Portable telephone

Details Portable telephone Portable telephone

2001-12-27

2004-08-31

Milord, Marceau (Department: 2682)

Telecommunications

Transmitter and receiver at same station

Having particular application of a transceiver

C455S090300, C455S300000, C455S301000, C455S106000, C455S575100, C455S575500, C455S575700, C455S128000, C455S117000

Reexamination Certificate

active

06785519

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a portable telephone and, in particular, it relates to a portable telephone capable of minimizing absorption of an electromagnetic energy radiated therefrom by a human body when in use thereof.
2. Description of the Related Art
FIG. 6
is a schematic diagram showing a conventional portable telephone. As shown in
FIG. 6
, a portable telephone
201
is used being held in a close proximity to a head (HEAD) of a user. The portable telephone
201
is comprised of an antenna
31
, a feeder
32
, a printed board
33
, a shield case
34
, semiconductor integrated circuits
35
A and
35
B, a microphone
36
, a keypad
37
, a liquid crystal display
38
, a speaker
39
and an insulated housing
40
.
The antenna
31
for use of signal transmission and reception is allowed to project upward from an upper edge of the housing
40
for transmitting electromagnetic waves to a base station in a transmission mode and receiving electromagnetic waves from the base station in a reception mode. The antenna
31
is a retractable antenna capable of retracting in a longitudinal direction of the housing
40
.
On one surface of the printed board
33
, there is mounted a semiconductor integrated circuit
35
A constructed including transistors, capacitors, resistors and so on. Also, on the other surface of the printed board
33
, there is mounted a semiconductor integrated circuit
35
B constructed likewise.
The printed board
33
and the semiconductor integrated circuits
35
A and
35
B in combination constitute a printed circuit board
35
. On this printed circuit board
35
, there are mounted a switch circuit, a control circuit, a transmitting circuit and a receiving circuit. Between the antenna
31
and the transmitting and the receiving circuits are connected via the switch circuit and the feeder section
32
.
The microphone
36
constitutes a transmitter (telephone microphone), and the speaker
39
constitutes a receiver (telephone earphone). The housing
40
is provided with an opening
36
H for the microphone
36
, an opening
39
H for the speaker
39
, a window
38
W for the liquid crystal display section
38
and the like. The housing
40
accommodates the printed circuit board
35
, the shield case
34
, the microphone
36
and the speaker
39
.
A voice or sound uttered by the user is supplied to the microphone
36
through the opening
36
H. The microphone to which the sound or the like uttered by the user is input generates a first audio signal corresponding to the sound uttered by the user. The printed circuit board
35
converts the first audio signal to a first radio signal. The first radio signal is transmitted from the antenna
31
to the base station. The base station sends a second radio signal to the portable telephone
201
.
The printed circuit board
35
converts the second radio signal having been input to the antenna
31
into a second audio signal to be supplied to the speaker
39
. The speaker
39
outputs a sound corresponding to the second audio signal to be supplied to the user.
Circuits such as the printed circuit board
35
, the microphone
36
, the speaker
39
, the liquid crystal display
38
and so on are supplied power from a drive source (a battery, not shown) within the portable telephone
201
.
The user uses the keypad
37
, which has ten key buttons and the like, for entering information such as telephone numbers or the like. The liquid crystal display
38
displays information such as characters, images and the like.
The shield case
34
which is connected to a ground layer of the printed circuit board
35
is arranged to surround the printed circuit board
35
in order to suppress an electromagnetic interference between the printed circuit board
35
and the antenna
31
. The shield case
34
is formed using an electrical conducting material such as a metal, or a plastic material which is coated with a metal or the like on the surface thereof.
In recent years, guidelines for an electromagnetic energy partial-body absorption directed to the portable telephone have been set up in the USA, Europe and Japan, consecutively. As a quantity of evaluation for the partial-body absorption, a power absorbed in a unit mass, that is, a specific absorption rate (SAR) is used. Assuming that an electric field invaded into a biological tissue is E, a conductivity of the biological tissue is &sgr; and its density is &rgr;, the SAR can be expressed by the following equation (1).
SAR=&sgr;
E
2/2&rgr;  (1)
For example, in the partial-body absorption guideline in the USA, that is, FCC's guideline, it is specified that a peak value in an average SAR per gram tissue does not exceed 1.6 W/kg. Also, in the partial-body absorption guidelines in Europe and Japan, it is specified that a peak value in an average SAR per 10 gram-tissue does not exceed 2 W/kg.
It is described in the paper titled “Reduction of the partial-body SAR and assurance of the communication characteristics by controlling the surface current in the housing of a portable telephone” published in the Transactions of Japan Society of Applied Magnetism Vol. 23, No. 10, pages 2005-2008, 1999 that the partial-body SAR can be reduced by attaching a ferrite sheet on the metal housing of the portable telephone.
The SAR tends to increase when a transmission power of the portable telephone becomes greater, and a distance between a radiation source of waves in the portable telephone and the body of the user becomes closer. It may occur that the partial-body SAR of the portable telephone becomes maximum in a part other than the antenna, for example, in the vicinity of the shield case.
This is caused partly due to that a size of the housing is too small compared to the electromagnetic wavelength used in the radio communications, i.e., less than one wavelength thereof.
For example, in contrast to that a wavelength of electromagnetic waves at a frequency of 900 MHz is 330 mm and that at a frequency of 2 GHz is 150 mm, a size of the portable telephone in the longitudinal direction is normally 120 mm or so. The power supplied to the antenna is also supplied to the conductive shield case. Thereby, the shield case, which apparently is not the antenna, functions as a part of the antenna serving as a radiation source of electromagnetic waves.
Another cause that the partial-body SAR becomes maximum not at the antenna but in the vicinity of the shield case is indicated due to that during use of the portable telephone, the shield case comes closer to the head of the user than the antenna. Portable telephones now available on the market have become more compact and thinner sized, in comparison with the portable radio transceiver equipment, which have been in use since before the proliferation of the portable telephones. Therefore, a distance in particular between a conductive portion of the housing and the body of the user is substantially reduced in comparison with that of the portable radio equipment, thereby substantially increasing the partial-body SAR in the vicinity of the shield case thereof.
FIG. 7
shows a schematic diagram of a portable telephone
202
in which an electromagnetic wave absorption layer
41
which contains a magnetic loss material is pasted on its shield case
34
. The portable telephone
202
indicated in
FIG. 7
has the electromagnetic wave absorption layer
41
formed into a sheet, and contains the magnetic loss material. The other components and parts except for the above layer
41
are the same as those of the portable telephone
201
indicated with reference to
FIG. 6
, and are depicted with the same numerals and symbols.
In the portable telephone
202
indicated in
FIG. 7
, as its magnetic loss material for use in the electromagnetic wave absorption layer
41
, there are cited, for example, ferrite, Permalloy, Sendust, stainless steel, silicon steel, ferro-amorphous alloys and the like.
Further, in the portable telephone
202
, its electromagnetic wave absorption layer
41
is pasted on its shield case
34

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