JP7716792B2 - NFC antenna for mobile phone and method for preparing electromagnetic wave absorbing material thereof - Google Patents

Description

The present invention relates to the technical field of antennas, and in particular to an NFC antenna for mobile phones and a method for preparing an electromagnetic wave absorbing material therefor.

NFC antennas for mobile phones are passive antennas that enable communication with other devices using near-field communication (NFC) technology. NFC antennas generally use coil antennas consisting of a conductor coil and magnetic shielding material. Mobile phone NFC antennas typically include the NFC antenna body and a metal base plate. Metal reflects and absorbs radio waves, and the metal base plate interferes with the NFC signal, resulting in reduced signal quality. Therefore, conventional technology combines magnetic shielding material with mobile phone NFC antennas to suppress metal interference.

In conventional technology, most magnetic shielding materials use ferrite (metal oxide) or amorphous or nanocrystalline (soft magnetic alloy). Patent Document 1 discloses a small NFC antenna whose antenna assembly includes an FPC board, a conductor, and a ferrite sheet. During use, the conductor is first inserted into an etched groove on the top edge of the FPC board, then the ferrite sheet is placed on the top edge of the FPC board, and finally the ferrite sheet is thermocompression bonded to complete the product. Patent Document 2 discloses an NFC antenna and tag that includes a PCB board, a metal base plate, a soft magnetic layer, and an NFC antenna body, with the metal base plate disposed on the PCB board, the soft magnetic layer disposed on the metal base plate, and the NFC antenna body disposed on the soft magnetic layer.

Currently, the problem with using ferrite (metal oxide) as a magnetic shielding material for NFC antennas in mobile phones is that ferrite (metal oxide) is relatively heavy, increasing the weight and volume of the mobile phone. The manufacturing method uses a sintering method, which requires temperatures of over 1100°C, resulting in low yields. Furthermore, because ferrite die-cutting contains scrap, it is necessary to cover the top and bottom with film and trim the edges, which increases costs.

Currently, the problem with using amorphous or nanocrystalline (soft magnetic alloys) as magnetic shielding materials for NFC antennas on mobile phones is that soft magnetic alloys, which are typical magnetic loss absorption materials, have advantages such as high saturation magnetization, good temperature stability, and low cost, but they have a large complex dielectric constant and poor impedance matching, making it difficult to meet the performance requirements for electromagnetic wave absorption materials for 5G communications.

Therefore, the object of the present invention is to provide a new radio wave absorbing material for mobile phone NFC antennas that is thin, lightweight, has strong magnetic shielding performance, effectively blocks metal interference with NFC antennas, and ensures the signal quality of NFC antennas.

Chinese Patent Application No. CN202320076225. Publication No. Chinese Patent Application No. CN202221616567.8

To overcome the above drawbacks, the object of the present invention is to provide an NFC antenna for mobile phones and a method for preparing the electromagnetic wave absorbing material thereof, which has a thin, lightweight, and powerful magnetic shielding layer between the NFC antenna body and the metal base plate, effectively shielding the NFC antenna from metal interference and ensuring the signal quality of the NFC antenna, and which is obtained by mixing the electromagnetic wave absorbing powder with a polymer elastomer in an evenly spread manner to form a uniform particle size distribution that can be easily processed into electromagnetic wave absorbing materials of various shapes, and which achieves high magnetic permeability, good impedance matching, stable electromagnetic wave absorption, and high reliability.

The objectives of the present invention are achieved by the following technical means:

An NFC antenna for a mobile phone, comprising an NFC antenna main body, an electromagnetic wave absorbing layer, and a metal base plate, with the electromagnetic wave absorbing layer disposed on the metal base plate, and the NFC antenna main body disposed on the electromagnetic wave absorbing layer, the electromagnetic wave absorbing layer being a film or sheet made of an electromagnetic wave absorbing material, the electromagnetic wave absorbing material including electromagnetic wave absorbing powder and a polymer elastomer, the electromagnetic wave absorbing powder being a soft magnetic alloy or soft magnetic composite material, and having a two-dimensional sheet structure that is spread evenly within the polymer elastomer, with the mass ratio of the electromagnetic wave absorbing powder to the polymer elastomer being 10-20:1-5.

Currently, most "magnetic shielding materials" use ferrite (metal oxide) or amorphous or nanocrystalline (soft magnetic alloy). However, the electromagnetic wave absorbing material used in this invention is an electromagnetic wave absorbing powder with a two-dimensional sheet structure laid flat on a polymer elastomer. The electromagnetic wave absorbing powder has high saturation magnetic induction strength and low coercive force, which can effectively isolate electromagnetic interference and magnetic field interference and improve the magnetic shielding performance of the electromagnetic wave absorbing material layer. Compared to ferrite, the electromagnetic wave absorbing material has a lower specific gravity, which can significantly reduce the weight of the entire antenna structure and increase the weight ratio of the entire device. Compared to amorphous and nanocrystalline materials, the present invention mixes the electromagnetic wave absorbing powder with the polymer elastomer in an evenly spread manner, forming a uniform particle size distribution that makes it easy to process into electromagnetic wave absorbing materials of various shapes. The polymer elastomer acts as a filler and binder within the electromagnetic wave absorbing material, uniformly dispersing the electromagnetic wave absorbing powder within the electromagnetic wave absorbing material and improving the magnetic shielding effect. It also tightly bonds the electromagnetic wave absorbing powder to the polymer elastomer, increasing the mechanical strength and stability of the electromagnetic wave absorbing material.

In the NFC antenna for a mobile phone, the electromagnetic wave absorbing powder has a powder thickness in the height direction of 0.5 to 1.5 μm and a median particle diameter D50 in the width direction of 30 to 100 μm.

Furthermore, in the above-mentioned NFC antenna for mobile phones, the soft magnetic alloy is at least one selected from the group consisting of iron-silicon-aluminum soft magnetic alloy, iron-silicon soft magnetic alloy, iron-nickel soft magnetic alloy, iron-nickel-molybdenum soft magnetic alloy, iron-aluminum soft magnetic alloy, iron-silicon-aluminum-nickel soft magnetic alloy, iron-chromium soft magnetic alloy, and iron-cobalt soft magnetic alloy.

Preferably, the soft magnetic alloy is an iron-silicon-aluminum soft magnetic alloy, also known as Sendust alloy, whose main components are Fe9.6-Si5.4-Al.

In the NFC antenna for a mobile phone, the soft magnetic composite material has a two-dimensional sheet-like multilayer structure including, from the inside to the outside, a soft magnetic alloy, an Al ₂ O ₃ layer, and an amorphous carbon layer.

The soft magnetic composite material uses a two-dimensional sheet-like multilayer structure, with an _Al2O3 layer between the soft magnetic alloy and the _amorphous carbon layer, which not only prevents the generation of carbon nanomaterials on the surface of the soft magnetic composite material, but also introduces multiple scattering and reflection mechanisms to improve the microwave absorption properties. At the same time, this multilayer structure also acts as a barrier protection, improving the corrosion resistance of the soft magnetic composite material.

Furthermore, in the above-mentioned NFC antenna for mobile phones, the inductance value of the antenna coil of the NFC antenna main body is 1.6 to 2.0 μH.

By setting the inductance value of the antenna coil of the NFC antenna body to 1.6 to 2.0 μH, capacitance matching becomes easier to achieve.

Preferably, the metal base plate includes, but is not limited to, aluminum, copper, or stainless steel materials.

In addition, in the above-mentioned NFC antenna for mobile phones, the electromagnetic wave absorbing material is made by laminating and spreading out electromagnetic wave absorbing powder in a two-dimensional sheet structure, and by interposing a polymer elastomer between the electromagnetic wave absorbing powder to block it, electrical continuity between the electromagnetic wave absorbing powder is prevented.

The industry's communications frequency is 13.56 MHz, and the structural design of the electromagnetic wave absorber makes it suitable for this frequency. When the electromagnetic wave absorbing powder conducts, alloy flakes are formed, resulting in extremely low magnetic permeability at 13.56 MHz and attenuating it by less than 50% at 1 MHz.

Furthermore, in the above-mentioned NFC antenna for mobile phones, the polymer elastomer is at least one of polyurethane, acrylic acid, organosilicon, and epoxy resin.

Preferably, the polymer elastomer is polyurethane.

The present invention also relates to a method for preparing the electromagnetic wave absorber for an NFC antenna for a mobile phone, comprising the following steps S1 to S5:
S1 raw material blending: a step of uniformly mixing an electromagnetic wave absorbing powder having a bulk density of 0.2 to 0.7 g/cm ³ and a tap density of 0.6 to 2.0 g/cm ³ and a polymer elastomer to obtain a raw material mixture;
S2 slurry stirring: adding the raw material mixture into a stirrer, then adding a solvent and auxiliary components, mixing in a mass ratio of solvent, raw material mixture, and auxiliary components of 40-80:10-50:0.5-2, and stirring thoroughly until homogenous, to produce a slurry with a viscosity of 1500-2000 mPa s;
S3 Slurry application: The slurry is applied onto a protective film, and spread evenly over the surface of the protective film with a scraper. The temperature of the application is set to 50 to 120°C, and the speed is set to 0.5 to 4 m/min. After drying, a dry film is obtained.
S4 dry film lamination: a process of placing the dried film after drying into a laminator, setting the temperature at 150-180°C and the pressure at 10-20 MPa to densify it and form an electromagnetic wave absorbing material; and S5 die-cutting: a process of cutting the laminated electromagnetic wave absorbing material according to the design requirements to obtain the required size and shape.

In conventional technology, the preparation method for ferrite (metal oxide) used in NFC antennas for mobile phones to prevent metallic interference involves a sintering process, which requires temperatures of over 1100°C, resulting in low yields and scraps being included when the ferrite is cut out, making it necessary to cover the top and bottom with film and trim the edges.

The method of the present invention for preparing electromagnetic wave absorbing material for NFC antennas for mobile phones is less expensive, and in particular, costs can be reduced by 20% in the case of an electromagnetic wave absorbing material with a magnetic permeability of 150 and a thickness of 0.08 mm.

The electromagnetic wave absorber produced using the above preparation method is a flexible product that can be designed into a variety of shapes compared to ferrites, etc., does not shed, does not require edging or double-sided coating, and reduces processes and costs. The above preparation method for the electromagnetic wave absorber is simple, can be prepared on a large scale, and has a wide range of application scenarios in the field of electromagnetic wave absorbers.

In addition, compared to conventional manufacturing methods such as rolling and casting, there is a possibility that certain defects and gaps may exist inside the particles of the electromagnetic wave absorbing material and the polymer elastomer due to the compatibility between them. The present invention uses a dry film lamination method of hot press molding, which helps to form an electromagnetic wave absorbing material with a uniform particle size distribution.

Preferably, the protective film is a PET film.

The method for preparing the above electromagnetic wave absorber is simple, can be prepared on a large scale, and has a wide range of application scenarios.

Furthermore, in the above-mentioned method for preparing an electromagnetic wave absorbing material for an NFC antenna for a mobile phone, the solvent in S2 is any one of methyl isopropyl ketone, acetone, cyclohexanone, and DMF, and the auxiliary component is at least one of a dispersant, an antifoaming agent, a leveling agent, and a surfactant.

Preferably, the solvent is methyl isopropyl ketone, and the auxiliary components include dispersant BYK-110, antifoaming agent BYK-141, leveling agent BYK-330, and SDBS. Methyl isopropyl ketone effectively dissolves and uniformly disperses the polymer elastomer and auxiliary, and the auxiliary promotes contact between the polymer elastomer and the electromagnetic wave absorbing powder, improves the compatibility of the slurry, adjusts the viscosity and fluidity, improves the coatability of the slurry, and increases the stability of the slurry.

In addition, in the above-mentioned method for preparing an electromagnetic wave absorbing material for an NFC antenna for a mobile phone, the electromagnetic wave absorbing powder is a soft magnetic composite material, and the preparation method includes the following steps S1 to S2:
S1: Mixing an ammonium formate solution, soft magnetic alloy powder, and aluminum sulfate, and ultrasonically dispersing the mixture for 10 to 3 minutes to obtain a mixed solution, heating the mixed solution in a water bath at 75 to 85°C, maintaining the mixture at that temperature and stirring for 1 to 2 hours to cause a reaction, washing the mixture with ethanol multiple times and separating it magnetically, drying it in an oven at 40 to 50°C for 1 to 3 days, and then annealing it at 350 to 450°C for 2 hours to obtain a soft magnetic alloy powder coated with _three layers of Al ₂ O 3 ; and _S2 : The soft magnetic alloy powder coated with _{the three} layers is spread evenly on a quartz boat, which is then placed in a CVD rotary tubular furnace and heated to 400°C at a rate of 3 to 6°C/min under an argon protective atmosphere with a gas flow rate of 50 to 100 mL/min. Acetylene gas is then introduced at a flow rate of 20 to 30 mL/min to cause a reaction for 0.5 to 1 hour. After the reaction is complete, the acetylene gas is stopped, the material is slowly cooled to 25°C, and the material is removed to obtain a soft magnetic composite material.

First, _{an Al2O3 layer} is coated on the surface of the soft magnetic alloy powder by the sol-gel method, and then an amorphous carbon layer is introduced on the surface of the soft magnetic alloy by the CCDV method. The highly resistive amorphous carbon layer can reduce the dielectric constant of the magnetic metal, achieve good impedance matching between the absorbing material and free space, and improve the microwave absorption properties and corrosion resistance.

Compared with the prior art, the present invention has the following advantageous effects:
(1) The NFC antenna for mobile phones disclosed in the present invention has an electromagnetic wave absorbing layer between the NFC antenna body and the metal base plate. The electromagnetic wave absorbing layer is thin, lightweight, and has strong magnetic shielding properties, effectively shielding the NFC antenna from metal interference and ensuring the signal quality of the NFC antenna.
(2) In the NFC antenna for mobile phones disclosed by the present invention, the electromagnetic wave absorbing powder is mixed with the polymer elastomer in a flat-spreading manner, thereby forming a uniform particle size distribution and facilitating processing into electromagnetic wave absorbing materials of various shapes. The polymer elastomer acts as a filler and binder within the electromagnetic wave absorbing material, dispersing the electromagnetic wave absorbing powder uniformly within the electromagnetic wave absorbing material and improving the magnetic shielding effect. In addition, the electromagnetic wave absorbing powder is tightly bonded to the polymer elastomer, thereby increasing the mechanical strength and stability of the electromagnetic wave absorbing material, thereby achieving high magnetic permeability, good impedance matching, stable electromagnetic wave absorption, and high reliability.
(3) The soft magnetic composite material of the NFC antenna for mobile phones disclosed by the present invention uses a two-dimensional sheet-like multilayer structure, and _{an Al2O3} layer is provided between the soft magnetic alloy and the amorphous carbon layer, which not only prevents the generation of carbon nanomaterials on the surface of the soft magnetic composite material, but also introduces a multiple scattering and reflection mechanism to improve the microwave absorption properties, and at the same time, this multilayer structure acts as a shielding protection and can improve the corrosion resistance of the soft magnetic composite material.
(4) The method for preparing an electromagnetic wave absorbing material for an NFC antenna for a mobile phone disclosed by the present invention is less expensive than ferrite, and the electromagnetic wave absorbing material produced by the above preparation method is a flexible product that can be designed into various shapes, does not shed, and does not require edging or double-sided coating, thereby reducing the process and cost.

1 is a schematic diagram illustrating the configuration of an NFC antenna for a mobile phone according to the present invention. 1 is a cross-sectional view of a soft magnetic composite material of an NFC antenna for a mobile phone according to the present invention. 1 is a cross-sectional SEM image of an electromagnetic wave absorber according to Example 1 of the present invention. 10 is a cross-sectional SEM image of an electromagnetic wave absorber according to Example 2 of the present invention.

The technical means in the embodiments of the present invention will be explained clearly and in detail below with reference to Examples 1, 2, Comparative Examples 1, 3, and 4, as well as specific test data and Figures 1 to 4. However, it goes without saying that the examples described only represent some of the embodiments of the present invention, and do not represent all of the embodiments. All other embodiments that can be obtained by a person skilled in the art based on the embodiments of the present invention without the need for creative activity are also within the scope of protection of the present invention.

The following Examples 1 and 2 provide electromagnetic wave absorbing materials, and the raw materials used in Examples 1 and 2 are commercially available raw materials commonly used in industry.

Example 1
The electromagnetic wave absorbing material of Example 1 includes a soft magnetic alloy and a polymer elastomer, the soft magnetic alloy is a sendust alloy, and the polymer elastomer is polyurethane. The preparation method includes the following steps:
S1 raw material blending: a step of uniformly mixing sendust alloy powder and polyurethane to obtain a raw material mixture with a mass ratio of sendust alloy powder to polyurethane of 85:15;
S2 slurry stirring: adding the raw material mixture to a stirrer, then adding methyl isopropyl ketone, dispersant BYK-110, antifoaming agent BYK-141, leveling agent BYK-330, and SDBS, and mixing the raw material mixture, methyl isopropyl ketone, dispersant BYK-110, antifoaming agent BYK-141, leveling agent BYK-330, and SDBS in a mass ratio of 100:150:1:0.8:0.5:0.3:0.3, and stirring thoroughly until uniform, to produce a slurry;
S3 Slurry application: The slurry is applied onto a protective film, and spread evenly over the surface of the protective film with a scraper. The temperature of the application is set to 100°C, and the speed is set to 1 m/min. After drying, a dry film is obtained.
S4 Dry film lamination: The dried film is placed into a laminator after drying, and the temperature is set to 160°C and the pressure to 15 MPa to densify it to form an electromagnetic wave absorbing material; and S5 Die-cutting: The laminated electromagnetic wave absorbing material is cut according to the design requirements to obtain the required size and shape.

Example 2
The electromagnetic wave absorber of Example 2 includes a soft magnetic composite material and a polymer elastomer, and polyurethane is used as the polymer elastomer. The preparation method includes the following steps:
Preparation of S1 soft magnetic composite material: 12.612 g of ammonium formate powder was added to 1 L of deionized water solution, and after dispersion, formic acid solution was added to adjust the pH to 4.4 to obtain an ammonium formate solution. The ammonium formate solution, soft magnetic alloy powder, and aluminum sulfate were mixed in a mass ratio of 506:6:3 and ultrasonically dispersed for 15 minutes to obtain a mixed solution. This mixed solution was heated to 75°C in a water bath, kept at that temperature, and reacted with stirring for 1.5 hours. After washing multiple times with ethanol and magnetic separation, the mixture was dried in an oven at 45°C for 23 days and then annealed at 380°C for 2 hours to obtain a soft magnetic alloy powder coated with _{an Al2O3} layer _. The soft magnetic alloy powder coated with _{the three} layers is spread evenly on a quartz boat, then placed in a CVD rotary tubular furnace, and heated to 400°C at a rate of 5°C/min under an argon protective atmosphere with a gas flow rate of 50 to 100 mL/min. Acetylene gas is then introduced at a flow rate of 25 mL/min to react for 1 hour to produce an amorphous carbon layer. After the reaction is complete, the acetylene gas is stopped and the material is slowly cooled to 25°C and taken out to obtain a soft magnetic composite material. As shown in Figure 2, the soft magnetic composite material comprises, from the inside to the outside, a soft magnetic alloy layer a, an Al ₂ O ₃ layer b, and an amorphous carbon layer c,
S2 raw material blending: A step of uniformly mixing a soft magnetic composite material and polyurethane to obtain a raw material mixture with a mass ratio of soft magnetic composite material to polyurethane of 88:12;
S3 slurry stirring: adding the raw material mixture to a stirrer, then adding methyl isopropyl ketone, dispersant BYK-110, antifoaming agent BYK-141, leveling agent BYK-330, and SDBS, and mixing the raw material mixture, methyl isopropyl ketone, dispersant BYK-110, antifoaming agent BYK-141, leveling agent BYK-330, and SDBS in a mass ratio of 100:145:0.8:0.8:0.6:0.4:0.3, and stirring thoroughly until uniform, to produce a slurry;
S4 Slurry application: The slurry is applied onto the protective film and spread evenly over the surface of the protective film with a scraper, and the application temperature is set to 105°C and the speed is set to 1 m/min;
S5 Dry film lamination: The dried film is placed into a laminator, and the temperature is set to 165°C and the pressure to 15Mpa, and the dried film is rapidly dried to form an electromagnetic wave absorber; and S6 Die-cutting: The laminated electromagnetic wave absorber is cut according to the design requirements to obtain the required size and shape.

Measurement of electromagnetic wave absorption properties: The electromagnetic parameters of the Sendust alloy of Example 1 and the soft magnetic composite material of Example 2 were measured using a vector analyzer, with the measurement frequency band being 0.5 to 18 GHz.

For the measurements, the Sendust alloy of Example 1 and the soft magnetic composite material of Example 2 were made into coaxial rings. Specifically, paraffin, the Sendust alloy of Example 1, and the soft magnetic composite material of Example 2 were thoroughly mixed in a mass ratio of 1:1 until homogeneous, and a coaxial ring with a thickness of approximately 2.5 mm, an inner diameter of approximately 3.0 mm, and an outer diameter of approximately 7.0 mm was fabricated.

Electromagnetic wave absorption property measurement results: Generally speaking, if RL<-10 dB, the material is considered to have an effective electromagnetic wave absorption bandwidth. In the frequency range of 0.5 to 18.0 GHz, the RL value of the sendust alloy of Example 1 was less than -10 dB in a bandwidth of less than 0.2 GHz, indicating that the sendust alloy of Example 1 has significant limitations in its practical application. The soft magnetic composite material of Example 2 had an RLmin of -23.9 dB at 6.8 GHz, and the effective electromagnetic wave absorption bandwidth could reach 3.4 GHz.

The above-mentioned measurement results of the electromagnetic wave absorption properties _show that the two-dimensional sheet-like multilayer structure of the soft magnetic composite material synthesized by first coating _Al2O3 by the sol-gel method and then coating an amorphous carbon layer by the CCDV method has significantly improved minimum microwave loss value RLmin and effective bandwidth, etc., compared with the two-dimensional sheet-like single-layer structure of the Sendust alloy of Example 1, and the electromagnetic wave absorption properties of the electromagnetic wave absorbing powder have been greatly improved.

SEM Characterization: SEM characterization was performed on the electromagnetic wave absorbers of Examples 1 and 2. Figures 3 and 4 show that the electromagnetic wave absorbers of Examples 1 and 2 are both made by stacking and flatly spreading electromagnetic wave absorbing powder with a two-dimensional sheet structure, and that the electromagnetic wave absorbing powder is blocked by the polymer elastomer interposed between the electromagnetic wave absorbing powder, preventing electrical continuity between the electromagnetic wave absorbing powder. The electromagnetic wave absorbing powder in the electromagnetic wave absorbers of Examples 1 and 2 has a smooth surface and is irregularly flaky in shape, indicating that the soft magnetic composite material coated using the sol-gel and CCVD methods has a good enveloping effect and can maintain the stability of its basic shape.

Measurement of magnetic permeability and inductance values: With reference to GB/T32596, the magnetic permeability and inductance values of the electromagnetic wave absorbers of Examples 1 and 2 were measured. The thicknesses were 0.1 mm and 0.08 mm, respectively. The measurement results are shown in Table 1.

From Table 1, we can see that when the thickness is approximately 0.08 mm, the magnetic permeability of Examples 1 and 2 is 221.4 and 220.5, respectively, and the inductance values are 368 μH and 353 μH, respectively; and when the thickness is approximately 0.1 mm, the magnetic permeability of Examples 1 and 2 is 151.2 and 150.7, respectively, and the inductance values are 365 μH and 352 μH, respectively.

Corrosion resistance measurement: Electrochemical corrosion parameters were calculated using electrochemical corrosion analysis. The measurement device was an electrochemical workstation. A three-electrode system was used for all measurement processes, with a silver chloride electrode as the reference electrode and a platinum electrode as the auxiliary electrode. Samples 1 to 4 were placed on copper foil to create the working electrode. The measurement results are shown in Table 2.

From Table 2, it can be seen that the electromagnetic wave absorber of Example 1 uses a sendust alloy as the electromagnetic wave absorbing powder, and its natural corrosion potentials E _corr are −0.31 V and −0.33 V, its corrosion current densities i _corr are 5.12×10 ⁻⁶ A/cm ² and 5.12×10 ⁻⁶ A/cm ² , its polarization resistances Rp are 1.75×10 ⁵ Ω/cm ² and 1.97×10 ⁵ Ω/cm ₂ , and its corrosion rates CR are 1.87×10 ⁻¹² m/s and 2.03×10 ⁻¹² m/s. The electromagnetic wave absorber of Example 2 uses a sendust alloy coated with _three layers of Al ₂ O and an amorphous carbon layer as the electromagnetic wave absorbing powder, and its natural corrosion potential E _corr increases to -0.05 V and -0.04 V, its corrosion current density i _corr decreases to 1.12×10 ^-6 A/cm ² and 1.08×10 _-6 A/cm ² , its polarization resistance Rp increases to 9.74×10 ⁵ Ω/cm ² and 19.82×10 ⁵ Ω/cm ² , and its corrosion rate CR decreases to 2.98×10 ^-13 m/s and 3.01×10 _-13 m/s, indicating that the electromagnetic wave absorber of Example 2 has better corrosion resistance and can have a longer life in various environments.

The following Comparative Example 1, Example 3, Example 4, Example 4, and Example 5 provide NFC antennas for mobile phones. The materials used in Comparative Example 1, Example 3, Example 4, Example 4, and Example 5 were commercially available raw materials commonly used in industry.

(Comparative Example 1)
The NFC antenna for a mobile phone of Comparative Example 1 comprises an NFC antenna main body 1 and a metal bottom plate 3, the coil inductance value of the NFC antenna main body 1 is 1.7 μH, the sensing distance is 3.67 mm, and the metal bottom plate 3 is made of aluminum foil material (simulating a battery exterior material) with a thickness of 0.05 mm, and the NFC antenna main body 1 and the metal bottom plate 3 are assembled to obtain the NFC antenna for a mobile phone of Comparative Example 1.

Example 3
As shown in FIG. 1 , the NFC antenna for a mobile phone of Example 3 comprises an NFC antenna main body 1, an electromagnetic wave absorbing material layer 2, and a metal bottom plate 3, the coil inductance value of the NFC antenna main body 1 is 1.7 μH, the sensing distance is 3.67 mm, the electromagnetic wave absorbing material layer 2 is made of the electromagnetic wave absorbing material of Example 1 and has a thickness of about 0.08 mm, and the metal bottom plate 3 is made of aluminum foil material with a thickness of 0.05 mm, and the NFC antenna main body 1, the electromagnetic wave absorbing material layer 2, and the metal bottom plate 3 are assembled in this order to obtain the NFC antenna for a mobile phone of Example 3.

Example 4
As shown in FIG. 1 , the NFC antenna for a mobile phone of Example 4 comprises an NFC antenna main body 1, an electromagnetic wave absorbing material layer 2, and a metal bottom plate 3, the coil inductance value of the NFC antenna main body 1 is 1.7 μH, the sensing distance is 3.67 mm, the electromagnetic wave absorbing material layer 2 is made of the electromagnetic wave absorbing material of Example 1 and has a thickness of about 0.1 mm, and the metal bottom plate 3 is made of aluminum foil material with a thickness of 0.05 mm, and the NFC antenna main body 1, the electromagnetic wave absorbing material layer 2, and the metal bottom plate 3 are assembled in this order to obtain the NFC antenna for a mobile phone of Example 4.

Example 5
As shown in FIG. 1 , the NFC antenna for a mobile phone of Example 5 comprises an NFC antenna main body 1, an electromagnetic wave absorbing material layer 2, and a metal bottom plate 3, the coil inductance value of the NFC antenna main body 1 is 1.7 μH, the sensing distance is 3.67 mm, the electromagnetic wave absorbing material layer 2 is made of the electromagnetic wave absorbing material of Example 2 and has a thickness of about 0.08 mm, and the metal bottom plate 3 is made of aluminum foil material with a thickness of 0.05 mm, and the NFC antenna main body 1, the electromagnetic wave absorbing material layer 2, and the metal bottom plate 3 are assembled in this order to obtain the NFC antenna for a mobile phone of Example 5.

Example 6
As shown in FIG. 1 , the NFC antenna for a mobile phone of Example 6 comprises an NFC antenna main body 1, an electromagnetic wave absorbing material layer 2, and a metal bottom plate 3, the coil inductance value of the NFC antenna main body 1 is 1.7 μH, the sensing distance is 3.67 mm, the electromagnetic wave absorbing material layer 2 is made of the electromagnetic wave absorbing material of Example 2 and has a thickness of about 0.1 mm, and the metal bottom plate 3 is made of aluminum foil material with a thickness of 0.05 mm, and the NFC antenna main body 1, the electromagnetic wave absorbing material layer 2, and the metal bottom plate 3 are assembled in this order to obtain the NFC antenna for a mobile phone of Example 6.

Antenna test: Refer to ISO/IEC 14443, and use a digital bridge with LCR 100 kHz. The test results are shown in Table 3.

The coil inductance value of the NFC antenna main body 1 was 1.7 μH, and the sensing distance was 3.67 mm. As can be seen from Table 3, when the NFC antenna main body 1 was assembled with the metal bottom plate 3 (Comparative Example 1), the metal reflected and absorbed radio waves, causing the metal bottom plate 3 to interfere with the NFC signal, resulting in a decrease in inductance value to 1.58 μH and a decrease in sensing distance to 1.01 mm.

An electromagnetic wave absorbing material layer 2 is provided between the NFC antenna main body 1 and the metal bottom plate 3 (Examples 3 to 5). In all of Examples 3 to 5, interference from the metal bottom plate 3 is effectively isolated from the NFC antenna main body 1, thereby improving the signal quality of the NFC antenna main body 1. The inductance values of Examples 5 and 6, which use the electromagnetic wave absorbing material of Example 2, are 1.71 μH and 1.73 μH, respectively, which are close to the coil inductance value of the NFC antenna main body 1. The sensing distances are 3.56 mm and 3.52 mm, respectively, which are close to the sensing distance of the NFC antenna main body 1. This indicates that Examples 5 and 6 have better compatibility between the NFC antenna main body 1 and the metal bottom plate 3, resulting in better magnetic shielding and electromagnetic wave absorption effects.

The specific applications of the present invention are numerous, and the above are merely preferred embodiments of the present invention. Please note that the above examples are used only to interpret the present invention and are not intended to limit the scope of protection of the present invention. Those skilled in the art may make some improvements without departing from the principles of the present invention, and these improvements should also be considered within the scope of protection of the present invention.

REFERENCE SIGNS LIST 1 NFC antenna body 2 Electromagnetic wave absorbing material layer 3 Metal bottom plate a Soft magnetic alloy b Al ₂ O ₃ layer c Amorphous carbon layer

Claims (9)

An NFC antenna for a mobile phone, comprising an NFC antenna main body (1), an electromagnetic wave absorbing material layer (2), and a metal bottom plate (3), wherein the electromagnetic wave absorbing material layer (2) is provided on the metal bottom plate (3), the NFC antenna main body (1) is provided on the electromagnetic wave absorbing material layer (2), the electromagnetic wave absorbing material layer (2) is a film or sheet made of an electromagnetic wave absorbing material, the electromagnetic wave absorbing material contains electromagnetic wave absorbing powder and a polymer elastomer and has a two-dimensional sheet-like structure in which the electromagnetic wave absorbing powder is spread evenly within the polymer elastomer, the electromagnetic wave absorbing powder is a soft magnetic composite material , the mass ratio of the polymer elastomer is 10-20:1-5, and the soft magnetic composite material contains, from the inside to the outside, a soft magnetic alloy, an Al ₂ O ₃ layer , and an amorphous carbon layer. 2. The NFC antenna for a mobile phone according to claim 1, wherein the electromagnetic wave absorbing powder has a powder thickness in a height direction of 0.5 to 1.5 μm and a median particle diameter D50 in a width direction of 30 to 100 μm. The NFC antenna for a mobile phone described in claim 1, characterized in that the soft magnetic alloy is at least one selected from the group consisting of an iron-silicon-aluminum soft magnetic alloy, an iron-silicon soft magnetic alloy, an iron-nickel soft magnetic alloy, an iron-nickel-molybdenum soft magnetic alloy, an iron-aluminum soft magnetic alloy, an iron-silicon-aluminum-nickel soft magnetic alloy, an iron-chromium soft magnetic alloy, and an iron-cobalt soft magnetic alloy. The NFC antenna for a mobile phone described in claim 1, characterized in that the inductance value of the antenna coil of the NFC antenna main body (1) is 1.6 to 2.0 μH. The NFC antenna for a mobile phone described in claim 1, characterized in that the electromagnetic wave absorbing material is made by stacking and spreading out the electromagnetic wave absorbing powder in a two-dimensional sheet-like structure, and the polymer elastomer is interposed between the electromagnetic wave absorbing powder to block the flow of the electromagnetic wave absorbing powder, thereby preventing electrical continuity between the electromagnetic wave absorbing powder. The NFC antenna for a mobile phone described in claim 1, characterized in that the polymer elastomer is at least one of polyurethane, acrylic acid, organosilicon, and epoxy resin. A method for preparing an electromagnetic wave absorber for an NFC antenna for a mobile phone according to any one of claims 1 to 6, comprising:
a raw material blending step S1 in which an electromagnetic wave absorbing powder having a bulk density of 0.2 to 0.7 g/cm ³ and a tap density of 0.6 to 2.0 g/cm ³ and a polymer elastomer are uniformly mixed to obtain a raw material mixture;
a slurry stirring step S2 in which the raw material mixture is added into a stirrer, a solvent and an auxiliary component are then added, and the mixture is mixed in a mass ratio of the solvent, the raw material mixture, and the auxiliary component of 40 to 80:10 to 50:0.5 to 2, and the mixture is thoroughly stirred until homogeneous, thereby producing a slurry having a viscosity of 1500 to 2000 mPa s;
a slurry application step S3 in which the slurry is applied onto a protective film, spread evenly over the surface of the protective film with a scraper, and the application temperature is set to 50 to 120°C and the speed is set to 0.5 to 4 m/min, and a dry film is obtained after drying;
a dry film lamination step S4 in which the dried dry film is placed in a laminator, and the temperature is set to 150 to 180°C and the pressure is set to 10 to 20 MPa to densify the dry film to form an electromagnetic wave absorbing material;
a die-cutting step S5 of cutting the laminated electromagnetic wave absorbing material according to design requirements to obtain a required size and shape. The method for preparing an electromagnetic wave absorbing material for an NFC antenna for a mobile phone described in claim 7, characterized in that the solvent in step S2 is one of methyl isopropyl ketone, acetone, cyclohexanone, and DMF, and the auxiliary component is at least one of a dispersant, an antifoaming agent, a leveling agent, and a surfactant. The electromagnetic wave absorbing powder is a soft magnetic composite material, and the preparation method thereof includes the steps of:
a step S1 of mixing an ammonium formate solution, soft magnetic alloy powder, and aluminum sulfate, and ultrasonically dispersing the mixture for 10 to 3 minutes to obtain a mixed solution, heating the mixed solution in a water bath at 75 to 85°C, maintaining the mixed solution at that temperature and stirring for 1 to 2 hours to cause a reaction, washing the mixed solution multiple times with ethanol, magnetically separating the mixed solution, drying the mixed solution in an oven at 40 to 50°C for 1 to 3 days, and then annealing the mixed solution at 350 to 450°C for 2 hours to obtain a soft magnetic alloy powder coated with an Al ₂ O ₃ layer;
and step S2 of spreading the soft magnetic alloy powder coated with the Al ₂ O ₃ layer evenly on a quartz boat, then placing it in a CVD rotary tubular furnace, heating it to 400°C at 3-6°C/min under an argon protective atmosphere with a gas flow rate of 50-100 mL/min, then introducing acetylene gas at a flow rate of 20-30 mL/min to react for 0.5-1 hour, and after completion of the reaction, stopping the acetylene gas, slowly cooling it to 25°C, and removing it to obtain the soft magnetic composite material.