WO2005112593A2

WO2005112593A2 - Body-worn radio signal transmitting apparatus

Info

Publication number: WO2005112593A2
Application number: PCT/US2005/017097
Authority: WO
Inventors: Alex Lax
Original assignee: Cellular3G, Inc.
Priority date: 2004-05-17
Filing date: 2005-05-17
Publication date: 2005-12-01
Also published as: WO2005112593A3

Abstract

Harmful radiation effects are reduced by automatically reducing the amount ofradiation being transmitted towards the human body. A measuring unit (310) measures a voltage standing wave ratio, VSWR, of the system. An antenna adjustment controller unit (330) determines changes to phases of an antenna and sends the changes to a phase shifting unit (340). A phase shifting unit changes the phase between elements of the antenna.

Description

BODY- WORN RADIO SIGNAL TRANSMITTING APPARATUS

CROSS-REFERENCE TO RELATED APPLICATIONS.

[0001] This application claims the benefit of U.S. Provisional Application No.

60/571,492, filed May 17, 2004, which is incorporated by reference, herein, in its entirety.

FIELD OF THE INVENTION.

[0002] Health and safety issues have now determined that any manufacturer offering equipment which radiates radio signals which is expected to be worn or used near a person's body is subject to the possibility of being affected by any effect that equipment might have on the user. The present invention is provided to reduce the amount of radiation which is radiated into the human body and, therefore, it will reduce many possible harmful effects. [0003] The invention is directed to a method and a system to reduce the amount of radiation to which the human body is exposed by a radio signal transmitting apparatus such as, e.g., a cellular handset. [000 ] The invention described herein is aimed at reducing any effects noticed by reducing the amount of radiation being transmitted towards the human body. [0005] The scheme described herein is totally automatic and always reduces the radiation absorbed by the body.

BACKGROUND OF THE INVENTION. [0006] The absorption of Electro-Mechanical (EM) radiation by the human body has been a health concern for some considerable time. The popularity of cellular phones has now brought this issue into the limelight and many reports have been issued on the subject and tests are being devised to see if cellular phones are a health risk. [0007] The following patents are cited as known prior art. [0008] JP3247021A2: PORTABLE RADIO EQUIPMENT (November 5,

1991): Use of two antennas, one providing performance when the radio is connected to the body and the other providing performance when the radio is not connected to the body. The use of multiple antennas is prior art, but the antennas do not operate together, and the patent is unrelated to reduction of radiation. [0009] JP7131241A2 DIVERSITY ANTENNA (May 19, 1995): This patent describes the use of multiple antennas to increase gain. The objective is to increase the SNR factor, or, as stated in the Purpose, to reduce "the influence of a human body on an internal antenna".

[0010] JP9247062A2 DIVERSITY ANTENNA (September 19, 1997): This patent describes another placement of multiple antennas, at specific angles to the human body and to each other. Again, there is no intention to reduce health risks, and apparently no such reduction. [0011] JP216610A2 METHOD AND DEVICE FOR SENSING AND

INFORMING CONTACT OF HUMAN BODY WITH ANTENNA FOR PORTABLE TELEPHONE SET (August 4, 2000): This patent explains that the presence of a body can be detected by use of the reflected power. This patent does not describe, however, any adjustment of the transmitting antenna or the transmitted field.

SUMMARY OF THE INVENTION. [0012] This invention reduces harmful radiation effects by reducing the amount of radiation being transmitted towards the human body. The invention is totally automatic, and always reduces the radiation absorbed by the body to either the minimum level possible or to a programmed level. The invention will operate for antennae transmitting at any frequency. Generally, antenna size decreases as the transmission frequency increases. As the frequency increases, so does the possibility of using multiple antennae in one device. The higher the frequency, the smaller will be the antenna. The invention may operate with any number of antennae from 1 up. [0013] The invention is taught below by way of various specific exemplary embodiments explained in detail, and illustrated in the enclosed drawing figures.

BRIEF DESCRIPTION OF THE DRAWINGS. [0014] The drawing figures depict, in highly simplified schematic form, embodiments reflecting the principles of the invention. Many items and details that will be readily understood by one familiar with this field have been omitted so as to avoid obscuring the invention. In the drawings: [0015] Fig. 1 is a plan view of a radiation pattern from a transmitter with directivity.

[0016] Fig. 2 shows an example of how the main radiated beam moves as the phase shift between the antennae changes.

[0017] Fig. 3 shows a block diagram of the feedback system providing minimum reflection.

[0018] Fig. 4 shows a flow diagram of a search for the minimum VSWR.

[0019] Fig. 5 shows one embodiment of a phase shifting circuit.

DETAILED DESCRIPTION.

[0020] The invention will now be taught using various exemplary embodiments. Although the embodiments are described in detail, it will be appreciated that the invention is not limited to just these embodiments, but has a scope that is significantly broader. The appended claims should be consulted to determine the true scope of the invention.

[0021] A radio antenna is a transducer that converts the electrical signals in the antenna circuit to EM radiation. Ideally, for maximum power transfer, the antenna impedance will match the impedance of free space. When bodies that affect the impedance of the space are positioned near the antenna, the impedance of the space around the antenna is modified. Bodies which cause this effect can be conducting or non-conducting. The human body can cause this effect. The non-perfect matching which occurs when such bodies are in the vicinity of the antenna can be measured in the electrical circuit around the antenna, since it produces a reflection of the signal to be transmitted. A standing wave is set up. The power of the standing wave is proportional to the amount of power being reflected by this mismatch.

[0022] A transmitting antenna is constructed with a device which provides a suitable transmitting signal. A suitable antenna can be made up of a single transmitting element or a set of transmitting elements each of which can be independently fed by the electrical circuit. The resulting EM field from a transmitter can be essentially omni-directional about the axis of the antenna or it can be non- omni-directional due to a physical shaping of the antenna elements (See Figure 1) or by modifying the radio frequency phase relationship between the signals transmitted from the individual transmitting elements. By adjusting the physical shape of the antenna or by changing the phase relationship between the signals fed into the different transmitting elements, the effective direction and shape of the power transmitting field (the radiation field) can be altered. With a suitable design, these changes can effectively change the direction of the transmitted signal. [0023 ] The ability to change the transmission direction is well known in the field. With 2 antennae, the transmitted field can be adjusted using the phase shift between the 2 antennae as shown in Figure 2. [0024] There are several options available to detect a body close to the transmitter. These options include measuring the power reflected from the body and also the effect on the tuning of the transmitting antenna element(s). Each of these phenomena produces an increase in Voltage Standing Wave Ratio (VSWR) in the transmitting circuit. These two different effects may well be closely related in practice and for the embodiments described here, a measure of the VSWR will be used to determine the amount of radiated power affecting the body. In further embodiments, other measurements may well be used, but a central principle remains the measuring of the effect on the antenna circuit and the adjusting of the direction of the antenna radiating field. [0025] In order to determine the proportion of the transmitted power that is reflected, a measurement of the VSWR is required. Techniques for obtaining the instantaneous value are well known in the field and may, in one embodiment, consist of measuring the ratio of power detected at ! and 5 wavelength from the antenna connection. [0026] If an antenna is constructed with such a means to measure the standing wave ratio (SWR) caused by reflections and the direction of transmission can be adjusted using methods as mentioned previously, it is possible to ensure that the direction of transmission is adjusted so that only a minimum of reflection is detected. [0027] As described above, if the antenna is such that it produces a non- uniform field of transmitted power, and if this non-uniform field can be adjusted in terms of direction of transmission, then it will be possible to adjust the field of transmission in order to minimise the reflections caused by bodies in the vicinity of the antenna. This adjustment can be effected by varying the physical size and/or shape of the antenna and also by adjusting the phase relationship if the antenna is made up of multiple transmitting elements. See Figure 3 for one embodiment of the system. A suitable phase shifting circuit may, in one embodiment, consist of the modification of the value of a capacitive component in the circuit. Figure 5 is an example of a suitable phase shifting circuit.

[0028] The combination of measuring the standing wave and adjusting the antenna radiation pattern to achieve a minimum reflection is a central feature of one embodiment according to the invention.

[0029] Assuming the properties of a particular body in the vicinity of a transmitter cannot be altered, when a minimum reflection has been detected in the antenna circuit, the proportion of the total power being transmitted towards the body causing the mismatch has been minimised. By designing antennas on apparatuses which are to be used on the body, so that a directivity in the transmission properties is achieved and that direction can be adjusted and that the amount of mismatch from free space can be measured, it is possible to detect the presence of bodies and adjust the antenna so that a minimum amount of power is radiated into the human body. [0030] If the construction of the system is such that the direction cannot be adjusted, it would then only be possible to reduce the power transmitted. This reduction in power can be effected by a variety of means but one embodiment is to reduce the gain of the amplifiers in the output stage. Of course, the VSWR measurement only defines the ratio of transmitted to reflected power and not the absolute reflected power. However by multiplying the value of the ratio and the known transmitted power, it is possible to derive the total received power. [0031] This reduction in power transmitted, without any adjustment in direction, can be used in cases where it is not possible to provide an adjustable field pattern but the power permitted to be transmitted towards a body is limited (since the VSWR measurement only measures the received power at the antenna, it is also necessary to calculate the power being transmitted towards the body. This calculation requires determination of the ratio of the power reflected by a body divided by the power transmitted to it at the frequency of interest. This factor will be called Cf. Therefore when it is determined that the received power is Rp, the worst case condition is that the body has received Rp/Cf). This will enable any effect to be reduced to a defined level. On these types of automatic power reduction systems, an apparatus can be used normally when kept away from human beings but kept to a low level near human bodies.

[0032] A further development of the system would be to set the reflected power to an absolute maximum and in the event of not being able to reach this level using the maximum power of the transmitter, the transmitter power is reduced until this level is reached in this way. When a "safe" level is defined, this system can always ensure that the power absorbed by any body in the vicinity of the apparatus is kept below the level specified.

[0033] In a further enhancement of the system, it is also possible and useful to add a time measuring device. When this time measuring device is combined with the estimate of the power being transmitted to the body, it is possible to calculate the total energy to which the body has been exposed. This is equal to the time multiplied by the power. This total energy can then be compared with the limits of the acceptable energy set by the authorities responsible for health and safety issues. Whether these bodies specify total energy or some combination of power and time, the relevant calculations can be obtained from the results of the measurements of time and from the reflected power as described herein. When the prescribed limit is about to be reached, either a warning (audible, visual or other) can be generated to alert the user; or the power can be reduced without any intervention form the user. Some authorities measure the maximum energy or power with respect to the weight of the body exposed to the radiation. The system described here cannot determine what part of the body, i.e., the head, leg, etc., is being exposed and therefore a worst case situation needs to be assumed to ensure that compliance with regulations is guaranteed. This worst case will therefore assume that only a low body weight is being exposed to the transmitted signals.

[0034] The operation of the system shown in Figure 3 can be described as follows. The VSWR measurement unit 310 generates an output 320 which is proportional to the VSWR. This signal 320 is used by the antenna adjustment controller unit 330 to determine the required phase shift, which is transferred to the phase shifting unit 340. A phase shifting unit is known in an of itself, but one example that may be used is shown in Fig. 5.

[0035] Under control of the antenna adjustment controller unit 330, the phase shifting unit 340 adjusts the phase between the 2 antennae until the signal from the VSWR measurement unit is minimised. The phase shift which produces the minimum VSWR is the correct setting for the system. This adjustment is advantageously carried out when the transmitted signal is below the peak output, so that at no time will the transmitter send strong signals to the body. [0036] In order to avoid local minima, a complete sweep of the full range of the possible phase shift is preferable. The antenna adjustment controller unit 330 controls the task of finding the minimum VSWR as a function of the phase shift. [0037] When more transmitting antennae are used, the phase adjustment unit will have to sweep over the full range of possible transmitting configurations to ensure that the global minimum is achieved.

[0038] These scans of the full adjustment range are preferably carried out again whenever the VSWR change detected reaches a defined threshold or at a predefined time interval. The timing of this process can also be controlled by the antenna adjustment controller unit 330.

[0039] The antenna units can be of any design. The specific design will depend on the specific requirement of the unit being used. When 2 omni-directional antennas are used, the resultant radiation pattern optimum will lie in a straight line at an angle which is a function of the phase shift between the 2 antennas. If each of the antennas has a non-o ni directional pattern, then the resultant pattern will be a function of this original pattern

[0040] An embodiment of the invention is represented by the logical flow diagram shown in Figure 4, which shows one approach to achieving a minimum VSWR. For simplicity, a 2 antenna system is described which requires only a single phase shift between the antennae in order to move the effective radiated field. [0041] When more than 2 antennae are used, a multiple sweep of phase shifts would be required to ensure that all possible field directions have been examined by the VSWR measurement unit.

[0042] In general, 2 antennae are needed to adjust the field in 2 dimensions while 3 will be needed to adjust in 3 dimensions. More complicated antenna arrays may be used to give particular adjustment patterns.

[0043] By varying the capacitors and/or resistors in the circuit of figure 5, a phase shift between the RF carrier between the 2 antennae can be changed. By using electrical variable components (such as varacters) these changes can be made very fast.

[0044] The present invention, in some of the aforementioned embodiments, has one or more of the following advantages over the prior art: 1) Flexible operation will work in pocket as well as held next to the ear. 2) Can be used with pre-defined limits for reflected power. 3) Can calculate and limit maximum total energy transmitted towards a body.

[0045] The combination of the measurement of the reflected power and the adjustable antenna radiated field is one of the several novel concepts included in the present invention. Many variations to the above-identified embodiments are, however, possible without departing from the scope and spirit of the invention as defined in the appended claims.

Claims

CLAIMS. There is claimed:

1. A system for reducing the amount of radiation absorbed by the human body from signal transmitting equipment, such system comprising: (a) a measuring unit to measure a voltage standing wave ratio (VSWR) of the system; (b) an antenna adjustment controller unit for determining changes to phases of an antenna and for sending the changes to a phase shifting unit; (c) a phase shifting unit to change the phase between elements of the antenna; (d) a plurality of antenna elements for generating and transmitting radio signals.

2. An antenna adjustment control unit, intended for use in a radio signal transmitting apparatus having a standing wave measurement unit, one or more antennae, and a phase shifting unit, the antenna adjustment control unit comprising: an input for receiving an indication of a standing wave magnitude; an output for indicating a required phase shift; and a logical control program for: detecting a phase shift corresponding to a minimum standing wave magnitude; and indicating, as a required phase shift, the phase shift corresponding to the minimum standing wave magnitude.

3. The antenna adjustment control unit as set forth in claim 2, wherein the detecting of the phase shift corresponding to the minimum standing wave magnitude is carried out by detecting the standing wave magnitude at the full range of possible transmitting configurations, and storing the phase shift corresponding to the one configuration, of the full range of possible transmitting configurations, at which a minimum standing wave magnitude is measured.

4. The antenna adjustment control unit as set forth in claim 2, wherein the detecting of the phase shift corresponding to the minimum standing wave magnitude is performed again at a predetermined time interval.

5. The antenna adjustment control unit as set forth in claim 2, wherein the detecting of the phase shift corresponding to the minimum standing wave magnitude is performed again when the indication of a current standing wave magnitude reaches a predetermined threshold.

6. An antenna adjustment control unit, intended for use in a radio signal transmitting apparatus having a standing wave measurement unit and an antenna, the antenna adjustment control unit comprising: an input for receiving an indication of a standing wave magnitude; an input for indicating transmit power in use; an output for indicating a desired increase or decrease in transmit power; and a logical control program for: determining the power Rp being transmitted, based on the transmit power in use; determining the power Cf being reflected by the body of the user, based on the indication of the standing wave magnitude; and setting the desired increase or decrease in transmit power based on a relation ofRp to Cf.

7. The antenna adjustment control unit as set forth in claim 6, wherein the relation is Rp/Cf, and wherein Rp/Cf is maintained within a predetermined threshold.

8. The antenna adjustment control unit as set forth in claim 6, further comprising a time measuring device, wherein an estimate of the power being transmitted to the body is calculated based on Rp, Cf, and an elapsed time indicated by the time measuring device.

9. The antenna adjustment control unit as set forth in claim 8, wherein a warning is indicated when the total energy during the elapsed time reaches a predetermined threshold.