Electromagnetically absorptive materials

Abstract

Thermally conductive and electromagnetically absorbing compositions include a mixture of particles dispersed in a binder, the mixture of particles includes a first set of particles that is a plurality of particles, and a second set of particles that is electrically conductive particles, where the electrically conductive particles have a particle size that is smaller than the particle size of the plurality of particles. The plurality of particles have a particle size distribution of at least three peaks, where at least a majority of particles within a half width at half maximum (HWHM) of one, but not the other ones, are at least partially coated with an electromagnetically absorbing coating.

Description

[0001] ELECTROMAGNETICALLY ABSORPTIVE MATERIALS

[0002] Summary

[0003] Disclosed herein are thermally conductive and electromagnetically absorbing compositions comprising a mixture of particles dispersed in a binder and articles containing these thermally conductive and electromagnetically absorbing compositions comprising a mixture of particles dispersed in a binder. Also disclosed herein are fifth generation (5G) wireless communication systems.

[0004] In some embodiments, the thermally conductive and electromagnetically absorbing composition comprising a mixture of particles dispersed in a binder, the mixture of particles comprises a first set of particles comprising a plurality of particles, and a second set of particles comprising electrically conductive particles, where the electrically conductive particles have a particle size that is smaller than the particle size of the plurality of particles. The plurality of particles has a particle size distribution comprising at least three peaks, where at least a majority of particles within a half width at half maximum (HWHM) of one, but not the other ones, are at least partially coated with an electromagnetically absorbing coating.

[0005] Also disclosed are articles containing these thermally conductive and electromagnetically absorbing compositions comprising a mixture of particles dispersed in a binder. In some embodiments, the article comprises a thermally conductive and electromagnetically absorbing composition, wherein the electromagnetically absorbing composition comprises the mixture described above.

[0006] Also disclosed are fifth generation (5G) wireless communication systems. In some embodiments, the fifth generation (5G) wireless communication system comprises an antenna comprising an array of distinct spaced apart antenna elements configured to at least one of receive and transmit a signal having a frequency of between about 1 GHz and about 120 GHz; and an electromagnetically absorbing material disposed between at least two antenna elements in the array of antenna elements, where the electromagnetically absorbing material comprises the mixture of particles described above. Brief Description of the Drawings

[0007] The present application may be more completely understood in consideration of the following detailed description of various embodiments of the disclosure in connection with the accompanying drawings.

[0008] Figure 1 is a graph of data of Permittivity vs Frequency for Examples E1A-E1C.

[0009] Figure 2 is a graph of data of Dielectric Loss Tangent vs Frequency for Examples E1A-E1C.

[0010] Figure 3 is a graph of data of Permittivity vs Frequency for Examples E2A-E2D.

[0011] Figure 4 is a graph of data of Dielectric Loss Tangent vs Frequency for Examples E2A-E2D.

[0012] Figure 5 is a graph of data of EMI Reflection Loss vs Frequency for Examples E1A-E1C.

[0013] Figure 6 is a graph of data of EMI Reflection Loss vs Frequency for Examples E2A-E2D.

[0014] Detailed Description

[0015] Electromagnetic interference (EMI) is the disturbance caused by electromagnetic radiation from an external source that interferes with the operation of an electronic device or system. EMI can be caused by natural sources such as lightning, or by man-made sources such as power lines, radio and TV signals, and electronic equipment.

[0016] EMI technology involves the development of techniques to mitigate or prevent the effects of electromagnetic interference. This includes designing electronic devices and systems with shielding, filtering, and grounding to reduce the impact of EMI. Techniques such as frequency hopping, spread spectrum, and encoding are used to reduce the impact of interference on wireless communication systems.

[0017] In addition, there are regulatory standards that specify limits for EMI emissions from electronic devices and systems, such as the Federal Communications Commission (FCC) regulations in the United States. Compliance with these standards is required for electronic devices and systems to be sold in many countries.

[0018] Reducing or eliminating undesired electromagnetic noise, in general, can be achieved by either reflection of the electromagnetic wave, absorption of the wave, or both. It is most common for a highly conductive metal sheet (known as an EM shield) to be used to reflect the undesired EM waves. However, in some cases, reflecting the waves is not sufficient or causes further problems.

[0019] EMI absorption is the process by which electromagnetic interference (EMI) energy is dissipated by a material through absorption and conversion into thermal energy. This process is important in applications where EMI needs to be absorbed and dissipated, such as in electronic devices, power distribution systems, and communication equipment. EMI absorption materials are often used in the form of sheets, coatings, or composites, and their effectiveness is measured by their shielding effectiveness, which is the ratio of the energy transmitted through the material to the energy incident on the material. The effectiveness of EMI absorption materials can be optimized through material design, including the use of appropriate fillers, surface modification, and the adjustment of material thickness and composition.

[0020] Current EMI composites for high GHz frequency band are based on highly loaded (28- 70 vol. % or 60 - 90 wt.%) dielectric and magnetic filler materials. However, such high loadings tend to degrade mechanical properties of the composites, and extrusion during production is cumbersome. Additionally, often the particles are abrasive and extruding high quantities of these abrasive particles can be damaging to the extrusion equipment.

[0021] Therefore, it is desirable to develop new fillers that can replace the current fillers. These alternate fillers have a wide range of property requirements including being able to be used at a lower level without diminishing the absorptivity over a wide range of wavelengths. The use of lower levels of fillers has the desirable features of a lower cost, better mechanical performance, ease of manufacturing and decrease in damage to extrusion equipment.

[0022] Disclosed herein are hybrid fillers. These hybrid fillers are mixtures of fillers for use as EMI absorption. These fillers comprise a first set of particles comprising a plurality of particles, where at least some of the particles are at least partially coated with an electromagnetically absorbing coating and a second set of particles comprising electrically conductive particles that are smaller than the particle size of the plurality of particles. Also disclosed are articles that comprise the mixture of particles and a fifth generation (5G) wireless communication system comprising the mixture of particles. The terms silicone or siloxane are used interchangeably and refer to units with dialkyl or diaryl siloxane (-SiR2O-) repeating units.

[0023] The terms "room temperature" and "ambient temperature" are used interchangeably to mean temperatures in the range of 20°C to 25°C.

[0024] The term “adjacent” as used herein when referring to two layers means that the two layers are in proximity with one another with no intervening open space between them. They may be in direct contact with one another (e.g. laminated together) or there may be intervening layers.

[0025] The terms “polymer” and “macromolecule” are used herein consistent with their common usage in chemistry. Polymers and macromolecules are composed of many repeated subunits. As used herein, the term “macromolecule” is used to describe a group attached to a monomer that has multiple repeating units. The term “polymer” is used to describe the resultant material formed from a polymerization reaction.

[0026] The term “alkyl” refers to a monovalent group that is a radical of an alkane, which is a saturated hydrocarbon. The alkyl can be linear, branched, cyclic, or combinations thereof and typically has 1 to 20 carbon atoms. In some embodiments, the alkyl group contains 1 to 18, 1 to 12, 1 to 10, 1 to 8, 1 to 6, or 1 to 4 carbon atoms. Examples of alkyl groups include, but are not limited to, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, n-hexyl, cyclohexyl, n-heptyl, n-octyl, and ethylhexyl.

[0027] The term “aryl” refers to a monovalent group that is aromatic and carbocyclic. The aryl can have one to five rings that are connected to or fused to the aromatic ring. The other ring structures can be aromatic, non-aromatic, or combinations thereof. Examples of aryl groups include, but are not limited to, phenyl, biphenyl, terphenyl, anthryl, naphthyl, acenaphthyl, anthraquinonyl, phenanthryl, anthracenyl, pyrenyl, perylenyl, and fluorenyl.

[0028] Disclosed herein are thermally and electromagnetically absorbing compositions. In some embodiments, the compositions comprise a mixture of particles dispersed in a binder. The mixture of particles comprises a first set of particles and a second set of particles. The first set of particles comprises a plurality of particles. The plurality of particles have a particle size distribution comprising at least three peaks, wherein at least a majority of particles within a half width at half maximum (HWHM) of one, but not the other ones, are at least partially coated with an electromagnetically absorbing coating. The second set of particles comprises electrically conductive particles having a particle size that is smaller than the particle size of the plurality of particles.

[0029] As mentioned above, the thermally and electromagnetically absorbing compositions of this disclosure comprise a first set of particles that comprises a plurality of particles. These particles are described in PCT Publication No. WO 2021 / 198849 or US Patent Publication No. US 2023 / 0119856.

[0030] The thermally conductive and electromagnetically absorptive particles are prepared by coating a thin layer of metal (e.g., tungsten) on thermally conductive non-electrically conductive particles. However, it is difficult to achieve a high thermal conductivity with monodispersed or approximately monodispersed particles. A multimodal distribution of the particles with a high volume loading (e.g., a volume loading of at least about 50% or at least about 60%) can be used to increase the thermal conductivity of compositions of these particles. However, it has been found that when a multimodal distribution of the thermally conductive electromagnetically absorptive particles with a high loading is used to increase the thermal conductivity, the electromagnetic absorption is reduced. Without intending to be limited by theory, it is believed that this is due, at least in part, to an increased reflectance which results in less electromagnetic energy propagating into the material that can be absorbed. However, it has been found that when only a fraction (e.g., less than 1% of the total number of particles) of the thermally conductive particles includes an electromagnetically absorptive coating, a high thermal conductivity (e.g., at least about 2 W / (m-K)) and a high electromagnetic absorptivity (e.g., at least about 5 dB / mm in a predetermined frequency range) can be achieved. By including the electromagnetically absorptive coating on only a fraction of the particles, the real part of the relative permittivity can be reduced compared to the case where all or even a majority of the particles are coated. This reduced relative real permittivity can result in reduced surface reflections from the thermally conductive electromagnetically absorptive material.

[0031] In some embodiments, the thermally conductive particles include at least one of metal oxides, metal carbides, metal hydrates or metal nitrides. In some embodiments, the thermally conductive particles include at least one of alumina (e.g., one or more of alpha alumina particles, substantially spherical alumina particles, or polyhedral alumina), boron nitride, magnesium oxide, zinc oxide, aluminum nitride, silicon carbide, or aluminum hydroxide. In some embodiments, the electromagnetically absorbing coating of the thermally conductive particles includes a metal or a semiconductor. In some embodiments, the electromagnetically absorbing coating includes one or more of tungsten, aluminum, titanium, steel, chromium, or nickel. Particularly suitable electromagnetically absorbing coatings are those that include tungsten. It is typically desired that when the electromagnetically absorbing coating is a metal that it is sufficiently thin that it results in significant electromagnetic absorption in a desired frequency range (e.g., via dielectric relaxation as described in Bowler, “Designing Dielectric Loss at Microwave Frequencies using Multi-Layered Filler Particles in a Composite”, IEEE Transactions on Dielectrics and Electrical Insulation Vol. 13, No. 4, pp. 703-711, August 2006 ). When the metal layer is sputtered onto the particle, metals such as tungsten that tend to form a monolayer are typically preferred.

[0032] In some embodiments, the particles coated with the electromagnetically absorbing coating are further coated with an electrically insulative material. The electrically insulative material can be a non-conductive metal oxide such as aluminum oxide.

[0033] The particles can have any suitable shape (e.g., at least one of flakes, plates, spheres, spheroids, ellipsoids, irregularly shaped particles). In some embodiments, at least a majority of the particles are substantially spherical. A particle can be considered substantially spherical if its outline fits within the intervening space between two, concentric, truly spherical outlines differing in diameter from one another by up to about 30% of the diameter of the larger of these outlines. In some embodiments, each particle in at least a majority of the particles fits within the intervening space between two, concentric, truly spherical outlines differing in diameter from one another by up to about 20% or 10% of the diameter of the larger of these outlines.

[0034] Particle size distributions can be characterized in terms of number distributions or volume distributions, for example. Volume distributions are often useful when a substantially smaller number of substantially larger particles and a substantially larger number of substantially smaller particles are present. A cumulative particle size distribution function V(S) can be defined such that V(S) is the fraction (or percent) of the total volume of the particles provided by particles having a size no more than S, where the particle size is the particle diameter or equivalent diameter (diameter of a sphere having the same volume as the particle). A particle size distribution function can be defined on a linear or log scale, for example. A log scale is often useful when particles having substantially different sizes are present. A particle size distribution f(S) can be defined as being proportional to dV(S) / dLog(S) so that an area under a plot of f(S) versus Log(S) between Log(Sl) and Log(S2) is proportional to the fraction (or percent) of the total volume of the particles provided by particles having sizes between SI and S2. The distribution function distribution f(S) is normalized so that the cumulative distribution function V(S) approaches 1 or 100% for large particle size. f(S) can be determined from laser light scattering techniques, for example, as is known in the art. A number distribution n(S) for the particle size can similarly be defined so that an area under a plot of n(S) versus Log(S) between Log(Sl) and Log(S2) is proportional to the fraction (or percent) of the total number of the particles provided by particles having sizes between S 1 and S2. The particle size distributions described herein can be understood to be volume distributions and plots of the particle size distribution can be understood to be linear-log plots (the distribution function values on a linear y-axis and the particle size on a logarithmic x-axis), unless indicated otherwise.

[0035] The particle size distribution comprises peaks at three particle sizes dl, d2 and d3, dl > d2 > d3, wherein at least a majority of particles within a half width at half maximum (HWHM) of the peak corresponding to the particles size dl, but not d2 and d3, are at least partially coated with an electromagnetically absorbing coating. In some embodiments, at least 20% of the at least majority of the particles within the HWHM of the one of the at least three peaks that are at least partially coated with the electromagnetically absorbing material, are only partially coated with the electromagnetically absorbing coating.

[0036] The particle size ranges for each of dl, d2, and d3 can vary. In some embodiments, dl is in a range of about 50 micrometers to about 100 micrometers, d2 is in a range of about 5 micrometers to about 20 micrometers, and d3 is in a range of about 1 micrometer to about 3 micrometers.

[0037] The quantity of the first set of particles within the thermally and electromagnetically absorbing composition can vary. Typically, the first set of particles comprise 15-50 volume% or 40-79 weight% of the composition.

[0038] The thermally and electromagnetically absorbing composition further comprises a second set of particles comprising electrically conductive particles. In some embodiments, the electrically conductive particles comprise particles of carbon black, carbon nanotubes, or graphene particles.

[0039] Typically, the conductive particles range in size from an average particle size of 5 nanometers-20 micrometers, more typically 5-500 nanometers.

[0040] The quantity of the second set of particles within the thermally and electromagnetically absorbing composition can vary. Typically, the second set of particles comprise 0.05-1.5 weight % of the composition.

[0041] The composition also includes a binder. A wide range of binders are suitable. Typically, the binder is a polymeric binder. In some embodiments, the binder includes at least one of nylon, polyolefin (e.g., thermoplastic polyolefin (TPO)), epoxy, silicone, or (meth)acrylate. The binder is present in sufficient quantities to effectively disperse the first and second sets of particles. In some embodiments, the binder is a curable 2-part silicone composition.

[0042] In some particularly suitable thermally and electromagnetically absorbing compositions of this disclosure, the first set of particles comprise 15-50 volume% or 40-79 weight% and the second set of particles comprise 0.05-1.5 weight % of the composition.

[0043] The thermally and electromagnetically absorbing compositions of this disclosure have variety of desirable properties and can be used in a variety of articles. In some embodiments, the thermally and electromagnetically absorbing compositions have an electromagnetic interference mitigating capability in a frequency range from about 1 GHz to about 120 GHz.

[0044] In some embodiments, the thermally and electromagnetically absorbing composition forms a component of a notch filter for EMI suppression. In other embodiments, the thermally and electromagnetically absorbing composition is present as a component of a flexible EMI shielding layer. In yet other embodiments, the thermally and electromagnetically absorbing composition is present as a component of an EMI shielding layer that at least partially surrounds one or more conductive lines of a cable comprising the one or more conductive lines. In some embodiments, the thermally and electromagnetically absorbing composition is in the form of a rigid body having a contoured shape.

[0045] The thermally and electromagnetically absorbing composition can be in a variety of forms and can be delivered in a variety of ways. In some embodiments, the composition is provided in the form of injection moldable pellets, a molded article, or a fdm. For example, the composition can be formed by mixing the particles with the binder at elevated temperatures (e.g., above a melting point of the binder). The composition can then be extruded as a fdm or a multi-layer fdm, for example, or pellets can be formed via extrusion palletization, for example. Alternatively, pellets can be formed from extruded or otherwise formed material by grinding or otherwise pelletizing the material. The pellets can be used to form an article via injection molding, for example. In other embodiments, the composition is in the form of an ink for mitigating electromagnetic interference and is adapted for printing on a workpiece.

[0046] Also disclosed herein are articles that contain a thermally conductive and electromagnetically absorbing composition. In some embodiments, the thermally conductive and electromagnetically absorbing composition comprises the mixture of particles described above. The mixture of particles comprises a first set of particles and a second set of particles. The first set of particles comprises a plurality of particles. The plurality of particles have a particle size distribution comprising at least three peaks, wherein at least a majority of particles within a half width at half maximum (HWHM) of one, but not the other ones, are at least partially coated with an electromagnetically absorbing coating. The second set of particles comprises electrically conductive particles having a particle size that is smaller than the particle size of the plurality of particles. The particles are described in detail above.

[0047] The articles typically comprise an anti-reflection film or coating or an antireflection injection molded article. Each of these types of articles have advantages and disadvantages. Regardless of the type of article, in some embodiments the thermally conductive and electromagnetically absorbing composition in the article is such that the first set of particles comprise 15-50 volume% or 40-79 weight%. In other embodiments, the thermally conductive and electromagnetically absorbing composition in the article is such that the second set of particles comprise 0.05-1.5 weight %. In some particularly suitable embodiments, the first set of particles comprise 15-50 volume% or 40-79 weight% and the second set of particles comprise 0.05-1.5 weight %.

[0048] In some embodiments, the article comprises an anti-reflection film that reflects at least one frequency in a range of about 1 GHz to about 120 GHz. In some embodiments, the film or the multi-layer film has a thickness of 0.1-1.5 millimeter. Also disclosed herein are fifth generation (5G) wireless communication systems. In some embodiments, the fifth generation (5G) wireless communication system comprises an antenna comprising an array of distinct spaced apart antenna elements configured to at least one of receive and transmit a signal having a frequency of between about 1 GHz and about 120 GHz; and an electromagnetically absorbing material disposed between at least two antenna elements in the array of antenna elements, wherein the electromagnetically absorbing material comprises: a mixture of particles dispersed in a binder, the mixture of particles comprising: a first set of particles comprising a plurality of particles, wherein the plurality of particles have a particle size distribution comprising at least three peaks, wherein at least a majority of particles within a half width at half maximum (HWHM) of one, but not the other ones, are at least partially coated with an electromagnetically absorbing coating; and a second set of particles comprising electrically conductive particles, wherein the electrically conductive particles have a particle size that is smaller than the particle size of the plurality of particles.

[0049] Examples

[0050] These examples are merely for illustrative purposes only and are not meant to be limiting on the scope of the appended claims. All parts, percentages, ratios, etc. in the examples and the rest of the specification are by weight, unless noted otherwise. The following abbreviations are used: mm = millimeters; cm = centimeters; nm = nanometers; rpm revolutions per minute; Pa = Pascals; kW = kiloWatts; GHz = gigahertz; kg = kilograms. The terms “weight %”, “% by weight”, and “wt.%” are used interchangeably.

[0051] Table of Abbreviations

[0052] Preparation of Particle Mixtures

[0053] The particle size distributions of the BAK-70 and BAK- 10 particles were measured by laser light scattering using a laser particle sizer (LS-POP(6) available from OMEC Instruments, Guangdong, China).

[0054] Tungsten Coating of BAK-70 Alumina Particles

[0055] A 5 inch x 12 inch (13 cm x 30 cm) rectangular tungsten (W) sputter target was used to produce W thin film coated alumina particles. The apparatus used for the preparation of W thin film coated particles is described in U.S. Pat. Nos. 8,698,394 (McCutcheon et al.). 5786.29g of BAK-70 alumina particles was loaded in the particle agitator assembly positioned inside the vacuum chamber. The vacuum chamber was pumped down to a base pressure of I xlO^torr (0.133 milliPascals). Tungsten was sputtered for 6 hours at 1.0 kW at an argon sputtering gas pressure of 5 millitorr (0.67 Pa). The chamber was backfilled with Argon, a small portion of the W coated alumina particles was removed, and a powder resistivity of 150 ohm-cm was measured. The estimated thickness of the W coating was 6-7 nm. Aluminum Oxide (AlOx) Coating on Tungsten Coated BAK-70 Alumina Particles

[0056] An aluminum oxide coating was made to encapsulate the W thin film to prevent from oxidation as generally described in U.S. Pat. No. 5,389,434 (Chamberlain et al.). A 5 inch x8 inch (13 cm x 20 cm) aluminum target was used in the same sputter coater and aluminum was sputtered. The AlOx layer was coated on top by admitting oxygen gas at a rate of 25 seem (standard cubic centimeter per minute), in addition to argon sputter gas. The total pressure was kept at 10 millitorr (0.13 Pascals). A cathodic power of 5.00 kW was applied for 5 hours with particle agitation of 15 rpm. At the end of 5 hours, the chamber was vented to ambient conditions and the particles were removed from the agitator. The powder resistivity of final aluminum oxide coating was in the >30 x 106ohm-cm range.

[0057] The W metal and AlOx oxide thin film coated alumina (combination of BAK-70, BAK -30, BAK-10, and TM-1250) particles are referred to as CP in the table above.

[0058] Test Methods

[0059] Determining EM characteristics

[0060] For determining the EM characteristics of the composite samples, the following procedure was used: -

[0061] Silicone samples (smooth and uniform) were cut to fit into the coaxial and transmission line fixtures and sized to have as small an airgap as possible inside a transmission line.

[0062] Complex dielectric and magnetic properties were calculated over the frequency range of 0.1 to 18 GHz from S parameters obtained using an Agilent E8363C Network Analyzer coupled with Model M07T from Damaskos Inc. air coaxial test fixture, using doughnut shaped samples at room temperature.

[0063] For measurements from 18- 40 GHZ, complex dielectric and magnetic properties were calculated from S parameters obtained using an Agilent E8363C Network Analyzer (from Agilent Technologies, Santa Clara, Calif.) using rectangular waveguides made using the silicone composites of the Examples.

[0064] The data are shown as the real part of dielectric permittivity (s’) and the imaginary part of dielectric permittivity (a”).

[0065] Calculation of Dielectric Loss Tangent

[0066] Dielectric loss tangent (tan 5 = 8” / s’) vs. frequency was calculated using the EM characteristic data described above, a’ is the real part of the dielectric permittivity; a” is the imaginary part of the dielectric permittivity.

[0067] Calculation of Reflection Loss

[0068] A known model, known as radar absorption or reflection loss model, assumes that electromagnetic wave is normally incident on a single layer composite absorber which is adhered to a well conducting metal plate (that prevents transmission), and then the EM wave absorbing performance can be evaluated in terms of the reflection loss (RL) in decibel (dB) units. In this model, lower reflection loss indicates higher electromagnetic absorption performance. In this case, the EM wave absorption performances are investigated based on the following equations: b) where Zo is the impedance of free space, t is the thickness of the absorber, and c is the speed of light. As indicated in Eq. (a), the input impedance of an absorber depends on six parameters: the real and imaginary parts of complex permeability (pr= p’- jp”) and complex permittivity (ar= a’- ja”) values, the thickness of an absorber (t), and the working frequency (f).

[0069] Reference: “Structural and high GHz frequency EMI (Electromagnetic Interference) properties of carbonyl iron and boron nitride hybrid composites”, Materials Research Express 6 (10), 106305, 2019 Using this radar absorption model the microwave absorber performance was calculated for the sample composites. A thickness (t) of 1.0 mm of the absorber composites was used.

[0070] Examples

[0071] Examples E1-E2

[0072] Preparation of Composite Matrices

[0073] A series of composite matrices were prepared using CP, CB, and Silicone according to the amounts shown in Table 1. First the CB was added to a plastic cup and then the CP fdler was added, where CB is 0.5 to 1.0 wt.% by weight relative to the CP fdlers. E.g., 1 wt.% CB in example E1A means 1 wt.% of CB added w.r.t CP particles (71 wt.%) and hence CB added is 0.71 wt.%. The cup lid was closed, and the mixture was hand mixed by shaking the cup for 20- 30 seconds. The required amount of Silicone Part A was added. The required amount of Silicone Part B, the curing agent, was added to Part A. The plastic cup was covered with a cap configured to allow speed mixing under vacuum (100 mbar, 10,000 Pa) for 2 minutes and 15 seconds. The mixture was then poured onto a stainless-steel plate. A second stainless steel plate was placed on top of the mixture. Teflon sheets were used to make smooth surface composites. Appropriate spacers were used between the two plates to separate them to a desired thickness (1.0 mm). The plates containing the mixture were hot pressed at a temperature of 118°C under a pressure of 3 tons (2700 kg) for 45-60 minutes. The plates were allowed to cool for 30- 45 minutes before the cured composite sheet was removed.

[0074] Table 1

[0075] Testing of Polymer Composites

[0076] The polymer composite samples described above were tested for EM characteristics using the test method described above.

[0077] The EM Characteristics (permittivity vs frequency) for Examples E1A-E1C are shown in Figure 1. In Figure 1: a’ and a” are shown. The calculated dielectric loss tangent for Examples E1A-E1C is shown in Figure 2.

[0078] The EM Characteristics (permittivity vs frequency) for Examples E2A-E2D are shown in Figure 3. In Figure 3: a’ and a” are shown. The calculated dielectric loss tangent for Examples E2A-E2D is shown in Figure 4.

[0079] Calculation of Reflection Loss

[0080] The reflection loss was calculated using the method described above for Examples E1A-E1C (shown in Figure 5) and Examples E2A-E2D (shown in Figure 6).

[0081] Data Analysis

[0082] As the loading levels for the hybrid fdlers (CP fillers and CB) increase, the dielectric polarization also increases and hence the value of dielectric permittivity also goes up. As a result, the values of for dielectric loss tangent (tan 5 = 8” / s’), also increases.

[0083] As the loading level of the EMI hybrid filler increases, the RL peaks shift to lower frequencies. They also show much enhanced EMI performance with increase in loading levels (e.g., the minimum RL peak is - 24dB at a frequency of ~ 26 GHz for the 40 vol.% loaded composites, while minimum RL peak is - 22 dB at a frequency of ~ 30 GHz for the 30 vol.% loaded composite and minimum RL peak is - 9.5 dB at a frequency of ~ 36 GHz for the 20 vol.% loaded composite) as depicted below in Table 2.

[0084] Table 2

[0085] As the loading level of the EMI hybridfiller increases, the RL peaks shift to lower frequencies. They also show much enhanced EMI performance with increase in loading levels (e.g., the minimum RL peak is - 42 dB at a frequency of ~ 28 GHz for the 40 vol.% loaded composites, while minimum RL peak is - 18 dB at a frequency of ~ 32 GHz for the 30 vol.% loaded composite), as depicted below in Table 3.

[0086] Table 3

Claims

What is claimed is:

1. A thermally conductive and electromagnetically absorbing composition comprising a mixture of particles dispersed in a binder, the mixture of particles comprising: a first set of particles comprising a plurality of particles, wherein the plurality of particles have a particle size distribution comprising at least three peaks, wherein at least a majority of particles within a half width at half maximum (HWHM) of one, but not the other ones, are at least partially coated with an electromagnetically absorbing coating; and a second set of particles comprising electrically conductive particles, wherein the electrically conductive particles have a particle size that is smaller than the particle size of the plurality of particles.

2. The thermally conductive and electromagnetically absorbing composition of claim 1, wherein the electrically conductive particles comprise particles of carbon black, carbon nanotubes, or graphene particles.

3. The thermally conductive and electromagnetically absorbing composition of claim 1, having an electromagnetic interference mitigating capability in a frequency range from about 1 GHz to about 120 GHz.

4. The thermally conductive and electromagnetically absorbing composition of claim 1, wherein the particle size distribution of the first set of particles comprises peaks at three particle sizes dl, d2 and d3, dl > d2 > d3, wherein at least a majority of particles within a half width at half maximum (HWHM) of the peak corresponding to the particles size dl, but not d2 and d3, are at least partially coated with an electromagnetically absorbing coating.

5. The thermally conductive and electromagnetically absorbing composition of claim 1, wherein at least 20% of the at least majority of the particles within the HWHM of the one of the at least three peaks that are at least partially coated with the electromagneticallyabsorbing material, are only partially coated with the electromagnetically absorbing coating.

6. The thermally conductive and electromagnetically absorbing composition of claim 1, wherein the first set of particles comprise 15-50 volume% or 40-79 weight%.

7. The thermally conductive and electromagnetically absorbing composition of claim 6, wherein the second set of particles comprise 0.05-1.5 weight %.

8. The thermally conductive and electromagnetically absorbing composition of claim 1, wherein the first set of particles comprise 15-50 volume% or 40-79 weight% and the second set of particles comprise 0.05-1.5 weight %.

9. The thermally conductive and electromagnetically absorbing composition of claim 1, where the composition forms a component of a notch filter for EMI suppression.

10. The thermally conductive and electromagnetically absorbing composition of claim 1, wherein the composition is present as a component of a flexible EMI shielding layer.

11. The thermally conductive and electromagnetically absorbing composition of claim 1, wherein the composition is present as a component of an EMI shielding layer that at least partially surrounds one or more conductive lines of a cable comprising the one or more conductive lines.

12. The thermally conductive and electromagnetically absorbing composition of claim 1, wherein the composition is in the form of a rigid body having a contoured shape.

13. The thermally conductive and electromagnetically absorbing composition of claim 1, wherein a precursor composition is in the form of an ink that is applied to a workpiece and is cured to form the thermally conductive and electromagnetically absorbing composition.

14. An article comprising a thermally conductive and electromagnetically absorbing composition, wherein the electromagnetically absorbing composition comprises: a mixture of particles dispersed in a binder, the mixture of particles comprising: a first set of particles comprising a plurality of particles, wherein the plurality of particles have a particle size distribution comprising at least three peaks, wherein at least a majority of particles within a half width at half maximum (HWHM) of one, but not the other ones, are at least partially coated with an electromagnetically absorbing coating; and a second set of particles comprising electrically conductive particles, wherein the electrically conductive particles have a particle size that is smaller than the particle size of the plurality of particles.

15. The article of claim 14, wherein the electrically conductive particles comprise particles of carbon black, carbon nanotubes, or graphene particles.

16. The article of claim 14, wherein the article comprises a multi-layered anti-reflection film or an anti -reflection injection molded article.

17. The article of claim 16, wherein the article comprises an electromagnetic interference mitigating capability in a frequency range from about 1 GHz to about 120 GHz.

18. The article of claim 16, wherein the first set of particles comprise 15-50 volume% or 40-79 weight%.

19. The article of claim 16, wherein the second set of particles comprise 0.05-1.5 weight 0 / / o.

20. The article of claim 16, wherein the first set of particles comprise 15-50 volume% or 40-79 weight% and the second set of particles comprise 0.05-1.5 weight %.

21. The article of claim 16, wherein the film has a thickness of 0.1 -1.5 millimeter.

22. A fifth generation (5G) wireless communication system comprising an antenna comprising an array of distinct spaced apart antenna elements configured to at least one of receive and transmit a signal having a frequency of between about 1 GHz and about 120 GHz; and an electromagnetically absorbing material disposed between at least two antenna elements in the array of antenna elements, wherein the electromagnetically absorbing material comprises: a mixture of particles dispersed in a binder, the mixture of particles comprising: a first set of particles comprising a plurality of particles, wherein the plurality of particles have a particle size distribution comprising at least three peaks, wherein at least a majority of particles within a half width at half maximum (HWHM) of one, but not the other ones, are at least partially coated with an electromagnetically absorbing coating; and a second set of particles comprising electrically conductive particles, wherein the electrically conductive particles have a particle size that is smaller than the particle size of the plurality of particles.

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