Reduction of Electromagnetic Waves Using a Lightweight Metal Foam

Abstract

Metal foam structures are used to shield or reduce harmful electromagnetic waves generated by electronic devices. The metal foam material has controlled pores and is incorporated into electronic devices. The metal foam structure shields, prevents, or reduces harmful electromagnetic waves generated by electronic devices from reaching the human body or interfering with sensitive electronic components. The metal foam is a relatively lightweight material with a controlled microscale pore structure. The pores in the metal foam can also direct the electromagnetic waves relative to their incident direction to more effectively reflect or absorb them. Metal foams can also be used as both electromagnetic shielding and heat dissipation components for electronic devices, including common consumer electronics such as mobile phones, notebooks, and high-power desktop computers.

Description

Technical Field

[0001] Description Cross - Reference to Related Applications This patent application claims the benefit of U.S. Patent Application No. 63 / 003,167, filed on March 31, 2020.

Background Art

[0002] Background of the Invention The present invention relates to metal foams, and more specifically, to a method or device for using metal foams to shield or reduce harmful electromagnetic (EM) waves generated by electronic devices.

[0003] With the dramatic increase in the development of electronic consumer displays, medical devices, and portable devices such as high - power mobile phones, smartphones, tablet computers, notebooks, and laptop computers, it has become increasingly important to shield or reduce harmful electromagnetic waves generated from such electric devices as much as possible. Furthermore, such electromagnetic waves can also cause failures or malfunctions of electronic components and should therefore be prevented.

Summary of the Invention

Problems to be Solved by the Invention

[0004] The most common materials used to shield or reduce electromagnetic waves are bulk heavy metals based on copper, iron, nickel, and aluminum. Carbon nanotubes or metal - coated plastic materials are also used for this purpose, but these are relatively expensive or have relatively small effects.

[0005] Therefore, there is an urgent need for a new material or device that can effectively shield electromagnetic waves and is lightweight and inexpensive. A metal foam material with a three-dimensional structure having uniform pores is an ideal candidate. Since this material has a pore structure, it is lightweight and can prevent or reduce harmful electromagnetic waves from reaching the human body, thereby removing or reducing brain damage, abnormal body temperature, and harm to embryos caused by such electromagnetic waves.

[0006] Brief Summary of the Invention The lightweight metal foam material has regulated pores and is incorporated into electronic devices. The metal foam structure shields, prevents, or reduces harmful electromagnetic waves generated by electronic devices from reaching the human body or sensitive electronic components. The metal foam is a relatively lightweight material with a regulated pore structure, having a specifically intended porosity and pore size. For example, the weight of a copper foam with a porosity of about 67 percent is only one-third of that of its bulk material. The metal foam can be used as an electromagnetic shielding component device for electronic devices, including general consumer electronic devices such as 5G mobile phones, notebooks, light-emitting diodes, and high-power desktop computers.

[0007] With the dramatic increase in the development of high-performance electronic products, electromagnetic wave material technologies that can shield or reduce harmful electromagnetic waves generated from such electric devices as much as possible have attracted great attention from the information technology industry. Here, the present invention relates to such metal foams, and more specifically, to devices or components that use metal foams to shield or reduce harmful electromagnetic waves generated from electronic devices. The metal foam material has regulated pores and is incorporated into an electronic device. The metal foam structure shields, prevents, or reduces harmful electromagnetic waves generated by an electronic device from reaching a human body or sensitive electronic components. This metal foam is a relatively lightweight material having a regulated micro-scale pore structure. Also, the pores in the metal foam can form a directionality with respect to the incident direction of electromagnetic waves in order to reflect the electromagnetic waves more effectively. Further, the metal foam can be used as both an electromagnetic shielding component and a heat dissipation device for electronic devices including general consumer electronic devices such as 5G mobile phones, notebooks, and high-power desktop computers.

Means for Solving the Problems

[0008] In one implementation form, the structure includes a metal foam material having a uniform micro-scale pore structure that effectively shields or reduces electromagnetic waves generated by an electronic device because of the increased surface area. The structure may be a sheet. The metal foam container may include the structure. Devices such as smartphones, computers, televisions, radios, or other electronic devices may include the structure.

[0009] Other objects, features, and advantages of the present invention will become apparent by considering the following detailed description and the accompanying drawings (in the drawings, like reference symbols represent like features throughout all the drawings).

Brief Description of the Drawings

[0010]

Figure 1A

Figure 1B

Figure 2A

Figure 2B

Figure 2C

Figure 3

Figure 4

Mode for Carrying Out the Invention

[0011] Detailed Description of the Invention Some materials are known to be able to reflect and absorb electromagnetic waves generated from consumer electronics and components contained therein, and as a result, reduce them. Such materials are generally selected from elements such as iron, copper, nickel, aluminum, and carbon or combinations thereof that have good electrical conductivity and permeability, and as a result, can reflect and absorb electromagnetic waves on their surface. Alternatively, by creating a composite material consisting of two or three elements, unique structures such as carbon-coated materials and core-shell structures are formed. Such materials are disadvantageous because they are costly, heavy, have a complex process, and cannot control the microstructure.

[0012] Metal foams can effectively shield electromagnetic waves by both reflection and absorption. In particular, metal foams having a relatively high porosity and small pore size (e.g., increased surface area) can reflect more effectively than their bulk materials. On the other hand, metal foams having relatively thick struts or walls in terms of dimensions can absorb efficiently.

[0013] The metal foam material is used in the form of parts (e.g., shields, cases, housings, or structures) of electronic devices that can generate harmful electromagnetic waves. Since the metal foam can reflect or absorb or both electromagnetic waves, it reduces the electromagnetic waves generated from consumer electronics and the parts contained therein.

[0014] Specifically, the metal foam can be created by freeze casting and is advantageous for use in the present application because the basic processing parameters can be manipulated to well control the pore size, porosity, pore orientation (e.g., for increasing the reflection efficiency), and uniform pore distribution. The manufacturing methods of the metal foam are described, for example, in U.S. Patent Application No. 13 / 930,887 filed on June 28, 2013, U.S. Patent Application No. 14 / 256,838 filed on April 18, 2014, U.S. Patent Application No. 15 / 215,519 filed on July 20, 2016 (U.S. Patent Publication No. 2017 / 0025683), U.S. Patent Application No. 15 / 215,541 filed on July 20, 2016 (U.S. Patent Publication No. 2017 / 0021416), and U.S. Patent Application No. 16 / 392,526 filed on April 23, 2019 (U.S. Patent Publication No. 2019 / 0247925).

[0015] Furthermore, metal foam parts attached to a device by common thermal interface materials, soldering, welding, or brazing can serve as both a heat sink and a shielding block for high-power semiconductors or any electronic device that generates strong electromagnetic waves.

[0016] This patent describes several implementation examples with specific dimensions, measurements, temperatures, and values. Such examples are not intended to comprehensively illustrate the present invention nor to strictly limit the present invention to the described forms. Such values, ratios, times, and temperatures are approximate values. Such values can vary, for example, due to measurement or manufacturing variations or tolerances, or other factors. For example, such values can vary within a range of ±5 percent, ±7.5 percent, ±10 percent, ±12.5 percent, ±15 percent, ±17.5 percent, ±20 percent, or ±25 percent depending on the tightness of manufacturing and measurement tolerances.

[0017] Furthermore, such values are for a specific implementation form, and other implementation forms may have different values. For example, a certain value may be larger in a large-scale process or product and smaller in a small-scale process or product. A device, apparatus, or process may be proportionally larger or smaller by proportionally adjusting relative measurements (for example, by maintaining the same or approximately the same ratio between different measurements). In various implementation forms, the value may be the same as the given value, approximately the same as the given value, larger than the given value if the given value is the minimum value, smaller than the given value if the given value is the maximum value, between any two of the given multiple values (with or without including the boundary values), or any combination thereof.

[0018] Figures 1A - 1B show schematic diagrams of a metal foam that can reflect and absorb electromagnetic waves generated from an electronic device. Arrow 101 represents the initial electromagnetic wave, arrow 103 represents the reflected electromagnetic wave, arrow 105 represents the absorbed electromagnetic wave, and arrow 107 represents multiple reflective electromagnetic waves. Figure 1B shows an enlarged view of section 109 of Figure 1A. Here, the large surface area of the "closed-cell" metal foam component is beneficial for effectively reflecting waves compared to a bulk material of the same size.

[0019] Figures 2A to 2C show schematic views of metal foams having different pore directions. In Figures 2A to 2C, pores having a certain directivity with respect to the direction of the electromagnetic wave reflect more efficiently than pores parallel to the direction of the electromagnetic wave. Arrow 203 represents the electromagnetic wave that has weakened after a part of the incident wave has been reflected or absorbed.

[0020] Figure 3 shows a schematic view of a metal foam container 303 as an electromagnetic wave shielding part of a component for use in an electronic device that can generate electromagnetic waves harmful to the human body or sensitive electronic components.

[0021] In one implementation form, the structure is a container or sheet device of a metal foam. The container or sheet device of the metal foam serves as both a heat sink and a shielding block for the electronic device by contacting the surface of the electronic device that generates electromagnetic waves.

[0022] The structure includes a metal foam material including a uniform microscale pore structure that effectively shields or reduces electromagnetic waves generated by the electronic device because of the increased surface area. The pore size of the metal foam material may range from about 0.1 micron to about 30,000 microns (for example, 0.3, 0.5, 0.65, 0.9, 1, 2, 3, 4, 5, 8, 10, 20, 30, 40, 50, 60, 66, 70, 80, 90, 100, 120, 140, 160, 170, 180, 200, 220, 240, 260, or 280 microns). The porosity of the metal foam material may range from about 50 percent to about 85 percent (for example, 51, 52, 53, 55, 56, 58, 59, 60, 63, 66, 67, 68, 72, 74, 75, 77, 78, 80, or 82 percent). The thickness of the metal foam material of the container or sheet may range from about 100 microns to about 1 millimeter (for example, 150, 200, 300, 400, 500, 600, 700, 800, or 900 microns).

[0023] In various embodiments, the metal foam material is a copper foam, a tin foam, a copper-tin alloy foam, a nickel foam, a copper-nickel alloy foam, an iron foam, a stainless steel foam, an aluminum foam, or a titanium foam. The pore shape is elongated, and the axis of this elongation has an angle of about 20 degrees to about 90 degrees (e.g., 22.5, 24, 25, 26, 27, 28, 30, 33, 36, 37, 38, 40, 45, 60, 66, 70, 75, 80, or 86 degrees) with respect to the direction of the electromagnetic wave.

[0024] FIG. 4 shows an example of a metal foam sheet 406 that serves as both a heat sink and an electromagnetic wave shielding block for an electromagnetic wave source 412. The EM wave source 412 is disposed in contact with the metal foam sheet 406. There may be a thermal interface material such as a compound like a thermal paste or a thermal adhesive between the EM wave source and the metal foam sheet. The thermal interface material (not shown) can improve the heat transfer from the EM wave source, which is a heat source during operation, to the metal foam sheet, and the metal foam sheet can more efficiently dissipate heat into the air, liquid (e.g., water), or fluid in contact with the metal foam due to the increased surface area of the metal foam. Also, the heat sink metal foam sheet can be attached to the EM source device by common welding methods, brazing methods, or soldering methods.

[0025] The EM wave source may be an integrated circuit that generates heat. A mechanism such as a fixture, a clamp, a screw, or a holder can hold the metal foam sheet and the EM wave source together. In addition to being a heat sink, the metal foam sheet can also serve as an electromagnetic wave shield for the electromagnetic waves generated by the EM wave source due to its increased surface area.

[0026] The manufacturing process for creating a metallic foam material comprises at least one of freeze casting, space holder, or dealloying. In one implementation form, the manufacturing process for forming a copper (or titanium) foam material with directional pores may include the freeze casting method. Briefly, freeze casting involves freezing a copper oxide powder (or titanium powder) slurry and then drying it under vacuum and at low temperature. As a result, a copper oxide (or titanium) substrate is obtained. This copper oxide (or titanium) foam substrate is sintered or reduced to obtain a copper (or titanium) foam. Sintering or reduction can occur in a hydrogen gas or argon gas (or other noble gas) environment.

[0027] Specifically, for the slurry, following the addition of a binder (e.g., polyvinyl alcohol (PVA)) and a dispersant, copper oxide powder is mixed in water (e.g., deionized water) at a volume fraction of about 6 volume percent to about 25 volume percent (e.g., 7, 8, 9, 10, 12.5, 15, 18, 19, 20, 22, or 25 percent). Titanium powder is mixed in water at a weight fraction of about 30 weight percent to about 70 weight percent (e.g., 32, 33, 35, 40, 45, 46, 48, 50, 53, 55, 57, 58, 59, 60, 63, 66, 67, or 68 weight percent) following the addition of a binder and a dispersant.

[0028] The aqueous copper oxide powder (or titanium powder) slurry is frozen and dried at a low temperature of about -10°C to about -80°C (e.g., -12, -15, -20, -30, -33, -34, -36, -40, -42, -45, -46, -47, -48, -50, -54, -56, -57, -59, -60, -64, -66, -68, -70, -72, or -76°C). As a result of this freeze casting technique, a copper oxide (or titanium powder) substrate is formed.

[0029] After sublimation, the dried copper oxide (or titanium) foam substrate is reduced and then sintered at a high temperature. For example, the substrate is reduced in a hydrogen (the balance being argon) gas environment at a temperature of about 250°C to 550°C (e.g., 260, 270, 280, 290, 300, 320, 325, 350, 360, 380, 390, 410, 420, 435, 452, 460, 463, 468, 470, 480, 490, 500, 525, 530, or 540°C) for about 3 hours to about 15 hours (e.g., 3.5, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, or 14 hours) at about 0 percent to about 10 percent (e.g., 0.5, 1, 2, 4, 5, 6, 7, 8, or 9 percent). Subsequently, the substrate is sintered in a hydrogen (the balance being argon) gas environment at a temperature of about 700°C to about 1100°C (e.g., 720, 740, 780, 800, 860, 900, 940, 960, 980, 1000, 1020, 1040, or 1080°C) for about 5 hours to about 30 hours (e.g., 6, 7, 8, 9, 10, 11, 12, 13, 14, 18, 20, 22, 24, 25, 26, 28, or 29 hours) at about 0 percent to about 10 percent (e.g., 0.5, 1, 2, 4, 5, 6, 7, 8, or 9 percent). Thereby, a three-dimensionally connected solid pore structure such as a copper foam material or a titanium foam material for electromagnetic shielding or thermal shielding (when used as is) or a combination thereof is created.

[0030] So far, the present invention has been described for purposes of illustration and description, but the above description is not intended to comprehensively describe the present invention nor to limit the present invention to the exact forms described above, and many modifications and variations are possible in view of the above teachings. To best explain the principles of the present invention and its practical applications, some embodiments have been selected and described. By this description, those skilled in the art can consider that the present invention can be optimally utilized and implemented in various embodiments with various modifications suitable for specific applications. The scope of the present invention is defined by the following claims.

Claims

1. A structure comprising a metallic foam material including a uniform micro-scale pore structure that effectively shields or reduces electromagnetic waves generated by an electronic device due to an increased surface area, wherein the shape of the pores is elongated, and the axis of this elongation has an angle of about 20 degrees to about 90 degrees with respect to the direction of the electromagnetic waves.

2. The structure according to claim 1, wherein the pore size of the metallic foam material ranges from about 0.1 micron to about 30,000 microns.

3. The structure according to claim 1, wherein the porosity of the metallic foam material ranges from about 50 percent to about 85 percent.

4. The structure according to claim 1, wherein the thickness of the metallic foam material ranges from about 100 microns to about 1 millimeter.

5. The structure according to claim 1, wherein the metallic foam material is at least one of a copper foam, a tin foam, a copper-tin alloy foam, a nickel foam, a copper-nickel alloy foam, an iron foam, a stainless steel foam, an aluminum foam, or a titanium foam.

6. The structure according to claim 1, wherein the metallic foam material acts as both a heat sink and a shielding block for the electronic device by contacting the surface of the electronic device that generates electromagnetic waves.

7. The structure according to claim 1, wherein the manufacturing process for creating the metallic foam material comprises at least one of freeze casting, space holder, or dealloying.

8. The structure according to claim 1, wherein the manufacturing process for creating the metallic foam material comprises a freeze casting method consisting of a freezing or drying process of a powder slurry and a reduction or sintering process, wherein an aqueous copper oxide powder or titanium powder slurry is frozen and dried at a low temperature of about -10°C to about -80°C to form a copper oxide or titanium substrate.

9. The structure according to claim 8, wherein after complete sublimation, the dried copper oxide substrate is reduced to form a copper foam, which is then sintered at a high temperature.

10. The structure according to claim 9, wherein the dried copper oxide substrate is reduced at a temperature of about 250°C to 550°C over about 3 hours to about 15 hours in a hydrogen (the remainder being argon) gas environment of about 0 percent to about 10 percent, resulting in the formation of the pore structure of the metallic copper foam.

11. The structure according to claim 10, wherein the reduced copper foam is sintered at a temperature of about 700 °C to about 1100 °C over about 5 hours to about 30 hours in a hydrogen (the balance being argon) gas environment of about 0 percent to about 10 percent.

12. The structure according to claim 8, wherein following the addition of the binder and the dispersant, the copper oxide powder is mixed in deionized water at a volume fraction of about 6 volume percent to about 25 volume percent.

13. The structure according to claim 8, wherein following the addition of the binder and the dispersant, the titanium powder is mixed in deionized water at a weight fraction of about 30 weight percent to about 70 weight percent.

14. The structure according to claim 1, wherein the structure is a sheet.

15. A metal foam container comprising the structure according to claim 1.

16. A device comprising the structure according to claim 1.

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