Broadband microwave absorbing material with optical transparency properties and applications thereof

Abstract

The application provides a broadband microwave absorbing material with optical transparency and an application thereof, and belongs to the technical field of wave-absorbing materials.The broadband microwave absorbing material comprises a non-patterned indium tin oxide film layer, a first polyethylene terephthalate layer, an air layer, a second polyethylene terephthalate layer and a patterned indium tin oxide film layer.The patterned indium tin oxide film layer is mainly used for introducing ohmic loss to consume the energy of incident microwaves, and the non-patterned indium tin oxide film layer is used as a reflective back plate of the wave-absorbing material.The patterned indium tin oxide film layer can effectively expand the low-frequency absorption bandwidth and has fourfold symmetry, thereby having good polarization insensitivity and good oblique incidence stability.The air layer in the middle can further expand the electromagnetic wave absorption bandwidth, and each layer structure is a transparent material, so that the whole has good light transmittance.

Description

Technical Field

[0001] This invention relates to the field of microwave absorbing materials technology, and in particular to a broadband microwave absorbing material with optical transparency and its applications. Background Technology

[0002] With the continuous development of science and technology, microwave absorbing technology has received increasing attention and has been widely used in electromagnetic compatibility, electromagnetic shielding, and other technical fields. The earliest absorbing materials can be traced back to the Salisbury and Jauman absorbing screens invented in the mid-to-late 20th century. The Salisbury absorbing screen utilizes the wave characteristics of microwaves by placing a purely resistive screen at λ / 4 intervals in front of an ideal conductor. The microwaves reflected directly from the surface of the resistive screen and reflected after entering the medium at the ideal conductor have a phase difference of exactly π, canceling each other out and achieving the purpose of absorption. The Salisbury absorbing screen has a very good absorption effect, but its absorption bandwidth is relatively narrow. Therefore, based on the Salisbury absorbing screen, the Jauman absorbing screen was developed, which involves placing multiple resistive screens spaced at λ / 4 intervals in front of an ideal conductor. This greatly improves the absorption bandwidth, but at the cost of a significant increase in the overall structural thickness, objectively limiting its application scenarios. Subsequently, various novel microstructures were proposed and integrated into the design of absorbing materials, forming a structural absorbing material.

[0003] Currently, the design of microwave absorbing materials mainly considers three indicators: 1. Broadband characteristics. This requires the designed absorbing material to cover a wide frequency band (usually several octaves) and maintain good absorption efficiency within this band. 2. Lightweight and thin structure. This requires the absorbing material to be lightweight and thin to meet the demands of miniaturized RF devices and various mobile communication markets. 3. Oblique incidence stability and polarization stability. This requires that the absorptivity degradation within the absorption bandwidth is within an acceptable range when microwaves are incident at an oblique angle. Simultaneously, the absorbing material must maintain a consistent absorptivity for different polarizations of TE and TM. In addition to these three requirements, a new demand has emerged in recent years: the optical transparency of absorbing materials. This requires the absorbing material to absorb microwaves while remaining transparent to visible light. Current absorbing materials struggle to simultaneously meet all of these requirements.

[0004] Therefore, there is an urgent need for a broadband microwave absorbing material with optical transparency. Summary of the Invention

[0005] The purpose of this invention is to provide a broadband microwave absorbing material with optical transparency and its applications. The absorbing material provided by this invention has a very wide operating bandwidth, good polarization insensitivity, good oblique incidence stability, and good light transmittance.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0007] This invention provides a broadband microwave absorbing material with optical transparency, comprising, from bottom to top, a patternless indium tin oxide (ITO) thin film layer, a first polyethylene terephthalate (PET) layer, an air layer, a second PET layer, and a patterned ITO thin film layer; the pattern of the patterned ITO thin film layer is a periodically arranged repeating unit, wherein the repeating unit is composed of a ring and a plurality of circumferential fan-shaped circumferences connected to the outer circumference of the ring, and the plurality of circumferential fan-shaped circumferences are uniformly and symmetrically distributed on the outer side of the ring.

[0008] Preferably, the inner diameter of the ring is 7.2 to 8.4 mm.

[0009] Preferably, the outer diameter of the ring is 12.5 to 13.2 mm.

[0010] Preferably, the radius of the circumscribed sector is 2.8 to 3.6 mm.

[0011] Preferably, the distance between the center of the outer sector circumference and the center of the annulus is 12.8 to 13.6 mm.

[0012] Preferably, the resistivity of the patterned indium tin oxide thin film layer is 70 to 100 ohm / sq.

[0013] Preferably, the resistivity of the patternless indium tin oxide thin film layer is 4 to 8 ohms / sq.

[0014] Preferably, the thickness of the first polyethylene terephthalate layer and the second polyethylene terephthalate layer is independently 0.17 to 0.18 mm.

[0015] Preferably, the thickness of the air layer is 14–16 mm.

[0016] This invention also provides the application of the microwave absorbing material described above in the fields of electromagnetic compatibility and electromagnetic shielding.

[0017] This invention provides a broadband microwave absorbing material with optical transparency, comprising, from bottom to top, a patternless indium tin oxide (ITO) thin film layer, a first polyethylene terephthalate (PET) layer, an air layer, a second PET layer, and a patterned ITO thin film layer; the pattern of the patterned ITO thin film layer is a periodically arranged repeating unit, wherein the repeating unit is composed of a ring and a plurality of circumferential fan-shaped circumferences connected to the outer circumference of the ring, and the plurality of circumferential fan-shaped circumferences are uniformly and symmetrically distributed on the outer side of the ring. The patterned indium tin oxide (ITO) thin film layer of this invention is mainly used to introduce ohmic loss and dissipate the energy of incident microwaves. The special structure of the patterned ITO thin film layer effectively extends the low-frequency absorption bandwidth. Multiple circumferential fan-shaped rings are uniformly and symmetrically distributed on the ring, thus possessing good polarization insensitivity and good oblique incidence stability. The unpatterned ITO thin film layer serves as the reflective backplate of the absorbing material, the polyethylene terephthalate (PET) layer supports the ITO layer, and the air layer in between further extends the bandwidth of electromagnetic wave absorption. All layers are transparent materials, resulting in good overall light transmittance. The results of the embodiments show that the operating bandwidth of the absorbing material provided by this invention is not less than 112.35% (1.88–6.70 GHz), and within this bandwidth, the absorption rate is higher than 90%. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of the broadband microwave absorbing material with optical transparency in Embodiment 1 of the present invention;

[0019] Figure 2 These are top and side views of a single cycle of the broadband microwave absorbing material with optical transparency of the present invention.

[0020] Figure 3 The reflection coefficient of the microwave absorbing material in Embodiment 1 of the present invention under perpendicular incidence.

[0021] Figure 4 The transmission coefficient of the microwave absorbing material in Embodiment 1 of the present invention under vertical incidence is shown.

[0022] Figure 5 This is the absorption rate curve of the microwave absorbing material in Example 1 of the present invention under vertical incident conditions;

[0023] Figure 6 This is the absorption rate curve of the microwave absorbing material in Example 1 of the present invention under oblique incidence in TE mode;

[0024] Figure 7 This is the absorption rate curve of the microwave absorbing material in Example 1 of the present invention under oblique incidence in TM mode. Detailed Implementation

[0025] This invention provides a broadband microwave absorbing material with optical transparency, comprising, from bottom to top, a patternless indium tin oxide (ITO) thin film layer, a first polyethylene terephthalate (PET) layer, an air layer, a second PET layer, and a patterned ITO thin film layer; the pattern of the patterned ITO thin film layer is a periodically arranged repeating unit, wherein the repeating unit is composed of a ring and a plurality of circumferential fan-shaped circumferences connected to the outer circumference of the ring, and the plurality of circumferential fan-shaped circumferences are uniformly and symmetrically distributed on the outer side of the ring.

[0026] The broadband microwave absorbing material with optical transparency provided by this invention includes a patternless indium tin oxide (ITO) thin film layer. In this invention, the ITO simultaneously possesses both conductive and transparent properties, achieving a light transmittance of over 90%, thus giving the microwave absorbing material excellent light transmittance. In this invention, the thickness of the patternless ITO thin film layer is preferably 40–50 nm, specifically 41, 42, 43, 44, 45, 46, 47, 48, and 49 nm in specific embodiments; the resistivity of the patternless ITO thin film layer is preferably 4–8 ohms / sq, more preferably 5–7 ohms / sq. In this invention, the relatively low resistivity of the patternless ITO thin film layer allows it to function as a reflective backplane for the microwave absorbing material. By limiting the thickness and resistivity of the patternless ITO thin film layer to the above ranges, this invention enables more thorough reflection of electromagnetic waves, improving its performance while allowing the microwave absorbing material to have a relatively thin thickness.

[0027] The present invention further includes a first polyethylene terephthalate (PET) layer superimposed on the patternless indium tin oxide (ITO) thin film layer. In the present invention, the first PET layer serves to support the patternless ITO thin film layer. In the present invention, the thickness of the first PET layer is preferably 0.17–0.18 mm, more preferably 0.175 mm. In the present invention, the PET layer has good light transmittance.

[0028] The present invention also includes an air layer superimposed on the first polyethylene terephthalate (PET) layer. In this invention, the thickness of the air layer is preferably 14–16 mm, more preferably 14.5–15.5 mm, and most preferably 15 mm. In this invention, the air layer can extend the bandwidth of electromagnetic wave absorption, and when the thickness of the air layer is within the above range, it allows the absorbing material to match the surrounding free space, thereby improving the wave absorption performance of the absorbing material.

[0029] The present invention preferably employs a three-dimensional frame to support the first polyethylene terephthalate layer and the second polyethylene terephthalate layer to form an air layer.

[0030] The present invention further includes a second polyethylene terephthalate (PET) layer superimposed on the air layer. In this invention, the second PET layer serves to support the patterned indium tin oxide (ITO) thin film layer. In this invention, the thickness of the second PET layer is preferably 0.17–0.18 mm, more preferably 0.175 mm.

[0031] The present invention also includes a patterned indium tin oxide thin film layer superimposed on the second polyethylene terephthalate (PET) layer.

[0032] In this invention, the pattern of the patterned indium tin oxide thin film layer is a periodically arranged repeating unit. The repeating unit is composed of a ring and a plurality of circumferential fan-shaped circumferences connected to the outer circumference of the ring. The plurality of circumferential fan-shaped circumferences are evenly and symmetrically distributed on the outer side of the ring.

[0033] In this invention, the thickness of the patterned indium tin oxide (ITO) thin film is preferably 40–50 nm; the resistance of the patterned ITO thin film is preferably 70–100 ohm / sq, more preferably 80–90 ohm / sq. In this invention, the relatively high resistance of the patterned ITO thin film is mainly used to introduce ohmic losses and dissipate the energy of the incident microwaves.

[0034] In this invention, the number of the outer sector-shaped circumferences is preferably four.

[0035] In this invention, the top view and side view of a single unit schematic diagram of the patterned indium tin oxide thin film layer are preferably as follows: Figure 2 As shown. In this invention, the inner diameter r2 of the ring is preferably 7.2–8.4 mm, more preferably 7.5–8 mm; the outer diameter r1 of the ring is preferably 12.5–13.2 mm, more preferably 12.7–13 mm; the radius r3 of the outer fan-shaped circumference is preferably 2.8–3.6 mm, more preferably 3.2–3.6 mm; the distance l from the center of the outer fan-shaped circumference to the center of the ring is preferably 12.8–13.6 mm, more preferably 13.0–13.5 mm; the angle α between the line connecting the center of the outer fan-shaped circumference and the center of the ring and the vertical line is preferably 45°; the length p of the single unit is preferably 27–28 mm. The special structure of the patterned indium tin oxide thin film layer of this invention can effectively extend the low-frequency absorption bandwidth. The outer fan-shaped circumference is uniformly distributed on the ring and has fourfold symmetry, thus possessing good polarization insensitivity and good oblique incidence stability.

[0036] In this invention, the periodic arrangement is preferably a rectangular array arrangement; the number of repeating units in each array is preferably ≥2.

[0037] This invention limits the parameters of the patterned indium tin oxide thin film layer to the above-mentioned range, which enables the microwave absorbing material to have a wide absorption bandwidth and high absorption efficiency, while having a thin thickness.

[0038] This invention provides a method for preparing a broadband microwave absorbing material with optically transparent properties as described in the above technical solution, preferably comprising the following steps:

[0039] (1) An indium tin oxide thin film layer was sputtered onto a first polyethylene terephthalate substrate by magnetron sputtering, followed by annealing to obtain a first polyethylene terephthalate layer with or without a patterned indium tin oxide thin film layer sputtered.

[0040] (2) According to the pattern described in the above technical solution, a patterned indium tin oxide thin film layer is sputtered on the second polyethylene terephthalate substrate by magnetron sputtering, and then annealed to obtain a second polyethylene terephthalate layer with a patterned indium tin oxide thin film layer sputtered.

[0041] (3) Using a three-dimensional frame as an air layer, the two sides of the three-dimensional frame are respectively bonded to the first polyethylene terephthalate layer with a patternless indium tin oxide thin film layer sputtered in step (1) and the second polyethylene terephthalate layer with a patterned indium tin oxide thin film layer sputtered in step (2) to obtain a broadband microwave absorbing material with optical transparency.

[0042] The steps (1) and (2) are not in any particular order.

[0043] The present invention obtains a first polyethylene terephthalate layer with or without a patterned indium tin oxide thin film by magnetron sputtering onto a first polyethylene terephthalate substrate, followed by annealing.

[0044] The present invention does not impose any special limitations on the operation of magnetron sputtering and annealing; any magnetron sputtering and annealing technical solutions known to those skilled in the art can be used.

[0045] According to the pattern described in the above technical solution, a patterned indium tin oxide thin film layer is sputtered onto a second polyethylene terephthalate substrate by magnetron sputtering, followed by annealing to obtain a second polyethylene terephthalate layer with a sputtered patterned indium tin oxide thin film layer.

[0046] The present invention does not impose any special limitations on the operation of magnetron sputtering and annealing; any magnetron sputtering and annealing technical solutions known to those skilled in the art can be used.

[0047] After obtaining the first polyethylene terephthalate layer sputtered with a patterned indium tin oxide thin film layer and the second polyethylene terephthalate layer sputtered with a patterned indium tin oxide thin film layer, the present invention uses a three-dimensional framework as an air layer, and bonds the two sides of the three-dimensional framework to the first polyethylene terephthalate layer sputtered with a patterned indium tin oxide thin film layer and the second polyethylene terephthalate layer sputtered with a patterned indium tin oxide thin film layer respectively, to obtain a broadband microwave absorption material with optical transparency characteristics.

[0048] In the present invention, the material of the three-dimensional framework is preferably an acrylic framework; the shape of the framework is preferably a "field" shape; the height of the framework is preferably the height of the air layer.

[0049] The present invention preferably bonds the three-dimensional framework to the first polyethylene terephthalate layer sputtered with a patterned indium tin oxide thin film layer and the second polyethylene terephthalate layer sputtered with a patterned indium tin oxide thin film layer through an optically transparent adhesive. The present invention has no special limitation on the type of the optically transparent adhesive, and an optically transparent adhesive well-known to those skilled in the art can be used. In the present invention, the optically transparent adhesive preferably includes an epoxy adhesive, a silicone gel or a photocurable adhesive. The present invention has no special limitation on the amount of the optically transparent adhesive, as long as it can stably bond the two. Bonding through the optically transparent adhesive in the present invention can enable the material to have good light transmittance while ensuring structural stability.

[0050] The present invention also provides an application of the microwave absorption material described in the above technical solution in the fields of electromagnetic compatibility and electromagnetic shielding.

[0051] The present invention has no special limitation on the operation of the application of the microwave absorption material in the fields of electromagnetic compatibility and electromagnetic shielding, and a technical solution of the application of the microwave absorption material well-known to those skilled in the art can be adopted.

[0052] Next, the technical solutions in the present invention will be clearly and completely described in conjunction with the embodiments in the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0053] Example 1

[0054] The structural schematic diagram of the broadband microwave absorption material with optical transparency characteristics in this example is as Figure 1As shown, the structure consists of, from bottom to top, an unpatterned indium tin oxide (ITO) thin film layer, a first polyethylene terephthalate (PET) layer, an air layer, a second PET layer, and a patterned ITO thin film layer. The patterned ITO thin film layer comprises repeating units arranged periodically in a 5×5 rectangular array. Each repeating unit consists of a circular ring and four circumscribed sector circles connected to the outer circumference of the circular ring. The four circumscribed sector circles are evenly and symmetrically distributed outside the circular ring.

[0055] The resistivity of the patterned indium tin oxide thin film is 90 ohms / sq, the thickness is 45 nm, the inner diameter r2 of the ring is 8 mm, the outer diameter r1 of the ring is 13 mm; the radius r3 of the outer sector is 3.6 mm; the distance l from the center of the outer sector to the center of the ring is 13.5 mm; the angle α between the line connecting the center of the outer sector and the center of the ring and the perpendicular line is 45°; the length p of a single unit is 27 mm, and the total length L of the microwave absorbing material is 135 mm.

[0056] The thicknesses of the first polyethylene terephthalate layer and the second polyethylene terephthalate layer are both 0.175 mm.

[0057] The thickness of the air layer is 15mm;

[0058] The resistivity of the patternless indium tin oxide thin film is 5 ohm / sq, and the thickness is 45 nm.

[0059] The total thickness of the microwave absorbing material is 15.35 mm, with a relative electrical thickness of only 0.22λ. c (λ c =69.93mm, which is the wavelength of the center frequency 4.29GHz.

[0060] Test Example 1: Reflectance coefficient S of microwave absorbing material under perpendicular incidence. 11 Transmission coefficient S 21 The absorption rate curves and results are as follows: Figures 3-5 As shown. The relationship between the three is as follows: Absorptivity = 1 - |S 11 | 2 -|S 21 | 2 .from Figure 3 It can be seen from this that: transmission coefficient S 21 Within the 1-8 GHz range, the difference is less than -30 dB, which is almost negligible. From Figure 4 It can be seen that, under vertical incidence, the bandwidth of the absorbing material with an absorption rate higher than 90% is 1.88-6.70GHz (center frequency 4.29GHz), and the relative bandwidth is 112.35%.

[0061] The absorptivity curve of the microwave absorbing material in Example 1 under oblique incidence in TE mode was tested, and the results are as follows: Figure 6 As shown; the absorptivity curve of the microwave absorbing material in Example 1 under oblique incidence in TM mode is shown in the figure. Figure 7 As shown. From Figure 6 and Figure 7 As can be seen, under TE mode oblique incidence, the absorbing material can effectively absorb microwaves within an incident angle of 45°, with an absorption bandwidth of 1.93-7.44GHz and an absorption rate of over 80%. Under TM mode oblique incidence, the absorbing material can also effectively absorb microwaves within an incident angle of 45°, with an absorption bandwidth of 2.7-7.45GHz and an absorption rate of over 80%. The absorbing material maintains a large absorption bandwidth and good absorption efficiency even under large incident angle (45°), and the structure has good oblique incidence stability while being insensitive to polarization.

[0062] In summary, the absorbing material of this invention has a large absorption bandwidth, thin thickness, stable oblique incidence, insensitive to incident wave polarization, excellent light transmittance, simple structure, and is easy to manufacture, thus having good market application prospects.

[0063] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A broadband microwave absorbing material with optical transparency, comprising, from bottom to top, a patternless indium tin oxide (ITO) thin film layer, a first polyethylene terephthalate (PET) layer, an air layer, a second PET layer, and a patterned ITO thin film layer; wherein the patterned ITO thin film layer is a repeating unit having a periodic arrangement of 5×5 rectangular arrays; the repeating unit is composed of a circular ring and a plurality of circumferential fan-shaped circumferences connected to the outer circumference of the circular ring, the plurality of circumferential fan-shaped circumferences being uniformly and symmetrically distributed on the outer side of the circular ring; the number of circumferential fan-shaped circumferences is 4; The inner diameter of the ring is 8 mm; the outer diameter of the ring is 13 mm. The radius of the circumscribed sector is 3.6 mm; The distance between the center of the outer sector circle and the center of the ring is 13.5 mm; The thickness of the first polyethylene terephthalate layer and the second polyethylene terephthalate layer is independently 0.175 mm; The thickness of the air layer is 15 mm; The thickness of the unpatterned indium tin oxide thin film is 45 nm; the thickness of the patterned indium tin oxide thin film is 45 nm. The resistivity of the patterned indium tin oxide thin film is 90 ohm / sq; the resistivity of the unpatterned indium tin oxide thin film is 5 ohm / sq.

2. The application of the microwave absorbing material of claim 1 in the fields of electromagnetic compatibility and electromagnetic shielding.

Images