Radiant energy – Radiation controlling means
Reexamination Certificate
1998-05-28
2001-06-19
Nguyen, Kiet T. (Department: 2881)
Radiant energy
Radiation controlling means
C250S515100
Reexamination Certificate
active
06249006
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an apparatus which shields an electromagnetic field emerging from the inside of an electrical device, and in particular to a resonance-type shield and an active shield which both use electronic circuitry.
DESCRIPTION OF THE PRIOR ART
Electrical and electronic devices can generate electromagnetic fields. While weak, such fields can make other devices work erroneously or have adverse effects on the health of users, so that devices need to be shielded.
Shield members made of electric conductors or ferromagnetic materials are conventionally used to shield the electromagnetic fields (see
Journal of the Electrical Society
Vol. 116, April 1996, p203-p217).
FIGS.
21
(
a
) and
21
(
b
) are drawings that show a conventional method for shielding an electromagnetic field with a shield member.
FIG.
21
(
a
) shows a state where an electromagnetic field generated in an electrical device is emerging from the opening
11
of the chassis
10
.
FIG.
21
(
b
) shows a state where the opening
11
is covered with the shield member
12
to shield the electromagnetic field.
When the shield member
12
is composed of an electrically conductive material, the generated electromagnetic field is reflected back into the device chassis by eddy currents which are generated in the shield member as a reaction to the leakage electromagnetic field. Conversely, when the shield member
12
is composed of a magnetic material that is more magnetically permeable than air, the magnetic component of the electromagnetic field is confined within the device by the shield member, thereby preventing the electromagnetic field from emerging from the opening.
As described below, however, there are problems with this conventional shield method using the shield member
12
.
The first problem is that the opening
11
needs to be covered with a sheet or mesh shield member
12
to produce a high shield effect. Therefore, if the opening
11
is an opening which something is inserted into or removed from, such as a disk slot of a floppy disk drive, or if the opening is positioned by a moving mechanism, it is not possible to apply these conventional methods as they are. A complicated shield mechanism interlocking with the moving mechanism is necessary.
The second problem is that when various kinds of electromagnetic fields of different strengths or frequencies are generated in a device or when the strength or frequency of an electromagnetic field varies over time, a uniform shield effect cannot be produced with a single shield member
12
.
The third problem is that when the shield member
12
is composed of a magnetic material, there will be a limit on the strength of the magnetic field which the shield member
12
can shield. For instance, it is very difficult for a shield member
12
of a magnetic material to shield a strong magnetic field over 1.5 tesla.
With regard to the above problems, the first object of the present invention is to provide an electromagnetic field shielding apparatus which shields an electromagnetic field that emerges from an opening of a chassis without covering the opening, thereby keeping the opening unobstructed.
The second object of the present invention is to provide a flexible electromagnetic field shielding apparatus which can easily cope with various kinds of electromagnetic fields of different strengths and frequencies.
The third object of the present invention is to provide an electromagnetic field shielding apparatus which can produce a uniform shield effect without changing parts or materials of the apparatus even if the strength or frequency of the electromagnetic field varies over time.
The fourth object of the present invention is to provide an electromagnetic field shielding apparatus which can shield a strong magnetic field over 1.5 tesla.
SUMMARY OF THE INVENTION
The resonance-type electromagnetic field shielding apparatus of the present invention includes an electromagnetic field detection means which includes a coil for detecting an electromagnetic field, and a resonance means which consumes electricity, where the circuit constants of respective parts of the resonance means are predetermined so that the resonance means is tuned to the frequency of the electromotive force induced by the electromagnetic field detection means.
With this apparatus, the electromagnetic field detection means detects an electromagnetic field, an electromotive force is induced in the coil, the electromotive force is supplied to the resonance means, and the energy of the electromotive force is consumed therein. As a result, the strength of the electromagnetic field is suppressed, thereby achieving a shield effect.
By providing the electromagnetic field detection means including a coil around the edge of an opening of an electrical device from which an unnecessary electromagnetic field is emerging, the strength of the electromagnetic field passing through the electromagnetic field detection means is suppressed. Therefore, the electromagnetic field emerging from the opening is shielded without covering the opening to keep it open, thereby achieving the first object.
Here, the resonance means may be a parallel resonance circuit including L, C, and R electronic parts or may be an electric conductor which can be used as a distributed constant circuit.
With this structure, by changing these circuit parts (the electronic parts or the electric conductor), a resonance means causing a different energy consumption or a resonance means having a different resonance frequency can be obtained without difficulty, thereby achieving the second and fourth objects.
The L, C, and R electronic parts may be circuit parts with variable circuit constants, and the electromagnetic field shielding apparatus may be provided with a means for identifying a center frequency of the electromotive force and a means for determining and controlling the circuit constants to produce resonance at the identified center frequency.
With this structure, the apparatus changes the resonance frequency to follow variation in the frequency or strength of an electromagnetic field, or changes the amount of the energy consumption, thereby achieving the third object.
The electromagnetic field shielding apparatus of the present invention may be an active electromagnetic field shielding apparatus which includes an electromagnetic field detection means for detecting an electromagnetic field, an electromagnetic field generation means for generating a counteractive electromagnetic field, and a control means for controlling the electromagnetic field generation means so that the electromagnetic field generation means generates a counteractive electromagnetic field for canceling out the electromagnetic field detected by the electromagnetic field detection means.
With this apparatus, the electromagnetic field generation means generates an electromagnetic field to counteract the leakage electromagnetic field detected by the electromagnetic field detection means. Therefore, by making the electromagnetic field detection means and the electromagnetic field generation means target the same space, the electromagnetic field in the space is canceled out.
Here, the electromagnetic field detection means and the electromagnetic field generation means may be hollow coils whose hollow parts are identical or have identical center axes, and may be provided around the edge of the opening of an electrical device from which an electromagnetic field is emerging.
In this manner, the electromagnetic field emerging from the inside of an electrical device through its opening is canceled out, thereby achieving the first object.
Also, by selecting the constants of the circuit parts appropriately or by replacing the circuit parts with parts having variable circuit constants, the second and third objects are achieved.
REFERENCES:
patent: 5270551 (1993-12-01), Kamimura et al.
patent: 5786975 (1998-07-01), Dunzan et al.
patent: 3938238 (1991-05-01), None
patent: 62-97399 (1987-05-01), None
patent: 2159595 (1990-06-01), None
patent: 3280595 (
Matsushita Electric - Industrial Co., Ltd.
Nguyen Kiet T.
Price and Gess
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