A multilayer dielectric window and a method of making the same

Abstract

The present application relates to a kind of multilayer dielectric window and its preparation method, belong to high power microwave device technical field, solve the technical problems that dielectric window elastic modulus is low, outgassing rate is high, air permeability is high, it includes the resin-based composite material layer, wave-transparent ceramic layer or glass layer of stacking of multilayer dielectric window, the thermal expansion coefficient of wave-transparent ceramic layer or glass layer is 5×10 ‑6 / K~10×10 ‑6 / K, the thermal expansion coefficient of wave-transparent ceramic layer or glass layer and the thermal expansion coefficient of resin-based composite material layer deviation is not more than 3×10 ‑6 / K.It includes plate material raw material processing, interval layering;With the resin-based composite material layer plate material, wave-transparent ceramic layer plate material or glass layer plate material of interval layering is aligned and stacked, be placed in vacuum device, sealed vacuumizing, heating, the step of heat preservation.The present application is used for high power microwave source hard tube or vacuum electron device.

Description

Technical Field

[0001] This invention belongs to the field of high-power microwave device technology, specifically relating to a multilayer dielectric window and its preparation method. Background Technology

[0002] High-power microwave (HPM) technology has made significant progress over the past few decades in achieving high peak power output. However, to realize the practical application of HPM systems, miniaturization and weight reduction are essential. Hard-tube technology is a crucial approach to achieving miniaturized, independently packaged high-power microwave sources capable of high-repetition-rate operation. Hard-tube high-power microwave sources need to meet ultra-high vacuum conditions while striving to reduce dependence on accelerators and large gas-feeding systems, achieving miniaturized, independently packaged operation with high-repetition-rate capability. The vacuum environment is a major limiting factor for the pulse power and high-repetition-rate operation of high-power microwave sources. Currently, one of the biggest constraints in hard-tube high-power microwave sources is the dielectric window problem.

[0003] Due to their high output power, current high-power microwave sources typically require large-diameter dielectric windows (approximately 0.6–1 m in diameter). Considering factors such as dielectric properties, mechanical properties, ease of processing, and cost, the most commonly used dielectric window materials are polymers or alumina ceramics. Polymers mainly include cross-linked polystyrene, polytetrafluoroethylene, and ultra-high molecular weight polyethylene. Conventional polymer materials generally have low elastic modulus (making them heavy and hindering lightweighting), high gas release rate, high gas permeability, and low temperature resistance (generally, their heat distortion temperature is no greater than 200°C). In addition to meeting basic dielectric and mechanical properties, rigid high-power microwave sources require dielectric windows that can be welded to metals, have extremely low gas release rate and gas permeability, and require the vacuum chamber walls to be baked at high temperatures to accelerate gas release and improve vacuum levels.

[0004] High-purity alumina ceramics are widely used in conventional vacuum electronic devices and some high-power microwave devices due to their good mechanical properties, high temperature resistance (upper limit temperature 2223℃), good airtightness, low loss, and easy airtight welding with metals after metallization. However, their high dielectric constant (9-10) makes them more prone to charge accumulation and breakdown on the material surface compared to polymer materials. In addition, welding large-size alumina ceramics to metal flanges is extremely difficult, resulting in high device fabrication and processing costs. The largest welded alumina window diameter currently achieved is about 400mm, which is still far from the commonly used diameter of 600-800mm.

[0005] Overall, the dielectric window materials currently in use cannot fully meet the requirements for hardening high-power microwave systems. Summary of the Invention

[0006] To overcome the shortcomings of media windows, such as low elastic modulus, high gas release rate, high air permeability, and low temperature resistance, this invention proposes a multilayer media window and its preparation method.

[0007] The technical solution adopted by this invention to solve its technical problem is:

[0008] A multilayer medium window includes a resin-based composite material layer and an air barrier layer.

[0009] The resin-based composite material layer is stacked with the gas barrier layer.

[0010] The gas barrier layer is a wave-transparent ceramic layer or a glass layer.

[0011] The resin-based composite material layer is a high-temperature resin reinforced with quartz fiber or low-dielectric glass fiber, with the weight percentage of quartz fiber or low-dielectric glass fiber being 50% to 70%. The resin-based composite material layer is subjected to high-temperature treatment at 150°C to 200°C.

[0012] The high-temperature resin is one of polyetheretherketone, polyphenylene sulfide, and polyimide, or a mixture of two or three of them.

[0013] The coefficient of thermal expansion of the microwave-transparent ceramic layer or glass layer is 5 × 10⁻⁶. -6 / K~10×10 -6 / K, the thermal expansion coefficient of the microwave-transparent ceramic layer or glass layer deviates from that of the resin-based composite material layer by no more than 3×10. -6 / K.

[0014] The aforementioned multi-layered dielectric window, wherein the wave-transparent ceramic layer is alumina ceramic and the wave-transparent glass layer is borosilicate glass, both possess the advantages of excellent wave transmission performance, extremely low gas permeability coefficient, and moderate thermal expansion coefficient.

[0015] In the aforementioned multilayer dielectric window, the resin-based composite material layer, the wave-transparent ceramic layer, or the glass layer are stacked alternately, and the surface layer is a resin-based composite material layer.

[0016] The aforementioned multi-layered medium window consists of a resin-based composite material layer and a glass layer stacked together.

[0017] The aforementioned multilayer dielectric window consists of a resin-based composite material layer and a microwave-transparent ceramic layer stacked together.

[0018] The aforementioned multi-layer media window also includes a metal flange.

[0019] The metal flange is annular, and the stacked resin-based composite material layer, microwave-transparent ceramic layer, or glass layer is located inside the annulus of the metal flange and bonded together.

[0020] In the aforementioned multi-layer media window, the metal flange material is titanium alloy.

[0021] A method for preparing a multilayer dielectric window includes the following steps:

[0022] Step S1, processing of raw material of board

[0023] Resin-based composite material laminates are prepared using a hot-pressing process and then machined to the required dimensions. Transparent ceramic or glass laminates are then machined to the required dimensions.

[0024] Step S2, intermittent layup

[0025] According to the design requirements, the processed resin-based composite material sheets, transparent ceramic sheets, or glass sheets are laid in alternating layers.

[0026] Step S3, Multi-layer medium window forming

[0027] Align and stack the spaced resin-based composite material layers, transparent ceramic layers, or glass layers, place them in a vacuum device, seal and evacuate, heat and keep warm until the resin-based composite material layers, transparent ceramic layers, or glass layers are bonded together to obtain a multilayer medium window.

[0028] In the above method for preparing a multi-layer media window, step S3 is the forming of a multi-layer media window including a metal flange.

[0029] Align and stack the spaced-lay resin-based composite material layers, transparent ceramic layers, or glass layers, and assemble them into a metal flange. Then, place the spaced-lay resin-based composite material layers, transparent ceramic layers, or glass layers with the metal flange together in a vacuum device, seal and evacuate, heat, and keep warm until the resin-based composite material layers, transparent ceramic layers, or glass layers and the metal flange are combined to obtain a multi-layer medium window including the metal flange.

[0030] In the above method for preparing multilayer dielectric windows, in step S3, the heating temperature is 340℃~390℃ and the holding time is 2 hours.

[0031] The outer diameter of the resin-based composite material layer plate, the transparent ceramic layer plate, or the glass layer plate is the same, all being 600mm. The inner diameter of the metal flange is 0.1mm to 0.2mm larger than the outer diameter of the resin-based composite material layer plate, and the outer diameter of the metal flange is 680mm.

[0032] The thickness of the resin-based composite material layer is greater than that of the transparent ceramic layer or glass layer.

[0033] The beneficial effects of this invention are:

[0034] A multi-layered dielectric window exhibits excellent vacuum sealing performance. The quartz fiber-reinforced high-temperature resin composite material used has a low air permeability, significantly lower than commonly used pure polymer dielectric window materials (PTFE, cross-linked polystyrene, etc.), but its overall air permeability is still significantly higher than quartz glass and alumina ceramic materials. This places some pressure on the vacuum holding system of the miniaturized microwave source. Adding a layer of microwave-transparent ceramic or glass further reduces the air permeability. Furthermore, due to the high sealing reliability between the selected composite material and the metal flange, when made into a high-power microwave window with a rigid tube enclosure, the overall vacuum sealing performance and reliability are superior to pure alumina ceramic dielectric windows welded to metal.

[0035] A multilayer dielectric window exhibits low gas release rate. The selected high-temperature resin (mainly including one or more of polyetheretherketone, polyphenylene sulfide, polyetherimide, or polyimide) has high temperature resistance (heat distortion temperature after composite reinforcement is above 200℃, capable of withstanding baking and degassing) and low gas release rate compared to ordinary polymers. After vacuum heat treatment at 150–200℃, the gas release rate is comparable to that of metals, and 2–3 orders of magnitude lower than that of ordinary polymers (below...).

[0036] 10 -11 Pam 3 s -1 cm -2 (); Among them, the gas-transparent ceramics or glasses, such as alumina and borosilicate glass, have very low gas release rates. After baking treatment, the gas release rate is less than 10%. -10 Pam 3 s -1 cm -2 The overall gas release rate of the medium window after the two material layers are combined is lower than that of pure ceramic or glass.

[0037] A multilayer dielectric window with well-matched thermal expansion coefficients of several materials. By adjusting the proportion of quartz fiber or low-dielectric glass fiber in the composite material, the thermal expansion coefficient of the composite material can be kept within a certain range (6~10×10). -6 / K) adjustment, with alumina ceramics (6~8×10) -6 / K) or borosilicate glass (6~10×10 -6 The coefficients of thermal expansion of both materials are matched ( / K). Furthermore, the coefficients of thermal expansion of both materials are similar to those of metal flange materials such as titanium alloys and Kovar alloys (approximately 8 × 10⁻⁶). -6 / K、6×10 -6 The basic matching of the composite material and metal flange allows them to withstand the thermal shocks (maximum temperature difference close to 400℃) during the thermoforming, baking and application processes without cracking and causing seal failure.

[0038] A multilayer dielectric window exhibits excellent mechanical properties. The composite material, reinforced with continuous quartz fiber or low-dielectric glass fiber in a high-temperature resin, achieves a flexural strength greater than 500 MPa and an impact strength greater than 100 kJ / m². 2 The overall mechanical properties are significantly better than those of pure polymer dielectric window materials or alumina ceramic materials. When resin-based composite materials are combined with wave-transparent ceramics or glass to form a multi-layer dielectric window, a multi-layer structure similar to bulletproof glass is formed. The composite material layer protects the ceramic or glass layer, giving the multi-layer dielectric window excellent overall mechanical properties and greatly improving the reliability of the dielectric window in practical application scenarios.

[0039] A multi-layer dielectric window, which is weldable, meets the rigid tube requirements of high-power microwave sources. The selected resin-based composite material has a high heat distortion temperature. After being combined with microwave-transparent ceramics or glass, the edges can be metallized and can withstand the temperature shock of soldering (using a soldering process with an operating temperature of approximately 300°C). It can be directly welded to the metal frame of the high-power microwave output system. Furthermore, through the integral molding of the multi-layer dielectric window with a metal flange, a strong and tight bond is achieved. The flange edge of the dielectric window can be directly welded to the metal frame of the high-power microwave source output cavity, meeting the airtightness requirements of the high-power microwave source vacuum system, with an air permeability far lower than that of conventional rubber ring seals.

[0040] A multilayer dielectric window, using mature raw materials, is fabricated into a multilayer dielectric window device for high-power microwave systems through a novel combination of these materials. This is based on a profound understanding of the hard tube encapsulation problem of high-power microwave sources and the characteristics of several materials (low gas release and low permeability of special high-temperature resins, adjustment of the coefficient of thermal expansion by quartz fiber and resin composites, matching of thermal expansion of various materials such as microwave-transparent ceramics or glass with composite materials and metal flanges, and effective combination of ultra-low permeability microwave-transparent ceramics or glass with composite materials, etc.). This innovative approach produces a dielectric window with excellent comprehensive performance and cleverly solves the problem of hard tube encapsulation of high-power microwave source dielectric windows, possessing great practical and economic value. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of the medium window structure of the present invention;

[0042] Figure 2 This is a schematic diagram of the medium window structure including a metal flange of the present invention.

[0043] Reference numerals: 1. Resin-based composite material layer, 2. Wave-transparent ceramic layer or glass layer, 3. Metal flange. Detailed Implementation

[0044] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0045] A multilayer dielectric window, comprising a resin-based composite material layer and a wave-transparent ceramic or glass layer, such as Figure 1 As shown.

[0046] The resin-based composite material refers to a high-temperature resin reinforced with quartz fiber or low-dielectric glass fiber, wherein the weight ratio of quartz fiber or low-dielectric glass fiber is between 50% and 70%, ensuring that the composite has a low coefficient of thermal expansion (6 to 10 × 10⁻⁶). -6 / K); the high-temperature resin can be one or a mixture of several resins such as polyether ether ketone, polyphenylene sulfide, and polyimide. Such resins have outstanding high-temperature resistance, and after being prepared into composite materials, they have extremely low gas release rates after being treated at high temperatures of 150-200℃. Moreover, the gas permeability of such composite materials is much lower than that of ordinary plastics or general resin-based composite materials, which is beneficial to improving the vacuum characteristics of media window related systems.

[0047] The microwave-transparent ceramic or glass used must meet the following requirements: a coefficient of thermal expansion of 5 to 10 × 10⁻⁶. -6 / K, the deviation between the coefficient of thermal expansion and the coefficient of thermal expansion of the composite material does not exceed 3×10 -6 / K, ensuring effective bonding between the two material layers and withstanding thermal shocks exceeding 300°C without cracking; to meet these requirements, alumina ceramic can be selected for the microwave-transparent ceramic, and borosilicate glass can be selected for the microwave-transparent glass. Due to the excellent mechanical properties, impact resistance, vacuum release rate characteristics, and gas barrier properties of fiber-reinforced resin matrix composites, and the extremely low release rate and permeability of microwave-transparent ceramics or glass, a high-power microwave dielectric window with high strength, thermal shock resistance, low release rate, and low permeability can be obtained through the combination of these two material layers.

[0048] To facilitate welding to the metal frame of the high-power microwave source output system and achieve high sealing performance, the dielectric window, composed of a composite material layer and a microwave-transparent ceramic or glass layer, can be tightly bonded to the outer metal flange via a direct molding process, resulting in a completely seamless mating surface. The metal flange can then be welded to the metal frame of the high-power microwave source output system, achieving a hard seal for the high-power microwave source. The metal flange material must be selected from materials such as titanium alloys or Kovar alloys with a thermal expansion coefficient of 5–10 × 10⁻⁶. -6 / K, its coefficient of thermal expansion must match that of the composite material, with a deviation not exceeding 3×10. -6 / K.

[0049] The medium window can be made of a single layer of composite material and a single layer of transparent ceramic or glass tightly bonded together, or it can be made of multiple layers of composite material and multiple layers of transparent ceramic or glass combined in different sequences and intervals tightly bonded together. Multiple layers are beneficial to further improve the overall mechanical reliability and vacuum sealing of the medium window.

[0050] The method for preparing a multilayer dielectric window consists of the following steps:

[0051] 1) Based on design requirements, resin-based composite material sheets are prepared using common hot-pressing processes and processed into the required dimensions; transparent ceramic or glass sheets are processed into the required dimensions for later use.

[0052] 2) Lay the prepared composite material plates and transparent ceramic or glass plates in alternating layers according to the designed combination, place them in a high-temperature resistant vacuum bag, seal and evacuate the bag, and heat it. The pressure difference between the inside and outside of the vacuum bag is used to bond the resin-based composite material and the transparent glass layers together, forming a multilayer dielectric window composite material. Using the vacuum hot-pressing bag method instead of molding can ensure pressure uniformity and a suitable pressure difference, avoiding the problem of cracking of the transparent ceramic or glass layers that is easily caused by the general molding method.

[0053] If the multi-layer media window and metal flange need to be integrally molded, a metal flange of appropriate size needs to be prepared in advance according to the requirements. The inner diameter (D1) of the metal flange should be slightly larger than the outer diameter (D2) of the composite material plate and glass plate, generally controlled within D1-D2 = 0.1~0.2mm. Using the above process, the composite material plate and ceramic or glass plate are laid inside the metal flange as required, and vacuum bag heating molding is used. Under the action of hot pressing, the excess resin in the composite material will effectively fill the gap between the multi-layer media window and the metal flange, tightly bonding the inner and outer materials together.

[0054] Example 1

[0055] Quartz fiber reinforced PEEK boards were prepared using a hot-pressing process, with a quartz fiber content of 60 at.%. The boards were processed into diameters of 600 mm and thicknesses of 6 mm for later use. A 3 mm thick borosilicate calcium glass board was also processed into a circular plate with a diameter of 600 mm for later use.

[0056] Align and stack the prepared composite material plate with the glass plate, place them in a vacuum bag (the vacuum bag is made of copper foil that is resistant to high temperature and has good toughness), seal and evacuate the vacuum, heat to 390°C for 2 hours, and use the pressure difference inside and outside the vacuum bag to bond the resin-based composite material and the transparent glass layer together to form a double-layer high-power microwave dielectric window.

[0057] After metallizing the edge surface of the dielectric window, it is soldered to the metal frame of the vacuum chamber to facilitate testing of vacuum holding characteristics. The vacuum holding performance and other properties of the obtained dielectric window are shown in Table 1. Its overall performance and economy are far superior to existing polymer dielectric windows or alumina ceramic dielectric windows.

[0058] Example 2

[0059] Quartz fiber reinforced PEEK boards were prepared using a hot pressing process, with a quartz fiber content of 60 at.%. The boards were processed into 600 mm diameter and 2 mm thickness plates, with 3 plates prepared for use. Two 1.5 mm thick borosilicate calcium glass plates were processed into 600 mm diameter circular plates, with 2 plates prepared for use. Flanges with inner and outer diameters of 600.2 mm and 680 mm respectively were processed from titanium alloy and prepared for use.

[0060] The prepared composite material plates are aligned and stacked with the glass plates in the order of composite material plate / glass plate / composite material plate / glass plate / composite material plate. They are then assembled into a titanium alloy flange and placed in a vacuum bag (the vacuum bag material is high-temperature resistant and tough copper foil). The bag is sealed and evacuated, then heated to 390°C for 2 hours. The pressure difference between the inside and outside of the vacuum bag causes the resin-based composite material and the transparent glass layers to bond together, forming a multi-layer high-power microwave dielectric window. Under pressure, the excess resin in the resin-based composite material will fill the gap between the composite material, the transparent glass, and the metal flange, achieving effective connection and sealing.

[0061] The vacuum retention performance and other properties of the obtained medium window are shown in Table 1. Its overall performance and economy are far superior to those of existing polymer medium windows or alumina ceramic medium windows.

[0062] Example 3

[0063] Quartz fiber reinforced PPS board was prepared by hot pressing process, with quartz fiber content of 65 at.%, board diameter of 600 mm and thickness of 5 mm, one piece was spared; 3 mm thick alumina ceramic board was processed into a circular plate with a diameter of 600 mm, one piece was spared; flanges with inner and outer diameters of 600.2 mm and 680 mm respectively were processed by titanium alloy and were spared.

[0064] The prepared composite material plate and glass plate are aligned and stacked, assembled into a titanium alloy flange, and then placed in a vacuum bag (the vacuum bag material is copper foil with high temperature resistance and good toughness). The bag is sealed and vacuumed, then heated to 340°C for 2 hours. The pressure difference inside and outside the vacuum bag causes the resin-based composite material and the transparent glass layer to bond together, forming a double-layer high-power microwave dielectric window. Under pressure, the excess resin in the resin-based composite material will fill the gap between the composite material, the transparent glass and the metal flange, achieving effective connection and sealing.

[0065] The vacuum retention performance and other properties of the obtained medium window are shown in Table 1. Its overall performance is far superior to that of existing polymer medium windows or alumina ceramic medium windows.

[0066] Table 1. Main performance characteristics of several different media windows

[0067]

[0068]

Claims

1. A multi-layered media window, characterized in that, It includes a resin-based composite material layer and a gas barrier layer; the gas barrier layer is a wave-transparent ceramic layer or a glass layer; The resin-based composite material layer is stacked with the gas barrier layer; The resin-based composite material layer is a high-temperature resin reinforced with quartz fiber or low-dielectric glass fiber, and the weight percentage of quartz fiber or low-dielectric glass fiber is 50% to 70%. The high-temperature resin is one of polyetheretherketone, polyphenylene sulfide, and polyimide, or a mixture of two or three of them; The coefficient of thermal expansion of the microwave-transparent ceramic layer or glass layer is 5 × 10⁻⁶. -6 / K~10×10 -6 / K, the thermal expansion coefficient of the microwave-transparent ceramic layer or glass layer deviates from that of the resin-based composite material layer by no more than 3×10. -6 / K.

2. The multilayer medium window according to claim 1, characterized in that, The wave-transparent ceramic layer is alumina ceramic, and the wave-transparent glass layer is borosilicate glass.

3. The multilayer medium window according to claim 1, characterized in that, The resin-based composite material layer, the microwave-transparent ceramic layer, or the glass layer are stacked alternately, and the surface layer is a resin-based composite material layer.

4. The multilayer medium window according to claim 1, characterized in that, It also includes metal flanges; The metal flange is annular, and the stacked resin-based composite material layer, microwave-transparent ceramic layer, or glass layer is located inside the annulus of the metal flange and bonded together.

5. The multilayer medium window according to claim 4, characterized in that, The metal flange is made of titanium alloy.

6. A method for preparing a multilayer dielectric window according to any one of claims 1 to 5, characterized in that, Includes the following steps: Step S1, processing of raw material: A hot-pressing process is used to prepare resin-based composite material sheets, which are then processed to the required dimensions; transparent ceramic sheets or glass sheets are also processed to the required dimensions. Step S2, intermittent lay-up: According to the design requirements, the processed resin-based composite material sheets, transparent ceramic sheets, or glass sheets are laid in alternating layers. Step S3, Multi-layer Medium Window Forming: Align and stack the spaced resin-based composite material layers, transparent ceramic layers, or glass layers, place them in a vacuum device, seal and evacuate, heat and keep warm until the resin-based composite material layers, transparent ceramic layers, or glass layers are bonded together to obtain a multilayer medium window.

7. The method for preparing a multilayer dielectric window according to claim 6, characterized in that, Step S3 specifically involves: aligning and stacking the spaced-lay resin-based composite material layer, the wave-transparent ceramic layer, or the glass layer, assembling them into a metal flange, and then placing the spaced-lay resin-based composite material layer, the wave-transparent ceramic layer, or the glass layer with the metal flange together in a vacuum device, sealing and evacuating the vacuum, heating, and maintaining the temperature until the resin-based composite material layer, the wave-transparent ceramic layer, or the glass layer and the metal flange are combined to obtain a multi-layer medium window including the metal flange.

8. The method for preparing a multilayer dielectric window according to claim 7, characterized in that, In step S3, the heating temperature is 340℃~390℃, and the holding time is 2 hours. The resin-based composite material layer, the microwave-transparent ceramic layer, or the glass layer all have the same outer diameter of 600 mm. The inner diameter of the metal flange is 0.1 mm to 0.2 mm larger than the outer diameter of the resin-based composite material layer, and the outer diameter of the metal flange is 680 mm. The thickness of the resin-based composite material layer is greater than the thickness of the microwave-transparent ceramic layer or the glass layer.

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