KR20130035747A - Antenna of ferrite crystal - Google Patents

Abstract

PURPOSE: An antenna using monocrystal ferrite is provided to maximize miniaturization while maintaining antenna gain over a certain level and to increase the bandwidth thereof. CONSTITUTION: Ferrite made of a single monocrystal is used as an antenna substrate and can be expressed as MFe12-xMexO19 in a chemical formula. The M is at least one type of element selected from Sr, Ba, and Pb; the Me is at least one metal selected from a group composed of Co, Ti, Ni, and Zn: and the x is equal to or greater than 0, and equal to or less than 2. M-type hexaferrite is used as the ferrite.

Description

Antenna using single crystal ferrite {Antenna of Ferrite crystal}

The present invention relates to an antenna using single crystal ferrite.

As shown in Fig. 1, the antenna is composed of a radiator, which is a metal conductor, and a support thereof made of plastic, ceramic, or the like.

Among them, radiator is a part where high frequency current flows, so it is designed in proper shape and structure in order to obtain specific frequency characteristics of antenna, and support plays a role of focusing electromagnetic field induced by current flowing in radiator. This may affect the speed of the current flowing through the radiator.

Accordingly, when the substrate has a high permeability μ or dielectric constant ε, the resonance frequency f _r of the antenna is lowered compared to when it is not, and miniaturization of the antenna can be achieved.

The following equation is a well-known formula for the relationship between wavelength (λ) derived from Maxwell's theory of electromagnetic waves, permeability, permittivity, and resonant frequency.

(One)

λ, λ / 2, λ / 4: antenna length, c : speed of light

Recently, in accordance with the trend of miniaturization of devices requiring an antenna, research on an antenna having small size and excellent performance has been continued.

There are two ways to achieve miniaturization of the antenna.

First, according to Equation 2, by increasing the length of the radiator to increase the inductance ( L ), or by increasing the capacitance ( C ) by reducing the gap of the patch antenna (gap; distance between the radiator and ground) This method reduces the LC resonance frequency.

(2)

If the resonance frequency is lowered, the antenna can be miniaturized, but in order to increase the length of the radiator within a predetermined volume, the radiator has a line shape and the line gap is tight. In this case, the electromagnetic radiation of the antenna is disturbed to each other, and thus the radiation efficiency is not good, and if the gap between the radiator and the ground is reduced to increase the capacitance, the electromagnetic radiation energy of the antenna is reduced. Since most of them go out to the ground, radiation efficiency becomes poor and the bandwidth of the antenna is reduced.

Therefore, there is a limit in degrading the performance (radiation efficiency, bandwidth) of the antenna in the method of miniaturizing the antenna only by design conditions such as the shape or length of the radiator.

The antenna was miniaturized by increasing the dielectric constant of the radiator. However, in this case too, the bandwidth is greatly reduced, so it is rare to increase the permittivity by more than 10. Equation (3) below represents the relationship between bandwidth (BW) and permeability, permittivity, distance between radiator and ground (t), and resonant wavelength (λ = c / f _r ).

In the following equation, it can be seen that as the permittivity increases, the BW decreases, and when the permeability increases, the sacrifice of the BW decreases more than when the permittivity is increased.

(3)

Therefore, when using permeability at the same time rather than using only the permittivity of the substrate (substrate), it is possible to increase the miniaturization rate of the antenna and to minimize the sacrifice of antenna performance due to miniaturization.

As such, a substrate material having both permeability and permittivity should have a low loss characteristic at the operating frequency of the antenna, and recently, ferrite has attracted attention.

Ferrite is a solid solution in which alloying elements or impurities are dissolved in iron of body-centered cubic crystals which are stable at 900 ° C or lower. As a metallographic term for steel, since it is a solid solution based on α iron, its appearance is the same as pure iron, but it is also called silicon ferrite or silicon iron by the name of the element dissolved. Under a microscope, it is a single phase, and a mixture of the white part of ferrite and the black part of pearlite where carbon is slightly dissolved appears. Ferrites are used in magnetic heads such as high frequency transformers, pickups and tape recorders.

In the case of using ferrite as a support material, it is possible to determine the characteristics of the required ferrite through the following formula.

As shown in Equation (4), the radiation efficiency (η) of the antenna is inversely proportional to the power loss ( P _Ω ). Equation (5) describes the term for radiated power, Equation (6) shows the relationship between power loss for R _c and R _m , and Equation (7) for R _{m in terms} of frequency and permeability loss. It shows that it is a related function.

(4)

(5)

(6)

(7)

Where P _rad : radiated power, P _acc : accepted power P _Ω power loss, E _c : radiated electric field from radiator, E _m : radiated electric field from ferrite core, I _c : electric current in the radiator, I _m : induced magnetic current in the ferrite core, R _c : ohmic resistance of the radiator, R _m : Resistance associated with the losses in the ferrite core, ω: angular frequency.

Therefore, in order to obtain the high radiation efficiency of the antenna, it can be seen that ferrite, which is a support material, should have a low permeability loss value at the operating frequency.

The operating frequency of the mobile phone main antenna is in the low band 700 ~ 960 MHz band, the high band is 1700 ~ 2200 MHz. In addition, since GPS 1.575 GHz, BlueTooth and W-LAN are 2.45 GHz, except for T-DMB and UWB, the 700 ~ 2500 MHz band is a frequency band related to mobile phone service.

The ferrite material that can be used as a low permeability loss in the corresponding frequency band is hexagonal ferrite, and among these hexagonal ferrites, Z-type hexagonal ferrite is soft magnetic. (soft magnetic) characteristics, so there is an example developed by utilizing as a GHz antenna support (substrate), as shown in Documents 1 to 3 below.

1.US 7786947, S. Bae, et al., "Broad-band antenna"

2. US 7324063, S. Bae, et al., "Retangular helical antenna"

3.US 7345650, S. Bae, et al., "Internal chip antenna

In addition, Y-type hexagonal ferrite (Y-type hexagonal ferrite) also has a lower permeability than the Z-type hexagonal ferrite (Z-type hexagonal ferrite), but can be used as a GHz antenna, there is a case developed as shown in Document 4 below.

4.US 2011/0025572 A1, JH Lee, et al., "Y-type hexagonal ferrite, fabrication method according, and antenna apparatus using the same"

However, the above-mentioned hexagonal ferrites for antenna materials are manufactured using a ceramic process or a chemical route process such as co-precipitation or sol-gel, and have a polycrystalline structure.

When the ferrite of such a polycrystalline structure is applied as an antenna material, there is a disadvantage in that the frequency and permeability are small, the antenna gain does not reach a satisfactory level, and the improvement in gain BW (gain bandwidth) is required.

The present invention has been devised to supplement the prior art as described above. The present invention provides a miniaturization (volume <2 cc) while maintaining an antenna gain of a certain level (average gain> -2 dB). The purpose is to provide an antenna that can be maximized and increased in bandwidth.

The present invention has been made to solve the above problems

Provided is a small antenna characterized by using a ferrite made of a single crystal as an antenna substrate.

In addition, the ferrite consisting of one single crystal is preferably M-type hexaferrite.

In addition, the ferrite consisting of one single crystal is preferably represented by the following formula (1).

[Formula 1] MFe _{12 - x} Me _x O ₁₉

M is at least one element selected from Sr, Ba and Pb, Me is at least one metal selected from the group consisting of Co, Ti, Ni, and Zn, and 0 ≦ x ≦ 2.

In addition, the ferrite consisting of one single crystal may be a hexagonal ferrite (hexagonal ferrite).

Furthermore, the ferrite composed of one single crystal has a liquid growth method, a Czochralski method, a Bridgman growth method, a floating zone method, and a solid state single crystal growth method. single crystal growth method) may be prepared through any one of the selected method.

In addition, the ferrite made of one single crystal may be processed into a ferrite block, and then manufactured in a ferrite matrix having a required size by combining a plurality of ferrite blocks.

The present invention also provides a device including the small antenna,

The device may be any one selected from the group consisting of a portable cordless phone, a notebook and a transistor.

The following effects can be expected through the single crystal ferrite antenna according to the present invention.

The single crystal ferrite applied to the antenna according to the present invention has a frequency that can be utilized for the antenna more than seven times larger than that of the polycrystalline ferrite, and also has a higher permeability than the polycrystalline ferrite. In addition, the single crystal ferrite antenna of the present invention can increase the antenna gain (gain) by 1 dB or more than the polycrystalline ferrite antenna, and further has an effect of significantly increasing the gain BW (gain bandwidth) than the polycrystalline ferrite antenna.

1 and 2 are graphs showing calculated complex effective permeability ( μ _eff ) and loss values (loss tan σ = μ _{eff ''} / μ _{eff '} ) for the ferrite frequency.
3 and 4 are graphs showing the effective permeability and losses for various α in single crystal ferrite, respectively.
5 and 6 are schematic diagrams of device components to which a single crystal ferrite antenna according to an embodiment of the present invention is applied.
7 is a graph measuring reflection characteristics of antennas manufactured in Examples 1 to 3 and Comparative Examples 1 and 2;
8 to 10 are graphs measuring gain patterns of YZ-plane (H), XZ-plane (E1), and XY-plane (E2), respectively, at a center frequency of 830 MHz.
11 to 13 are graphs for calculating average gains for YZ-plane (H), XZ-plane (E1), and XY-plane (E2) according to frequency.
14 to 16 are graphs for calculating maximum gains for YZ-plane (H), XZ-plane (E1), and XY-plane (E2) according to frequency.

The present invention provides a small antenna characterized by using a ferrite consisting of a single crystal as an antenna support to solve the above problems.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated concretely.

Hexagonal ferrites used for the conventional small antenna materials mentioned above are used by sintering ferrite powder produced by a chemical route process such as ceramic process or coprecipitation method or sol gel method. There was a problem with the polycrystalline structure.

Two mechanisms are involved in the high frequency loss of ferrite.

One is the loss of magnetic domain rotation, which is dominant in the band below several hundred MHz, and the second is the loss of magnetic spin rotation, which is dominant above several hundred MHz.

High frequency switching is easy when the magnetic domain rotation occurs easily, but when the magnetic domain rotation is disturbed by impurities, grain boundary precipitates, defects, stresses, etc., more energy is used for magnetic domain rotation, leading to energy loss. This can be expressed by the magnetic domain damping constant β.

In addition, if the spin rotation is interrupted by defects, grain boundaries, impurities, etc., the energy loss value is also increased, and thus it can be expressed as a spin damping constant α (magnetic spin damping constant).

These α and β are intrinsic values of ferrite, which depend on defect density and grain boundary distribution, which means that a large part of ferrite properties can be controlled by the process.

In mobile phone antennas utilizing the 700 ~ 2500 MHz frequency, α is the mechanism mainly responsible for the loss of ferrite. In other words, lowering α can reduce loss of ferrite at high frequencies and can be used as an antenna support.

However, it is known that α is about 0.1 to 1 in a bulk state, and about 0.01 to 0.1 in a thin film process because polycrystalline ferrite is formed as a known general ferrite process. However, since the thin film process is difficult to utilize in a ferrite antenna, it is reasonable to assume that the α value, that is, 0.1 to 1 value can be obtained in the bulk block state.

The complex permeability of the ferrite frequency can be calculated using the Landau-Lifshitz-Gilbert equation (LLG equation).

Equations (8) and (9) below are simplified LLG equations, omitting β.

(8)

(9)

Equation (10) was used to convert the complex permeability calculated using Equations (8) and (9) into an effective permeability, and 0.333 (assuming perfect sphere) was used for the demagnetization factor. .

(10)

The complex permeability and the loss value calculated by using Equation (10) were respectively calculated and described in FIGS. 1 and 2.

1 and 2 attached below show the calculated effective permeability ( μ _eff ) and the loss value (loss tan σ = μ _{eff ' '} / μ _{eff '} ).

H _k is anisotropic magnetic field and in the case of ferrite material, it is a controllable variable from 0 to 3000 Oe. Constants γ = 1.75 x 10 ⁷ , α = 0.1, M _s = 300 emu / cc were used for the calculation.

The calculated results show that the effective permeability is inversely proportional to the anisotropic field ( H _k ). In addition, the loss value tan σ is proportional to H _k , but when the loss is low, the effective permeability is also lowered, which makes it difficult to expect a large effect on the miniaturization of the antenna.

Therefore, it is impossible to derive the maximum characteristics of the ferrite material for the antenna only by the control of H _k .

Thus, in Figures 3 and 4 below, the effective permeability and loss graphs for various α are calculated and described.

As can be seen in the graphs of FIGS. 3 and 4 attached below, it can be noted that the loss tan σ graph is suppressed close to zero when α 0.001 to 0.01, which is a level obtained from single crystal ferrite.

This means that when α = 0.01, the effective permeability 4.1 can be kept below 0.01 GHz to 3.2 GHz, and when α = 0.001, the effective permeability 4.1 can be kept below 0.01 by 6.2 GHz.

However, in the polycrystalline state α = 0.1, a loss of 0.01 can be achieved below 452 MHz. That is, in the case of single crystal ferrite, the antenna usable frequency range is increased by at least 7 times than polycrystalline ferrite.

Accordingly, the present invention provides an antenna using such a single crystal ferrite.

5 and 6 illustrate an example of designing an inverted F antenna of a simple type that is widely employed in a mobile phone main antenna using single crystal ferrite as an exemplary embodiment of the present invention.

However, the antennas shown in FIGS. 5 and 6 are only for showing the application of the single crystal ferrite according to the present invention, and other design techniques for improving the antenna characteristics have not been used. It is not limited to the drawings shown.

Meanwhile, the ferrite made of one single crystal applied to the small antenna according to the present invention is not particularly limited, but may be preferably M-type hexaferrite.

The single crystal ferrite to be applied to the present invention does not specifically specify the composition as long as it consists of one single crystal, and all ferrites of various compositions may be applied, and may be appropriately selected according to required properties in a general composition range.

If the oxides as the main components are Fe ₂ O ₃ , NiO, CuO and ZnO, respectively, the general composition of these components is as follows:

Fe ₂ O ₃ : 35-50 mol%, NiO: 4-50 mol%, CuO: 4-16 mol%, and ZnO: 5-40 mol% That is, the single crystal ferrite according to the present invention has a Fe ₂ O ₃ content Many high permeability materials or low permeability materials with low Fe ₂ O ₃ content are also possible, and the reason for limiting the content of the main component oxide is as follows.

If the amount of Fe ₂ O ₃ is too small, the amount of nonmagnetic phase produced increases, causing an increase in loss. If the amount of Fe ₂ O ₃ is excessively large, the sinterability is remarkably deteriorated.

On the other hand, if the amount of NiO is too small, the loss becomes large, and if the amount of NiO is too large, it becomes expensive. Furthermore, when there is too little CuO, sinterability will worsen, and when there is too much CuO, since NiO will become comparatively small, a loss will increase. In addition, when there is too little ZnO, permeability will become low, and when there is too much ZnO, curie temperature will become too low.

In the ferrite powder, other metal oxides such as Co, W, Bi, Si, B, Mn, Zr, Ca, Ta, Mo, P, Y, Mg, as addition components or inevitable components, in addition to the main component oxide, May be included as needed.

Preferably, the single crystal ferrite of the present invention may be represented by the following formula (1).

[Formula 1] MFe _{12 - x} Me _x O ₁₉

M is at least one element selected from Sr, Ba and Pb, Me is at least one metal selected from the group consisting of Co, Ti, Ni, and Zn, and 0 ≦ x ≦ 2.

Furthermore, the ferrite consisting of one single crystal according to the present invention may be more preferably hexagonal ferrite (hexagonal ferrite).

The production method of the single crystal ferrite according to the present invention is not particularly limited and may be prepared using a known method, for example, a liquid growth method, a Czochralski method, and Bridman. It may be prepared by any one method selected from a growth method (Bridgman growth method), (Floating zone method), a solid state single crystal growth method (Solid state single crystal growth method).

However, in order to increase the crystallinity and reproducibility of the single crystal ferrite and to obtain a ferrite single crystal having more excellent physical properties, it is more preferable in terms of the effect and the manufacturing cost among the above-mentioned methods.

In this case, the ferrite made of one single crystal is preferably used by growing into a single crystal of a desired size, but more preferably, a ferrite block made of a small size is prepared, and then a plurality of the ferrite blocks are combined to form a ferrite matrix of a desired size. Make and use.

In this case, the ferrite block is preferably manufactured in a small unit so as to produce a ferrite matrix of various sizes by a combination, it can be variously combined to produce a ferrite matrix of a desired size using this.

The present invention further provides a device including a small antenna using the single crystal ferrite, wherein the device may be any one selected from the group consisting of a portable wireless telephone, a notebook, a transistor, and the like, but is not limited thereto.

Hereinafter, the present invention will be described in more detail with reference to specific examples.

Example  One

These oxides were weighed to a ratio of 49 mol% Fe ₂ O ₃ , 18 mol% NiO, 12 mol% CuO, and 21 mol% ZnO, and wet-mixed for 4 hours using a wet media stirring grinder. Pure water was used as the dispersion medium in this wet mixing.

Subsequently, the mixture was dried with a spray dryer and calcined at 700 ° C. for 2 hours to obtain a calcined product of Ni—Cu—Zn ferrite.

This calcined product was mixed with pure water to prepare a slurry for grinding. Solid content (plastics) concentration in this grinding | pulverization slurry was 25 weight%.

The slurry for grinding was pulverized with a wet media stirring grinder for 7 hours, and then dried with a spray dryer to obtain Ni-Cu-Zn ferrite powder.

By this grinding | pulverization, the specific surface area of the ferrite powder became 4.4 m <2> / g (average particle diameter 1.4 micrometers). The ferrite powder prepared as described above was grown by Bridgman's growth method to prepare single crystal ferrite, and the permeability, permittivity, and their respective loss values are shown in Table 1 below.

In addition, a small antenna of 30 x 5 x 3 mm ² size and 0.45cc volume using the prepared single crystal ferrite was applied to the mobile phone.

Example  2

By varying the material and single crystal growth conditions, single crystal ferrite was prepared in the same manner as in Example 1, and the permeability, permittivity, and respective loss values of the single crystal ferrite thus prepared are shown in Table 1 below. A small antenna was manufactured under the same conditions as 1 and applied to a mobile phone.

Example  3

The single crystal ferrite was prepared in the same manner as in Example 1 by varying the material and the single crystal growth conditions, and the permeability, permittivity, and respective loss values of the single crystal ferrite thus prepared are shown in Table 1 below, Example 1 A small antenna was manufactured under the same conditions as the above and applied to a mobile phone.

Comparative example  One

The ferrite of the polycrystal was obtained using a ferrite powder material of the same composition as in Example 1, the permeability and permittivity of the polycrystalline ferrite and their respective loss values are described in Table 1 below, under the same conditions as in Example 1 Small antennas were manufactured and applied to mobile phones.

Comparative example  2

Ferrite of polycrystalline was obtained by the same method as Comparative Example 1, and the polycrystalline ferrite permeability and permittivity and their respective loss values are shown in Table 1 below, and a small antenna was manufactured under the same conditions as in Example 1. Applied to the mobile phone.

Comparative example  3

An antenna support having the same size as that of Example 1 was prepared using a plastic injection molding, and the antenna using the same was applied to a mobile phone.

division Crystal form μ Loss tanδ _μ ε Loss tanδ _ε Example 1 (F1) Single crystal 2.5 0 12 0 Example 2 (F2) Single crystal 2.5 0.01 12 0.01 Example 3 (F3) Single crystal 2.5 0.03 12 0.02 Comparative Example 1 (F4) Polycrystalline 2.5 0.05 12 0.02 Comparative Example 2 (F5) Polycrystalline 2.5 0.1 12 0.02

The reflection characteristics of the antennas were measured by using a mobile phone including the antennas manufactured in Examples 1 to 3 and Comparative Examples 1 and 2, respectively, and are described in FIG. 7.

In addition, graphs measuring the gain patterns of the YZ-plane (H), the XZ-plane (E1), and the XY-plane (E2) at the center frequency of 830 MHz are shown in FIGS. 8 to 10, respectively.

In addition, graphs for calculating average gains for YZ-plane (H), XZ-plane (E1), and XY-plane (E2) according to frequency are described in FIGS. 11 to 13, respectively, and YZ-plane according to frequency. Graphs for calculating the maximum gains for (H), XZ-plane (E1), and XY-plane (E2) are described in FIGS. 14 to 16, respectively.

As a result of comparing the performance of the antenna according to Examples 1 to 3 and Comparative Examples 1 to 3 are shown in Table 2 below.

Material volume Fc AV. Gain Peak gain BW (based on AV.gain> -2dB) Example 1 (F1) Single crystal ferrite 0.45 828 0.885 1.229 455 Example 2 (F2) Single crystal ferrite 0.45 826 0.406 0.746 445 Example 3 (F3) Single crystal ferrite 0.45 828 -0.227 0.109 428 Comparative Example 1 (F4) Polycrystalline ferrite 0.45 828 -0.589 -0.251 417 Comparative Example 2 (F5) Polycrystalline ferrite 0.45 828 -1.217 -0.881 396 Comparative Example 3 Plastic injection molding 2.8 880 -0.6 -0.3 350

The reflection characteristic of the ferrite antenna according to the present invention can be confirmed by the graph of FIG. 7. The center frequency ( f _c ) of the antenna is set to 830 MHz, which is the center of the low band (700 to 960 MHz), indicating that there is no problem in miniaturizing all the ferrite types used in the design. In general, since the main antenna of the mobile phone has a volume of about 2 to 3 cc, the miniaturization rate of the ferrite antenna is very high.

Also, the gain patterns for YZ-plane (H), XZ-plane (E1), and XY-plane (E2) at the center frequency of 830 MHz are confirmed by the graphs shown in FIGS. 8 to 10. Can be. The YZ-plane is important in cell phone antennas, all of which show good omni-directional patterns.

In the graphs illustrated in FIGS. 11 to 13, average gains for the YZ-plane (H), the XZ-plane (E1), and the XY-plane (E2) according to frequencies can be confirmed.

Referring to the graph, it can be seen that an average gain of 1 dB or more is obtained in the case of a single crystal ferrite antenna.

In addition, the graphs described with reference to FIGS. 14 to 16 can confirm the maximum gains for the YZ-plane (H), the XZ-plane (E1), and the XY-plane (E2) according to the frequency. In the case of the single crystal ferrite antenna, it can be seen that a maximum gain of 1 dB or more is also obtained than that of the polycrystalline ferrite antenna.

When calculating the bandwidth based on the average gain, the radiation efficiency of the main antenna of a mobile phone which is generally used is about 35 to 40%, so the gain is about -4 dB. . Considering that each antenna case has 2dB of interference and attenuation in the active state, the antenna in the caseless case can see more than -2 dB as a criterion for bandwidth estimation. In this case, it can be seen that the performance of the single crystal ferrite antenna according to the present invention is significantly superior.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the scope of the present invention is not limited to the disclosed exemplary embodiments but is to be construed as being limited only by the appended claims. Should be construed as being included in the scope of the present invention.

Claims (8)

Small antenna, characterized in that the ferrite consisting of a single crystal as an antenna substrate.
The method of claim 1,
The ferrite consisting of one single crystal is a small antenna, characterized in that the M-type hexaferrite (M-type hexaferrite).
The method of claim 1,
The ferrite consisting of the single crystal is a small antenna, characterized in that represented by the following formula (1).
[Formula 1] MFe _{12 - x} Me _x O ₁₉
M is at least one element selected from Sr, Ba and Pb, Me is at least one metal selected from the group consisting of Co, Ti, Ni, and Zn, and 0 ≦ x ≦ 2.
The method of claim 1,
The ferrite consisting of one single crystal is a small antenna, characterized in that the hexagonal ferrite (hexagonal ferrite).
The method of claim 1,
Ferrite made of one single crystal has a liquid growth method, a Czochralski method, a Bridgman growth method, a floating zone method, and a solid state single crystal. Small growth antenna characterized in that it is manufactured by any one method selected from crystal growth method).
The method of claim 1,
The ferrite made of one single crystal is processed into a ferrite block, and then a plurality of combinations thereof are manufactured in a ferrite matrix of a required size (matrix).
A device comprising the small antenna of claim 1. The method of claim 7, wherein
And the device is any one selected from the group consisting of a portable cordless phone, a notebook and a transistor.

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