronic
device 200 of the present disclosure. The electronic device 200
includes an electrically-conductive fiber layer 210, an optional
fabric layer 220, a substrate 230, an optional reinforcing layer
240, a ground plane 250, and a via hole 260 electrically connecting
the fiber layer 210 to the ground plane 250.
[0030] The substrate 230 may comprise a polymer. The substrate may
also comprise a ceramic material. In some embodiments, the ceramic
material is dispersed in a matrix of the polymer to form a
composite. In some embodiments, the substrate has a thickness in
the micrometer or centimeter range. The substrate may be
pre-stretched prior to stitching. The term "pre-stretched" refers
to the substrate being in a stretched position during stitching.
Stitching on a pre-stretched substrate may be used to ensure that
the electrically-conductive fiber will have sufficient leeway
during subsequent stretching and relaxation of the substrate.
[0031] In some embodiments, the polymer is a liquid crystal
polymer, Parylene-N, or a silicon-based polymer. Exemplary
silicon-based polymers include polysiloxanes and
polysilsesquioxanes. The polysiloxane may be polydimethylsiloxane
(PDMS). PDMS can be used in flexible substrates and exhibits low
dielectric loss (tan .delta.), high water resistivity, high
temperature stability, high physical stability, and high chemical
stability. PDMS is also a relatively low cost material and is
relatively easy to use in fabrication processes. PDMS is also
compatible with ceramic materials, such as dielectric ceramic
powders. The density of PDMS is comparable to that of water and
less than many other potential substrate materials which allows
lighter-weight devices to be fabricated. This property may be
important for wearable devices and aerospace applications in
particular.
[0032] The ceramic material may comprise a titanate. Titanate
powders exhibit relatively high relative permittivities (.di-elect
cons..sub.r) at microwave frequencies. In some embodiments, the
titanate is a rare earth titanate (RET).
[0033] The dielectric properties of the substrate may be tuned by
varying the relative amounts of the polymer and the ceramic
material. The ability to tune the dielectric properties of the
substrate permits designing the substrate for a specific
application depending on the application frequencies. For example,
PDMS has an .di-elect cons..sub.r of about 3. By dispersing
TAMTRON.RTM. COG820MW (commercially available from Ferro), in a
PDMS matrix at varying concentrations of from 0 vol % to 30 vol %,
the .di-elect cons..sub.r of the resultant composite material can
be varied from about 3 to about 13. COG820MW is a barium neodymium
titanate-based material containing bismuth. For example, at 10 vol
% loading of COG820MW, an .di-elect cons..sub.r of about 4.2 and an
overall tan .delta. of less than 0.01 at 1 GHz can be achieved.
This particular relationship between ceramic material loading and
.di-elect cons..sub.r is specific to the polymer and ceramic
materials used. Relationships for other material systems can be
determined via experimentation.
[0034] Flexible polymer-ceramic substrates also provide versatile
dimensions, e.g. micrometer and centimeter range dimensions, for
printing highly detailed electronics.
[0035] The substrate may be formed by casting a substrate
composition comprising a polymer and, optionally, an amount of a
ceramic material sufficient to achieve desired dielectric
properties. The composition is preferably homogenously mixed to
disperse the ceramic material in the polymer matrix prior to
casting.
[0036] The substrate may be casted directly or tape-casted. In
direct casting, the substrate composition is poured into a target
mold. The mold is typically made of PMMA or glass, and preferably
has smooth, flat edges. For a PDMS matrix, shrinkage is typically
negligible after curing. Accordingly, the desired thickness of the
final substrate can be marked on the mold for guidance. Direct
molding may be performed for substrates having relatively small
lateral dimensions, e.g. on the order of several cm.
[0037] Tape-casting is commonly used for thick film fabrication and
low temperature co-fired ceramic (LTCC) processes. Tape-casting may
be particularly suitable for substrates having a thickness of 9 mm
or less. In tape-casting, the substrate composition is poured into
a film applicator. The applicator is glided smoothly across a flat
supporting platform. The supporting platform may include glass or
silicon. The thickness of the casted composition is controlled by
the applicator blade gap, viscosity, and casting speed.
[0038] The casted substrate is optionally degassed and partially
cured. Partial curing may be performed in an oven, on a hot plate,
or at room temperature. The oven may be at a temperature of from
about 50.degree. C. to about 100.degree. C., including about
60.degree. C. The hot plate may be at a temperature of from about
70.degree. C. to about 100.degree. C., including about 80.degree.
C. The partial curing may last for a period of from about 15 to
about 30 minutes, including from about 20 to about 25 minutes. The
partial curing time period could be reduced if the PDMS had been
precured. For example, if the PDMS was cured at room temperature
for about 9 hours before casting, then the partial curing step
length could be as short as 1.5 minutes.
[0039] In some embodiments, the electrically-conductive fiber layer
210 is secured directly to the substrate 230 by passing the
assistant thread through the substrate 230. A fabric layer 220 may
be included between the fibers 210 and the substrate 230 in these
embodiments. In other embodiments, the electrically-conductive
fibers 210 are secured to a fabric 220 to form an embroidered
fabric. The embroidered fabric may then be secured to the substrate
230. In these embodiments, that assistant thread passes through the
fabric layer 220 but need not pass through the substrate 230.
[0040] The embroidered fabric may be secured to the partially cured
substrate by contacting the embroidered fabric with a surface of
the substrate followed by curing. In some embodiments, the side of
the embroidered fabric which does not include
electrically-conductive fibers is the side brought into contact
with the substrate.
[0041] Electronic devices with multiple layers of
electrically-conductive fibers may be fabricated by securing each
electrically-conductive fiber-containing layer to a different
substrate. The surfaces to be joined may be cleaned and contacted
with an uncured or partially cured composition comprising the
substrate materials followed by lamination and curing. Curing may
be performed at a temperature of about 60.degree. C. for about 3
hours. In some embodiments, contact between the
electrically-conductive fibers and the uncured or partially cured
composition is avoided to prevent increasing the resistance of the
fibers.
[0042] Via holes 260 may be included to provide electrical paths
between different circuit layers within and/or on surfaces of the
substrate. The via holes may be created by piercing the substrate
with sharp needles. Conductive elements may be guided through the
holes to connect the circuit layers. In some embodiments, the
conductive elements are electrically-conductive fibers. These
elements may provide the additional benefit of further increasing
the mechanical strength of the overall structure of the electronic
device.
[0043] The fabric may comprise cotton, polyester, nylon, silk,
composites thereof, or any other fabric materials.
[0044] The electrically-conductive fibers may include one or more
threads having cores and conductive coatings or shells; yarns
bundled with thin metal filaments; yarns or fabrics embedded with
carbon nanotubes; and fabrics embedded with metal filaments. Fibers
having polymeric cores and metallic shells are preferred due to
their high mechanical strength and low material losses in radio
frequency applications. In some embodiments, each thread has a
diameter of from about 7 to about 15 .mu.m, including about 10
.mu.m. Each fiber may include from about 50 to about 2,000 threads,
including from about 150 to about 700 threads.
[0045] The core may comprise an aramid fiber or a polyoxazole. The
aramid fibers may be para-aramid fibers such as the KEVLAR.RTM.
fibers (commercially available from DuPont). The polyoxazole may be
p-phenylene-2,6-benzobisoxazole (PBO) such as ZYLON.RTM.
(commercially available from Toyobo). The core material imparts
mechanical strength and flexibility to the threads. The core may
have a diameter of from about 3 to about 10 .mu.m, including about
7 .mu.m.
[0046] The conductive shell may comprise a metal or carbon
nanotubes. In some embodiments, the metal is selected from the
group consisting of silver, copper, and nickel. The conductive
shell imparts electrical conductivity to the threads. The
conductive shell is preferably a uniform coating on the core and
may have a thickness of from about 1 to about 3 .mu.m.
[0047] A plurality of the threads may be bundled together to
achieve a desired thickness for the electrically-conductive fiber
and to enhance conductivity. The desired thickness may depend on
the specific circuit component being fabricated. Each fiber may
include from about 150 to about 700 threads. The fiber may have a
thickness of from about 0.05 to about 0.50 millimeters.
[0048] The fabric or substrate may be embroidered with the
electrically-conductive fibers at a stitching density greater than
30 stitches per cm.sup.2, including greater than 50 stitches per
cm.sup.2 and greater than 70 stitches per cm.sup.2. Increasing the
stitching density increases the surface conductivity of the device
since more conductive material is present per unit area.
[0049] The electrically-conductive layer may have a surface
conductivity of from about 0.2 to about 0.5 m.OMEGA./.quadrature.,
including from about 0.3 to about 0.4 m.OMEGA./.quadrature..
[0050] In some embodiments, a second layer of
electrically-conductive fiber(s) may be embroidered atop the first
layer. This process may be referred to as double-layer embroidery
and allows higher stitching density and thus conductivity to be
achieved.
[0051] The assistant thread may comprise cotton, polyester, nylon,
silk, or a composite thereof. In some embodiments, the assistant
thread comprises the same type of material as the fabric.
[0052] The optional reinforcement layer 240 may be added to enhance
the mechanical strength of the device. In some embodiments, the
reinforcement layer may not extend through the entire substrate,
such that the sections of the substrate to either side of the
reinforcement layer are in physical contact with each other. For
example, the reinforcement layer may have a grid configuration. The
reinforcement layer may comprise an aramid fiber or a polyoxazole.
In some embodiments, the reinforcement layer is woven into the
substrate.
[0053] The ground plane 250 comprises a conductive material. The
conductive material may be selected from the group consisting of
carbon nanotubes, metals, and electrically-conductive fibers. In
some embodiments, the metal is selected from the group consisting
of silver, nickel, and copper. The ground plane may be in the form
of a grid. In addition to serving an electrical function, the
ground plane may also reinforce the device mechanically. The
electrically-conductive fibers in the ground plane, in the via
holes, and in the electrically-conductive fiber layer may be the
same or different.
[0054] The manufacturing methods of the present disclosure may be
performed manually and/or through an automated process. The
automated process may include making or providing a design pattern
in an embroidery design computer program; and realizing the design
pattern on a fabric layer or substrate using a computerized sewing
machine. The design pattern may be selected based on the desired
properties for a particular application.
[0055] Aspects of the present disclosure may be further understood
by referring to the following examples. The examples are
illustrative, and are not intended to be limiting embodiments
thereof.
Examples
[0056] AMBERSTRAND.RTM. fibers (commercially available from Syscom
Advanced Materials), which include PBO cores and silver coatings,
were utilized as the electrically-conductive fibers in the
Examples. AMBERSTRAND.RTM. fibers exhibit high tensile strength,
flexibility, and a very low resistivity of 0.8 .OMEGA./m. These
fibers possess high strength needed for load-bearing applications
while maintaining high electrical conductivities at radio
frequencies.
Substrate Formation and Single Layer Embroidered Fabric
Attachment
[0057] SYLGARD.RTM. 184 (commercially available from Dow Corning),
a silicone elastomer including a base and a curing agent,
(commercially available from Dow Corning) was added to a high
density polyethylene (HDPE) container at a weight ratio of 10:1 (50
g PDMS base and 5 g curing agent). The HDPE container had a smooth
internal surface to minimize bubble formation.
[0058] The inner and outer caps of the container were closed and
the container was weighed. The container was placed inside a vacuum
mixer. The vacuum mixer was adjusted to the container's weight. The
mixer was set to a rotation speed of from 1,500 to 2,000 rpm, a
vacuum pressure of 10 kPa, and a mixing time of 100 to 120 seconds.
The container was removed from the mixer after mixing. Four
separate batches were prepared.
[0059] COG820MW was added to three of the four batches in varying
amounts of 10 vol %, 20 vol %, and 30 vol %.
[0060] Each batch was tape-casted on a glass platform to form a
thick substrate having smooth surfaces and a uniform thickness.
[0061] The casted substrate was partially cured at a temperature
about 55.degree. C. for about 10 minutes. The partially cured
substrate had a tacky surface.
[0062] The backside of an embroidered fabric was cleaned using
isopropanol and de-dusted with compressed air. The fabric was
flattened in a hoop and clamped on a supporting frame. The backside
of the fabric was oriented to face a top surface of the partially
cured PDMS.
[0063] The clamp height was gradually adjusted to lower the hoop
onto the PDMS surface. Due to its high viscosity, the PDMS adhered
to the fabric without flowing over the conductive, embroidered
portions.
[0064] The PDMS was cured for from about 2.5 to 3 hours at a
temperature of about 100.degree. C. The substrate was not tacky on
its surface after curing was completed. The cured structure was
removed from the mold or support.
[0065] FIG. 3 is a graph illustrating the dielectric constant for
composite substrates including varying amounts of the ceramic
material.
Electrically-Conductive Fiber Transmission Lines
[0066] Three devices with single layer 50.OMEGA. transmission lines
on substrates were fabricated. The substrates comprised PDMS with
.di-elect cons..sub.r=3. Device 1 included an
electrically-conductive fiber conductor and an
electrically-conductive fiber ground plane. Device 2 included an
electrically-conductive fiber conductor and a copper ground plane.
Device 3 included a copper conductor and a copper ground plane. The
S-parameters of all three transmission lines were measured using a
2-port Agilent N5230 network analyzer at frequencies of 10 MHz to 4
GHz. The results are included in Table 1:
TABLE-US-00001 TABLE 1 Device Max |S.sub.21| Number Conductor
Ground Plane (dB/cm) 1 Electrically-conductive
Electrically-conductive 0.21 fiber fiber 2 Electrically-conductive
Copper 0.17 fiber 3 Copper Copper 0.14
[0067] Device 1 had a maximum insertion loss of 0.21 dB/cm at
frequencies up to 4 GHz, 0.07 dB/cm higher than that of the all
copper transmission line of Device 3. The corresponding insertion
loss of Device 2 was 0.17 dB/cm, only 0.03 dB/cm greater than that
of Device 3. Since the only difference between Devices 2 and 3 was
the surface conductor material, it can be concluded that the
electrically-conductive fiber and copper exhibit comparable
performance. Without wishing to be bound by theory, it is believed
that the insertion loss of Device 1 resulted from (1) impedance
mismatch caused by parasitic reactance from silver epoxy paste at
junctions; and (2) higher resistance of the electrically-conductive
fiber ground plane. Overall, the measurements demonstrated that the
embroidered electrically-conductive transmission lines exhibited
good conductivity at radio frequencies.
[0068] A double layer device, Device 4, was fabricated by bringing
together two PDMS substrates. Each substrate included an outer
surface having an embroidered transmission line and an inner
surface opposite the outer surface. The inner surfaces of the
substrates were laminated together using a thin layer of fresh,
i.e. uncured, PDMS in between. The fresh layer was cured in an over
or on a hot plate for about one hour. The two transmission lines
were connected by a via hole. The via hole was created by pushing
an electrically-conductive fiber through the PDMS using a needle. A
silver epoxy was used to connect the electrically-conductive fiber
in the via hole to the transmission lines. A control double layer
device including a copper conductor and copper ground plane (Device
5) was also fabricated. The S-parameters of both devices were
measured using a 2-port Agilent N5230 network analyzer at
frequencies of 10 MHz to 4 GHz. The results are included in Table
2:
TABLE-US-00002 TABLE 2 Device Max |S.sub.21| Number Conductor
Ground Plane (dB/cm) 4 Electrically-conductive
Electrically-conductive 0.34 fiber fiber 5 Copper Copper 0.14
[0069] The measured S.sub.21 of the electrically-conductive fiber
transmission line had a maximum loss of 0.34 dB/cm at frequencies
of up to 4 GHz, only 0.20 dB/cm higher than that of the copper
transmission line. The higher S.sub.21 was primarily due to the
imperfect via hole connection between the transmission lines and
power loss on the ground plane.
[0070] Both the single- and double-layer transmission line
structures exhibited satisfactory radiofrequency properties.
Furthermore, both structures maintained these properties after
repeated flexing.
Embroidered Patch
[0071] An embroidered patch comprising electrically-conductive
fibers was fabricated and secured to a composite PDMS/RET substrate
to form an antenna. The patch had a thickness of about 2 mm. The
composite substrate comprised 10 vol % of RET, had an .di-elect
cons..sub.r of 4.2, and exhibited a tan .delta.<0.01. The patch
was probe-fed at a specific location to achieve an impedance match
to a 50.OMEGA. coaxial cable. The probe was connected to the
antenna using silver epoxy. When tested on a planar surface, the
resonant frequency of the patch was 2.20 GHz which matched that of
a simulated, perfectly electrical conducting (PEC) patch. The match
indicated that the embroidered patch generated an effectively
continuous conductive surface at UHF frequencies. The flat patch
antenna exhibited a realized gain of 5.7 dB, only 0.2 dB less than
that of the PEC patch. The performance of the antenna did not
degrade after repetitive flexing.
[0072] To further evaluate radiofrequency performance, the antenna
was mounted on a metal cylinder having a diameter of about 80 mm.
The measured S11 and radiation patterns of the patch were similar
to predictions based on an HFSS simulation. The realized gain was
only 1 dB lower than simulated. Compared to the planar orientation,
the curvilinear-oriented patch had a lower resonant frequency of
2.06 GHz and a reduced gain of 3.0 dB. The frequency change was due
to a 13% elongation of the patch dimension in the H-plane cut.
However, the gain reduction (compared to the PEC) was primarily
caused by stretching the conductive patch and the resultant higher
resistance of the patch's surface.
[0073] A summary of the results of the performance testing of the
antenna comprising the patch is shown in Table 3:
TABLE-US-00003 TABLE 3 Planar Surface Curvilinear Surface
f.sub.resonant Realized Realized gain Conductor (GHz) gain (dB)
f.sub.resonant (GHz) (dB) PEC 2.20 5.9 2.06 4.1 Electrically- 2.20
5.7 2.06 3.0 conductive fiber
Embroidered Array
[0074] An antenna comprising a 4.times.1 electrically-conductive
fiber array on a substrate was fabricated, analyzed on a planar
surface, and compared to corresponding copper and PEC arrays on
substrates. The composite substrate comprised 10 vol % of RET, had
an .di-elect cons..sub.r of 4.2, and exhibited a tan
.delta.<0.01. The antenna had a resonance frequency of 2.31 GHz
and a realized gain of 7.0 dB. The resonance frequency was
comparable to that of the copper and PEC antennas. The slight
difference was likely due to imperfect geometric accuracy of the
fabricated array.
[0075] The antenna was also analyzed on a curvilinear surface by
attachment to a cylinder. The realized gain of the
electrically-conductive fiber array was 4.6 dB, only 1 dB less than
that of the copper array. The increased spacing during bending led
to the difference between the radiation patterns of the curvilinear
and planar configurations of the antenna.
[0076] A summary of the results of the performance testing of the
antenna comprising the array is shown in Table 4.
TABLE-US-00004 TABLE 4 Planar Surface Curvilinear Surface
f.sub.resonant Realized Realized gain Conductor (GHz) gain (dB)
f.sub.resonant (GHz) (dB) PEC 2.34 7.8 2.33 5.7 Copper 2.34 7.6
2.33 5.4 Electrically- 2.31 7.0 2.33 4.6 conductive fiber
[0077] The present disclosure has been described with reference to
exemplary embodiments. Obviously, modifications and alterations
will occur to others upon reading and understanding the preceding
detailed description. It is intended that the present disclosure be
construed as including all such modifications and alterations
insofar as they come within the scope of the appended claims or the
equivalents thereof.
* * * * *