JP4479059B2 - Radio wave absorber with frequency selectivity - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a radio wave absorber, and more particularly to a radio wave absorber that selectively shields radio waves of a specific frequency.
[0002]
[Prior art]
In recent years, it has become indispensable to prepare the radio environment in the office from the viewpoints of preventing information leakage and malfunction and noise due to invading radio waves from the outside as the use of PHS and wireless LAN in offices is spreading. Various types of members have already been proposed as members for maintaining such a radio wave environment.
[0003]
For example, in Japanese Patent Publication No. 6-99972, an electromagnetic shield member such as metal or ferrite is added to a building frame so that information communication can be performed using radio waves of an arbitrary frequency in a wide frequency band. -It is stated that Ludo Intelgent Building will be provided.
[0004]
However, in the case where a radio wave reflector such as an iron plate, a metal net, a metal mesh, a metal foil or a radio wave absorber such as ferrite as shown in the patent is used as an electromagnetic shield member, those electromagnetic shields are used. Since there is no frequency selectivity, the radio wave other than the frequency to be shielded is blocked.
[0005]
As a result, important information on public communication radio waves such as broadcast radio waves such as mobile phones, pagers, and AM / FM radios used throughout the building is blocked. In addition, the radio wave reflector reflects a TV radio wave and causes reception trouble (ghosting), so that the locations where it can be used are limited. Furthermore, since the shield performance is greatly reduced by the gaps between the electromagnetic shield members, the strictness in construction, such as connection between members and grounding, is necessary to fully demonstrate the shield performance of each member. Is required.
[0006]
Japanese Patent Laid-Open No. 10-169039 eliminates the above-described problems, and shields only radio waves of a specific frequency to be shielded by periodically arranging linear antenna elements. It is excellent that connection between members and grounding are not necessary.
[0007]
However, since the shielding is mostly due to reflection in the direction of arrival of radio waves, so-called reflection loss, it is effective for intrusion from the outside, but it is almost the same as the specific frequency that the electromagnetic shielding member tries to shield inside the office. In a communication system (so-called wireless LAN) using a plurality of wireless devices using the same frequency band, the radio waves of each wireless device are reflected, and as a result, communication such as reduced sensitivity of radio devices and interference due to interference caused by reflected waves. The problem is that the line performance may be degraded.
[0008]
JP-A-5-335832 discloses a configuration for selectively absorbing radio waves of a specific frequency in order to solve such problems caused by reflected waves inside the office. Is a so-called λ / 4 type in which a resistive film and a radio wave reflector are disposed with a dielectric (thickness is ¼ of the radio wave wavelength in the dielectric) between them to selectively absorb only radio waves of a specific frequency. It relates to a radio wave absorber.
[0009]
However, this radio wave absorber also has the following drawbacks. In other words, the radio wave coming from the resistive film side that is going to be shielded has a large amount of absorption and excellent frequency selectivity, but the back side of the dielectric is backed by a radio wave reflector such as a metal foil or a metal net. The radio wave other than the frequency to be shielded is reflected and cannot be transmitted. That is, the frequency selectivity exhibits an effect on the reflected component of the radio wave coming from the resistance film side.
[0010]
In addition, when the incoming radio wave is incident on the λ / 4 type radio wave absorber obliquely, the length of transmission through the dielectric is not less than ¼ of the radio wave wavelength, so that the absorption characteristics are deteriorated. That is, the radio wave absorber has directivity. Furthermore, radio waves coming from the reflector side are reflected regardless of the frequency, and when used on a building window or wall surface, this may cause the above-mentioned television radio wave reception failure. Furthermore, in the λ / 4 type wave absorber, the lower the shielding frequency, the greater the thickness of the dielectric layer, making it difficult to handle during construction.
[0011]
In addition, as disclosed in Japanese Patent Laid-Open No. 9-162589, this is to absorb incoming radio waves by arranging elements having electrical resistance values larger than the conductor and smaller than the insulator.
[0012]
This invention also has the effect of absorbing radio waves, but has the following drawbacks. First, if the length of the element is configured independently of the frequency of the incoming radio wave, no frequency selectivity can be obtained in the radio wave absorption characteristics.
[0013]
In addition, if the length of the element is slightly shorter than half the wavelength of the radio wave of the frequency to be absorbed, it is said that the element can be efficiently absorbed. Therefore, in the half-wave dipole antenna created by the element, the loss resistance of the antenna is increased, and as a result, the reception efficiency is lowered as compared with a normal half-wave dipole antenna. In addition, as the resistance increases, the resonance characteristics of the antenna element become flat, and there is a problem that the frequency selectivity of radio wave absorption is lowered.
[0014]
[Problems to be solved by the invention]
The object of the present invention is to eliminate the disadvantages of the conventional wave absorber as described above.
[0015]
In other words, it is a radio wave absorber excellent in workability that does not require connection or grounding between radio wave absorbers. When an office or the like is formed using this radio wave absorber, dedicated communication in the room (such as business office PHS or Radio equipment used for wireless LAN etc.) will not degrade the sensitivity of wireless devices due to interference caused by reflected waves on the indoor wall of the room, interference, etc. Communication line performance will not deteriorate, and leaked radio waves outside and intrusion from outside The radio wave is lost and the security of information is improved.
[0016]
Furthermore, radio waves other than those described above can be transmitted in both directions to communicate with the outside and receive public broadcasts. When used on a building window or wall, it does not cause a TV reception problem. Moreover, since it can be processed thinly, handling becomes easy. The object is to provide such a radio wave absorber.
[0017]
[Means for Solving the Problems]
The present invention is for achieving the above-described object, and has at least a film and a specific length corresponding to the frequency of the radio wave to be shielded disposed on one surface of the film. in wave absorber and a conductive element, a portion in the cutout portion of the conductive element is provided, the electrodes provided at both ends of the notch, a position overlapping the electrode of the other surface of the film Another object is to provide a radio wave absorber having frequency selectivity, characterized in that another electrode is provided and the other electrodes are connected by a resistor .
In this configuration using the resistor, the energy of the incoming radio wave to be shielded is induced in each conductive element provided, and the energy is converted into heat and consumed by the resistor. Therefore, incoming radio waves are absorbed. Moreover, it is almost irrelevant to the direction of incoming radio waves and exhibits absorption performance in all directions. In addition, with such a configuration, the conductive element and the resistor are present with the dielectric film interposed therebetween, so that the radio wave absorber can be formed into a film by thinning the dielectric film. Become.
Here, the notch means a place where conductivity does not work between both ends. It may be a portion made of a high resistance material or a portion constituting a portion where no member itself is present.
[0020]
According to a second aspect of the invention, the conductive element according to claim 1 having an open end, approximately one-half wave wavelength distance between the open end is to shield (However, the radio wave is the film a medium wavelength in), wave absorber having frequency selectivity according to claim 1, characterized by having the resistor at the midpoint of the length of the conductive elements, also third aspect of the present invention the conductive element according to claim 1 is annular, wave wavelength (however, the radio wave wavelength is the wavelength in said film in) the length of its circumference is to shield, characterized in that substantially have equal to claims An electromagnetic wave absorber having frequency selectivity according to Item 1 is provided.
[0021]
With such a configuration, incoming radio waves for shielding can be efficiently absorbed. In addition, the shape of the annular conductive element, that is, the shape of the annular conductive element is effective for the plane of polarization of all incoming radio waves, and enables more efficient absorption.
[0022]
The inventions according to claims 4 and 5 provide a radio wave absorber having frequency selectivity, characterized in that a foil or a linear metal element is used for the conductive element according to claims 1 to 4. .
[0023]
By using a metal element having a low resistivity as the conductive element, the selectivity of the incoming radio wave to be shielded is improved, which is an effective means when the frequencies of the shielded radio wave and the transmitted radio wave are close.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the drawings.
FIG. 1 is a front view of a radio wave absorber having frequency selectivity according to one embodiment of the present invention. FIG. 2 shows a cross-sectional view of FIG. 1, and the radio wave absorber 10 includes a frequency selective surface 14 provided with a conductive element 13 and a support or protective material 15.
[0025]
In FIG. 1, the conductive element 13 in the present invention is separated at the midpoint.
[0026]
FIG. 3 is a cross-sectional view of one element of the conductive element 13 shown in FIG. As shown in FIG. 3, the radio wave absorbing surface 14 is provided with electrode pads 18 a and 18 b on one side of the film 16 at positions where the two elements 17 a and 17 b and the two elements 17 a and 17 b face each other. Similarly, electrode pads 19a and 19b are provided at positions overlapping the electrode pads 18a and 18b on the other surface, respectively, and a load resistor 20 is formed across the electrode pads 19a and 19b.
[0027]
As a result, as shown in FIG. 4, the electrode pads 18a and 18b and the electrode pads 19a and 19b shown in FIG. 3 form capacitors 21a and 21b using the film 16 as a dielectric, thereby constituting an antenna element.
[0028]
Here, the conductive element 13 may be provided directly on the surface of the support or the protective material 15 and a film-like load resistor 20 may be attached via a binder, or on other polymer film, glass, ceramics, paper, etc. Even if the conductive element 13 is provided, a capacitive body may be formed by a means such as providing a dielectric medium between the elements 17a and 17b and the load resistor 20 to form a capacitor.
The capacitance body is a portion where capacitance is generated between both ends. In addition to a commercially available capacitor, a capacitor that generates capacitance due to a structure sandwiching a dielectric film may be used.
[0029]
When a conductor such as a metal rod or metal wire that is not grounded is placed in a space where radio waves arrive, some radio waves are absorbed and others interact with the electromagnetic field created by the alternating current flowing in the conductor. Reflected by action. At this time, the ratio (absorption amount / reflection amount) between the radio wave absorption amount and the reflection amount varies depending on the impedance of the conductor, and if the impedance is almost zero, the ratio is also almost zero (total reflection).
[0030]
However, the configuration shown in FIG. 4 in the present invention is a configuration of a half-wave dipole antenna element through capacitors 21a and 21b at the antenna element intermediate portion, and a load resistor 20 is connected to the reception input portion thereof. Therefore, the radio wave energy received by the antenna element is converted into thermal energy by the load resistor 20.
[0031]
Therefore, it is equivalent to absorbing incoming radio waves. In the present invention, the length of the two elements 17a and 17b, the capacitance values of the capacitors 21a and 21b formed by the electrode pads 18a and 18b and the electrode pads 19a and 19b, and the resistance value of the load resistor 20 are incoming radio waves to be shielded. Is set to a value that is efficiently absorbed.
[0032]
Further, this absorption occurs not only for radio waves directly incident on the surface of the conductor but also for radio waves around the conductor (however, the farther away from the conductor, the smaller the amount of absorption). In other words, it depends on the effective aperture area in the half-wave dipole antenna element. Therefore, if the optimum antenna element interval is formed in consideration of the effective aperture area of each antenna element and the interaction between each antenna element, the absorption efficiency of incoming radio waves increases and the transmitted radio waves decrease.
[0033]
In addition, because of the characteristics of the half-wave dipole antenna, it is almost omnidirectional and is not affected by the direction of incoming radio waves.
[0034]
In general, in a half-wave dipole antenna, the received power is maximized when the linear direction of the element coincides with the electric field component direction of the radio wave, that is, when the plane of polarization is the same. Therefore, when antenna elements are arranged in a horizontal row as shown in FIG. 1, it is particularly effective for radio waves having a plane of polarization in a specific direction.
[0035]
However, the polarization plane of the actual incoming radio wave is not constant, and there are various polarization planes. Therefore, it is possible to cope with incoming radio waves of any plane of polarization by adopting a Y-shaped configuration as shown in FIG. 5 or an annular shape as shown in FIG. These shapes are not limited. For example, although not shown, the antenna elements may be arranged in a combination of vertical, horizontal, and diagonal arrangements as shown in FIG.
[0036]
The interaction (absorption, reflection) between the conductor and the radio wave is increased when the conductor and the radio wave resonate. That is, as shown in FIG. 1 to FIG. 5, the surface on which linear conductors having open ends are arranged resonates efficiently when the distance between the open ends of the conductors is approximately one half of the radio wave wavelength. Becomes larger. In other words, for a radio wave having a wavelength (frequency) that does not resonate with the conductor of this length, this surface does not become a reflection / absorption surface, but most of the surface is transmitted.
[0037]
In the case of the linear shape as shown in FIG. 1, the length of the conductive element is approximately one half of the radio wave wavelength, and in the shape having a branch as shown in FIG. 5, the distance from the center point to the open end is the radio wave wavelength. It becomes approximately one quarter of. Absorption characteristics were given by connecting a load resistance to the center point.
[0038]
In addition, when the annular conductor as shown in FIG. 6 is arranged, it efficiently resonates when the circumference of the annular conductor, which is a conductive element, is substantially equal to the radio wave wavelength, and this array surface absorbs radio waves of a specific frequency. It becomes a surface. In the case of an annular conductor, a part was cut out and a resistor was connected between them.
[0039]
Furthermore, by using a metal element having a low resistivity as the conductor used for the antenna element which is a conductive element, the resonance characteristics become sharp and the selectivity of incoming radio waves to be shielded is improved. Therefore, this method is effective when the frequencies of the shielded radio wave and the transmitted radio wave are close to each other.
[0040]
The present invention utilizes the properties of the linear conductor, which is a conductive element as described above, and resonates with a radio wave having a frequency to be shielded (however, the wavelength is a wavelength in a dielectric). A radio wave absorbing surface is formed by arranging antenna elements having resistors at midpoints of such a length.
[0041]
The absorption characteristic of such a radio wave absorption surface is actually determined by the reception capability of the incoming radio wave in the antenna element, and in addition, it is determined by efficiently converting the resistor disposed at the center of the antenna element into thermal energy. That is, it is important to match the radiation impedance of the antenna element with the resistor.
[0042]
In practice, the line width and thickness of the conductive elements and the spacing between the individual conductive elements are determined in consideration of the absorption characteristics and frequency selectivity for the radio wave having the frequency to be shielded.
[0043]
Here, three types of conductive elements are shown in FIGS. 1 to 6, but it is apparent from the above description that the shape of the conductive elements is not limited to these.
[0044]
In the description of the present invention described so far, the incoming radio wave to be shielded is limited to one frequency. However, for the purpose of shielding incoming radio waves of a plurality of frequencies, each incoming radio wave frequency is supported. A radio wave absorber in which a large number of antenna elements according to the present invention are arranged is also included in the present invention.
[0045]
In addition, when making a radio wave shielding room using the radio wave absorber of the present invention, since the arrangement surface of the conductive elements that are independent from each other is used as the radio wave absorber surface, connection and grounding of the radio wave absorbers are not necessary. . This greatly simplifies the workability and is a great advantage of the radio wave absorber of the present invention.
[0046]
【The invention's effect】
As is clear from the above description, according to the present invention, it is possible to supply a radio wave absorber excellent in workability that does not require connection or grounding between the radio wave absorbers. And it can also be finished in a thin wave absorber.
[0047]
Further, the radio wave absorber of the present invention absorbs the energy of the radio wave coming from both sides and having the frequency to be shielded by the resistor connected to the conductive element, and the radio wave (electromagnetic wave) of other frequencies is It has the property of transmitting in both directions.
[0048]
In addition, since it is almost irrelevant to the direction of incoming radio waves and exhibits absorption performance in all directions, when a building or room is formed using the radio wave absorber of the present invention, internal dedicated communication (business office PHS or wireless LAN) Etc.), it is possible to prevent deterioration of communication line performance such as reduced sensitivity and interference of wireless devices due to indoor reflection of radio waves and intrusion from outdoors, and leakage of information, as well as necessary communication with the outside It is possible to receive public broadcasts and prevent the occurrence of disturbances in the reception of external TV radio waves caused by radio wave absorbers.
[0049]
In addition, when used as a room partition in a building, radio waves having the same frequency can be used in two rooms sandwiching the partition, so that the problem of insufficient frequency channels can be solved.
[Brief description of the drawings]
FIG. 1 is a front view showing a radio wave absorption surface (conductive element array surface) of a radio wave absorber having frequency selectivity according to the present invention.
2 is a cross-sectional view of the embodiment according to FIG. 1 of a radio wave absorber having frequency selectivity according to the present invention.
3 is a cross-sectional view of the antenna element shown in FIG.
4 is an electrical equivalent circuit diagram of the antenna element shown in FIG. 3. FIG.
FIG. 5 is a front view showing another radio wave absorption surface (conductive element array surface) of a radio wave absorber having frequency selectivity according to the present invention.
FIG. 6 is a front view showing another radio wave absorption surface (conductive element array surface) of a radio wave absorber having frequency selectivity according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 13 ... Conductive element 14 ... Frequency selective surface 15 ... Support body or protective material 16 ... Film 17a, 17b ... Element 18a, 18b, 19a, 19b ... Electrode pad 20 ... Load resistance 21a, 21b ... Capacitor

Claims (5)

At least, the film and, in the radio wave absorber and a number of conductive elements having a specific length corresponding to the frequency of the radio wave to be one shielded disposed on a surface of said film,
A notch is provided in a part of the conductive element,
Provide electrodes at both ends of the notch,
Provide another electrode at a position overlapping the electrode on the other side of the film,
A radio wave absorber having frequency selectivity, wherein the other electrodes are connected by a resistor . Wherein the conductive element has an open end, said open about half of the electric wave wavelength length is to shield between end 1 (however, the radio wave wavelength is the wavelength in said film in), and the conductive wave absorber having a frequency selectivity of claim 1, wherein the component having a resistor at the midpoint of the length of the element. Wherein the conductive element is annular, wave wavelength (however, the radio wave wavelength is the wavelength in said film in) the length of its circumference is to shield according to claim 1, wherein the substantially have equal to A radio wave absorber with frequency selectivity. Wave absorber having frequency selectivity according to any one of claims 1 to 3, characterized in that Ru with foil to the conductive elements. Wave absorber having frequency selectivity according to any one of claims 1 to 4, characterized in that Ru using the linear-shaped metal element to the conductive element.

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