Patent Application
20110182763
The present invention relates to a method of manufacturing an electronic component for RF applications comprising a ferrite by sintering, and more particularly to a method of manufacturing an electronic component for RF applications by sintering, in which ammonium alginate is added to the ferrite so that the cohesion of the ferrite can be enhanced to facilitate the molding of the ferrite, the magnetic loss tangent of the ferrite can be reduced and the permeability thereof can be increased.
In general, the term “wireless device” refers to any device capable of transmitting and receiving information anywhere regardless of location, including mobile phones, palm PCs or PDAs (Personal Digital Assistants), or HPCs (Hand-Held Pet). In such wireless devices, antennas for transmitting and receiving electronic information through wireless communication are placed. In such antennas, RF (Radio Frequency) magnetic devices for wireless transmission and reception of information are placed.
The term “electromagnetic wave” refers to a phenomenon where electromagnetic waves with periodically changing intensities are propagated through space.
Electromagnetic waves are classified, according to their frequency or wavelength, into low-frequency, high-frequency, short-wavelength, and long-wavelength electromagnetic waves. These electromagnetic waves have various electromagnetic properties, and thus are used in various fields and applications, including electrical devices, electronic devices, and communication devices.
The effect of electromagnetic waves on the human body can be seen through various syndromes found to be caused by electromagnetic waves, such as the thermal effects caused by microwaves used in electronic ranges, mobile phones and the like, or video display terminal syndromes indicating syndromes, such as headaches or sight disturbance, which are caused by electromagnetic waves. In addition, there are a number of study results, such as an increase in the cancer development of residents in the vicinity of power transmission lines, or an attack of brain tumor in long-term users of mobile phones.
In particular, due to the development of mobile communication technology and the public use of personal mobile communication, there are continued studies on the possibility of adverse effects on the human body and the suggestion of problems, for example, the defenseless exposure of users to high-frequency electromagnetic waves generated from mobile communication devices, such as mobile phones, and an increase in body temperature at cranial sites during the use of such mobile communication devices. For this reason, in highly developed countries where personal mobile communication is commonly used, the standards for the protection of the human body from electromagnetic waves are made and provided as recommendation standards by private organizations, such as associations or societies, on the assumption that electromagnetic waves are harmful to the human body. In some countries, these standards are in force. Also, the recognition of consumers is spread that judges not only the function of products but also the non-harmfulness of products to the human body as important quality factors. As concern and consciousness about the harmfulness of electromagnetic waves to the human body are increased as described above, research and development on electrical/electronic devices with minimized generation of electromagnetic waves or materials for absorbing generated electromagnetic waves are now actively conducted. Particularly, various forms of electromagnetic wave-absorbing materials, which are attached to various electrical/electronic devices so as to absorb the generated harmful electromagnetic waves, are developed and applied as internal or external parts in antennas or monitors.
The electromagnetic wave-absorbing material can be typically exemplified by a ferrite. As used herein, the term “ferrite” refers to a solid solution in which allaying elements or impurities melt in iron having a body-centered cubic crystalline structure, which is stable at a temperature of 900 ° C or below. The ferrite is manufactured into an electromagnetic wave-absorbing material, mainly by sintering. This ferrite electromagnetic wave-absorbing material manufactured by sintering has a shortcoming in that it is weak against impact, and thus is likely to undergo brittle fracture. Also, the electromagnetic wave-absorbing material manufactured using the ferrite disadvantageously has low dimensional stability due to a shrinkage phenomenon occurring in a sintering process in which ferrite powder is placed and molded in a mold under pressure, followed by heating. Furthermore, the mold should be manufactured in view of shrinkage rate, thus making the molding process difficult. In addition, the characteristics of the sintering process make it difficult to apply a mold of complex shape, thus reducing the formability of the ferrite.
Particularly, in view of the fact that the electromagnetic wave-absorbing material is most frequently used for various mobile electrical/electronic devices, such as mobile phone antennas, the electromagnetic wave-absorbing material is likely to be exposed to vibration or impact when it is carried, and thus the weakness of the electromagnetic wave-absorbing material against impact can be considered as a serious problem. In addition, an increase in production cost due to low formability and dimensional stability can be seen as a serious disadvantage when considering a rapidly increasing demand for the electromagnetic wave-absorbing material.
Binders which are generally added to increase the formability of the ferrite during a process of molding the ferrite include polyvinyl alcohol (PVA). However, PVA is difficult to grind and mix in a dried state and results in a non-uniform molded body. For this reason, a method of forming and drying a binder solution and molding the dried material is used, but this method involves a relatively complex process.
Accordingly, the present invention has been made in order to solve the above-described problems occurring in the prior art, and it is an object of the present invention to provide a method of manufacturing an electronic component for RF applications by sintering, which can reduce the magnetic loss tangent of the electronic component and increase the permeability of the electronic component.
Another object of the present invention is to provide a method of manufacturing an electronic component by sintering, which can enhance the cohesion of a ferrite to facilitate the molding of the ferrite.
To achieve the above objects, according to a preferred embodiment of the present invention, there is provided a method of manufacturing an electronic component for RF applications comprising a ferrite by sintering, wherein ammonium alginate is added to the ferrite before the ferrite is sintered.
In the method of the present invention, the ferrite preferably has a spinel structure, and the ammonium alginate is preferably added to the ferrite in an amount of 3 wt%.
Also, the ferrite is preferably is sintered at a temperature ranging from 600 ° C to 1400 1 ° C.
According to another preferred embodiment of the present invention, there is provided a method of manufacturing an electronic component for RF applications by sintering, the method comprising the steps of: adding 3 wt% of ammonium alginate to a ferrite to form a mixture, and stirring the mixture while adding water thereto to form a gel; drying the gel at a temperature ranging from 85 ° C to 95 ° C to form a dried material; grinding the dried material to produce a ferrite powder coated with the ammonium alginate; subjecting the ferrite powder to compression molding; and sintering the compression-molded ferrite powder.
In the method of the present invention, the ferrite preferably is a spinel ferrite having a composition of MXFe(3−X)O4, wherein M is at least one of Mg and Co, and X is an integer of 1 or 2.
Also, the compression-molding step is preferably carried out by compressing the ferrite powder with a load of 2-6 tons.
In addition, the sintering step is preferably carried out at a temperature ranging from 600 ° C to 1400 ° C.
The present invention can reduce the magnetic loss tangent of the ferrite molded material and increase permeability of the ferrite molded material, thus increasing the efficiency of the ferrite molded material.
Also, by adding ammonium alginate to the ferrite, the cohesion of the ferrite can be enhanced, thus facilitating the molding of the ferrite.
For this reason, the density of the ferrite molded material can be maintained at a relatively uniform level, and thus the magnetic loss tangent and permeability of the ferrite molded material can be maintained at constant levels.
Also, because the binder PVA is not used in the process of molding the ferrite in the present invention, a process of preparing a solution of the binder can be omitted, thus making the mixing process simple. Accordingly, the ferrite can be molded using a simple process.
Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings, but the scope of the present invention is not limited by the embodiment. For reference, like reference numerals designate like elements throughout the specification.
A method of manufacturing an electronic component for RF applications by sintering according to a preferred embodiment of the present invention will now be described.
A method of manufacturing an electronic component for RF applications comprising a ferrite will be described as a typical example.
The electronic component for RF applications is manufactured by adding ammonium alginate to the ferrite and sintering the ferrite.
Alginate is a polysaccharide material that is contained in algae and bacterial in large amounts. It is a polymer of β-1, 4-D-manuronic acid and β-1, 4-L-glucuronic acid, extracted from algae, and when it comes into contact with divalent or higher-valent metal ions, such as Ca and Al (excluding Mg), it will be easily gelled. The carboxyl group of manuronic acid or glucuronic acid is crosslinked by chelation with miltivalent metal ions. Because alginate is harmless to the human body and gelled at room temperature, it is frequently used for the immobilization of animal cells.
In microbial culture, alginate allows the metabolic activity of microorganisms to be maintained for a long period, and thus is mainly used as an immobilization agent. Also, an immobilization process that uses alginate is very simple and relatively inexpensive.
Also, ammonium alginate is a white or light yellow fibrous grain, granule or powder, is substantially odorless and tasteless and has a chemical formula of (C6H7O6NH4)n. Generally, it is a milky powder, very easily dissolves in water, and becomes a highly viscous gel even when a small amount of water is added thereto. It becomes a viscous solution when being dissolved in water, and slowly dissolves in sodium carbonate, sodium hydroxide and sodium phosphate.
As described above, the ferrite is a metal oxide which is subjected to a heat-treatment process (i.e., sintering process) at a temperature of about 600-1400 ° C, and the sintered metal oxide powder has low cohesion, and thus does not provide a molded material in a process of molding the ferrite. For this reason, according to the present invention, ammonium alginate is added to the ferrite in order to increase the formability of the ferrite.
Namely, the binder PVA is not used in the process of molding the ferrite in the present invention, so that a process of preparing a solution of the binder can be omitted, thus making the mixing process simple. Accordingly, the ferrite can be molded using a simple process.
The ammonium alginate is added to the ferrite in an amount of 3 wt%, and water is added thereto while the mixture is stirred. Then, due to the above-described properties of the ammonium alginate, the ferrite can be dried and molded. The method of manufacturing the electronic component for RF allocations comprising the ferrite will now be described in further detail with reference to
As shown therein, ammonium alginate is added to a ferrite to form a mixture, and water is added thereto while the mixture is stirred to form a gel (S1). As described above, the ammonium alginate is added to the ferrite in an amount of 3 wt%.
The ferrite that is used in the present invention is a spinel ferrite having a composition of MXFe(3−X)O4, wherein M is at least one of Mg and Co, and X is an integer of 1 or 2.
The spinel ferrite is a ferrite having a spinel structure that is a crystalline structure which can be seen in an oxide represented by a chemical formula of XYA, similar to spinel (MgAl2O4). The spinel structures are divided into a normal spinel structure and an inverse spinel structure and generally exhibit ferromagnetic or ferromagnetic properties.
In the normal spinel structure, X2+ metal ions occupy tetrahedral sites and Y3+ metal ions occupy octahedral sites in a matrix composed of cubic closed-packed oxygen ions. On the other hand, in the inverse spinel structure, the tetrahedral sites are occupied by Y3+, and the octahedral sites are occupied by half X2+ and half Y3+.
The normal spinel structure and the inverse spinel structure comprise eight formula units XY2O4 per unit cell, and crystals having this structure generally exhibit ferromagnetic or ferromagnetic properties.
Then, a step (S2) of drying the gel to form a dried material is carried out. In this step, the gel is preferably dried at a temperature between 85 ° C and 95 ° C. More preferably, the gel is dried at a temperature of 90 ° C. The drying step yields the dried material in which the ferrite and the ammonium alginate remain and from which the water has been removed.
Then, a step (S3) of grinding the dried material to produce a ferrite powder coated with the ammonium alginate is carried out.
Then, a step (S4) of subjecting the ferrite powder to compression molding is carried out. As described above, it is difficult to mold a general ferrite, because the ferrite has a relatively low cohesion; however, according to the present invention, the ferrite powder can be easily molded due to the ammonium alginate.
The step of subjecting the ferrite powder to compression molding is preferably carried out by compressing the ferrite powder with a load of 2-6 tons.
Then, a step (S5) of sintering the compression-molded ferrite powder is carried out, thereby manufacturing an electronic component for RF applications.
The efficiency of an antenna among electronic components for RF applications is greatly influenced by the magnetic loss tangent and permeability thereof. Particularly, a decrease in the magnetic loss tangent of the antenna leads to a very great increase in the efficiency thereof, and an increase in the permeability of the antenna leads to an increase in the aspect ratio thereof, indicating that a more miniaturized antenna can also be manufactured.
Table 1 below shows the change in efficiency of the ferrite according to the dielectric loss tangent and magnetic loss tangent of the ferrite.
As can be seen in Table 1 above, as each of the dielectric loss tangent and magnetic loss tangent of the ferrite having a permeability of 10 and a permittivity of 10 increases, the efficiency of the ferrite greatly decreases.
As can be seen in
As used herein, the term “permeability” is a coefficient indicating the ratio, in any substance, of the magnetic flux density (B) to the magnetic field strength (H), and is expressed by p.
More specifically, the permeability is a coefficient indicating how the magnetic flux easily passes. Thus, as the permeability (μ) increases, the magnetic flux more easily passes. Accordingly, when the external magnetic flux comes in, as the permeability increases, the magnetization more easily occurs.
The magnetic flux has the same meaning as the current of electric force and means the degree of operation as a magnetic material. In the electronic component for RF applications, the term “magnetic material” is not frequently used, but in the case in which a ferrite is used, the permeability of the ferrite should be considered.
As used herein, the magnetic loss tangent, that is, tangent delta as graphically shown in
Namely, when the permeability (i.e., real part) is assumed as μ1, the imaginary part is expressed as μ2, and the magnetic loss tangent is expressed as the ratio of μ2 to μ1.
Accordingly, the magnetic loss tangent of the electronic component for RF applications according to the preferred embodiment of the present invention is 0.03 which is lower than that (0.06) of the ferrite molded using PVA according to the conventional method. Namely, the present invention can reduce the magnetic loss tangent of the ferrite by about 50% compared to the conventional method. In addition, according to the present invention, the permeability of the ferrite is increased from 7 to 9, indicating that the present invention increases the permeability by about 30% compared to the conventional method.
Although the preferred embodiment of the present invention has been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2008-0096601 | Oct 2008 | KR | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/KR09/05517 | 9/28/2009 | WO | 00 | 3/31/2011 |
