Telecommunications – Transmitter – With electrical protection of transmitter circuit or operator
Reexamination Certificate
2001-02-02
2003-01-07
Maung, Nay (Department: 2681)
Telecommunications
Transmitter
With electrical protection of transmitter circuit or operator
C455S090300, C455S550100, C455S575100, C343S702000
Reexamination Certificate
active
06505036
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method and apparatus for mobile telephony radiation effect reduction, in particular to methods of reducing the radiation power radiated into a user's head, hand and. body and also, though not exclusively, to enhancing the wireless system efficiency and quality.
BACKGROUND OF THE INVENTION
The present invention concerns wireless handsets, where the number of users is increasing at a very large rate. Such wireless handsets include cellular phones, wireless phones, personal communication and walkie-talkie systems and equipment. Most of these portable devices are held very close to the user's head (and ear) during operation, as typically illustrated in
FIGS. 1 and 2
.
The normal distance between the input of the handset antenna, typically, from where most of the radiated energy is developed; typical distances from the handset antenna to the user's head may be only from 1.5 to 3 cm. At these small distances, strong coupling occurs between the handset case, antenna, user's head and hand which may result in up to 60% of the radiated. energy being absorbed within a small volume of the user's head, as described in “Electromagnetic Compatibility Handbook”, Chapters 1, & 24 and Appendix H, Editor R. Perez, and published by Academic Press, 1995, and in “EM Interaction of Handset Antennas”, by M. A. Jensen and Y. Rahmat Samii, Proceedings of the IEEE, January 1995, pp. 5-17. The contents of these documents are hereby incorporated by reference.
This undesired RF radiation absorption may influence, enhance or even cause the development of natural or spontaneous head tumors or cancer, as described in “Potential Public Health Risks from Wireless Technology”, Scientific Advisory Group on Cellular Telephone Research, Washington DC, August 1994, Editor G. L. Carlo, (Fax number 202-833-2801). The contents of this document is hereby incorporated by reference. Furthermore, this absorption of radiation by the user's body, reduces the efficiency of desired radiation towards the base station which may require increasing the handset transmission power to achieve a high quality communication link, as described by Perez and in “Personal Communication Services, Technology and Health Concerns Modern Radio Science, 1996, pp. 263-277, by M. A. Stuchly, hereby incorporated by reference.
The significant scientific literature relating to the health hazards resulting from portable cellular or wireless phone, while providing useful information, is inadequate for drawing definitive conclusion about possible health risks. Therefore it is suggested to take precautions and reduce as much as possible, the radiation and the Specific Absorption Rate (SAR) reaching the human body, especially in the head region, as discussed in “Mobile Communication Safety”, Chapman-Hall, 1997, Editors N. Kuster, Q. Balzano and W. C. Lin,: “Wireless Technology Research (WTR) Public Health Research”, Activities June 1993-96, (June 1996), pp. 18, Editor G. L. Carlo; “Electromagnetic Fields 300 Hz to 300 GHz”, Environmental Health Criteria 137, The WHO, World Health Organization, Geneva 1993, hereby incorporated by reference.
The effects of Portable Cellular Phone Radiation on the Users is quantifiable in terms of the SAR, mentioned above. The SAR is a very convenient unit to measure, simulate and evaluate the radiation health threat to a biological systems and represents the rate of radio frequency (RF) coupling to the biologic object of interest. The SAR indicates the rate at which energy is absorbed by an incremental mass of an exposed object, such as human tissue, divided by the incremental mass. The units of SAR are expressed in Watt/Kg. As defined by Kuster et al. and the WHO, the SAR can be computed using the following relations:
SAR
=
σ
2
ρ
*
[
E
(
t
)
]
⋀
2
(
1
)
P
ab
=
1
2
∫
σ
*
[
E
(
t
)
]
⋀
2
*
ⅆ
V
(
2
)
SAR
=
C
*
Δ
T
t
(
3
)
P
rad
=
1
2
Re
∫
(
E
_
x
H
_
)
*
n
_
*
ⅆ
A
(
4
)
η
a
=
P
t
ad
P
r
ad
P
ab
(
5
)
where &sgr; and &rgr; are the conductivity in mho/m and the specific density in Kg/mA{circumflex over ( )}3, E(t) represents the total electric field in a voxel of tissue in (V/m), P
ab
is the power absorbed in the head and hand model in (Watt) and V represent the volume concerned.
C, &Dgr;T, & t represent respectively the specific heat of the tissue in J/(kg, °C.), the difference of temperature and the time exposure due to the radiation absorption, respectively.
P
rad
is the radiated power in Watt at far field distances, and A is the area element in m{circumflex over ( )}2, &eegr;
a
is the radiated efficiency of the desired signal.
The European and IRPA radiation safety standard have some difference from the ANSI-IEEE new standards, “American National Standard Safety Levels with Respect to Human Exposure to RF EMF 300 KHz to 100 GHz”, ANSI C95.1, The IEEE Inc., New York 1992, and also found in the WHO manual, Kuster, and Carlo, 1996. These disclosures of these documents are hereby incorporated by reference.
In the cellular 900 MHz band, the threshold SAR averaged over the whole body should not exceed 0.4 Watt/Kg for exposed workers for an averaging time of 6 minute and 0.08 Watt/Kg for the general population. In case of hands, wrist, feet and ankles radiation absorption, the threshold SAR should nor exceed 4 Watt/Kg for any 10 grams tissue and for more vulnerable tissues, such as in the human head, the radiation should not exceed 2 Watt/Kg or 1.6 Watt/Kg peak SAR, averaged over 1 gram of tissue in reference to the last ANSI/IEEE standard and also in Carlo, 1996.
The standard authorities also provide tables of threshold limits for the unperturbed root mean square electric field strength E (V/m), magnetic field strength H(A/m) and equivalent plane wave power density S in mWatt/cm{circumflex over ( )}2. These threshold values are function of the radiation frequency range due to the resonant frequency of an average human body. For the cellular frequency range of 900 MHZ, concerning general population exposure limit to RF fields the threshold S, is f(MHz)/2000 on 0.45 mWatt/cm{circumflex over ( )}2 related to IRPA and 0.30 mWatt/cm{circumflex over ( )}2 related to IEEE/ANSI standards; double values for the PCS, and the future cellular band of 1800 MHz. In the 55 MHz range, used for the indoor home wireless phone, the general population threshold limits is 0.2 mWatt/cm{circumflex over ( )}2, related to IRPA and 10/f(MHz) or 0.18 mWatt/cm{circumflex over ( )}2 related to ANSI/IEEE standard, as in the WHO standards and “CENELEC Readies Provisional Rad-Hazard Requirement”, Newswatch EMC, Compliance Eng. European Ed., April 1995, pp. 60-64, hereby incorporated by reference.
The present cellular handset transmitter power ranges extend from 0.2 to 6 Watt. The power range generates non-ionizing radiation, with a minor increase in the body or head temperature. However recent models, as described by Carlo 1994, Newswatch and “Numerical and Experimental Procedure for SAR Distributions Due to Mobile Telephones: an Overview”, EMC Int. Symp. Proceedings Tutorial Roma 9.96, by G. Lazzi, Om P. Gandhi, pp. 79-86, hereby incorporated by reference, postulate that even Electromagnetic Fields (EMF) may change the biologic cellular growth control mechanism and for the human head may change the blood brain permeability. Groups of Swedish and Australia scientists recently reported, that amplitude modulated (AM), RF energy could affect the blood brain barriers of exposed users by a mechanism different than simple heating. Calcium effects and the increase of the head cellular division rate from low power level RF radiation, which may not produce cancer, but may influence or enhance the development of natural and spontaneous carcinogram tumors, which may develop into cancer.
Thus the newer generation of digital portable phone, using TDMA or CDMA multiplexing techniques, include low frequency Amplitude modulati
Gavan Jacob
Zilberberg David
Lipsitz Barry R.
Maung Nay
Persino Raymond
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