Patent Publication Number: US-8525750-B2

Title: Varying angle antenna for electromagnetic radiation dissipation device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 12/868,287, filed Aug. 25, 2010, which is a continuation of application Ser. No. 12/215,231, filed Jun. 26, 2008, which issued as U.S. Pat. No. 7,800,554 on Sep. 21, 2010,. 
    
    
     FIELD OF INVENTION 
     This invention relates generally to antennas that receive electromagnetic radiation. This invention relates more specifically to antennas adapted to be placed in the vicinity of an active electromagnetic radiation emission source to reduce undesirable radiation that emanates from the active emission source. 
     BACKGROUND 
     Many devices transmit electromagnetic radiation when in operation. For example, wireless communication devices intentionally emanate electromagnetic radiation when transmitting. Other devices transmit inadvertently, for example when a microwave oven is cooking, microwaves may inadvertently escape the oven. The widespread acceptance and use of hand-held, portable cellular telephones has been accompanied by increasing concern regarding possible harmful effects of such radiation. New hand-held cellular telephone typically have an elongated housing with an internal antenna, and older hand-held cellular telephones typically have an elongated housing with an antenna extending upward vertically from the housing. When using either type of telephone, the user&#39;s head comes into close proximity to the antenna when his head is placed adjacent to the cellular telephone. The antenna emanates radiation when the cellular telephone is transmitting, and such an antenna is referred to herein as a transmitting antenna. Thus, when the user is talking, the device is emanating radiation from the transmitting antenna, and a substantial amount of electromagnetic energy is projected directly onto the user&#39;s head at close range. 
     Each cellular telephone has to meet certain government guidelines as to the amount of radiation the user is exposed to. The amount of RF radiation absorbed by the body is measured in units known as SARs, or specific absorption rates. It would be desirable to reduce the SARs without significantly adversely affecting the operation of the telephone. 
     There have been attempts to shield the body from the electromagnetic energy emanating from the transmitting antenna. For example, U.S. Pat. No. 5,613,221 issued to Hunt discloses a conductive strip placed between the transmitting antenna and the user&#39;s head, to conduct radiation away from the user&#39;s head. There have also been some attempts to move the source of electromagnetic energy away from the body by changing the transmitting antenna location or radiation pattern. For example, U.S. Pat. No. 6,356,773 issued to Rinot removes the transmitting antenna from the phone and places it atop the user&#39;s head. An insulating shield is disposed between the transmitting antenna and the user&#39;s head, like a cap, for blocking emissions so that they do not penetrate through to the user. U.S. Pat. No. 6,031,495 issued to Simmons et alia uses a conducting strip between two poles of a transmitting antenna to create an end fire bi-directional pattern away from the user&#39;s head. Others have tried to reduce exposure to harmful emission by canceling the radiation. For example, U.S. Pat. No. 6,314,277 issued to Hsu et alia, is a cellular telephone antenna that cancels transmitted radiation of the cellular telephone with an absorbent directional shield by feeding the signal back into the cellular telephone. 
     One method of reducing electromagnetic radiation is to capture the radiation with an antenna, convert it to an electric current, and then dissipate the current, as described in U.S. Published Patent Application 2008/0014872. Antennas, however, are designed to receive RF signals in particular frequency bands, and cellular telephones operate generally in one or more of four different bands. For example, in Europe, GSM cellular telephones operate in the 900 MHz and 1800 MHz bands. In the United States, GSM and CDMA cellular telephones operate in the 850 MHz or 1900 MHz bands. It would be desirable to design an antenna for electromagnetic dissipation devices that is capable of capturing radiation across most or all of the cellular telephone frequency bands. 
     Meander antennas have become popular for receiving cellular telephone signals due to their small size, lightweight, ease of fabrication, and omni-directional radiation patterns. Meander antennas generally comprise a folded wire printed on a dielectric substrate such as a printed circuit board (PCB). Meander antennas have resonance in a particular frequency band in a much smaller space than many other antenna designs. The resonant frequency of a meander antenna decreases as the total wire length of the meander antenna element increases. In addition, if the turns in the meander antenna are very close so as to have strong coupling, there can also be capacitive loading of the antenna, which will increase bandwidth. Total antenna geometry, wire length, and layout must be optimized for each given antenna&#39;s purpose. It would be desirable to design a meander antenna for use with an electromagnetic radiation dissipation device that is effective across the cellular telephone frequency bands. 
     Therefore, it is an object of this invention to provide an antenna design to be used with a device that decreases the SARs to the user of an active emission source without significantly adversely affecting the desired performance of the emission source. It is a particular object to provide an antenna design specifically tuned for reducing the undesirable radiation a user is exposed to from a cellular telephone. It is a further object to provide an antenna design that can capture electromagnetic radiation from a cellular telephone operating in any of the four predominant frequency bands allotted for cellular telephone communication. 
     SUMMARY OF THE INVENTION 
     The present invention is a varying angle antenna to be used with an electromagnetic radiation dissipation device that reduces exposure to undesirable electromagnetic radiation or with a device that indicates the presence of known or unknown electromagnetic radiation. The dissipation device uses a varying angle antenna to capture radiation from an active emission source, such as a cellular telephone when it is transmitting. The device converts the captured radiation into an electric current and dissipates the collected current by spending it to operate a current-using device, which may be a thermal, mechanical, chemical or electrical device, or combination thereof. The varying angle antenna is a PCB trace antenna comprising a microstrip having several serially connected meandering segments. One or more meandering segments include 90-degree bends in the microstrip, and one or more meandering segments include bends of more and less than 90 degrees. Horizontal portions of the microstrip are all parallel, while vertical portions of the microstrip can be parallel or angled, depending on the bend angle. Additionally, near the center of the varying angel antenna, the microstrip segments are narrower than the microstrip segments near the ends of the antenna. In general, the meandering segments include varying angles, which maximizes the operation of the antenna for absorbing undesirable electromagnetic radiation from cellular telephones. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating the antenna of the present invention in cooperation with an electromagnetic radiation dissipation device. 
         FIG. 2  is block diagram illustrating an electromagnetic radiation dissipation device incorporating the antenna of the present invention positioned near an emission source. 
         FIG. 3  is a block diagram of a printed circuit board incorporating the antenna of the present invention for use with a cellular telephone. 
         FIG. 4  depicts the preferred dimensions of the antenna. 
         FIG. 5  is a perspective view of a cellular telephone with the electromagnetic radiation dissipation device adhered to the outside shell. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is a varying angle antenna  14  for use with an electromagnetic radiation dissipation device  10  that reduces undesirable radiation. Dissipation device  10  comprises antenna  14  and a dissipation assembly  17 , as illustrated in  FIG. 1 . When an emission source  11 , as shown in  FIG. 2 , is in operation it transmits electromagnetic radiation. When antenna  14  is bombarded by the radiation, electrons are stirred up in the antenna  14 , generating an electron flow (current). To continue to absorb the electromagnetic radiation, the current eventually must be drained from the antenna. This current is drained from the target antenna  14  with a conductor  12  and moved to a dissipation assembly  17 , which spends the current by operating an electrical, mechanical or thermal device. For small emission sources, the current is small and the conductor may be as simple as a wire or printed circuit board lead. For larger emission sources, a heavier-duty conductor may be required. 
       FIG. 3  illustrates a PCB  30  incorporating the antenna  14  of the present invention. As is known in the art, an antenna is any conducting mass that functions as a receiver or collector of electromagnetic energy. Additionally, antennas have a number of important parameters; those of most interest include the gain, radiation pattern, bandwidth and polarization. In a receiving antenna, the applied electromagnetic field is distributed throughout the entire length of the antenna to receive the undesirable radiation. If the receiving antenna that the signal strikes has a certain length relative to the wavelength of the received radiation, the induced current will be much stronger. The desired length of the antenna can be determined by using the well-known equation:
 
(λ)( f )= c  
 
where λ is the wavelength of the incident radiation, f is the frequency of the incident radiation, and c is the speed of light. For example, if a signal at 1900 MHz travels through the air, it completes a cycle in approximately 32 cm. If the signal strikes a 32 cm antenna or certain fractions of it (½ or ¼ or 1/16 wavelength), then the induced current will be much higher than if the signal struck a target antenna that was not some appreciable fraction of the wavelength.
 
     Typically, cellular phones and other wireless communications technologies such as PCS, G3 or Bluetooth® emit radiation in the radio or microwave ranges, or both, when transmitting. These and other consumer products often emit multiple wavelengths (frequencies). Cellular telephones, in particular, emit radiation in the 450 MHz, 850 MHz, 900 MHz, 1800 MHz, and 1900 MHz ranges when transmitting. This means that the varying angle antenna  14  must perform well over a range of frequencies. The corresponding wavelengths for cellular telephone frequencies are summarized below: 
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                 f 
                 λ 
                 ½ λ 
                 ¼ λ 
                  1/16 λ 
               
               
                   
               
             
            
               
                 450 MHz 
                 64 cm 
                 32 cm 
                 16 cm  
                 4 cm 
               
               
                 850 MHz 
                 33.88 cm   
                 16.9 cm   
                 8.47 cm   
                 2.12 cm   
               
               
                 900 MHz 
                 32 cm 
                 16 cm 
                 8 cm 
                 2 cm 
               
               
                 1800 MHz  
                 16 cm 
                  8 cm 
                 4 cm 
                 1 cm 
               
               
                 1900 MHz  
                 15.16 cm   
                 7.58 cm   
                 3.79 cm   
                 0.95 cm   
               
               
                   
               
            
           
         
       
     
     The varying angle antenna  14  herein is a receiving antenna and does not intentionally transmit electromagnetic energy. Varying angle antenna  14  is preferably a monopole PCB trace antenna comprised of a 1 oz copper microstrip arranged in a serpentine or meandering pattern. PCB trace antennas, microstrips, and methods for making them are well known in the art. PCB  30  has a top surface that includes the microstrip. In the preferred embodiment, the PCB is a standard 0.8 mm FR4 substrate material that is nonconducting at 1.8 GHz. For increased flexibility, a 0.5 mm substrate may be substituted. For example, to allow the PCB antenna to mount to an irregular or rounded cellular telephone or other device, a PCB thickness of 0.5 mm or less is desirable. In the preferred embodiment, the PCB is a bottle shape as shown in  FIG. 3 , and rather than using a ground plane for the antenna, the antenna is connected to a bridge rectifier to turn alternating current into direct current for lighting an LED. 
     The microstrip on the top surface of the PCB  30  is preferably 0.020 inches wide, and the overall length of the microstrip is 3.86165 inches. The preferred overall antenna area of copper is 0.0798 inches squared, and the preferred circumference of the antenna is 7.9349 inches. The pattern, as shown in  FIG. 3 , incorporates several 90-degree turns or bends in addition to several turns or bends of greater or lesser degree. The specific dimensions of the segments and angles of the preferred embodiment are shown in  FIG. 4 . All of the measurements are in inches in  FIG. 4 , and the tolerances are ±0.5° for angular measurements and ±0.015 for linear measurements. For the sake of convenience and with respect to  FIGS. 3 and 4 , the portions of varying angle antenna  14  that extend in the y direction will be considered vertical portions (or vertically-oriented portions), and the portions of varying angle antenna that extend in the x direction will be referred to herein as horizontal portions (or horizontally-oriented portions). As is shown in  FIGS. 3 and 4 , all of the horizontal portions of varying angle antenna  14  are parallel to one another. The vertical portions, however, can be parallel or angled. The vertical portions are consistent in height (or y displacement) for each meander portion. As shown in  FIG. 4 , they are uniform and 0.07 inches throughout (not all of the heights are shown but should be considered consistent throughout). The horizontal portions and vertical portions are connected to one another at an angle or “bend angle.” Bend angles can be any interior angle between 0 degrees and 180 degrees. 
       FIG. 3  illustrates that varying angle antenna  14  can be broken into several serially connected microstrip segments  31 - 35 . First microstrip segment  31  includes a vertical portion that is coupled at its proximal end to capacitors  15 . Segment  31  then bends 90 degrees at bend  31   a  to a horizontal portion  31   b  that is half the overall width of segment  31 . Segment  31  then meanders back and forth and includes another four 90-degree bends. In segment  31 , the vertical portions are parallel to one another. The distal end of segment  31  is coupled to the proximal end of second microstrip segment  32  bend  32   a  that is less than 90 degrees. Segment  32  tapers from the overall width of segment  31  to a smaller width and includes a meander pattern involving bends greater and less than 90 degrees, such that each vertical portion is angled toward the centerline along the y axis of the antenna. The distal end of segment  32  is coupled to the proximal end of third microstrip segment  33  at bend  33   a . Segment  33  is narrower than segment  31  but includes seven more 90-degree bends. In segment  33 , the vertical portions are parallel to one another. The distal end of segment  33  is coupled to the proximal end of fourth microstrip segment  34  at bend  34   a . Segment  34  tapers from the width of segment  33  to a larger width and includes bends greater and less than 90 degrees, such that the vertical portion is angled away from the center. Finally, the distal end of segment  34  is coupled to the proximal end of fifth microstrip segment  35  at bend  35   a . Segment  35  is the same overall width as segment  31  and includes eight 90-degree bends. The final portion of segment  35  is horizontal and is one half the length of the other horizontal portions of segment  35 . The vertical portions of section  35  are parallel to one another. For the preferred embodiment, there are 21 angles of 90 degrees, 3 angles of less than 90 degrees, and 3 angles of more than 90 degrees. Alternative embodiments can have varying numbers of angles, however the general bottle shape shown in  FIGS. 3 and 4  incorporating bends of various angles gives the broadest range of reception. 
     Varying angle antenna  14  cooperates with dissipation assembly  17  of dissipation device  10  to effectively decreasing the SARs to the user of a cellular telephone without significantly adversely affecting the transmission from the cellular telephone to the cell tower, or base station. As shown in  FIG. 3 , varying angle antenna  14  is connected to capacitors  15  and diodes  16 , to drive the LED  18 . This further permits the dissipation device to also indicate to its user that electromagnetic radiation is present. The capacitors and diodes act as a voltage multiplier to generate sufficient voltage to drive the LED  18 . For example, in this low-level application, four capacitors  15  are used with two diodes  16 . Preferably the diodes  16  are high-frequency RF Schottky diodes, which have a very low forward voltage of about 0.2-0.3 V. Such diodes are available commercially from, for example, Aeroflex/Metelics, Inc. of Sunnyvale, Calif. Preferably the capacitors are 1.0 uf, 6 VDC ceramic capacitors such as the AVX 0603ZD105KAT2A available from AVX of Myrtle Beach, S.C. Additionally, the LED is preferably a low current 632 nm red LED such as the APT1608SEWE available from Kingbright Corp. of City of Industry, Calif. 
     The number of capacitors and diodes can be increased or decreased as necessary when cooperating with emission sources of different levels of radiation. For example, when reducing undesirable emission from an emission sources emanating higher energy, such as short-wave radio, the number of capacitors can be reduced because the voltage draining off the antenna is itself sufficient to drive a dissipater assembly. 
     The collected current can be used to operate any dissipation assembly  17 , which is defined as one or more users of current. For example, the dissipation assembly  17  can be one or more of a buzzer, bell or any other transducer that converts electrical energy to sound; motor or any other transducer that converts electrical energy to motion; heater or any other transducer that converts electrical energy to heat; lamp or any transducer that converts electrical energy to light; or a combination thereof. The current may be used to catalyze a chemical reaction. In the preferred embodiment, the current is directed to an LED that lights up when supplied with the current, serving a secondary purpose of showing the user when the device  10  is working or when electromagnetic radiation is present. In another embodiment, the current is directed to an LCD display. The dissipation assembly  17  may be used to operate one or more users of current within the emission source  11 . 
       FIG. 5  illustrates device  10  incorporating varying angle antenna  14  as it is applied to a cellular telephone  50 . Cellular telephone  50  is the electromagnetic emission source  11 . Dissipation device  10  does not have to be connected in any way to the emission source  11 . For example, in the preferred embodiment, the dissipation device  10  is not connected electrically to the cellular telephone  50 . Additionally, dissipation device  10  can simply rest near cellular telephone  50  by being worn on a persons clothing or integrated into accessories, such as jewelry, lanyards, hats or scarves. Preferably, however, dissipation device  10  is connected physically to the emission source  11 , simply so that dissipation device  10  does not inadvertently get separated from the emission source  11  and stop functioning as intended. For example, dissipation device  10  may be adhesively attached to the outer housing  51  of the cellular telephone  50 , as shown in  FIG. 5 . Dissipation device  10  may be attached to the emission source  11  using other mechanisms, such as a screw, pin, compression or friction fit, for example, or dissipation device  10  may be integrally formed with the emission source  11 . Regardless of whether dissipation device  10  is physically attached to emission source  11 , it must be within a certain distance to capture the undesirable radiation. This distance depends on a number of factors, including the emission frequency, power, medium through which the radiation is traveling, etc. The acceptable distance  20  is symbolically indicated in  FIG. 2  with the dotted line. Preferably, the dissipation device  10  is positioned within 6 inches of a cellular telephone or other emission source. 
     In addition to use with cellular telephones, the present invention may be used with other emission sources such as other wireless communication devices such as satellite phones, BlackBerry® and other email-transmitting devices; wide area wireless local area networks; microwave ovens; portable radios, music players, and video players; automatic garage door and building door openers; police radar guns; short-wave and other ham radios; televisions or other cathode ray tube and plasma displays; power transmission lines; radioactive chemicals; or any other emission source. The present invention may also be used to indicate when electromagnetic radiation is present yet the emission source is unknown. 
     While there has been illustrated and described what is at present considered to be the preferred embodiment of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made and equivalents may be substituted for elements thereof without departing from the true scope of the invention. Therefore, it is intended that this invention not be limited to the particular embodiment disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.