JPH0336795A - Radio wave absorber, radio wave absorption wall using same and varying method for matching frequency characteristic - Google Patents

Abstract

PURPOSE:To obtain a radio wave absorber in which arbitrary matching frequency characteristic can be realized over a wide band by disposing a conductor plate having a function of controlling a short-circuiting plate and the magnetic field of a magnet or further a spacer having a short-circuiting plate on a front face of the magnet having a predetermined coercive force, and bringing ferrite into close contact with the front face. CONSTITUTION:A radio wave absorber has a ferrite 1, a waveguide plate 2, and a magnet 3 disposed from its front face. Here, the magnet 3 is so magnetized as to hold a magnetic field of maximum limit to be determined according to the frequency of the upper limit of high frequency side to be matched. The magnetic field of the magnet 3 is magnetized to the maximum limit, magnetic field intensity to be applied to the ferrite 1 is controlled by altering the thickness of a conductor plate 2, and matching frequency characteristic is varied by altering the thickness of the ferrite 1. A spacer 6 of a dielectric, etc., is interposed to be held between the plate 2 and the magnet 3, the plate 2 is reduced in thickness to be reduced in weight. The magnetic field intensity to act the ferrite 1 is controlled by changing the thickness of the spacer 6.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a radio wave absorber, a radio wave absorbing wall, and a method of varying the matching frequency characteristics thereof. More specifically, the present invention relates to a radio wave absorber and a radio wave absorption wall having a structure in which matching frequency characteristics can be changed using the same radio wave absorbing material, and a method for varying the frequency characteristics thereof over a wide band.

(Prior art) As shown in Figure 6, the basic structure of a conventional ferrite radio wave absorber is to manufacture ferrite (1) in the form of a tile or sheet, which is then lined with a conductor plate. The ferrite radio wave absorber of
It was a trial-and-error manufacturing method in which the matching frequency and matching thickness unique to the material were determined by manufacturing conditions such as firing.

Therefore, in order to design a radio wave absorber with desired matching frequency characteristics, it is necessary to go back to the beginning, consider the manufacturing conditions of ferrite again, and manufacture ferrite. With this conventional manufacturing method, it is difficult to achieve arbitrary matched frequency characteristics.
This has the major drawback of being extremely difficult to absorb, and ferrite must be developed for each frequency of radio waves to be absorbed. Therefore, we first proposed a radio wave absorber that can obtain arbitrary matching frequency characteristics by applying a DC magnetic field to ferrite (Utility Application 1986-10).
No. 6915). This is designed to change the matching frequency by adjusting the static magnetic field applied to the ferrite and the ferrite thickness.

(Problem to be Solved by the Invention) However, although this radio wave absorber is effective as a single ferrite radio wave absorber, it is difficult to form a radio wave absorber by pasting many of these single radio wave absorbers on a wall surface. Therefore, there is a problem in that a repulsive force is generated between adjacent magnets that are in close contact with the back surface of the ferrite, and the magnetic field distribution is disturbed. Furthermore, in order to change the matching frequency characteristics, it is necessary to replace the magnet with a magnet of a different coercive force each time. The present invention relates to a radio wave absorber with variable matching characteristics that can realize arbitrary matching frequency characteristics over a wide range using the same ferrite material and magnets with the same magnetic field strength, a method for manufacturing the same, and radio wave absorption using the same. It is an object of the present invention to provide a method for varying wall and matching frequency characteristics.

(Means for Solving the Problem) In order to achieve this objective, the radio wave absorber of the present invention has a conductive plate that has both a shorting plate and a function of controlling the magnetic field of the magnet in front of a magnet having a certain coercive force. Alternatively, a spacer having a short circuit plate is further arranged, and the ferrite is closely attached to the front surface of the spacer.

Furthermore, the magnet in this case is made by connecting magnetic powder or small pieces of magnet with a binder to solve the problems of disturbance of the magnetic field and generation of repulsive force between adjacent magnets.

This makes it possible to construct a radio wave absorption wall by gathering a large number of the radio wave absorbers described above. In addition, this magnet powder or magnet pieces bound together with a binder can be used as a joint material when arranging solid magnets to construct the absorption wall of the present invention, and can also be used as a joint material for the entire wall surface on which the absorption band is installed or coated. It can be constructed into a continuous magnet surface with no overlapping seams.

The radio wave absorber and radio wave absorbing wall configured in this way can be varied to any matching frequency characteristic by changing the thickness of the ferrite and the thickness of the above-mentioned conductive plate or spacer interposed between the ferrite and the magnet. be.

Furthermore, as a means of changing the matching frequency characteristics, a DC magnetic field or an AC magnetic field is applied perpendicularly to the surface of the radio wave absorber or radio wave absorbing wall configured as described above, and the coercive force of the magnet is controlled to further increase the ferrite content. Any matched frequency characteristics can be achieved by varying the ferrite thickness by stacking or scraping.

This method is also an effective means for correcting a decrease in the coercive force of the magnet.

In order to realize arbitrary matching frequency characteristics over as wide a band as possible, the ferrite in the above configuration method is designed to reduce the frequency at which the real part of the relative permeability is 1 as much as possible in the frequency dispersion characteristics of the complex relative magnetic permeability of the ferrite. A wide band can be achieved by manufacturing ferrite or selecting such a ferrite material so as to have a low resistance.

(Function) With the above configuration method, the magnetic field applied to the ferrite depends on the thickness of the conductor or spacer, and the magnetic field strength can be controlled by changing the thickness of the conductor plate or spacer. This radio wave absorption mechanism controls the spin using a static magnetic field from a magnet, and changes the thickness of the ferrite accordingly to determine the magnetic permeability characteristic that satisfies the radio wave absorption conditions, that is, the frequency at which the real part of the complex relative magnetic permeability is 1. It changes the matching frequency by changing it, and has the effect of converting and absorbing radio wave energy into heat over a wide range of frequencies.

(Example) Hereinafter, the structure of the present invention will be described in detail based on an example shown in the drawings. FIG. 1 is a perspective view of an example of the radio wave absorber of the present invention. In Figure 1, the ferrite (1), waveguide plate (2), and magnet (3) are arranged from the front. Here, the magnet (3) is magnetized so as to maintain the maximum magnetic field determined by the upper limit frequency on the high frequency side for which matching is to be achieved. The magnetic field of the magnet (3) is magnetized to the maximum, and the magnetic field strength applied to the ferrite (1) is controlled by changing the thickness of the conductor plate (2), and the thickness of the ferrite (1) is controlled. This means that, for example, when matching in the high frequency UHF band, it is necessary to use a thinner ferrite and apply a stronger static magnetic field than in the VHF band. However, in order to construct an absorber that can be matched in the VHF band, it is based on the principle that the ferrite chamber should be made thicker and the applied static magnetic field should be made weaker.Figure 7 shows this. An example showing the relationship is N
This is actual measurement data when using i-Zn-based ferrite material. The vertical axis represents the standing wave ratio, which represents the amount of radio wave absorption, that is, VS
In WR, the horizontal axis represents the matching frequency. For example, the seventh
The graph 7-A in the figure shows the case where no magnetic field is applied, and the thickness of the ferrite is d = 6. 2 [mml, frequency f
The standing wave ratio becomes the minimum value at =0.18 [GH2], indicating a state where matching is best achieved. On the other hand, graph 7-B shows the case where the ferrite thickness d=3 rmml,
It can be seen that the best matching state is obtained when the magnetic field applied to the magnet surface is about 710 [Gauss] and the frequency is about 0.35 [G)IZI. In other words, it can be seen that when a magnetic field is applied to the ferrite and the ferrite thickness is made thinner, the matching frequency shifts to the higher frequency side compared to the matching frequency when no static magnetic field is applied to the ferrite. Ultimately, in order to embody this principle, the first step is to
When changing the matching frequency characteristics in the figure, use the waveguide (
2) and ferrite (1) with different thicknesses can be attached to a magnet. In this case, the design guideline is to realize a desired matching frequency using a design chart showing that the relationship between the ferrite thickness and the applied magnetic field is approximately linear.

By the way, in this configuration, if a normal magnetic plate is used as the magnet (3), there is no problem when using a radio wave absorber as shown in Figure 1, but when a large number of these are assembled to form a radio wave absorbing wall. This causes problems such as repulsive force acting between adjacent magnets and disturbance of magnet distribution near the magnet boundary. Second
The figure shows that in order to solve this problem, as a magnet (3),
Samarium cobalt magnet materials, etc., are crushed into powder, particles, or pieces, which are sucked onto a substrate conductor, and then a binder is applied or sprayed to harden them, and binder and these magnets are mixed. In this embodiment, a painted magnet (5) is constructed by spraying or coating a painted magnet material onto a substrate (4) and applying a magnetic field perpendicularly to the magnet surface. By using this painted magnet, it is possible to construct a seamless, continuous, single magnet surface that covers the entire wall surface over a wide area, and the above-mentioned problems can be solved.

As the binder, epoxy resin type, vinyl acetate resin type, cyanoacrylate type, etc. may be used depending on the purpose and the properties of the coated substrate. If the size of the magnetic powder, particles, or pieces is too small, the coercive force will decrease, so choose a size that is as large as possible without interfering with painting or spraying.

In addition, in Figure 2, a spacer (6) such as a dielectric material is sandwiched between the conductor plate (2) and the magnet (3) in Figure 1.
) to reduce weight.

Ferrite (
1) Control the magnetic field strength that acts on. Of course conductor plate (2)
It is also possible to change the thickness.

As the spacer (6), any lightweight material such as plastic, styrofoam, or fibers can be used, and if it is a wall of a building, concrete may be used. The spacer (6), conductor plate (2), ferrite (1), and painted magnet (5) are fixed using a strong adhesive such as cyanoacrylate or vinyl acetate adhesive for the styrofoam spacer. be done. Furthermore, these mutual adhesives are structured to have finely uneven surfaces or serrated surfaces to prevent them from peeling off and falling, thereby strengthening their adhesion. Of course, when a strong magnetic field is required in Figures 1 and 2, the conductor plate (2) and spacer (6) may be omitted.

In Figure 3, the magnet (3) in Figure 1 is replaced with a disc-shaped magnet (7).
) and the above-mentioned painted magnet (5) are used as joint parts. This is an example of a method in which disk-shaped magnets are used and the magnets are in point contact with each other in order to minimize the interaction of magnetic fields on the side surfaces of adjacent magnets. Of course, the magnetic field can be strengthened and made uniform by stacking the disc-shaped magnets (7) in layers or by coating the coated magnets (5) so as to cover these magnets. In addition to samarium cobalt magnet material, inexpensive ferrite magnet powder can be used as the joint material. If such a magnet plate is used and constructed as shown in FIGS. 1 and 2, a static magnetic field can be effectively imparted to the ferrite, which is advantageous for the construction of a radio wave absorber.

FIG. 4 is a perspective view of an embodiment in which a magnet coated with paint is applied to the wall of a building and a radio wave absorber according to the present invention is bonded thereto to form a radio wave absorbing wall. In this embodiment, the ferrite (1), the conductor plate (2), the spacer (6), and the coated magnet (5>) are each bonded to each other.

The construction method in this case is (a) applying a paint-containing magnet (5) to the wall surface (8) of the building. The thicker the coating, the stronger the magnetic field strength. Also, even if the painted surface is somewhat random, apply a spacer (6) such as a plastic plate to the surface of the painted magnet (5) before the binder such as adhesive that makes up the painted magnet (5) dries. This allows you to maintain a constant thickness.

(b) Next, temporarily apply the conductive plate (2) to the surface of the spacer (6).

(c) Here, in order to efficiently magnetize the painted magnet (5) perpendicularly to the surface of the conductor plate (2), apply a DC magnetic field in the manner shown in the side view of Fig. 5. .

In other words, in Fig. 5, a pole (12) is attached to the magnetic core (9) so that a constant magnetic field can be applied by a magnetizing magnet (11>) consisting of a magnetic core (9) and a coil (10>), and a caster (1
3) so that the surface of the conductor plate (2) can be moved smoothly while maintaining a constant interval.

(d) After this operation, measure the strength of the magnetic field on the conductor surface with a Gaussmeter. As a result, if the desired magnetic field is not obtained and is too strong, the temporarily applied conductor plate (2) is removed and the conductor plate (2) or spacer (6) is made thicker. If the magnetic field is too weak, try polishing the spacer to make it thinner, or remove the coil (10) of the magnetizing magnet (11).
A method is used to weaken the magnetizing force of the paint magnet (5) by passing an alternating current through the magnet.

(E) As a result, if the desired magnetic field is obtained, the ferrite (1) is adhered to the surface of the conductor plate (2), and the construction of the radio wave absorbing wall of the present invention is completed.

Now, FIG. 8 shows an actual measurement example of the frequency distribution characteristics of the return relative magnetic permeability μr=μr l−jμrIs corresponding to each of the VSWR characteristics shown in FIG. 7. Comparing with FIG. 7, it can be seen that the real part μr' of the relative magnetic permeability is well matched at approximately the frequency of l. In other words, the theoretically derived perfect matching condition is μr″=1.μr* 1 >> 1, and the above actual measurement example matches this condition. Therefore, the relative permeability when no magnetic field is applied is 1. By manufacturing a material whose frequency is as low as possible, or by selecting a material that satisfies such conditions from existing ferrite materials, it is possible to apply a magnetic field and reduce the ferrite thickness in a higher frequency region. By doing this, a radio wave absorber can be created that can be matched arbitrarily over a wide frequency range.Also, when the ferrite thickness and applied magnetic field are determined, in order to make the desired matching frequency range as wide as possible,
It is clear from a comparison between FIGS. 7 and 8 that a material in which the slope of the graph of the real part of the relative magnetic permeability in the vicinity of the frequency at which the relative magnetic permeability becomes 1 is gentle should be used. Although the above-described embodiments are preferred embodiments of the present invention, the present invention is not limited thereto, and various modifications can be made without departing from the gist of the present invention.

(Effects of the Invention) As described above, the present invention solves the method of controlling the static magnetic field applied to ferrite in a relatively simple manner, and when configuring a ferrite radio wave absorption wall using this method, the To solve the problem of repulsive force and non-uniform magnetic field, it is possible to minimize the contact surface by using circular magnets, to form the entire wall surface with a single magnet using painted magnets, or to use it as a joint material for magnets. The problem is solved by essentially configuring a single magnet. In addition, the present invention can be applied to ferrite by arranging a magnet on the back side of ferrite with a conductor interposed between them, interposing a spacer made of a non-conductor between the conductor and the magnet, and changing the thickness of the conductor or spacer. By varying the applied magnetic field strength without changing the magnet, and in conjunction with varying the ferrite thickness, the matching frequency characteristics can be arbitrarily varied.

In addition, the present invention provides a method for changing the matching frequency of a radio wave absorbing wall once attached to a wall, by applying a DC magnetic field or an alternating current magnetic field from the surface of the radio wave absorbing wall using a magnetizing magnet to increase or weaken the coercive force. By laminating the ferrite to make it thicker or scraping it to make it thinner, it is possible to achieve any matching frequency characteristic without destroying the entire ferrite radio wave absorption wall surface.

As mentioned above, it is extremely difficult to achieve the desired matching frequency characteristics with conventional ferrite radio wave absorbers.
The radio wave absorber was designed by trial and error after considering material composition, firing conditions, etc., but with the present invention, we have developed a radio wave absorber and a radio wave absorber that can relatively easily achieve arbitrary matching frequency characteristics over a wide band using the same material. It provides a method for constructing and manufacturing a radio wave absorbing wall, and has extremely significant practical effects.

[Brief explanation of drawings]

FIG. 1 is a perspective view of an embodiment of the present invention showing the structure of a radio wave absorber in which a conductive plate is interposed between a ferrite and a magnet. FIG. 2 is a perspective view of an embodiment of the structure of a radio wave absorber using a non-conductor spacer according to the present invention. FIG. 3 is a perspective view of an embodiment showing a method of constructing a magnet surface according to the present invention. FIG. 4 is a perspective view of one embodiment of the construction method of the radio wave absorbing wall of the present invention. FIG. 5 is a front view showing an embodiment of the method of magnetizing a radio wave absorber according to the present invention. FIG. 6 is a perspective view showing the structure of a conventional ferrite radio wave absorber. FIG. 7 is an example of an SWR characteristic diagram of a radio wave absorber showing the principle of the present invention. FIG. 8 is a frequency dispersion characteristic diagram of relative permeability characteristics corresponding to FIG. 10. 1... Ferrite 3... Magnet 5... Painted magnet 7... Disc-shaped magnet 9... Magnetic core 11... Magnetizing magnet 6 13... Caster 2... Conductor plate 4... Board 6... Spacer 8... Wall surface 10... Coil 12... Support

Claims (10)

[Claims] (1) A radio wave absorber made by arranging a magnet on the back surface of ferrite with a conductor interposed. (2) The radio wave absorber according to claim 1, characterized in that a spacer made of a non-conductor is interposed between the conductor plate and the magnet. (3) The radio wave absorber according to claim 1 or 2, wherein the magnet is a combination of magnet powder or small magnet pieces connected with a binder. (4) A radio wave absorbing wall constructed by assembling the radio wave absorbers according to any one of claims 1 to 3. (5) A radio wave absorbing wall characterized in that a joint material containing magnet powder or small pieces of magnet is filled between the magnets constituting the radio wave absorbing wall according to claim 4. (6) The radio wave absorbing wall according to claim 4, wherein the magnet is a seamless, continuous single magnet that covers the entire wall surface by connecting magnet powder or small pieces of magnet with a binder. (7) A method of varying the matching frequency of the radio wave absorber according to claim 1, characterized in that the matching frequency characteristic is changed by adjusting the thickness of the conductor and the ferrite. (8) In the radio wave absorber according to claim 2, the matching frequency characteristic of the radio wave absorber is characterized in that the matching frequency is changed by adjusting the thickness of the ferrite and the thickness of the conductor or the spacer or both. Variable method. (9) Applying a direct current or alternating magnetic field to the surface of the radio wave absorption wall to control the coercive force of the magnet and layering or scraping off the ferrite on the surface of the absorption wall to vary the ferrite thickness. Features a radio wave absorption wall. (10) As the ferrite according to claim 1, a ferrite is produced whose frequency dispersion characteristic of relative magnetic permeability is such that the lowest frequency is the frequency at which the real part of the relative magnetic permeability is 1, and using this ferrite, matching characteristics are obtained over a wide band. A radio wave absorber characterized by being able to vary the