JP2000091780A - Electromagnetic wave absorbing body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent leakage of electromagnetic wave with a simple configuration. SOLUTION: An electromagnetic wave absorbing body comprises a flat plate part 2 of a strip-like metal plate and a cylindrical part 3 of a metal plate fitted to its end part. When the cylindrical part 3 is inserted in an antenna 13 of a portable telephone 10 so that the flat plate part 2 tightly contacts the side surface of a case 15, the interaction between a metal plate 14 inside a case and the flat plate 2 converts the electromagnetic wave at high frequency band into a heat for consumption.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electromagnetic wave absorber for preventing leakage of electromagnetic waves from, for example, various electronic devices.

[0002]

2. Description of the Related Art In recent years, with the spread of various electronic devices such as personal computers and portable telephones, undesired electromagnetic waves radiated from the electronic devices have caused serious interference or obstacles to other electronic devices or electric devices. It is becoming a problem. Such undesired electromagnetic waves not only cause noise to other electronic devices such as radios and televisions, but also sometimes cause medical electronic devices used in medical procedures to malfunction or are mounted on a moving automobile. There is a possibility that the control circuit used may malfunction, and that there is a possibility that human lives may be endangered. In addition, although no clear confirmation has been obtained at this time, it has been pointed out that a large amount of electromagnetic waves may directly adversely affect human health.

[0003]

Conventionally, various measures have been taken in various electronic devices to minimize leakage of electromagnetic waves generated inside the electronic devices to the outside. However, unlike electrostatic shielding, shielding of electromagnetic waves is inherently very difficult. In addition, portable electronic devices aiming at reduction in size and weight, such as mobile phones, have various materials such as the material and thickness of the housing. These measures have made the measures even more difficult.

[0004] In particular, since a portable telephone uses a source of electromagnetic waves very close to a human head, it is used.
If electromagnetic waves have any adverse effect on health, it is desirable to minimize the leakage of unwanted electromagnetic waves that are unnecessary for communication.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and an object of the present invention is to provide an electromagnetic wave absorbing device having a simple structure and capable of effectively preventing or reducing electromagnetic wave leakage. Is to provide the body.

[0006]

According to a first aspect of the present invention, there is provided a high-frequency electromagnetic wave absorbing device mounted outside a housing of an electromagnetic wave generating apparatus having a housing made of an insulating resin. The body is characterized by comprising a metal plate disposed inside the housing and an elongated conductor plate facing the housing with the metal plate interposed therebetween.

A second invention for solving the above-mentioned problem is a high-frequency electromagnetic wave absorber used for an electromagnetic wave generator having a housing made of an insulating resin,
It is characterized by comprising an elongated conductor plate buried in the resin of the housing facing the metal plate disposed inside the housing.

The length of the conductor plate in the longitudinal direction is as follows:
One half of the wavelength of the electromagnetic wave of interest or of high radiation intensity
It should be set to a range of about １.

[0009]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing an embodiment of an electromagnetic wave absorber according to the present invention. Although this electromagnetic wave absorber is used by being attached to a mobile phone, the present invention can be applied to other various electromagnetic wave generators.

FIG. 1 is an external perspective view of the electromagnetic wave absorber of the present embodiment. This electromagnetic wave absorber 1 has a length L, a width W, and a thickness D
And a cylindrical portion 3 made of a metal plate attached to an end of the flat plate portion 2.
Although not shown, these components are entirely covered with a very thin synthetic resin film for insulation from the outside.

FIG. 2 shows the electromagnetic wave absorber 1 as a mobile phone 1.
FIG. 2 is a view showing a state where the mobile phone 10 is attached to the mobile phone 10. The cylindrical portion 3 of the electromagnetic wave absorber 1 is fitted to a telescopic antenna 13 of the mobile phone 10 and fixed to the base thereof. In order to stably fix, the inner diameter of the cylindrical portion 3 may be approximately the same as or slightly larger than the outer diameter of the root portion of the antenna 13. By such mounting, the flat plate portion 2 is almost in close contact with the side surface of the mobile phone 10.

According to the results of experiments conducted by the present inventors, 80
For a mobile phone using a frequency of 0 MHz band, a copper plate is used for the flat plate portion 2 and the cylindrical portion 3, and L = 75 mm, W = 5
mm, D = 0.1 mm, the cell phone 10
It was confirmed that the electromagnetic waves leaking to the outside after passing through the respective surfaces of the housing 15 were reduced to an almost unmeasurable degree.
As a result of an experiment in which W = 5 mm and D = 0.1 mm were fixed and the length L was changed, it was also confirmed that the above-described effect was maximized when the length L was around 75 mm.

When only the flat plate portion 2 is attached to the side surface of the housing 15 without providing the cylindrical portion 3, leakage of electromagnetic waves from the housing surface (the right surface in FIG. 2) on which the antenna 13 is mounted is provided. However, it was confirmed that the leakage of the electromagnetic wave from the other housing surface could be prevented with almost no change. That is, since electromagnetic waves passing through the housing surface closest to the head side (around the ears) of the mobile phone are reduced, a sufficient effect can be obtained in reducing the influence on the human body.

Further, generally, in a portable telephone, an antenna 13 is provided.
In the most contracted state, the tip is in close contact with the root. Therefore, a structure may be adopted in which the cylindrical portion 3 of the electromagnetic wave absorber 1 is just fitted to the tip of the antenna 13. According to this, the electromagnetic wave leaking to the surroundings via the antenna 13 can be almost completely absorbed, so that a higher effect is achieved. Electromagnetic waves used for telephone communication are much stronger than leaked electromagnetic waves, so they do not hinder communication. In such a structure, when the antenna 13 is used in an extended state, the flat plate portion 2 is separated from the housing 15 and the effect is weakened. However, in the actual mobile phone, the communication state hardly changes due to the expansion and contraction of the antenna 13, so that a good communication can be performed even when the antenna 13 is contracted.

For the measurement of the electromagnetic wave, a local electromagnetic wave measuring device which can measure only an electromagnetic wave emitted from a small area is proposed which has been proposed by the present applicant in Japanese Patent Application No. 10-220136.

Although the reason why the above-described effect of reducing electromagnetic waves can be obtained has not been sufficiently elucidated, it is presumed that the reason may be as follows. Since 800 MHz radio waves are used as communication frequencies in mobile phones (there may be other frequencies), the 800 MHz band signal and its harmonic components are dominant in the frequency of leaked electromagnetic waves. The length L of the flat plate portion 2 of the electromagnetic wave absorber 1 corresponds to substantially a quarter wavelength of a signal having that frequency.

On the other hand, generally, in a mobile phone, as shown in FIG.
Are provided, and many electronic circuits 11 are provided in other portions. Further, the housing 15 itself is a molded product made of a synthetic resin which is an insulator, and a metal plate 14 for the purpose of shielding or the like is provided inside the housing 15 in close contact with the housing 15. The metal plate 14 serves as a common ground for the electronic circuit 11 in many cases.

It is considered that the flat plate portion 2 and the metal plate 14, which extend substantially in parallel and whose both ends are open, form a distributed constant circuit in a high frequency range, and exhibit characteristics of a resonance circuit as shown in FIG. The frequency of the resonance is an 800 MHz band corresponding to a wavelength four times the length L of the flat plate portion 2. However, since the Q of the resonance circuit is not so high, it oscillates in a wide frequency range around the frequency. Conceivable. When the electromagnetic wave radiated from the electronic circuit 11 reaches the flat plate portion 2, a current I is induced in the resonance circuit, and is converted into heat by the resistance component R and consumed. Thereby, the energy of the electromagnetic wave is attenuated, and leakage to the outside is prevented.

It is to be noted that, besides mounting the electromagnetic wave absorber on the outside of the housing 15, the structure shown in FIG. 4 can be adopted. In this example, a metal plate 4 having the same dimensions as the flat plate portion is embedded in a housing 15 made of a synthetic resin. With such a configuration, the same effect as in the above example can be obtained.

[0020]

As described above, the electromagnetic wave absorber according to the first and second aspects of the present invention is used by being mounted on an electromagnetic wave generating device such as a mobile phone or embedded in a housing itself, and is formed by a conductor plate. The energy of electromagnetic waves leaking from inside the device is converted into heat and consumed. Therefore, the electromagnetic wave can be efficiently attenuated, and, for example, the suppression of the leakage of the electromagnetic wave from the inside of the housing of the device to the outside can be easily realized at low cost. Therefore, for example, a user of a mobile phone can be prevented from being exposed to a large amount of leakage electromagnetic waves radiated from the mobile phone.

Also, in order to prevent unnecessary leakage of electromagnetic waves, a complete shield was conventionally required, which increased the weight of the device itself and was not suitable for small and lightweight electronic devices such as mobile phones. If the electromagnetic wave absorber according to the present invention is used, even if the shield is incomplete, it is possible to effectively reduce the leakage electromagnetic wave, which contributes to the reduction in size and weight of the device itself.

Further, according to the electromagnetic wave absorber according to the present invention, for example, in a mobile phone, noise superimposed on a call voice can be removed to improve clarity. This is considered to be because the electromagnetic wave absorber also attenuates the energy of the electromagnetic wave flying in the space inside the housing of the electronic device and reduces the noise jumping into the audio circuit.

[Brief description of the drawings]

FIG. 1 is an external perspective view of an embodiment of an electromagnetic wave absorber according to the present invention.

FIG. 2 is a state diagram in which the electromagnetic wave absorber of FIG. 1 is attached to a mobile phone.

FIG. 3 is a circuit diagram showing an equivalent resonance circuit using an electromagnetic wave absorber.

FIG. 4 is a diagram showing a state in which an electromagnetic wave absorber according to another embodiment is used in a mobile phone.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Electromagnetic wave absorber 2 ... Flat plate part 3 ... Cylindrical part 4 ... Metal plate 10 ... Cellular phone 13 ... Antenna 14 ... Metal plate 15 ... Housing

Claims (2)

[Claims] An electromagnetic wave absorber for high frequency mounted outside a housing of an electromagnetic wave generating device having a housing made of an insulating resin, comprising: a metal plate disposed inside the housing; An electromagnetic wave absorber comprising an elongated conductor plate facing and sandwiched therebetween. 2. A high-frequency electromagnetic wave absorber used for an electromagnetic wave generator having a housing made of an insulating resin,
An electromagnetic wave absorber comprising an elongated conductor plate buried in a resin of the housing facing a metal plate disposed inside the housing.