U.S. patent application number 16/274926 was filed with the patent office on 2019-08-22 for iron oxide nanoparticle-based magnetic ink for additive manufacturing.
The applicant listed for this patent is King Abdullah University of Science and Technology. Invention is credited to Farhan Abdul Ghaffar, Atif Shamim, Mohammad Vaseem.
Application Number | 20190259517 16/274926 |
Document ID | / |
Family ID | 67618150 |
Filed Date | 2019-08-22 |
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United States Patent
Application |
20190259517 |
Kind Code |
A1 |
Vaseem; Mohammad ; et
al. |
August 22, 2019 |
IRON OXIDE NANOPARTICLE-BASED MAGNETIC INK FOR ADDITIVE
MANUFACTURING
Abstract
Embodiments of the present disclosure describe magnetic ink
compositions, methods of making magnetic ink compositions, methods
of printing magnetic ink compositions, magnetic substrates based on
the magnetic ink compositions for microwave and/or RF devices,
methods of making the microwave and/or RF devices, and the
like.
Inventors: |
Vaseem; Mohammad; (Thuwal,
SA) ; Ghaffar; Farhan Abdul; (Thuwal, SA) ;
Shamim; Atif; (Thuwal, SA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
King Abdullah University of Science and Technology |
Thuwal |
|
SA |
|
|
Family ID: |
67618150 |
Appl. No.: |
16/274926 |
Filed: |
February 13, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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62633416 |
Feb 21, 2018 |
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62742675 |
Oct 8, 2018 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C01P 2004/51 20130101;
H01F 41/02 20130101; C01P 2004/62 20130101; B82Y 40/00 20130101;
B29K 2105/162 20130101; B33Y 70/00 20141201; C01P 2004/38 20130101;
C01P 2006/42 20130101; B29K 2509/00 20130101; C01P 2004/45
20130101; C01P 2002/72 20130101; C01P 2002/84 20130101; C01P
2002/82 20130101; H01F 1/445 20130101; B29K 2995/0008 20130101;
B82Y 25/00 20130101; B33Y 10/00 20141201; C01G 49/06 20130101; C01P
2004/04 20130101; C01P 2004/32 20130101; C01P 2006/22 20130101;
C01G 49/08 20130101; C01P 2006/40 20130101; C01P 2004/64 20130101;
B22F 3/008 20130101; H01F 41/043 20130101; C01P 2002/85 20130101;
C01P 2004/03 20130101; B29C 64/112 20170801; C01P 2004/10
20130101 |
International
Class: |
H01F 1/44 20060101
H01F001/44; H01F 41/04 20060101 H01F041/04; B33Y 70/00 20060101
B33Y070/00 |
Claims
1. An ink composition, comprising: a plurality of magnetic iron
oxide nanoparticles dispersed in a solution containing a carrier
and a surface tension adjusting agent to form an iron oxide
nanoparticle-based magnetic ink, wherein a concentration of the
magnetic iron oxide nanoparticles is about 10 wt %.
2. The ink composition of claim 1, wherein the plurality of
magnetic iron oxide nanoparticles include one or more of
Fe.sub.2O.sub.3 and Fe.sub.3O.sub.4 nanoparticles.
3. The ink composition of claim 1, wherein the plurality of
magnetic iron oxide nanoparticles are characterized as one or more
of superparamagnetic and ferromagnetic.
4. The ink composition of claim 1, wherein the carrier is water or
a water-compatible solvent.
5. The ink composition of claim 1, wherein the surface tension
adjusting agent is ethanol, methanol, propanol, Triton X-100, CTAB,
or SDS.
6. The ink composition of claim 1, wherein a viscosity is less than
about 2 cP and/or a surface tension is less than about 45 mN
m.sup.-1.
7. The ink composition of claim 1, wherein an average diameter of
the Fe.sub.3O.sub.4 nanoparticles ranges from about 15 nm to about
20 nm and/or a particle aggregate size is less than about 450
nm.
8. A method of preparing an ink composition, comprising: mixing a
carboxylic acid with an aqueous solution of an iron compound to
form a mixture; heating the mixture to or at a select temperature;
adding a base to the mixture upon reaching the select temperature
to form magnetic iron oxide nanoparticles; separating the magnetic
iron oxide nanoparticles from one or more residual species; and
dispersing the magnetic iron oxide nanoparticles in deionized water
to form an iron oxide nanoparticle-based magnetic ink.
9. The method of claim 8, wherein the carboxylic acid includes one
or more of acetic acid, carbonic acid, formic acid, propionic acid,
butyric acid, pentanoic acid, and salts thereof.
10. The method of claim 8, wherein the iron compound includes one
or more of iron (II) chloride, iron (III) chloride, iron (II)
fluoride, iron (III) fluoride, iron (II) bromide, iron (III)
bromide, iron (II) iodide, iron (III) iodide, iron (II) nitrate,
iron (III) nitrate, iron (II) acetate, iron (III) acetate, iron
(II) sulfate, iron (III) sulfate, iron (II) oxalate, and iron (III)
oxalate.
11. The method of claim 8, wherein the select temperature is about
90.degree. C.
12. The method of claim 8, wherein the base includes one or more of
metal hydroxides, metal oxides, metal alkoxides, ammonia, and
derivatives thereof.
13. The method of claim 8, wherein the base and carboxylic acid
disassociate precipitates at about the select temperature for a
formation of uniform and disperse iron oxide nanoparticles.
14. The method of claim 8, wherein the one or more residual species
includes one or more of the carboxylic acid and base.
15. The method of claim 8, further comprising contacting the iron
oxide nanoparticle-based magnetic ink with one or more alcohols to
adjust a surface tension.
16. The method of claim 8, further comprising filtering the iron
oxide nanoparticle-based magnetic ink prior to jetting.
17. The method of claim 16, wherein the filtering includes
separating the iron oxide nanoparticle-based magnetic ink from
particle aggregates greater than about 0.45 am.
18. A method of printing a magnetic ink composition, comprising:
printing a functionalized iron oxide nanoparticle-based magnetic
ink composition containing functionalized magnetic iron oxide
nanoparticles and a photocurable polymeric resin onto a removable
substrate, heating the printed magnetic ink composition to or at a
select temperature for a select duration, curing the printed
magnetic ink composition sufficient to solidify the mixture; and
removing the removable substrate to provide a freestanding magnetic
substrate.
19. The method of claim 18, wherein the magnetic iron oxide
nanoparticles include one or more of Fe.sub.2O.sub.3 and
Fe.sub.3O.sub.4 nanoparticles.
20. The method of claim 18, wherein the photocurable polymer resin
is a UV-curable resin.
Description
BACKGROUND
[0001] As printing technology presents a low-cost, high throughput,
and completely digital fabrication process, it is becoming popular
with electronics manufacturing. The roll-to-roll manufacturing
capability of printing makes it a viable option for mass production
to meet the medium to large volume production requirements. Several
reports have described the development of conductors, dielectric,
and semiconductor inks for transistors, photovoltaic, memory
devices, sensors, biological devices, and radio-frequency (RF)
electronics. However, there are only a few reports of fully
inkjet-printed devices. For fully printed components and devices,
different materials inks must be developed since this field is
still immature. Fully printed microwave components were recently
demonstrated by combining 3D inkjet printing of dielectrics with 2D
printing of metallic inks. The next generation of fully printed
components and systems should have the ability to control their
performance, such that they can be tuned or reconfigured when
necessary; this requires the development of functional inks that
are magnetic, ferroelectric, or piezoelectric.
[0002] In radio-frequency (RF) electronics, tunable or
reconfigurable components are becoming important due to the
proliferation of new wireless devices, different wireless standards
in different parts of the world, and high congestion in the
existing bands of wireless communication. Furthermore, magnetic
materials have been used effectively for tunable and reconfigurable
components such as inductors, antennas, and phase shifters.
Recently, many such designs have been shown in multilayer ferrite
LTCC (low temperature co-fired ceramic) technology. But, LTCC
technology is quite expensive and it will be really neat if the
same things can be done through printing technologies. However,
there is a paucity of functional inks with magnetic properties and
few reports on magnetic ink-printing. For example, one report
demonstrated inkjet printing of commercially available,
cobalt-based, ferromagnetic nanoparticles (.apprxeq.200 nm) for the
miniaturization of flexible printed inductors. These metallic
cobalt nanoparticles usually require surface passivation to avoid
the oxidation problem. Another report utilized an interesting
approach to align the cobalt nanoparticle ink with an external
magnetic field during printing to enable prototyping and
development of novel, magnetic, composite materials and components.
In another report, inkjet-printed NiZn-ferrite films were described
using NiZn-ferrite nanoparticle-based ink, completing its magnetic
characterization. All the above inks are metallic in nature, but a
magnetic ink with dielectric (insulator) properties is required for
tunable RF applications. Though there is a commercial magnetic ink
solution available, it has a low concentration (<1 wt %) of iron
oxide nanoparticles and is not suitable for these RF applications.
Thus, no tunable or reconfigurable, fully printed RF component
based on magnetic ink has been reported to date.
SUMMARY
[0003] In general, embodiments of the present disclosure describe
magnetic ink compositions, methods of making magnetic ink
compositions, methods of printing magnetic ink compositions,
magnetic substrates based on the magnetic ink compositions for
microwave and/or RF devices, methods of making the microwave and/or
RF devices, and the like.
[0004] Embodiments of the present disclosure describe magnetic ink
compositions comprising a plurality of magnetic iron oxide
nanoparticles dispersed in a carrier.
[0005] Embodiments of the present disclosure describe a method of
making magnetic iron oxide nanoparticles comprising one or more of
the following steps: mixing a carboxylic acid with an aqueous
solution of an iron compound to form a mixture; heating the mixture
to or at a select temperature; adding a base to the mixture upon
reaching the select temperature to form magnetic iron oxide
nanoparticles; and separating the magnetic iron oxide nanoparticles
from one or more residual species.
[0006] Embodiments of the present disclosure describe a method of
making a magnetic ink composition comprising one or more of the
following steps: contacting magnetic iron oxide nanoparticles with
a carrier to form an iron oxide nanoparticle-based magnetic ink;
adding one or more surface tension adjusting agents to the iron
oxide nanoparticle-based magnetic ink; and filtering the iron oxide
nanoparticle-based magnetic ink.
[0007] Embodiments of the present disclosure describe a method of
making a magnetic ink composition comprising one or more of the
following steps: contacting a carboxylic acid with an aqueous
solution of an iron compound to form a mixture; heating the mixture
to or at a select temperature; adding a base to the mixture upon
reaching the select temperature to form magnetic iron oxide
nanoparticles; separating the magnetic iron oxide nanoparticles
from one or more residual species; contacting the magnetic iron
oxide nanoparticles with a carrier to form an iron oxide
nanoparticle-based magnetic ink; adding one or more surface tension
adjusting agents to the iron oxide nanoparticle-based magnetic ink;
and filtering the iron oxide nanoparticle-based magnetic ink.
[0008] Embodiments of the present disclosure describe a method of
printing a magnetic ink composition comprising printing one or more
layers of an iron oxide nanoparticle-based magnetic ink onto a
substrate; and heating the printed substrate to or at a select
temperature sufficient to dry the printed substrate.
[0009] Embodiments of the present disclosure describe a magnetic
ink composition comprising a mixture containing one or more of a
plurality of functionalized magnetic iron oxide nanoparticles, a
photocurable polymeric resin, and a solvent.
[0010] Embodiments of the present disclosure describe a method of
functionalizing magnetic iron oxide nanoparticles comprising one or
more of the following steps: contacting one or more of magnetic
iron oxide nanoparticles, a solvent, and a functionalizing agent to
form a solution; mixing the solution sufficient for the
functionalizing agent to sorb on a surface of the magnetic iron
oxide nanoparticles; removing excess functionalizing agent; and
contacting the functionalized magnetic iron oxide nanoparticles
with a photocurable polymeric resin to form a functionalized iron
oxide nanoparticle-based magnetic ink.
[0011] Embodiments of the present disclosure describe a method of
printing a magnetic ink composition comprising printing a
functionalized iron oxide nanoparticle-based magnetic ink
composition containing functionalized magnetic iron oxide
nanoparticles and a photocurable polymeric resin onto a removable
substrate, heating the printed magnetic ink composition to or at a
select temperature for a select duration, and curing the printed
magnetic ink composition sufficient to solidify the mixture.
[0012] The details of one or more examples are set forth in the
description below. Other features, objects, and advantages will be
apparent from the description and from the claims.
BRIEF DESCRIPTION OF DRAWINGS
[0013] This written disclosure describes illustrative embodiments
that are non-limiting and non-exhaustive. In the drawings, which
are not necessarily drawn to scale, like numerals describe
substantially similar components throughout the several views. Like
numerals having different letter suffixes represent different
instances of substantially similar components. The drawings
illustrate generally, by way of example, but not by way of
limitation, various embodiments discussed in the present
document.
[0014] Reference is made to illustrative embodiments that are
depicted in the figures, in which:
[0015] FIG. 1 is a flowchart of a method of making magnetic iron
oxide nanoparticles, according to one or more embodiments of the
present disclosure.
[0016] FIG. 2 is a flowchart of a method of making a magnetic ink
composition, according to one or more embodiments of the present
disclosure.
[0017] FIG. 3 is a flowchart of a method of making a magnetic ink
composition, according to one or more embodiments of the present
disclosure.
[0018] FIG. 4 is a flowchart of a method of printing a magnetic ink
composition, according to one or more embodiments of the present
disclosure.
[0019] FIG. 5 is a flowchart of a method of functionalizing
magnetic iron oxide nanoparticles, according to one or more
embodiments of the present disclosure.
[0020] FIG. 6 is a flowchart of a method of printing a magnetic ink
composition, according to one or more embodiments of the present
disclosure.
[0021] FIGS. 7A-7B illustrates a surface tension (SFT) measurement
of the ink (a) without ethanol and (b) with about 10 vol % ethanol,
according to one or more embodiments of the present disclosure.
[0022] FIG. 8 is a jetting waveform for as-formulated iron oxide
nanoparticles ink, according to one or more embodiments of the
present disclosure.
[0023] FIGS. 9A-9G show a) an illustrative diagram of the
functionalization of iron oxide nanoparticles and mixing with SU8,
with SEM and EDX analysis of b,e) pure iron oxide, c,f) oleic acid
functionalized, and d,g) SU8-mixed iron oxide nanoparticles; the
inset in (d) is showing low-resolution iron oxide nanoparticles
embedded in SU8 matrix, according to one or more embodiments of the
present disclosure.
[0024] FIGS. 10A-10C are TEM, HR-TEM images, and SAED patterns of
(a) pure iron oxide, (b) oleic acid functionalized, and (c)
SU8-mixed iron oxide nanoparticles, according to one or more
embodiments of the present disclosure.
[0025] FIGS. 11A-11B show (A) FT-IR spectra and (B) XRD patterns of
a) pure iron oxide, b) oleic acid functionalized iron oxide
nanoparticles, and c) SU8-mixed iron oxide nanoparticles, according
to one or more embodiments of the present disclosure.
[0026] FIG. 12 is a graphical view of UV-Vis absorption spectra of
pure and oleic acid functionalized iron oxide NPs, according to one
or more embodiments of the present disclosure.
[0027] FIGS. 13A-13B are graphical views of a) Hysteresis loop of
(i) pure iron oxide and b) oleic acid functionalized iron oxide
nanoparticles at (a) 300 K and (b) 5 K, along with the full range
of the hysteresis measured between -10 000 and 10 000 Oe (inset);
the insets in (a) and (b) show the pictorial presentation of
loosely bound nanoparticles in a freezing state, according to one
or more embodiments of the present disclosure.
[0028] FIG. 14 is a graphical view of temperature dependence
magnetization of (i) pure and (ii) oleic acid functionalized iron
oxide NPs in field cooled (FC) and zero field cooled (ZFC) at an
applied field of 100 Oe, according to one or more embodiments of
the present disclosure.
[0029] FIG. 15 is a graphical view of particle size distribution,
where before analysis, the as-formulated iron oxide nanoparticles
ink were diluted 10-times with deionized (DI) water, according to
one or more embodiments of the present disclosure.
[0030] FIGS. 16A-16B are (a) a 2D image of printed dots and its
corresponding (b) surface profile, with the inset in (a) showing
the 3D view of the printed dots, according to one or more
embodiments of the present disclosure.
[0031] FIGS. 17A-17C are 3D, 2D and cross-sectional surface
profiler images of inkjet-printed iron oxide: (a) single printing,
(b) 2 over-layer, and (c) 3 over-layer, according to one or more
embodiments of the present disclosure.
[0032] FIGS. 17D-17E are 3D, 2D and cross-sectional surface
profiler images of inkjet-printed iron oxide: (d) 4 over-layer, and
(e) 5 over-layer, according to one or more embodiments of the
present disclosure.
[0033] FIG. 18 is a graphical view of thicknesses of inkjet-printed
lines with number of printing, according to one or more embodiments
of the present disclosure.
[0034] FIGS. 19A-19C illustrate a schematic diagram of the
fabrication of a fully printed tunable inductor, according to one
or more embodiments of the present disclosure.
[0035] FIGS. 20A-20B are graphical views of VSM measured hysteresis
curves of (a) printed magnetic film using the iron oxide
nanoparticles based ink and (b) using commercially available ink
(the inset in (a) and (b) showing zoomed hysteresis curve), where
commercial ink showed the saturation magnetization of approximately
0.18 memu under applied field of 3 kOe and the coercivity is found
to be 51 Oe, as shown in (b), according to one or more embodiments
of the present disclosure.
[0036] FIGS. 21A-21B are graphical views of a) measured inductance
showing the self-resonance frequency (SRF) and b) zoom-in view to
show the change in inductance with magnetic field bias, according
to one or more embodiments of the present disclosure.
[0037] FIGS. 22A-22B are graphical views of (a) measured inductance
for fully printed tunable inductor using commercial iron oxide ink
and (b) change in inductance with magnetic field bias (with the
inset in (b) showing a zoomed-in view), where commercial ink was
printed with 10 layers with each layer having a thickness of around
100 nm and the magnetic layer then being heated for 5 minutes at
160.degree. C. to evaporate the solvent, wherein the measured SRF
of the inductor is .about.1.4 GHz as shown in (a), according to one
or more embodiments of the present disclosure.
[0038] FIGS. 23A-23F illustrate a schematic diagram of the
fabrication of freestanding magnetic substrate followed by inkjet
printing of a patch antenna, according to one or more embodiments
of the present disclosure.
[0039] FIGS. 24A-24B are graphical views of a) Measured B(H) curve
of printed freestanding substrate and b) product of permittivity,
and permeability and loss tangent of the magnetic ink versus
frequency, according to one or more embodiments of the present
disclosure.
[0040] FIGS. 25A-25D show a) fabricated antenna on freestanding
magnetic substrate, b) measured frequency tuning, c) measured 3D
radiation pattern, and d) S.sub.11 measurements for no bias and 3.7
kOe bias for the inkjet-printed patch antenna, according to one or
more embodiments of the present disclosure.
DETAILED DESCRIPTION
[0041] The invention of the present disclosure relates to magnetic
ink compositions. In particular, the invention of the present
disclosure relates to magnetic ink compositions containing magnetic
iron oxide nanoparticles for a variety of applications, such as
printed electronics, among others. For example, the magnetic ink
compositions may be used to produce tunable and/or reconfigurable
fully-printed RF components and devices, such as inductors,
antennas, and phase shifters, among other things. The magnetic ink
compositions may be inkjet-printed as magnetic films. The magnetic
ink compositions may be mixed with a polymeric resin and printed to
form freestanding magnetic substrates. Other components may be
printed onto the magnetic films and/or freestanding magnetic
substrates to form fully printed, magnetically controlled RF
devices.
[0042] The magnetic ink compositions may be used to produce
fully-printed RF components and devices that may be tuned and/or
reconfigured upon application of an external magnetic field. For
example, an inductor may be inkjet-printed on top of an
inkjet-printed magnetic film to produce a tunable fully-printed
inductor. A tuning of about 24% may be observed upon application of
an external magnetic field to the tunable fully-printed inductor.
An adjustable capacity of greater than about 20% for a
fully-printed inductor is unprecedented, as conventional magnetic
inks only exhibit about 0.8% tuning. The magnetic ink compositions
may be mixed with, for example, a photocurable polymeric resin to
form a magnetic substrate with magnetic iron oxide nanoparticles
embedded therein. The magnetic substrate may be used to fabricate a
linear patch antenna that may be tuned for its frequency upon
application of a magnetic field. These are provided as non-limiting
examples, as other tunable and reconfigurable fully-printed
microwave/RF devices and components may be realized with the
magnetic ink compositions.
Definitions
[0043] The terms recited below have been defined as described
below. All other terms and phrases in this disclosure shall be
construed according to their ordinary meaning as understood by one
of skill in the art.
[0044] As used herein, "adding" refers to any process and/or method
of placing one component in or on another component, joining one or
more components with another component, and/or bringing two or more
components together, as in contacting. The components may be in
contact or in immediate/close proximity. Adding may include one or
more of pouring, dumping, mixing, depositing, providing, placing,
putting, inserting, injecting, introducing, dropping, contacting,
and any other methods known in the art.
[0045] As used herein, "contacting" refers to the act of touching,
making contact, or of bringing to close or immediate proximity,
including at the cellular or molecular level, for example, to bring
about a physiological reaction, a chemical reaction, or a physical
change (e.g., in solution, in a reaction mixture, in vitro, or in
vivo). Contacting may refer to bringing two or more components in
proximity, such as physically, chemically, electrically, or some
combination thereof. Mixing is an example of contacting.
[0046] As used herein, "heating" refers to increasing to or at a
temperature. For example, heating may refer to exposing or
subjecting any object, material, etc. at or to a temperature that
is greater than a current or previous temperature. Heating may also
refer to increasing a temperature of any object, material, etc. to
a temperature that is greater than a current or previous
temperature of the object, material, etc.
[0047] As used herein, "separating" refers to any process of
removing a substance from another. The process may employ any
technique known in the art suitable for separating. Centrifugation,
filtration, and evaporation are examples of separating.
Magnetic Iron Oxide Nanoparticles
[0048] FIG. 1 is a flowchart of a method of making magnetic iron
oxide nanoparticles, according to one or more embodiments of the
present disclosure. As shown in FIG. 1, the method 100 may comprise
one or more of the following steps: mixing 101 a carboxylic acid
with an aqueous solution of an iron compound to form a mixture;
heating 102 the mixture to or at a select temperature; adding 103 a
base to the mixture upon reaching the select temperature to form
magnetic iron oxide nanoparticles; and separating 104 the magnetic
iron oxide nanoparticles from one or more residual species.
[0049] The step 101 includes contacting a carboxylic acid with an
aqueous solution of an iron compound to form a mixture. In this
step, one or more of a carboxylic acid, iron compound, and water
are brought into physical contact and/or immediate or close
proximity, sequentially and/or simultaneously, in any order. For
example, the carboxylic acid may be contacted with, or added to, an
aqueous solution containing the iron compound to form the mixture.
The contacting of the carboxylic acid to the aqueous solution
containing the iron compound may optionally proceed under stirring.
The carboxylic acid can be a short chain carboxylic acid having 1-3
carbons and salts thereof. In an embodiment, the carboxylic acid
may include one or more of acetic acid, carbonic acid, formic acid,
propionic acid, butyric acid, pentanoic acid, and salts thereof. In
preferred embodiments, the carboxylic acid includes acetic acid.
The iron compound may include any iron salt or hydrated iron salt.
For example, the iron compound may include, but is not limited to,
one or more of iron (II) chloride, iron (III) chloride, iron (II)
fluoride, iron (III) fluoride, iron (II) bromide, iron (III)
bromide, iron (II) iodide, iron (III) iodide, iron (II) nitrate,
iron (III) nitrate, iron (II) acetate, iron (III) acetate, iron
(II) sulfate, iron (III) sulfate, iron (II) oxalate, and iron (III)
oxalate. In an embodiment, the iron compound may include one or
more iron chlorides, such as one or more of iron (II) chloride and
iron (III) chloride. In an embodiment, the iron compound includes
iron (II) chloride and iron (III) chloride.
[0050] The step 102 includes heating the mixture to or at a select
temperature. In this step, the mixture containing the carboxylic
acid, iron compound, and water may be heated to or at a select
temperature. In an embodiment, the heating of the mixture may
proceed slowly. In an embodiment, the heating of the mixture may
proceed slowly, optionally under stirring. The select temperature
may range from about 50.degree. C. to about 120.degree. C. In
preferred embodiments, the select temperature is about 90.degree.
C.
[0051] The step 103 includes adding a base to the mixture upon
reaching the select temperature to form magnetic iron oxide
nanoparticles. In this step, once the mixture is heated to or at
about the select temperature, such as about 90.degree. C., the base
may be added to the mixture. The base may include any suitable
base, such as metal hydroxides, metal oxides, metal alkoxides,
ammonia, and derivatives thereof. For example, in an embodiment,
the base is sodium hydroxide. In an embodiment, the addition of the
base to the mixture may result in a black colloidal solution. The
presence of the carboxylic acid and the addition of the base upon
reaching about the select temperature may facilitate the formation
of small magnetic iron oxide nanoparticles suitable for the
magnetic ink composition. The higher temperatures may increase the
reaction rate such that large amounts of nuclei are formed in a
short period of time, leading to the formation of small
nanoparticles. For example, the base and carboxylic acid may, under
the reaction conditions, disassociate or break the precipitates for
the formation of uniform and/or disperse iron oxide nanoparticles.
In some embodiments, the mixture may, upon adding the base, be
refluxed for a period of time (e.g., about 10-15 minutes).
[0052] The step 104 is optional and includes separating the
magnetic iron oxide nanoparticles from one or more residual
species. In this step, the solution of magnetic iron oxide
nanoparticles may be centrifuged, optionally followed by washing
with one or more solvents, such as water and an alcohol (e.g.,
ethanol) to obtain the iron oxide nanoparticles. Iron-Oxide
Nanoparticle-Based Magnetic Ink Compositions
[0053] Embodiments of the present disclosure describe an ink
composition comprising a plurality of magnetic iron oxide
nanoparticles in a solution containing one or more of a carrier
(e.g., solvent) and a surface tension adjusting agent. In an
embodiment, the plurality of magnetic iron oxide nanoparticles may
be dispersed and/or suspended in the solution containing one or
more of the carrier and the surface tension adjusting agent. For
example, in an embodiment, the plurality of magnetic iron oxide
nanoparticles may be uniformly (e.g., substantially uniformly)
dispersed, suspended, and/or mixed in the solution containing one
or more of the carrier and the surface tension adjusting agent.
[0054] The plurality of magnetic iron oxide nanoparticles may
include any suitable iron oxide nanoparticle with magnetic
properties. In an embodiment, the plurality of magnetic iron oxide
nanoparticles may include magnetic iron oxide nanoparticles
prepared according to any of the methods described herein. In an
embodiment, the plurality of magnetic iron oxide nanoparticles
include one or more of Fe.sub.3O.sub.4 nanoparticles and
Fe.sub.2O.sub.3 nanoparticles. In an embodiment, the plurality of
magnetic iron oxide nanoparticles include Fe.sub.3O.sub.4
nanoparticles. In an embodiment, the plurality magnetic iron oxide
nanoparticles include Fe.sub.2O.sub.3 nanoparticles. The plurality
of magnetic iron oxide nanoparticles may be uniform (e.g.,
substantially uniform) in size and/or shape, such as spherical,
cubic, and/or elongated. An average diameter of the plurality of
magnetic iron oxide nanoparticles may range from about 1 nm to
about 50 nm. In an embodiment, an average diameter of the plurality
of magnetic iron oxide nanoparticles may range from about 15 nm to
about 20 nm. In other embodiments, the average diameter may be less
than about 1 nm and/or greater than about 50 nm. A
concentration/loading of the magnetic iron oxide nanoparticles may
be greater than or equal to about 1 wt %. In an embodiment, a
concentration/loading of the magnetic iron oxide nanoparticles may
be about 10 wt %.
[0055] The carrier may include any carrier suitable for dispersing,
suspending, and/or mixing the magnetic iron oxide nanoparticles.
For example, in an embodiment, the carrier includes water. In an
embodiment, the carrier includes deionized water. In an embodiment,
the carrier includes water-compatible solvents, which may include,
but are not limited to, alcohol (e.g., ethanol, methanol,
propanol), glycol (ethylene glycol, 1,2-Butanediol, 1,
3-Butanediol, 1,4-Butanediol, 1,3-Propanediol, 1,5-Pentanediol,
propylene glycol, triethylene glycol, glycerol), and other such
solvents. The surface tension adjusting agent may optionally be
included to adjust a surface tension of the ink composition and/or
providing stable jetting performance. In an embodiment, the surface
tension adjusting agent includes an alcohol. For example, the
surface tension adjusting agent may include one or more of
methanol, ethanol, propanol, Triton X-100, centrimonium bromide
(CTAB), sodium dodecyl sulfate (SDS), and other such agents. In an
embodiment, the surface tension adjusting agent is ethanol. The
alcohol is provided as an example of a suitable surface tension
adjusting agent and shall not be limiting as any suitable surface
tension adjusting agent known in the art may be used herein.
[0056] FIG. 2 is a flowchart of a method of making a magnetic ink
composition, according to one or more embodiments of the present
disclosure. The method 200 may comprise one or more of the
following steps: contacting 205 magnetic iron oxide nanoparticles
with a carrier to form an iron oxide nanoparticle-based magnetic
ink; adding 206 one or more surface tension adjusting agents to the
iron oxide nanoparticle-based magnetic ink; and filtering 207 the
iron oxide nanoparticle-based magnetic ink.
[0057] The step 205 includes contacting magnetic iron oxide
nanoparticles with a suitable carrier to form an iron oxide
nanoparticle-based magnetic ink. In this step, the magnetic iron
oxide nanoparticles may be brought into physical contact and/or
immediate or close proximity to the one or more carriers sufficient
to form the iron oxide nanoparticle-based magnetic ink. The
contacting may be sufficient to disperse, suspend, and/or mix the
magnetic iron oxide nanoparticles in the carrier. The contacting
may optionally proceed under stirring. A content of the magnetic
iron oxide nanoparticles may generally be greater than about 0 wt
%. For example, in an embodiment, a content of the magnetic iron
oxide nanoparticles may be greater than about 1 wt %. In an
embodiment, a content of the magnetic iron oxide nanoparticles may
be about 10 wt % or greater. The magnetic iron oxide nanoparticles
may include any of the magnetic iron oxide nanoparticles prepared
according to the methods of or described in the present
disclosure.
[0058] The carrier may include any of the carriers of the present
disclosure. For example, in an embodiment, the carrier includes
water. In an embodiment, the carrier includes deionized water. The
amount of carrier used in this step may be varied in order to
adjust a viscosity of the iron oxide nanoparticle-based magnetic
ink, which may depend on the concentration of the magnetic iron
oxide nanoparticles. For example, in an embodiment, the amount of
carrier may be increased (e.g., added to the ink) to reduce a
viscosity. In an embodiment, the amount of carrier may be decreased
(e.g., removed by evaporation, etc.) to increase a viscosity. In an
embodiment, the viscosity can be adjusted by adding a viscofier,
such as HEC, 2-HEC, 2,3-butanediol, glycerol, ethylene glycol, and
combinations thereof. The viscosity may be less than about 20 cP.
In many embodiments, the viscosity may be less than about 12.5 cP.
For inkjet printing, the viscosity may range from about 1-10 cps.
For example, in preferred embodiments, the viscosity may be about 2
cP.
[0059] The step 206 is optional and includes adding one or more
surface tension adjusting agents to the iron oxide
nanoparticle-based magnetic ink. The adding may proceed by
contacting. In an embodiment, the adding may optionally proceed
under stirring. For example, a duration of the stirring may range
from about 1 min to about 48 h. In an embodiment, a duration of the
stirring may be about 24 h. Any of the surface tension adjusting
agents of the present disclosure may be used herein. For example,
in an embodiment, the surface tension adjusting agents include one
or more alcohols, such as methanol, ethanol, and/or propanol. In an
embodiment, the surface tension adjusting agents include ethanol.
The surface tension adjusting agents may be added to the iron oxide
nanoparticle-based magnetic ink to adjust the surface tension of
the ink to a suitable range, such as a range suitable for stable
jetting performance. For example, the surface tension of the iron
oxide nanoparticle-based magnetic ink may range from about 20 to
about 350 mN m.sup.-1. In many embodiments, the surface tension may
range from about 40 to about 65 mN m.sup.-1. In preferred
embodiments, the surface tension may be about 44 mN m.sup.-1.
[0060] The step 207 is optional and includes filtering the iron
oxide nanoparticle-based magnetic ink. In this step, the iron oxide
nanoparticle-based magnetic ink may be subjected to filtration to
separate oversized particle aggregates. In an embodiment, it may be
desirable to subject the iron oxide nanoparticle-based magnetic ink
to filtration in order to avoid clogging and/or blockage during
jetting and/or printing. Oversized particle aggregates may be
defined according to the printing application and/or apparatus used
for printing. In some embodiments, oversized particle aggregates
include particle aggregates greater than about 450 nm in size. For
example, 0.45 m polypropylene Whatman paper may be used for the
filtering. These shall not be limiting as other techniques known in
the art suitable for filtering may be used herein.
[0061] FIG. 3 is a flowchart of a method of making a magnetic ink
composition, according to one or more embodiments of the present
disclosure. As shown in FIG. 3, the method 300 may comprise one or
more of the following steps: contacting 301 a carboxylic acid with
an aqueous solution of an iron compound to form a mixture; heating
302 the mixture to or at a select temperature; adding 303 a base to
the mixture upon reaching the select temperature to form magnetic
iron oxide nanoparticles; separating 304 the magnetic iron oxide
nanoparticles from one or more residual species; contacting 305 the
magnetic iron oxide nanoparticles with a carrier to form an iron
oxide nanoparticle-based magnetic ink; adding 306 one or more
surface tension adjusting agents to the iron oxide
nanoparticle-based magnetic ink; and filtering 307 the iron oxide
nanoparticle-based magnetic ink.
[0062] In an embodiment, the method may comprise one or more of the
following steps: mixing acetic acid with an aqueous solution of
iron (II) chloride and/or iron (III) chloride to form a mixture,
heating the mixture to or at a select temperature, wherein the
select temperature is about 90.degree. C., adding sodium hydroxide
to the mixture upon reaching the select temperature to form
magnetic iron oxide nanoparticles, separating the magnetic iron
oxide nanoparticles from one or more residual species, and
dispersing the magnetic iron oxide nanoparticles in deionized water
to form an iron oxide nanoparticle-based magnetic ink.
Printing Iron-Oxide Nanoparticle-Based Magnetic Ink
Compositions
[0063] FIG. 4 is a method of printing a magnetic ink composition,
according to one or more embodiments of the present disclosure. As
shown in FIG. 4, the method 400 may comprise printing 401 one or
more layers of an iron oxide nanoparticle-based magnetic ink onto a
substrate; and heating 402 the printed substrate to or at a select
temperature sufficient to dry the printed substrate. Any of the
iron oxide nanoparticle-based magnetic inks of the present
disclosure may be used herein. The method may be used to form,
among other things, magnetic substrates including a magnetic film
on a surface of a substrate, wherein the magnetic film includes
magnetic iron oxide nanoparticles.
[0064] The step 401 includes printing one or more layers of an iron
oxide nanoparticle-based magnetic ink on a substrate. In many
embodiments, the printing includes inkjet printing. For example,
the printing may proceed by ejecting one or more droplets of the
magnetic ink from a suitable printer, such as a 2D printer and/or
3D printer, onto the substrate in any form or pattern, such as dots
and/or lines. In an embodiment, the printing may proceed by
vertically dropping or ejecting droplets of the magnetic ink. In an
embodiment, the printer may include a drop-on-demand piezeoelectric
ink-jet nozzle. The printing may proceed continuously (e.g.,
substantially continuously) or non-continuously (e.g.,
substantially non-continuously), optionally under constant printing
conditions.
[0065] The printing may include printing at least one layer of the
iron oxide nanoparticle-based magnetic ink on the substrate. In
many embodiments, the printing may include printing at least about
2 overlayers, preferably about 5 overlayers, of the iron oxide
nanoparticle-based magnetic ink to, for example, achieve a uniform
or substantially uniform density of the nanoparticles. The number
of layers of the iron oxide nanoparticle-based magnetic ink printed
on the substrate may be selected to achieve a desired thickness.
For example, a thickness of the iron oxide nanoparticle-based
magnetic ink may be increased by increasing the number of printed
layers and/or decreased by decreasing the number of printed layers.
In addition or in the alternative, the drop spacing may be adjusted
to achieve a desired thickness of the printed lines. The printed
magnetic ink may not exhibit any coffee-ring effects and/or line
bulging.
[0066] The printing and/or ejection of ink may be characterized by,
among other things, one or more of a drop volume, jetting velocity
of ejected droplets, cartridge print height, and drop spacing. In
an embodiment, the drop volume may be about 10 pL. In an
embodiment, the jetting velocity of ejected droplets may be about
3.3 m s.sup.-1. In an embodiment, the cartridge print height may be
about 0.3 mm. In an embodiment, the drop spacing may be about 40
.mu.m. In other embodiments, one or more of the drop volume,
jetting velocity of ejected droplets, cartridge print height, and
drop spacing may be greater or less than the values described
herein.
[0067] The substrate may include any suitable substrate for
printing the iron oxide nanoparticle-based magnetic ink. For
example, the substrate may include one or more of PI, PET, PEN,
glass, and other 3-D printed substrates, such as those formed from
acrylic and/or molten plastic (acrylonitrile butadiene styrene
(ABS), polylactic acid (PLA), etc.) based materials. In an
embodiment, the substrate is glass.
[0068] The step 402 includes heating the printed substrate to or at
a select temperature sufficient to dry the printed substrate. In
this step, the printed substrate is treated by heating the printed
substrate and/or an environment in which the printed substrate is
present to or at a select temperature sufficient to solidify and/or
dry the iron oxide nanoparticle-based magnetic ink. In many
embodiments, the select temperature is about 80.degree. C. In other
embodiments, the select temperature may be less than or greater
than about 80.degree. C. The heating may proceed for any duration
suitable for drying and/or solidifying the printed iron oxide
nanoparticle-based magnetic ink.
Fully/Partially Printed Tunable/Reconfigurable RF
Devices/Components Based on the Iron Oxide Nanoparticle-Based
Magnetic Inks
[0069] The iron oxide nanoparticle-based magnetic inks of the
present disclosure may be printed according to the methods of the
present disclosure and incorporated into tunable and/or
reconfigurable RF devices and/or components. The RF devices and/or
components may be fully and/or partially printed (e.g., inkjet
printed).
[0070] In an embodiment, the tunable and/or reconfigurable RF
devices and/or components are fully printed to form a fully printed
tunable inductor. For example, embodiments of the present
disclosure describe a tunable and/or reconfigurable inductor
including the printed iron oxide nanoparticle-based magnetic ink,
which may be printed as a film, among other forms, according to the
methods of the present disclosure. In an embodiment, a tunable
inductor may be fabricated on a top of an inkjet-printed magnetic
film prepared from the iron oxide nanoparticle-based magnetic inks
of the present disclosure. For example, the iron oxide
nanoparticle-based magnetic ink may be inkjet printed on a
substrate, such as a plastic substrate, with one or more
overprinted layers and then dried via heating at about 80.degree.
C. for about 30 min to form a printed magnetic film. After printing
the magnetic film, a tunable inductor may be printed on the inkjet
printed film. For example, in an embodiment, one or more layers of
silver-organo-complex (SOC) based silver ink may be printed and
cured (e.g., using infrared (IR) heating) to obtain a fully printed
tunable inductor. Optionally, the fully printed tunable inductor
may be supported on any suitable substrate, such as FR-4 board.
Functionalized Iron Oxide Nanoparticle-Based Magnetic Ink
Compositions
[0071] Embodiments of the present disclosure further describe an
ink composition comprising a mixture containing one or more of a
plurality of functionalized magnetic iron oxide nanoparticles, a
photocurable polymeric resin, and a solvent. The magnetic iron
oxide nanoparticles may include any of the magnetic iron oxide
nanoparticles of the present disclosure. For example, in an
embodiment, the magnetic iron oxide nanoparticles may include one
or more of Fe.sub.3O.sub.4 nanoparticles and Fe.sub.2O.sub.3
nanoparticles. The photocurable polymeric resin and the solvent may
include any suitable polymer with photocurable capabilities
dissolved in a suitable solvent, such as an organic solvent. For
example, in an embodiment, the photocurable polymeric resin may
include SU8, an epoxy dissolved in organic solvents, such as
cyclopentanone. The SU8 may be cross-linked through polymerization
by UV exposure to make solid films (e.g., thick solid films). In
many embodiments, the photocurable polymeric resin may be present
in low amounts (e.g., with a low wt %) and/or with a low viscosity
solvent composition. The photocurable polymeric resin may be
solidified (e.g., immediately solidified) upon exposure to, for
example, ultraviolet light, among other wavelengths of light. The
photocurable polymer resin may include UV-curable resins based on
acrylated epoxies, acrylated polyesters, acrylated urethanes,
acrylated silicones, and other such resins.
[0072] The magnetic iron oxide nanoparticles should be compatible
with the polymer and solvent of the photocurable polymeric resin
such that it may be incorporated into and/or embedded in the
matrix. To be compatible with the photocurable polymeric resins,
the magnetic iron oxide nanoparticles may be functionalized such
that the magnetic iron oxide nanoparticles may be combined with one
or more of the photocurable polymeric resins. The magnetic iron
oxide nanoparticles may be functionalized with any element or
compound suitable for embedding the nanoparticles in the
photocurable polymeric resin. For example, in many embodiments, the
magnetic iron oxide nanoparticles may be functionalized with oleic
acid, which is compatible with a large number of organic solvents,
including, for example, cyclopentanone. The oleic acid may be
physically sorbed (e.g., adsorbed) onto a surface of the magnetic
iron oxide nanoparticles such that the long chain of the oleic acid
may interact with the organic solvent. In other embodiments, the
magnetic iron oxide nanoparticles may be functionalized with one or
more of oleic acid, elaidic acid, oleylamine, oleamide, and oleyl
alcohol.
[0073] FIG. 5 is a flowchart of a method of making functionalized
iron oxide nanoparticle-based magnetic ink compositions, according
to one or more embodiments of the present disclosure. As shown in
FIG. 5, the method may comprise one or more of the following steps:
contacting 501 one or more of magnetic iron oxide nanoparticles, a
first solvent, and a functionalizing agent to form a solution;
mixing 502 the solution sufficient for the functionalizing agent to
sorb on a surface of the magnetic iron oxide nanoparticles;
removing 503 excess functionalizing agent; and contacting 504 the
functionalized magnetic iron oxide nanoparticles with a
photocurable polymeric resin to form a functionalized iron oxide
nanoparticle-based magnetic ink.
[0074] The step 501 includes contacting one or more of magnetic
iron oxide nanoparticles, a first solvent, and a functionalizing
agent to form a solution. The contacting may proceed by bringing
one or more of the magnetic iron oxide nanoparticles, first
solvent, and functionalizing agent into physical contact and/or
immediate or close proximity, sequentially and/or simultaneously,
in any order. In an embodiment, the magnetic iron oxide
nanoparticles may be dispersed in the first solvent, followed by
addition of the functionalizing agent. The magnetic iron oxide
nanoparticles may include any of the magnetic iron oxide
nanoparticles of the present disclosure, either in dry or wet form,
preferably wet form. The first solvent may include any solvent
suitable for dispersing and/or functionalizing the magnetic iron
oxide nanoparticles. For example, the first solvent may include an
alcohol solvent, such as ethanol, methanol, propanol, butanol,
pentanol, and other such solvents. The functionalizing agent may
include any functionalizing agent compatible with a desired
solvent, such as solvents in which the photocurable polymeric resin
is dissolved (e.g., organic solvents). For example, the
functionalizing agent may include one or more of oleic acid,
elaidic acid, oleylamine, oleamide, and oleyl alcohol.
[0075] The step 502 includes mixing the solution sufficient for the
functionalizing agent to sorb on a surface of the magnetic iron
oxide nanoparticles. The mixing may include any technique
sufficient for the functionalizing agent to sorb onto a surface of
the magnetic iron oxide nanoparticles. For example, the mixing may
be achieved by stirring, among other techniques known in art, for a
select duration. The duration of the mixing may range from about 1
min to about 48 h. In an embodiment, the duration of the mixing is
about 24 h. The functionalizing agent may be physically and/or
chemically sorbed (e.g., absorbed and/or adsorbed) onto a surface
of the magnetic iron oxide nanoparticles. In many embodiments, the
functionalizing agent may be physically absorbed onto a surface of
the magnetic iron oxide nanoparticles such that the functionalizing
agent is available to interact with the desired solvent (e.g., the
solvent in which the photocurable polymeric material is dissolved).
In this way, the functionalized iron oxide nanoparticles may be
compatible with the photocurable polymeric resin matrix.
[0076] The step 503 is optional and includes removing excess
functionalizing agent, if necessary. In this step, it may be
desirable to remove, among other things, excess functionalizing
agent from the mixture, which may contain one or more of
functionalized magnetic iron oxide nanoparticles, magnetic iron
oxide nanoparticles, first solvent, and functionalizing agent. The
removing may include one or more of centrifuging and washing with a
solvent, such as ethanol. For example, in an embodiment, the
mixture may be centrifuged (e.g., at about 4000 rpm for about 2
min) and washed with ethanol about 2-3 times to remove any excess
oleic acid. In an embodiment, the removing may further comprise
removing one or more of magnetic iron oxide nanoparticles, first
solvent, and functionalizing agent to, for example, obtain
functionalized magnetic iron oxide nanoparticles.
[0077] The step 504 includes contacting the functionalized magnetic
iron oxide nanoparticles with a photocurable polymeric resin to
form a functionalized iron oxide nanoparticle-based magnetic ink.
Any of the photocurable polymer resins of the present disclosure
may be used herein. In an embodiment, the photocurable polymeric
resin may be dissolved in a second solvent, such as organic
solvents (e.g., cyclopentanone). In an embodiment, one or more of
magnetic iron oxide nanoparticles, first solvent, and
functionalizing agent may be present during the contacting. In an
embodiment, one or more of magnetic iron oxide nanoparticles,
solvent, and functionalizing agent may not be present during the
contacting. The contacting may proceed by bringing the
functionalized magnetic iron oxide nanoparticles, photocurable
polymeric resin, and second solvent into physical contact and/or
immediate or close proximity. For example, in an embodiment, the
contacting may proceed by mixing using stone mortar and pestle. The
functionalized magnetic iron oxide nanoparticles and photocurable
polymeric resin may be mixed at a 1:100 wt % ratio to a 100:1 wt %
ratio. In an embodiment, the functionalized magnetic iron oxide
nanoparticles and photocurable polymeric resin may be mixed at a
50:50 wt % ratio. In an embodiment, the functionalized iron oxide
nanoparticle-based magnetic ink may be in a form of an ink
paste.
Printing Functionalized Iron Oxide Nanoparticle-Based Magnetic
Inks
[0078] FIG. 6 is a flowchart of a method of printing a magnetic ink
composition, according to one or more embodiments of the present
disclosure. As shown in FIG. 6, the method 600 may comprise
printing 601 a functionalized iron oxide nanoparticle-based
magnetic ink composition containing functionalized magnetic iron
oxide nanoparticles and a photocurable polymeric resin onto a
removable substrate, heating 602 the printed magnetic ink
composition to or at a select temperature for a select duration,
curing 603 the printed magnetic ink composition sufficient to
solidify the mixture; and optionally removing 604 the removable
substrate. The method may be used to form, among other things,
freestanding magnetic substrates including magnetic iron oxide
nanoparticles embedded in a polymeric material. The freestanding
magnetic substrates formed according to the methods of the present
disclosure may be used to form tunable, fully printed microwave or
RF devices, among other things.
[0079] The step 601 includes printing a functionalized iron oxide
nanoparticle-based magnetic ink onto a removal substrate. The
functionalized iron oxide nanoparticle-based magnetic ink may
include any of the magnetic ink compositions of the present
disclosure. For example, in an embodiment, the functionalized iron
oxide nanoparticle-based magnetic ink may contain one or more of
functionalized magnetic iron oxide nanoparticles and a photocurable
polymeric resin. In an embodiment, the functionalized iron oxide
nanoparticle-based magnetic ink may further contain one or more
residual species, such as one or more of magnetic iron oxide
nanoparticles, solvent, and functionalizing agent. The removable
substrate may be used as a support until the magnetic substrate is
solidified (e.g., after curing). For example, the removable
substrate may include an FR-4 board with sacrificial paper on a
backside. This shall not be limiting as any other material known in
the art may be used as a removable substrate.
[0080] Depending on a viscosity of the magnetic ink composition,
the magnetic ink composition may be provided in the form of a
paste. In an embodiment, a slot may be created on the removable
substrate to facilitate printing of the magnetic ink composition to
achieve a desired magnetic substrate thickness. In an embodiment,
the printing may proceed by a manual screen-printing technique,
such as a squeegee, to print the magnetic ink paste on the
removable substrate. For example, the magnetic ink paste may be
printed by filling (e.g., pouring, depositing, dropping, applying,
etc.) the slot created on the removable substrate with the magnetic
ink paste, optionally with the use of a squeegee or other similar
instrument. Any thickness of the magnetic substrate to be formed
may be achieved by varying a depth of the slot.
[0081] The step 602 includes heating the printed magnetic ink
composition to or at a select temperature for a select duration.
The heating may include heating the printed magnetic ink
composition and/or an environment in which the printed magnetic ink
composition is present to or at the select temperature. The select
temperature may include any suitable temperature. In many
embodiments, the select temperature may be about 80.degree. C. In
other embodiments, the select temperature may be less than about
and/or greater than about 80.degree. C. The select duration may
include any suitable duration. In many embodiments, the select
duration may be about 15 min. In other embodiments, the select
duration may be less than or more than about 15 min.
[0082] The step 603 includes curing the printed magnetic ink
composition sufficient to solidify the mixture and obtain, for
example, a freestanding magnetic substrate. The curing may include
any wavelength of light, which may depend on the selection of the
photocurable polymeric resin. In some embodiments, the curing may
include ultraviolet (UV) and/or infrared (IR) curing. The curing
may proceed for any suitable time, such as about 15 minutes. The
freestanding magnetic substrate may include functionalized iron
oxide nanoparticles embedded in the polymeric matrix. In an
embodiment, a fully inkjet-printed linear patch antenna including
the freestanding magnetic substrates of the present disclosure
[0083] In some embodiments, steps 601 to 603 may proceed one or
more times. For example, the slot created in the removable
substrate may be filled with the magnetic ink paste in one or more
cycles, wherein in each cycle, the ink is printed 601, heated 602,
and cured 603. The step 604 is optional and includes removing the
removable substrate. The removing may include one or more of
cutting the removable substrate from the edges and/or immersing the
removable substrate in a warm bath, such as a warm water bath
(e.g., for about 10 min).
Fully/Partially Printed Tunable/Reconfigurable RF
Devices/Components Based on the Iron Oxide Nanoparticle-Based
Magnetic Inks
[0084] The functionalized iron oxide nanoparticle-based magnetic
inks of the present disclosure may be printed according to the
methods of the present disclosure and incorporated into tunable
and/or reconfigurable devices and/or components. The RF devices
and/or components may be fully and/or partially printed.
[0085] In an embodiment, the functionalized iron oxide
nanoparticle-based magnetic inks are fully printed to form tunable
and reconfigurable passive microwave components. For example,
embodiments of the present disclosure describe printed linear patch
antennas including the functionalized iron oxide nanoparticle-based
magnetic ink described herein and which may be printed as
freestanding magnetic substrates according to the methods of the
present disclosure. In an embodiment, a smoothening layer may be
inkjet printed and cured on a top and bottom surface of the
freestanding magnetic substrate. In an embodiment, one or more
layers of a silver-organo-complex (SOC) silver ink may be printed
and cured using, for example, IR heating to obtain the patch
antenna. The SOC ink is more fully described in WO 2017/103797 A1,
which is hereby incorporated by reference in its entirety.
[0086] The following Examples are intended to illustrate the above
invention and should not be construed as to narrow its scope. One
skilled in the art will readily recognize that the Examiners
suggest many other ways in which the invention could be practiced.
It should be understand that numerous variations and modifications
may be made while remaining within the scope of the invention.
Example 1
[0087] The field of printed electronics is still in its infancy and
most of the reported work is based on commercially available
nanoparticle-based metallic inks. Although fully printed devices
that employ dielectric/semiconductor inks have recently been
reported, there is a dearth of functional inks that can demonstrate
controllable devices. The lack of availability of functional inks
is a barrier to the widespread use of fully printed devices. For
radio-frequency electronics, magnetic materials have many uses in
reconfigurable components, but rely on expensive and rigid ferrite
materials. A suitable magnetic ink can facilitate the realization
of fully printed, magnetically controlled, tunable devices.
[0088] The present Example describes the development of an iron
oxide nanoparticle-based magnetic ink. First, a tunable inductor
was fully printed using iron oxide nanoparticle-based magnetic ink.
Furthermore, iron oxide nanoparticles were functionalized with
oleic acid to make them compatible with a UV-curable SU8 solution.
Functionalized iron oxide nanoparticles were successfully embedded
in the SU8 matrix to make a magnetic substrate. The as-fabricated
substrate was characterized for its magnetostatic and microwave
properties. A frequency tunable printed patch antenna was
demonstrated using the magnetic and in-house silver-organo-complex
inks. This was a step toward low-cost, fully printed, controllable
electronic components.
[0089] The iron oxide nanoparticle-based magnetic ink was
completely characterized for its material properties, and then its
utility was demonstrated through fully printed, magnetically
controllable RF devices. A simple solution method to synthesizing
well-dispersed, uniform, magnetic, iron oxide NPs was adopted.
These iron oxide NPs were used for ink-formulation and then used to
demonstrate the fully inkjet-printed tunable inductor. These iron
oxide nanoparticles were also used with the aim of making
freestanding magnetic substrates. SU8 polymer was selected to
develop thick substrates, a polymeric resin materials that can
immediately solidify on exposure to a low-cost UV lamp. This SU8
solution was cross-linked through polymerization by UV exposure to
make thick solid films. Through functionalization of iron oxide
nanoparticles with oleic acid (to make it compatible with a
UV-curable SU8 solution), the functionalized iron oxide
nanoparticles were successfully embedded in the SU8 matrix,
creating a freestanding, magnetic substrate. The magnetic ink was
characterized for its magnetic and high frequency properties.
Finally, a patch antenna was printed on the magnetic substrate with
an in-house silver ink; the printed antenna was tuned for its
frequency by applying magnetic fields across it. This first
demonstration of a fully printed controllable RF device was an
important milestone for the next generation of low-cost tunable and
reconfigurable components that can be completely realized through
additive manufacturing.
EXPERIMENTAL SECTION
[0090] Chemicals: Iron (II) chloride tetrahydrate
(FeCl.sub.2.4H.sub.2O, reagent plus, 98%), iron (III) chloride
hexahydrate (FeCl.sub.3.6H.sub.2O, ACS, 97-102%), sodium hydroxide
(NaOH, Sigma Aldrich), acetic acid (CH.sub.3COOH, ACS reagent,
.gtoreq.99.7%), oleic acid
[CH.sub.3(CH.sub.2).sub.7CH.dbd.CH(CH.sub.2).sub.7COOH, technical
grade, 90%], SU8 2002 (MicroChem), and ethanol (absolute, VWR
Chemicals) were used as they were received, without further
purification.
[0091] Synthesis of Iron Oxide NPs: As in a typical synthesis
process, 0.01 M iron (II) chloride (.apprxeq.0.596 g) and 0.02 M
iron (III) chloride (.apprxeq.1.621 g) were dissolved in about 300
mL of DI water, followed by mixing of about 1 mL of acetic acid.
The resulting solution was then slowly heated in a three-necked
refluxing pot while stirring (1000 rpm). When the temperature
reached about 90.degree. C., about 2 g of NaOH was added. This
resulted in a black solution, indicating the formation of
Fe.sub.3O.sub.4 NPs. In this reaction condition, sodium hydroxide
acted as a basic source and acetic acid to break the precipitates
for the formation of uniform and disperse Fe.sub.3O.sub.4 NPs.
After about 10-15 min of refluxing, the black colloidal solution
was obtained followed by centrifugation at about 3000 rpm for about
2 min, and washing with deionized water and ethanol.
[0092] Ink Formulation and Inkjet Printing Using Iron Oxide NPs:
The as-prepared iron oxide NPs were formulated as ink in about 3 mL
of deionized water. Initially, the ink exhibited a high surface
tension (SFT) of .apprxeq.63 mN m.sup.-1 which was adjusted with
the addition of about 10 vol % of ethanol. After the addition of
ethanol, ink exhibited an SFT of .apprxeq.44 mN m.sup.-1, which was
good for stable jetting performance, as shown in FIGS. 7A-7B. The
resulting solution was then stirred for about 24 h. Subsequently,
the formulated iron oxide ink was filtered by 0.45 .mu.m
polypropylene (PP) Whatman paper before jetting. The observed
viscosity of as-formulated ink for ink jet printing was
.apprxeq.1.74 cP, using a spindle speed of about 100 rpm and shear
rate of about 132 s.sup.-1 at about room temperature. However, the
SU8 embedded iron oxide nanoparticles were showing the viscosity of
about 37.8 cP, using a spindle speed of about 100 rpm and shear
rate of about 132 s.sup.-1 at about room temperature. The iron
oxide dot and line patterns were directly printed on glass
substrate using a drop-on-demand piezoelectric ink-jet nozzle
(manufactured by Dimatix) with a diameter of 16 jam; the drop
volume was about 10 pL. The uniform and continuous ejection of
droplets was achieved by adjusting various wave forms while
applying a firing voltage of 33.2 V at a 5 kHz printer velocity, as
shown in FIG. 8. The jetting velocity of ejected droplets was
.apprxeq.3.3 m s.sup.-1 and the cartridge print height was
.apprxeq.0.3 mm. The thickness of as-printed lines was varied by
the number of overprinting layers using about 40 .mu.m drop
spacing.
[0093] Functionalization of Iron Oxide NPs and Their Ink
Formulation: For functionalization, the wet form of iron oxide NPs
was dispersed in about 50 mL of ethanol, followed by the addition
of about 0.2 mL of oleic acid. The resulting solution was then
stirred for about 24 h to ensure the physical absorption of oleic
acid molecules on surfaces of iron oxide NPs. After stirring, the
resulting solution was centrifuged at about 4000 rpm for about 2
min and washed with ethanol about 2-3 times cycle.sup.-1 to remove
access oleic acid molecules. The resulting functionalized iron
oxide NPs were then ready to mix with the SU8 2002 solution.
[0094] Fabrication of a Printed Antenna on Magnetic Substrate: An
in-house SOC ink was utilized in this work to print an antenna on
magnetic substrate. The SOC ink produced smooth and dense films; it
was stable and transparent. The antenna was printed on magnetic
substrate (t.apprxeq.1500 .mu.m) using eight layers of AOC ink at
about 30 .mu.m drop spacing with a 10 pL Dimatix DMP 2831 inkjet
printer. A low-cost 250 W IR lamp was used to cure the ink by
placing the substrate under the lamp for about 5 min after each
printed layer. The maximum measured temperature of the substrate
was about 80.degree. C.
[0095] Characterization: The structural properties were examined
using scanning electron microscopy (Zeiss Merlin with Gemini 2
column) and transmission electron microscopy (FEI Titan G2 80-300
kV equipped with a 2 k.times.2 k CCD camera model US4000, Gatan,
Inc.). The elemental quantification was examined with EDS equipped
with FEI Nova Nano. In addition, the thicknesses and uniformity of
printed features on substrates were measured using a surface
profiler (Veeco Dektak 150). The crystallinity of the iron oxide
powders was examined by X-ray diffraction (Bruker D8 Advance) in
the range of 20.degree.-70.degree. at 40 kV. Furthermore, the
UV-vis absorption spectrum of the ink was obtained using a UV-vis
spectrophotometer (Cary 100 UV-vis-NIR) with a standard 1 cm liquid
cuvette and a background calibration that was run using ethanol.
The chemical functionalization was characterized by FTIR
spectrometers (Nicolet 6700). The FTIR sample was prepared using
KBr pellet method. .apprxeq.0.1-1.0% sample was well mixed into
.apprxeq.200 mg fine KBr powder and then finely pulverized using
stone mortar and pestle. After pulverization, the resultant powder
was placed in to a pellet-forming die for making transparent
pellets. In order to correct the infrared light scattering loses in
the pellet, a background measurement was done on a pellet holder
with a pellet of KBr only. Finally, the sample was loaded and its
measured infrared spectrum was recorded. Furthermore, viscosities
of the inks were measured using a Brookfield Rheometer (DV3T). The
surface tensions of the inks were measured by using a KRUSS DSA100
based on pendant drop method. The particle size analysis of the ink
was done using Zetasizer (Malvern Instrument). Before analysis, ink
was diluted ten times with DI water. The magnetic properties of
iron oxide nanoparticles were examined by SQUID-VSM.
Synthesis and Functionalization of Iron Oxide NPs
[0096] Iron oxide NPs were prepared at about 90.degree. C. with
iron (II) chloride, iron (III) chloride, NaOH, and acetic acid
using the hot-injection solution method for about 30 min, without
the use of any complex reagents. The presence of acetic acid and
addition of sodium hydroxide at heating temperature played an
important role in the formation of small iron oxide NPs. If sodium
hydroxide was added to the boiling solution with the presence of
acetic acid, higher temperatures generally caused faster reaction
rates, generating large amounts of nuclei in a short time and
leading to the formation of small nanoparticles. Iron oxide NPs
usually possess typical magnetic behavior at about room temperature
(RT). To the best of present knowledge, there is no report of any
iron oxide NP-based ink formulation for inkjet printing. Several
significant issues related to magnetic ink formulation must be
addressed. For example, magnetic materials should be nanoparticle
sized and be well dispersed during formulation, ink viscosity and
surface tension must be suited for inkjet printing, and ink must
contain the appropriate concentration and a carrier vehicle
(solvent). In the field of printed electronics, similar to other
emerging electronic technologies, new materials and processing
methods are required for their continually improving development
and performance.
[0097] The as-prepared iron oxide NPs showed good dispersion with
deionized (DI) water and were successfully utilized as a solvent
for inkjet printing. To be compatible with SU8 polymeric resin,
iron oxide required functionalization on the surfaces of
nanoparticles. SU8 2002 manufactured by Micro-Chem is usually
composed of an epoxy that is dissolved into an organic solvent
(e.g., cyclopentanone). Oleic acid was successfully used as a
molecule for functionalization of iron oxide nanoparticles. The
selection of oleic acid was due to its compatibility with
cyclopentanone of SU8 polymeric resin in addition to many common
organic solvents. Furthermore, the choice of SU8 was also due to
its low wt % of resin with low viscosity solvent composition and
its photocuring capability. A number of other photocurable
polymeric resins were available but due to their high content of
resin (>99%) and high viscosity, it may be very challenging to
embed the nanoparticles in those resins. Thus, for compatibility
with SU8 2002, iron oxide nanoparticles were functionalized with
oleic acid, as shown in FIG. 9A. The physical adsorption of oleic
acid molecules on the surfaces of iron oxide NPs led to
compatibility with the SU8 matrix, as the long chain of oleic acid
interacted with the organic solvent. Subsequently, these SU8-mixed
nanoparticles were pre-heated at about 80.degree. C. for about 15
min, followed by UV curing with a wavelength of about 365 nm for
about 30 min to solidify the mixture. FIGS. 9B-9G show the scanning
electron microscopic (SEM) images and energy-dispersive
spectroscopic (EDS) spectrum taken from the as-prepared,
functionalized, SU8-mixed iron oxide NPs. The SEM image (FIGS. 9B,
9C) shows that the NPs are almost spherical shape; they were
uniformly grown at a high density with an average diameter of about
15-20 nm. It should be noted that due to charging effect and
magnetization of iron oxide nanoparticles, high-resolution images
were difficult to capture. The EDS spectrum (FIG. 9E) demonstrates
that the as-prepared NPs are made of Fe and O only, and the atomic
ratio of Fe and O is .apprxeq.3:4. In contrast to pure iron oxide
NPs, the oleic acid functionalized sample (FIG. 9F) shows the
carbon content in addition to Fe and O, which confirmed the
functionalization on the surfaces of iron oxide NPs. The SU8 mixed
iron oxide NPs (FIG. 9G) show even higher carbon content, primarily
due to SU8 molecules. The SU8-mixed, iron oxide morphology (FIG.
9D) confirmed that nanoparticles were well-embedded in the SU8
matrix. The particle's size and shape were further confirmed by its
corresponding transmission electron microscopic (TEM) images. FIGS.
10A-10C show TEM image, high-resolution TEM (HRTEM) image, and
selected area diffraction (SAED) pattern of (FIG. 10A) pure, (FIG.
10B) functionalized, and (FIG. 10C) SU8-mixed iron oxide NPs. From
the TEM images, it was confirmed that nanoparticles were in various
shapes such as spherical, cubic, and elongated. Such shapes are
common in iron oxide nanoparticles during the nucleation and growth
formation. The functionalization of iron oxide was also visualized
by an HRTEM image (FIG. 10B2), showing .apprxeq.2-3 nm of carbon
shell on the core of the nanoparticles. Furthermore, the HRTEM
image (FIG. 10C2) of the SU8-mixed sample showed a thick boundary
of the SU8 carbon-coated matrix, in which iron oxide nanoparticles
were suspended. The SAED patterns (FIGS. 10A3-10C3) for all the
samples, confirmed the polycrystallinity phase of as-grown iron
oxide NPs, corresponded to the cubic spinel structure. Due to thick
boundary of SU8 matrix, the intensity of SAED pattern was faded
which further confirmed that iron oxide nanoparticles were embedded
in the SU8 matrix. It should be noted that TEM analyses were only
for morphological characterization purpose. However,
functionalization and embedding could be efficiently confirmed by
Fourier transform infrared (FTIR) analysis.
Chemical Nature and Crystalline Phase of Iron Oxide NPs
[0098] The quality and chemical composition of (a) as-synthesized,
(b) oleic acid functionalized, and (c) SU8-mixed ironoxide NPs were
further examined by FTIR spectroscopy in transmission mode and are
shown in FIG. 11A. In the as-synthesized sample, weak adsorption
bands appeared at 3412 and 1587 cm.sup.-1 as well as a strong
adsorption band at 581 cm.sup.-1. The weak adsorption bands were
attributed to the stretching vibration and bending vibration of the
absorbed water and surface hydroxyls, respectively. Moreover, the
presence of the strong band was due to Fe--O stretching vibration.
Surface absorbed moisture was common during sample preparation for
FTIR analysis. Therefore, the FTIR spectrum confirmed that the
synthesized product was pure iron oxide NP (a). The bands at 1395
and 1458 cm.sup.-1 were ascribed to the symmetric and asymmetric
stretches of COO--, indicating that the oleic acid molecule was
attached to the iron oxide nanoparticles in a bidentate mode, with
two oxygen atoms symmetrically coordinated to iron (b). The
characteristic vibrational bands at 2852 and 2920 cm.sup.-1 were
attributed to the symmetric and antisymmetric --CH2 stretching from
the structure of oleic acid. In addition, the band at 1639
cm.sup.-1 was due to C.dbd.C from oleic acid. The SU8-mixed iron
oxide sample showed several characteristic bands at 830, 1245,
1608, and 1738 cm.sup.-1, which, respectively, corresponded to an
epoxide, aromatic ring, and carbonyl group from the SU8 molecules.
FIG. 11B shows the X-ray diffraction (XRD) patterns that were
implemented to examine the crystal structure of iron oxide
nanoparticles (a) before and (b) after functionalization, and (c)
SU8-mixed samples. All characteristic peaks are matched with the
cubic spinal-structured magnetite (JCPDS card no. 65-3107). The
optical properties of the as-synthesized and functionalized samples
were also investigated by UV-vis absorption (FIG. 12). The UV-vis
absorption spectrum showed that, as the wavelength decreased,
absorbance increased monotonically. The UV-vis spectrum indicated
that the wide absorption range from 300 to 900 nm occurred with a
broad peak center at 400 nm, corresponded to iron oxide absorption.
The wide absorption may be caused by cluster formation of iron
oxide NPs in an ethanol solution, which scattered almost UV
radiation and provided long-tail-type features in the UV-vis
absorption spectrum.
Magnetic Properties of Iron Oxide NPs
[0099] FIGS. 13A-13B demonstrate the magnetization versus magnetic
field plots (M-H loops) measured at 300 K, in addition to the full
range of hysteresis between .+-.10 kOe for the as-synthesized and
oleic acid functionalized iron oxide NPs. The samples showed no
hysteresis at RT, signifying the superparamagnetic nature of the
resultant NPs (a). A well-developed hysteresis loop was observed at
5 K, signifying the ferromagnetic nature of the resultant NPs (b).
While not wishing to be bound to a theory, it was believed that,
due to the air-gap condition and loosely bound nanoparticles at RT
measurement, the samples were superparamagnetic nature. In contrast
to RT measurement, the freezing state (at 5 K) condition satisfied
the gap and loosely bound state, demonstrating the ferromagnetic
nature, as shown with the pictorial presentation in FIGS. 13A-13B.
Furthermore, the saturation magnetization (M.sub.S), remanent
magnetization (M.sub.R), and coercivity (H.sub.C) were calculated
as 51-53 emu g.sup.-1, 20.31 emu g.sup.-1, and 400 Oe for
as-synthesized and oleic acid functionalized iron oxide NPs,
respectively (FIG. 3B). Compared to the bulk iron oxide, the
decrease in M.sub.S was attributed to the decreased particle size
and an increase in surface area.
[0100] The energy of a magnetic particle in an external field is
proportional to its size or volume via the number of magnetic
molecules in a single magnetic domain. When this energy becomes
comparable to the thermal energy, thermal fluctuations will
significantly reduce the total magnetic moment at a given field.
Such a phenomenon is more prominent with small nanocrystals. The
temperature-dependent magnetization was also characterized (FIG.
14), which was typical to magnetic nanoparticles. Zero-field cooled
(ZFC) and field-cooled (FC) curves were measured in a magnetic
field of 100 Oe in the temperature range of 5-300 K. The graph
shows the two FC and ZFC curves, which have a divergence point
close to room temperature. Moreover, FC magnetization remains
nearly constant as the temperature decreased, whereas ZFC
magnetization decreased as the temperature decreased. There was no
distinctive blocking temperature (TB), which must be investigated
further by varying the magnetic field.
Inkjet Printing of Magnetic Ink and Fabrication of Fully Printed
Tunable Inductor
[0101] As-synthesized iron oxide NPs were used for ink formulation
with about 10 wt % loading in water solvent. To confirm the
particle size aggregate in the ink, the ink was diluted ten times
with deionized (DI) water and characterized using Zetasizer (as
shown in FIG. 15). The graph clearly shows the size distribution
with number of particles. The .apprxeq.51.7% particle aggregates
corresponded to 121.5 nm, 48% for 242 nm, and 0.2% for 2582 nm. The
ink was inkjet printed under constant printing conditions and
vertically dropped from the nozzle, which formed dots (FIGS.
16A-16B) and lines (FIGS. 17A-17E) on the glass substrate. The 3D
image of the dots showed the uniform dot pattern with a high
density of NPs covering the entire dot area (FIG. 16A). The 3D
surface profiler measured the dot width as .apprxeq.55 .mu.m and
the thickness was .apprxeq.160 nm (FIG. 16B). To further study the
effect of overprinting on the substrate-surface-ink interaction and
line uniformity, the line patterns with a drop spacing of 40 .mu.m
were printed on glass substrates while varying the number of
overlayers (n.sub.ol). The as-printed iron oxide lines were
analyzed by the 3D surface profiler with varying n.sub.ol (FIGS.
17A-17E). The printed lines showed a width of 70.+-.10 .mu.m with
number of overlayers. FIG. 17A corresponds to the single printing,
which revealed that the density of NPs was not uniform along the
width (i.e., there was a higher density at the edge of line than in
the middle area; a-2). The first layer of printing was directly
related to the substrate-ink interaction and its compatible
properties, such as the surface tension of ink and surface energy
of the substrate, directed the quality of printed lines. With
successive overprinting, the edge area may be covered with more NPs
and eventually printed with a more uniform pattern line. To confirm
this, an overprinted layer was printed over the first-printed
layer. As shown in FIGS. 17B-17C, line uniformity and density was
substantially improved by increasing the number of overlayers from
1 to 5. In addition, all the printed lines with the ink did not
show any coffee-ring effects or line bulging. The thickness of the
as-printed lines with n.sub.ol was summarized in FIG. 18. The
thicknesses of printed lines was controlled by the number of
overprinted layers and by varying the drop spacing.
[0102] In order to evaluate the functional properties of the
magnetic ink, a tunable inductor was fabricated on top of an
inkjet-printed magnetic film, as shown in FIGS. 19A-19C. First,
iron oxide nanoparticles ink were inkjet printed on a plastic
substrate with five overprinted layers, followed by drying at about
80.degree. C. for about 30 min (FIG. 19A). The printed film
resulted in a saturation magnetization of .apprxeq.12.4 memu under
an applied field of about 1 kOe, while the coercivity was found to
be 46 Oe, as shown in FIGS. 20A-20B. After printing the magnetic
film, a total of eight layers of silver-organo-complex (SOC) based
silver ink was printed and cured using infrared (IR) heating for
about 5 min (FIG. 19B). Finally, the fully printed tunable inductor
was attached on an FR4 board (support substrate) for testing
purpose, as shown in (FIG. 19C). For RF characterization of the
inductor, two port S-parameter measurements were performed using
Agilent E8361C PNA series network analyzer. The inductor was fed by
a 50.OMEGA. microstrip transmission line. The measured inductance
of the printed inductor is shown in FIGS. 21A-21B. At 100 MHz, it
had an inductance of about 19.6 nH and self-resonant frequency
(SRF) of about 870 MHz (a). To measure the tunability of the
printed inductor, an external magnetic field of up to 12 kOe was
applied using MicroMag 3900 vibrating sample magnetometer (VSM).
The inductance versus the frequency under the influence of external
magnetic field for printed inductor is shown in FIGS. 21A-21B. A
tuning of about 24% was observed when about 12 kOe magnetic field
was applied. A smaller tuning of about 18% was observed when lower
magnetic field of about 2 kOe was applied. The fully printed
inductor realized with the formulated ink described herein showed
much higher tuning than the case when commercial iron oxide
nanoparticles ink were used (only 0.8% tuning with 5 kOe magnetic
field, FIGS. 22A-22B). The results summarized in Table 1 clearly
indicated superior performance and suitability to tunable RF
components as compared to the commercially available ink.
Fabrication of Freestanding Magnetic Substrate and Its
Characterization
[0103] Functionalized iron oxide nanoparticles were successfully
embedded in the SU8 matrix to develop freestanding magnetic
substrate. The functionalized iron oxide nanoparticles were mixed
using stone mortar and pestle with the SU8 2000 (Microchem) epoxy
resist at a 50:50 wt % ratio to formulate ink paste. When the ink
paste was ready, it was printed using a manual screen-printing
technique (i.e., squeegee). The steps for the fabrication process
are displayed in FIGS. 23A-23F. An FR-4 board with a sacrificial
paper on the backside was used as a support material in this work,
though any other material can be used instead of FR-4. The
sacrificial paper was used because the ink was initially in a paste
form and a support substrate was required until it solidified after
UV exposure. A slot was created in the support material using LPKF4
Protomat S103 (a) to facilitate the printing of magnetic ink for a
precise substrate thickness of about 1.5 mm. The empty slot was
filled with the ink paste in three cycles. For each cycle, the
filled materials were heated to about 80.degree. C. for about 15
min followed by UV curing (.lamda.=365 nm) for about 15 min (b).
Once the ink was solidified with three cycles of the heating and
the curing process, it was separated from the support material by
cutting it from the edges (c). The sacrificial paper on the back of
the magnetic substrate was removed by immersing it in warm water
for about 10 min. An about 10 .mu.m smoothening layer of "3D vero
black plus" material was then inkjet printed and photocured on the
top (d) and bottom (e) of the magnetic substrate. A total of eight
layers of SOC ink each for ground plane and patch antenna were
printed and cured using IR heating for about 5 min (f). The final
prototype of patch antenna is shown in the inset of FIG. 23F. The
preparation of freestanding substrate was performed through manual
printing. However, through integrating advanced printing
technology, such as a 3D printer equipped with a UV curing system,
in-demand magnetic objects may be easily be created.
Magnetostatic and Microwave Characterization
[0104] Once the magnetic substrate was prepared, it was important
to characterize its magnetostatic and microwave properties. A VSM
was used for the B(H) curve measurements of the magnetic substrate,
where B was the magnetic flux density and H was the magnetic field
strength. The substrate, without any metallic layers on top, was
placed in the VSM; the measured B(H) curve results are displayed in
FIG. 24A. The substrate demonstrated a saturation magnetization
(4.pi.MS), coercive field (HC), and remanent magnetization (BM) of
about 1560 Gauss (G), about 46 Oe, and about 350 Gauss,
respectively. For microwave tunable designs, stronger the
saturation magnetization, larger is the tunability of the
component. Here, the value of 1560 G was acceptable and provided
decent tuning. This value may be increased by modifying the
composition of the ink. After obtaining saturation magnetization,
the next important parameter was the magnetization frequency of the
substrate. The magnetization frequency was an important
characteristic of ferrites because the ferrites do not show any low
field losses after this frequency. From the saturation
magnetization, the magnetization frequency of the material was
calculated using the following formula:
f.sub.m=.gamma.4.pi.M.sub.S=4.37 GHz. It was recommended that the
center frequency of a microwave device be higher than the
magnetization frequency of the substrate to avoid any low field
losses.
[0105] Once the magnetostatic properties of the material were
known, it can be studied for its high-frequency and microwave
properties. To extract the microwave properties of the printed
substrate, a coplanar waveguide (CPW) based ring resonator was
designed and fabricated on top of the substrate. The resonator was
characterized for its S parameters from 1 to 10 GHz, and the
fundamental resonance of the design was measured at 2.4 GHz. These
results were used to extract the dielectric constant of the
material. Since this was a magnetic material, the result obtained
from the equation provided a product of the initial permeability
and permittivity. This product was displayed in FIG. 24B. The value
of this product varied with respect to the frequency, which was
expected due to the varying initial permeability of the ferrite
material. Using this equation, the permittivity and permeability of
the medium at different frequencies were calculated and are listed
in Table 2. Since the material was lossy below f.sub.m, frequencies
above f.sub.m were considered in the table since these were the
frequencies that may be used for the antenna design. In the initial
design of any microwave device, this product can directly be used
in the equation of the resonant frequency. In addition to the
dielectric constant, the loss tangent (tan .delta.) of the material
was calculated from the measured results. The conductor losses were
calculated using the transmission line calculator of the Keysight
in the Advanced Design System (ADS). The measured conductivity of
the metal was about 5.times.106 S m.sup.-1, which was used to
evaluate the conductor loss for different frequencies. Once the
conductor loss was known, the dielectric loss of the material was
evaluated. The loss tangent of the substrate at frequencies below
f.sub.m was relatively high. For example, at about 2.4 and about 4
GHz, the loss tangent values were 0.13 and 0.015, respectively, due
to the low field losses of the magnetic material in the absence of
the magnetic bias. However, the loss tangent values at frequencies
above f.sub.m are in the acceptable range.
Printed Linear Patch Antenna
[0106] The magnetostatic and microwave characteristics of the
printed magnetic ink were then used for the design of a patch
antenna. The patch antenna design was used as proof of concept to
show the viability of this ink in the implementation of tunable and
reconfigurable passive microwave components. A rectangular patch
antenna operating at about 8 GHz was designed and fabricated using
inkjet printing, as shown in FIG. 25A. The frequency of operation
was almost twice the value of f.sub.m, thus avoiding the lossy
spectrum of the substrate. The antenna had dimensions of about
6.4.times.7 mm. The antenna was initially measured for its
impedance properties without any magnetic bias, as shown in FIG.
25B. Subsequently, the antenna was characterized for its 3D
radiation pattern, as shown in FIG. 25C. The maximum gain of the
antenna was .apprxeq.-0.7 dBi at about 8.2 GHz. The radiation
pattern of the antenna showed directional properties with maximum
gain in the bore-sight direction as expected with a patch antenna.
To test the tuning capability, the impedance of the antenna was
measured in the presence of a magnetostatic field which was
generated by an electromagnet. The strength of the applied magnetic
field varied from about 0 Oe to about 5 kOe. No change in the
resonant frequency of the antenna was observed up to a bias
strength of about 2 kOe because the magnetic fields were lost in
the air due to the demagnetization effect. Above about 2 kOe, the
frequency of the antenna began to tune down as shown in FIG. 25D.
Increasing the fields beyond this value reduced the center
frequency to about 3.7 kOe. A total tuning range of 1.25 GHz was
obtained, which was about 12.5% of the center frequency. Further
increasing the bias resulted in a slight increase in the resonant
frequency of the antenna, which could be because the substrate was
saturated for a bias field strength of about 3.7 kOe. After this
value, strong fields were required to tune the antenna using the
Polder's equations. The measured reflection coefficient of the
antenna at a bias value of 3.7 kOe was shown in FIG. 25B. The
antenna maintained its matching condition during the entire tuning
range, which was required from such a design. No significant effect
was expected on the antenna radiation pattern due to the applied
bias, as it was reported that the radiation pattern of a
ferrite-based patch antenna did not change significantly in the
biased state.
[0107] In conclusion, this Example successfully performed the
preparation of the iron oxide nanoparticles and their ink
formulation to demonstrate the fully printed highly tunable
inductor. Further, oleic acid functionalization and integration of
nanoparticles with SU8 was performed to fabricate the first printed
freestanding magnetic substrate. The materials were characterized
in detail to obtain the morphological, structural, chemical,
optical, and magnetic properties. Furthermore, the printed
substrate was characterized for its magnetostatic and microwave
properties. The magnetic substrate demonstrated a saturation
magnetization of 1560 G and a calculated magnetization frequency of
4.37 GHz. To prove the functionality of the ink, a patch antenna
design was implemented. The antenna successfully demonstrated the
frequency tuning due to the application of magnetostatic fields
across it. For a center frequency of 8 GHz, a tuning range of 12.5%
was achieved at a magnetic field strength of 3.7 kOe. Such a
functional ink was not only highly suitable for tunable and
reconfigurable microwave devices, but could also be explored in
sensing, biotechnology, and biomedical areas.
[0108] Other embodiments of the present disclosure are possible.
Although the description above contains much specificity, these
should not be construed as limiting the scope of the disclosure,
but as merely providing illustrations of some of the presently
preferred embodiments of this disclosure. It is also contemplated
that various combinations or sub-combinations of the specific
features and aspects of the embodiments may be made and still fall
within the scope of this disclosure. It should be understood that
various features and aspects of the disclosed embodiments can be
combined with or substituted for one another in order to form
various embodiments. Thus, it is intended that the scope of at
least some of the present disclosure should not be limited by the
particular disclosed embodiments described above.
[0109] Thus the scope of this disclosure should be determined by
the appended claims and their legal equivalents. Therefore, it will
be appreciated that the scope of the present disclosure fully
encompasses other embodiments which may become obvious to those
skilled in the art, and that the scope of the present disclosure is
accordingly to be limited by nothing other than the appended
claims, in which reference to an element in the singular is not
intended to mean "one and only one" unless explicitly so stated,
but rather "one or more." All structural, chemical, and functional
equivalents to the elements of the above-described preferred
embodiment that are known to those of ordinary skill in the art are
expressly incorporated herein by reference and are intended to be
encompassed by the present claims. Moreover, it is not necessary
for a device or method to address each and every problem sought to
be solved by the present disclosure, for it to be encompassed by
the present claims. Furthermore, no element, component, or method
step in the present disclosure is intended to be dedicated to the
public regardless of whether the element, component, or method step
is explicitly recited in the claims.
[0110] The foregoing description of various preferred embodiments
of the disclosure have been presented for purposes of illustration
and description. It is not intended to be exhaustive or to limit
the disclosure to the precise embodiments, and obviously many
modifications and variations are possible in light of the above
teaching. The example embodiments, as described above, were chosen
and described in order to best explain the principles of the
disclosure and its practical application to thereby enable others
skilled in the art to best utilize the disclosure in various
embodiments and with various modifications as are suited to the
particular use contemplated. It is intended that the scope of the
disclosure be defined by the claims appended hereto
[0111] Various examples have been described. These and other
examples are within the scope of the following claims.
* * * * *