JP2003115694A - Wave absorber and electronic appliance provided with the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wave absorber for which a noise absorption performance is easily fixed and a manufacture cost is reduced, and an electronic appliance provided with it. SOLUTION: The wave absorber A is arranged near a noise generation source inside the electronic appliance. The wave absorber A is positioned in a state of facing a propagation direction of noise N and is composed of a resistance film 1, a height H of a counter surface is set to about 1/2 of the wavelength of the noise N or set to about 1/4 of the wavelength of the noise N and one end edge in a height direction is conducted to a conductor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radio wave absorber and an electronic device including the same.

[0002]

2. Description of the Related Art Conventionally, the increase in traffic accidents has become a social problem, and the safety of traffic depends on human ability. For this reason, the physical and mental burden on the driver is large.
Therefore, in order to reduce the burden, automobile collision prevention radar systems have been put into practical use. This car collision prevention radar system measures the distance between vehicles and the ground speed,
According to the situation, it is a system that automatically and automatically controls a vehicle, which assists driving and reduces the burden on the driver.

A radio wave transmitter / receiver (the used radio wave is a millimeter wave) is used to measure the inter-vehicle distance and is installed in an automobile. As shown in FIG. 7, this radio wave transmitter / receiver includes an aluminum casing 5 having a transmission circuit 6 and a reception circuit 7, and a transmission antenna 6 a connected to the transmission circuit 6.
And a receiving antenna 7a connected to the receiving circuit 7.

However, in the above radio wave transmitter / receiver, when the transmission circuit 6 and the reception circuit 7 are close to each other, the radio wave directly circulates from the transmission circuit 6 to the reception circuit 7 and interferes with the measurement of the inter-vehicle distance. There are things to do. That is, the radio wave may be noise (unnecessary radio wave) N. Therefore, the radio wave absorber B is attached to a part of the casing 5 (usually, the ceiling portion of the casing 5 corresponding to the transmitting circuit 6 and the receiving circuit 7) with the adhesive 3 or the like, whereby the transmitting circuit 6 The noise N from is absorbed. The radio wave absorber B is a general one in which the metal plate 12 is lined on the absorber 11.

The problem of the noise N is not limited to the above-mentioned radio wave transmitter / receiver but also applies to other electronic devices. That is, the noise N generated in a part of the electronic device may adversely affect the function of the electronic device. Therefore, also for such an electronic device, by attaching the electromagnetic wave absorber B to a part of the housing, as described above,
The noise N is absorbed.

The absorbing material 11 of the electromagnetic wave absorber B used in this way includes a dielectric loss type in which carbon or a metal filler is dispersed in rubber, and a magnetic loss type in which ferrite is used. .

[0007]

However, in such a radio wave absorber B, a high degree of thickness accuracy is required in order to exhibit the noise absorbing performance. However, such a thickness adjustment is difficult with the conventional absorbent material 11. Further, in the above conventional absorber 11, it is necessary to mix a predetermined material in order to adjust the dielectric constant and the magnetic permeability, but the noise absorption performance varies depending on the mixed state. For this reason, in order to constantly provide the radio wave absorber B having a constant noise absorbing performance, it takes time and labor, and there is a problem that the manufacturing cost increases.

The present invention has been made in view of the above circumstances, and provides a radio wave absorber which can easily reduce the noise absorption performance and can reduce the manufacturing cost, and an electronic apparatus including the radio wave absorber. Is its purpose.

[0009]

In order to achieve the above object, the present invention is a radio wave absorber arranged in the vicinity of a source of unwanted radio waves, which is made of a resistance film and is provided in a propagation direction of the unwanted radio waves. The gist is a radio wave absorber that is positioned in a substantially straight state. Further, the electromagnetic wave absorber whose height of the direct surface of the resistance film in the substantially direct direction is set to about 1/2 of the wavelength of the unnecessary radio wave is an important element, and Another important element is a radio wave absorber whose height on the facing surface is set to about 1/4 of the wavelength of the unnecessary radio wave and one edge of which is orthogonal to the height direction is electrically connected to the conductor. Further, an electronic device provided with such a radio wave absorber is defined as a second gist. Usually, the unnecessary radio waves are millimeter waves or microwaves.

That is, the radio wave absorber of the present invention is made of a resistance film and is positioned in a state in which the radio wave absorber is oriented substantially straight in the propagation direction of unnecessary radio waves. Therefore, the unnecessary electric wave can resonate with the resistive film by using the resistive film itself as an antenna, and the energy of the unnecessary electric wave can be greatly attenuated. As described above, since the radio wave absorber of the present invention absorbs unnecessary radio waves by utilizing the resonance phenomenon in the antenna function, a high degree of thickness accuracy is not required, and noise (unnecessary radio waves) due to the thickness of the resistive film is absorbed. There is no variation in performance. Further, since the radio wave absorber of the present invention is composed of a resistance film, it is not necessary to mix a predetermined material for adjusting the dielectric constant and magnetic permeability, and the noise absorption performance does not vary depending on the mixed state. For these reasons, the radio wave absorber of the present invention can be easily manufactured so that the noise absorption performance is constant, and the manufacturing cost can be reduced.

In particular, when the height of the direct surface of the resistance film is set to about 1/2 of the wavelength of the unnecessary radio wave, the resonance phenomenon of the resistance film is effectively exhibited, so that it is effective. The energy of unnecessary radio waves can be attenuated. Therefore, the same action and effect as those of the radio wave absorber can be obtained. Further, when the height of the direct surface of the resistance film is set to about 1/4 of the wavelength of the unnecessary radio wave and one end edge orthogonal to the height direction is conducted to the conductor, resonance phenomenon of the resistance film occurs. Is effectively exhibited, and the energy of unnecessary radio waves can be effectively attenuated in a small size, and at the same time, a grounding effect can be achieved. For this reason, it is possible to achieve the same action and effect as the above-mentioned radio wave absorber, while being smaller in size.

Since the electronic equipment of the present invention is provided with the radio wave absorber, even if noise is generated in a part of the inside of the electronic equipment, the noise is absorbed by the radio wave absorber and It is possible to prevent the function of the electronic device of the invention from being adversely affected.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Next, embodiments of the present invention will be described in detail with reference to the drawings.

1 and 2 show an embodiment of a radio wave absorber of the present invention and an electronic apparatus equipped with the same. In this embodiment, a radio wave transmitter / receiver used for measuring an inter-vehicle distance in an automobile collision prevention radar system will be described as an electronic device. This radio wave transmitter / receiver is the same as the conventional one shown in FIG. 7 except for the radio wave absorber B, and the same parts are denoted by the same reference numerals (a transmitting antenna and a receiving antenna are omitted in the drawing). And
The radio wave absorber A according to this embodiment is hung down on the ceiling portion of the casing 5 corresponding to the space between the transmission circuit 6 and the reception circuit 7 by using the adhesive 3 or the like, and noise from the transmission circuit 6 (unnecessary radio wave )
It is positioned so as to face the N propagation direction. Further, the radio wave absorber A is composed of the resistance film 1, and the height (vertical length) H of the direct surface is set to ½ or approximately ½ of the wavelength of the noise N. Is longer than the lengths of the transmission circuit 6 and the reception circuit 7, and the ends thereof are set to project beyond the front and rear ends of the transmission circuit 6 and the reception circuit 7. The resistance film 1 is supported on the surface of the film material 2.

More specifically, the above resistance film 1
Is, for example, indium tin oxide (ITO), tin oxide (S
nO ₂ ), zinc oxide (ZnO), titanium nitride (TiN)
Made of a metal oxide or a metal nitride, etc., and is usually formed on the surface of the film material 2 by ion plating, vapor deposition,
It is used after being sputtered. In particular, indium tin oxide (ITO) is preferable because it is excellent in heat resistance, and even if the radio wave transmitter / receiver is installed in the vicinity of the engine room, the noise absorption performance described below hardly deteriorates. Further, the surface resistance of the resistance film 1 is preferably in the range of 1 to 3000 Ω from the viewpoint that the resistance film 1 can be stably manufactured. Furthermore, the thickness of the resistance coating 1 is not particularly limited as long as the resistance coating 1 has a surface resistance in the above range.

The film material 2 is not particularly limited, and polyethylene terephthalate (PE
T), polyimide (PI), polycarbonate (P
C), polymethylmethacrylate (PMMA), polyethylene naphthalate (PEN) and the like. The thickness of the film material 2 is not particularly limited, but is preferably set in the range of 50 to 350 μm from the viewpoint of manufacturability of the resistance film 1.

As described above, the radio wave absorber A is made of the resistance film 1, and the height H of the direct surface of the electromagnetic wave directing from the transmitting circuit 6 in the propagation direction of the noise N is approximately 1 of the wavelength of the noise N. /
Since it is set to 2, the radio wave absorber A can resonate the noise N with the resistance film 1 by using the resistance film 1 as an antenna and attenuate the energy of the noise N. That is, the radio wave absorber A can absorb the noise N. As is clear from the above,
Making the electromagnetic wave absorber A substantially straight in the propagation direction of the noise N has a broad meaning including all angles at which a resonance phenomenon due to the antenna occurs.

Since the radio wave transmitter / receiver is equipped with the radio wave absorber A, even if noise N is generated from the transmission circuit 6, the noise N is absorbed by the radio wave absorber A and the reception circuit is received. It is possible to prevent the noise N from directly entering the vehicle 7, and it is possible to prevent the measurement of the inter-vehicle distance from being disturbed.

Such noise absorbing performance is best exhibited when the height H of the radio wave absorber A is 1/2 of the wavelength of the noise N. Even if the height H of the radio wave absorber A is slightly deviated from the half of the height H, the deviated range, for example, the noise 1 / 2.5-1 / of the wavelength of N
It is meant to include the range of 1.5.

Further, as described above, the radio wave absorber A uses the resonance phenomenon in the antenna function to generate the noise N.
Therefore, high thickness accuracy is not required.
Therefore, in the radio wave absorber A, the noise absorption performance does not vary depending on the thickness of the resistance film 1. Therefore,
It can be easily manufactured so that the noise absorption performance is constant, and the manufacturing cost can be reduced.

Further, the radio wave absorber A is the resistance film 1
Therefore, it is not necessary to mix a predetermined material for adjusting the dielectric constant and the magnetic permeability. Therefore, the radio wave absorber A
Does not cause variations in noise absorption performance due to its mixed state. Therefore, it is possible to easily manufacture the device with a constant noise absorption performance, and it is possible to reduce the manufacturing cost.

When a conductive adhesive is used as the adhesive 3, the noise N can be released to the housing 5 by the earth action, and the energy of the noise N can be attenuated surely. become.

FIG. 3 shows another embodiment of the radio wave absorber of the present invention and an electronic apparatus including the same. In this embodiment, the height H of the electromagnetic wave absorber A is equal to the noise N.
The wavelength is set to 1/4 or approximately 1/4 of the wavelength. Then, the electromagnetic wave absorber A is made of an aluminum casing (conductor).
The conductive adhesive 4 is used to hang it down to 5 so that the upper edge of the radio wave absorber A is conducted to the housing 5 to perform a grounding action, and the energy of the noise N is efficiently attenuated. It has become. The other parts are the same as those in the above embodiment, and the same parts are denoted by the same reference numerals.

In this embodiment, the noise absorption performance is
It is best exhibited when the height H of the radio wave absorber A is ¼ of the wavelength of the noise N. Then, also in this embodiment, the same operation and effect as those of the above-described embodiment are exhibited. Further, in this embodiment, since the height H of the radio wave absorber A is set to 1/4 or approximately 1/4 of the wavelength of the noise N, the height of the case 5 of the radio wave transmitter / receiver is set as described above. It can be made lower than that of the embodiment.

FIG. 4 shows still another embodiment of the radio wave absorber of the present invention and the electronic equipment provided with the same.
In this embodiment, the inside of the housing 5 of the radio wave transmitter / receiver in each of the above embodiments is filled with a potting material (dielectric material) P. The other parts are the same as those in the above-mentioned respective embodiments, and the same parts are denoted by the same reference numerals.

Also in this embodiment, the same operation and effect as those of the above-mentioned respective embodiments are exhibited. Further, in this embodiment, inside the potting material (dielectric) P,
Due to the action of the dielectric, the wavelength of the noise N becomes 1 / ε times (ε: dielectric constant of the potting material P, ε> 1). Therefore, the height H of the radio wave absorber A and the housing 5 of the radio wave transmitter / receiver The height can be made lower than that of each of the above embodiments.

FIGS. 5A to 5D show modifications of the radio wave absorber A in each of the above embodiments. These are the lower edges of the resistive film 1 (one edge that is orthogonal to the height direction).
Are formed in a waveform that rises and falls in the height direction along the length direction (lateral direction) of the direct surface that is directly in the propagation direction of the noise N from the transmission circuit 6. That is, in FIG. 5A, the lower end edge of the resistance film 1 has a waveform in which triangular peaks and inverted triangular valleys are alternately and continuously formed. Figure 5 (b)
Indicates that the lower end edge of the resistance film 1 has a waveform in which triangular peaks are intermittently formed. In FIG. 5C, the lower edge of the resistance film 1 has a waveform in which semi-circular peaks are continuously formed. In FIG. 5D, the lower edge of the resistive film 1 has a waveform in which semi-circular peaks are intermittently formed.

When the radio wave absorber A of such a modified example is used, the height h of the radio wave absorber A in the corrugated portion takes a predetermined range, so that the wavelength (wavelength in a range corresponding to the range of the height h is It is possible to absorb noise N that is twice or four times the height h of the waveform portion. That is, it is possible to absorb a plurality of noises N having different wavelengths. Even if the radio wave transmitter / receiver is installed in the vicinity of the engine room and the height H of the radio wave absorber A increases due to thermal expansion, the expansion rate of the radio wave absorber A can be increased by using the radio wave absorber A of the above modification. By considering, the height h of the waveform portion can be set to a value corresponding to the wavelength of the predetermined noise N (1/2 or 1/4 of the wavelength of the noise N), and the predetermined noise N is absorbed. can do.

As still another embodiment, a plurality of the radio wave absorbers A and the modifications thereof in the above-mentioned respective embodiments are used for one radio wave transmitter / receiver, or a plurality of radio wave absorbers A having different heights H are used. May be used for one radio wave transmitter / receiver. The arrangement of the radio wave absorbers A in this case is as follows.
May be in parallel or in a line. By doing this, noise N of a wide range of wavelengths can be obtained.
Can be absorbed. Therefore, it is possible to absorb a plurality of noises N having different wavelengths.

Next, examples will be described together with comparative examples.

[0031]

[Embodiment 1] As shown in FIG. 6, three radio wave absorbers A are arranged in parallel in a radio wave transmitter / receiver used for measuring an inter-vehicle distance in an automobile collision prevention radar system. The resistance film 1 of each radio wave absorber A is made of indium tin oxide (ITO), sputtered on a polyethylene terephthalate (PET) film material 2 having a thickness of 100 μm, and then polycarbonate (PC) having a thickness of 0.5 mm.
The film material 2 side was attached to the plate-making material 8 to prepare a three-layer laminate. The surface resistance of the resistance film 1 was 400Ω. The wavelength of the noise N from the transmission circuit 6 is 4 m.
m (frequency is 75 GHz). Therefore, the height H of the laminate is adjusted to be 2 mm, which is 1/2 the wavelength of the noise N. The laminated body is provided between the transmission circuit 6, the transmission circuit 6 and the reception circuit 7, and the reception circuit 7.
The adhesive 3 was hung on the ceiling part of the housing 5 corresponding to each of the above. The height of the inside of the housing 5 is 2.8.
It was mm.

[0032]

Comparative Example 1 The height H of the laminate was adjusted to be about 1.5 mm, which is 1 / 2.6 of the wavelength of the noise N. Other than that was the same as that of Example 1.

[0033]

Comparative Example 2 The height H of the laminate was adjusted to be about 2.8 mm, which is 1 / 1.4 of the wavelength of the noise N. Other than that was the same as that of Example 1.

In the radio wave transmitters and receivers of the above-mentioned examples and comparative examples, the attenuation amount of noise N (noise absorption performance) was measured. As a result, in the first embodiment, the attenuation amount of the noise N is 20d.
B was 5 dB in Comparative Example 1, and 5 dB in Comparative Example 2.
Was 10 dB. From this result, it is understood that the radio wave absorber A of the radio wave transmitter / receiver of Example 1 has excellent noise absorption performance.

In each of the above-described embodiments and examples, the radio wave transmitter / receiver used for measuring the inter-vehicle distance in the automobile collision prevention radar system has been described, but the same can be said for other electronic devices.

[0036]

As described above, the electromagnetic wave absorber of the present invention is
It consists of a resistance film and is positioned almost directly in the propagation direction of noise (unnecessary radio waves). Therefore, the unnecessary electric waves resonate with the resistance film by using the resistance film itself as an antenna, and the energy of the unnecessary electric waves is greatly attenuated. be able to. Therefore, the radio wave absorber is not required to have a high degree of thickness accuracy, and since it is not necessary to mix a predetermined material for adjusting the permittivity and the magnetic permeability, the radio wave absorber is manufactured to have a constant noise absorbing performance. This can be done easily and the manufacturing cost can be reduced.

Particularly, in the radio wave absorber of the present invention, the height of the direct surface of the resistance film is set to be approximately 1 / the wavelength of the unnecessary radio wave.
When the value is set to 2, the resonance phenomenon of the resistance film is effectively exhibited, and thus the energy of unnecessary radio waves can be effectively attenuated. Therefore, the same action and effect as those of the radio wave absorber can be obtained.

In the radio wave absorber of the present invention, the height of the direct surface of the resistance film is set to be approximately 1 / the wavelength of the unnecessary radio wave.
When 4 is set and one end edge orthogonal to the height direction is conducted to the conductor, the resonance phenomenon of the resistance film is effectively exhibited,
It is compact and can effectively attenuate the energy of unnecessary radio waves, and can also act as a ground. For this reason, it is possible to achieve the same action and effect as the above-mentioned radio wave absorber, while being smaller in size.

Further, in the radio wave absorber of the present invention, when the edge in the height direction of the resistive film is formed in a wave shape that rises and falls in the height direction along the length direction of the direct surface, Since the height of the electromagnetic wave absorber is within a predetermined range in the corrugated part,
It is possible to absorb a plurality of noises having different wavelengths, and it is also possible to absorb noises of a predetermined wavelength even if the radio wave absorber is thermally expanded and its height becomes high.

According to the electronic device provided with the radio wave absorber of the present invention, since the radio wave absorber absorbs noise, the function of the electronic device of the present invention can be hardly adversely affected. it can.

In particular, in the electronic device of the present invention, when a plurality of types of the electromagnetic wave absorber of the present invention having different types and heights of the direct surfaces are used in one electronic device, noise of a wide range of wavelengths is generated. Since it can be absorbed, a plurality of noises having different wavelengths can be absorbed.

Further, in the electronic device of the present invention, when a dielectric is provided between the noise source and the radio wave absorber, the noise inside the dielectric is affected by the action of the dielectric. Since the wavelength becomes 1 / ε times (ε: dielectric constant of the dielectric, ε> 1), the height of the radio wave absorber and the radio wave transmitter / receiver can be further reduced.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an embodiment of a radio wave absorber of the present invention and an electronic device including the same.

FIG. 2 is a perspective view showing a part of the radio wave absorber and the electronic device.

FIG. 3 is an explanatory diagram showing another embodiment of a radio wave absorber of the present invention and an electronic device including the same.

FIG. 4 is an explanatory diagram showing still another embodiment of a radio wave absorber of the present invention and an electronic device including the same.

5A to 5D are perspective views showing modified examples of the radio wave absorber.

FIG. 6 is an explanatory diagram showing an example and a comparative example of a radio wave transceiver.

FIG. 7 is an explanatory diagram showing a conventional radio wave transmitter / receiver.

[Explanation of symbols]

A radio wave absorber H height N noise 1 Resistive film

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Claims (8)

[Claims] 1. A radio wave absorber arranged near a source of unwanted radio waves, comprising a resistance film, and positioned in a state of being substantially straight in a propagation direction of the unwanted radio waves. body. 2. The radio wave absorber according to claim 1, wherein the height of the direct surface of the resistance film which is directed substantially directly is set to about 1/2 of the wavelength of the unnecessary radio wave. 3. The height of the straight surface of the resistance film which is substantially straight is set to approximately 1/4 of the wavelength of the unnecessary radio wave, and one end edge orthogonal to the height direction is electrically connected to the conductor. The electromagnetic wave absorber according to item 1. 4. The edge of the resistance film in the height direction is formed in a corrugated shape that moves up and down in the height direction along the length direction of the straight surface. The radio wave absorber described. 5. The radio wave absorber according to claim 1, wherein the surface resistance of the resistance film is in the range of 1 to 3000 Ω. 6. An electronic device comprising the radio wave absorber according to at least one of claims 1 to 5. 7. The electronic device according to claim 6, further comprising a plurality of radio wave absorbers having different heights of the direct surface. 8. The electronic device according to claim 6, wherein a dielectric is provided between the unnecessary radio wave generation source and the radio wave absorber.