Abstract:
The invention relates to a method for enhancing an antenna performance, wherein the property of the antenna substrate is modified by using an ultra-sonic field. The invention also relates to an antenna comprising the modified antenna substrate, and to an apparatus comprising the modified antenna substrate.

Description:
TECHNICAL FIELD OF THE INVENTION 
       [0001]    The invention relates to a method for enhancing the performance of communications antennas. The invention also relates to an antenna having an enhanced performance. Furthermore, the invention relates to an apparatus comprising an antenna having an enhanced performance. 
       BACKGROUND OF THE INVENTION 
       [0002]    An antenna tuning can be achieved for example by connecting lumped elements (capacitors, inductors) to an antenna structure or by manually changing antenna structural dimensions, such as the electrical length of the antenna element or a distance to a ground. 
         [0003]    Moreover, it is possible to use different materials, which have a certain magnetic permeability or dielectric constant, embedded in between a ground plane and an antenna element. Also, it is possible to switch between different matching circuit states for varying an antenna matching band. 
         [0004]    Several articles in the open scientific literature describe tuning methods for microstrip antenna elements. For example reference [1], wherein especially included papers [P8] and [P9], and the references therein. Proposals have been made, for example, to connect a tunable reactance (e.g. tunable capacitor) between an antenna element and a ground plate, to utilise switchable slots, or to utilise a switchable matching circuit for tuning a matching band location. In addition, in reference [2] is presented an overview of RF-MEMS enabled tunable antennas, in reference [3], which corresponds to preceding paper [P9], is presented a transmission line tuning, and in reference [4], for one, is disclosed a movable dielectric material together with a tunable planar inverted F antenna (PIFA). 
         [0005]    Since the trend in a communications antenna design is towards smaller physical dimensions and as small as possible number of antennas, the antenna tuning plays an important role. The efficient re-use of the mobile phone antennas through a low cost tuning would be highly desirable, particularly if very fast tuning would be possible. 
       SUMMARY OF THE INVENTION 
       [0006]    One object of the invention is to provide a method for enhancing an antenna performance, an antenna having an enhanced performance, and an apparatus comprising an antenna having an enhanced performance. 
         [0007]    The object of the invention is fulfilled by providing a method, wherein a property of an antenna substrate is modified by using an ultrasonic field. 
         [0008]    The object of the invention is also fulfilled by providing an antenna, which comprises an antenna substrate having a property, which is modifiable by an ultrasonic field. 
         [0009]    The object of the invention is also fulfilled by providing an apparatus, which comprises an antenna substrate having a property, which is modifiable by an ultrasonic field. 
         [0010]    According to an embodiment of the invention the electrical length of the antenna element is altered dynamically through a sophisticated parameter modification of the antenna substrate material for changing the resonant frequency of the antenna. 
         [0011]    An embodiment of the present invention relates to a method comprising modifying a property of an antenna substrate ( 130 ,  210 ) by using an ultrasonic field. 
         [0012]    In addition, an embodiment of the present invention relates to an antenna comprising an antenna substrate ( 130 ,  210 ) having a property, which is modifiable by an ultrasonic field. 
         [0013]    Furthermore, an embodiment of the present invention relates to an apparatus comprising an antenna substrate ( 130 ,  210 ) having a property, which is modifiable by an ultrasonic field. 
         [0014]    Further embodiments are defined in dependent claims. 
         [0015]    According to an embodiment of the invention a property of an antenna substrate is modified by using an ultrasonic field, whereupon said antenna substrate is exposed to the ultrasonic field produced by an ultrasonic transducer. 
         [0016]    According to an embodiment of the invention at least a portion of the antenna substrate comprises magnetic particles, which can be metallic particles and/or ceramic particles. On the other hand, it is possible that the magnetic particles comprise composite particles having metallic cores with electrically insulating coatings and/or electrically insulating cores with metallic coatings. At least some of these magnetic particles are submicron particles, i.e. at least some of the particles having a largest dimension that is less than one micron. 
         [0017]    According to an embodiment of the invention at least some of the magnetic particles, which are disclosed in any of previous embodiments, each having a refractive index differing from a refractive index of the at least a portion of said antenna substrate. 
         [0018]    According to an embodiment of the invention at least a portion of the antenna substrate, which is disclosed in any of previous embodiments, comprises a dielectric fluid, which, for one, includes the magnetic particles. Since the magnetic particles are surrounded by the dielectric fluid, the particles have a freedom to move if the ultrasonic field provided by the ultrasonic transducer is applied into the dielectric fluid. 
         [0019]    According to an embodiment of the invention the magnetic particles, which are disclosed in any of previous embodiments, are arranged into a new arrangement in the at least a portion of said antenna substrate by said ultrasonic field in order to modify the property of the antenna substrate comprising the particles. 
         [0020]    According to an embodiment of the invention, in the re-arranging of the magnetic particles, which is disclosed in any of previous embodiments, the ultrasonic field is applied into the at least a portion of the antenna substrate and that induces the concentration of the magnetic particles in areas of a high pressure. When the ultrasonic field is shut off, the magnetic particles will distribute evenly in the at least a portion of said antenna substrate. 
         [0021]    According to an embodiment of the invention, in the re-arranging of the magnetic particles, which is disclosed in any of previous embodiments, a standing wave is established into the antenna substrate portion or the antenna substrate, whereupon it is achieved the concentration of the magnetic particles (one or more magnetic particle layer) into one or more nodal planes of the standing wave. 
         [0022]    According to an embodiment of the invention, in the re-arranging of the magnetic particles, which is disclosed in any of previous embodiments, a frequency of the ultrasonic field provided by the ultrasonic transducer is adjusted in order to control a number of the nodal planes of the standing wave in the at least a portion of the antenna substrate. 
         [0023]    According to an embodiment of the invention the property of the antenna substrate, which is disclosed in any of previous embodiments, is a magnetic permeability or dielectric constant. 
         [0024]    According to an embodiment of the invention an antenna, which has an antenna substrate having a property modifiable by an ultrasonic field according to any of embodiments described in this document, is a patch antenna. The antenna can also be any other microstrip antenna type such as a stacked microstrip antenna. 
         [0025]    According to an embodiment of the invention an apparatus, which has an antenna substrate having a property modifiable by an ultrasonic field according to any of embodiments described in this document, is a mobile communications device such as a mobile station. The apparatus can also be a smaller unit than the mobile communications device. It can be e.g. a component having an antenna substrate with a property modifiable by an ultrasonic field, which can be installed inside the mobile communications device. 
         [0026]    The method offers a simple approach to the antenna tuning and enables the use of a single antenna at different frequencies. The method further provides a low cost and fast antenna tuning method. Also, this method provides the accurate spatial control of the nanoparticles in an antenna substrate. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]    Next, the aspects of the invention will be described in greater detail with reference to exemplary embodiments in accordance with the accompanying drawings, of which 
           [0028]      FIG. 1  illustrates a schematic diagram of a patch type antenna, 
           [0029]      FIGS. 2   a - 2   c  illustrate an exemplary view of the control of the magnetic particles according to an advantageous embodiment of the invention, and 
           [0030]      FIG. 3  illustrates an exemplary flowchart of the method for modifying an antenna substrate according to an advantageous embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0031]      FIG. 1  illustrates a possible setup in case of a patch antenna  100 , with a thin radiating patch  110  on one side and a ground plane  120  on another side. Between the patch  110  and the ground plane  120  is an antenna substrate  130 . The antenna substrate  130  is a dielectric material having a certain dielectric constant, which defines the electric features of the antenna substrate  130 . 
         [0032]    In addition, the patch antenna  100  comprises a feed line  140  and a probe feed  150  (of a coaxial cable) for coupling electromagnetic energy into the patch  110  and/or out of the patch  110 . Naturally, in patch type antennas, coupling can be provided either by contacting feeds (e.g. the aforesaid coaxial cable or a microstrip line) or by non-contacting feeds (e.g. an aperture or a proximity coupling). 
         [0033]    Although the patch antenna  100  has been chosen as an example, it must be noticed that the antenna tuning method according to the embodiment of the invention is not limited to this particular antenna type. 
         [0034]    In order to execute the antenna tuning method according to the embodiment of the invention, the antenna substrate  130  is constituted in a known manner so that said antenna substrate  130  comprises a dielectric fluid including added magnetic particles having a freedom to move if an ultrasonic field provided by an external ultrasonic transducer is applied, or the portion of the antenna substrate comprises the dielectric fluid including the magnetic particles having a freedom to move if an ultrasonic field provided by an external ultrasonic transducer is applied (not shown in the figure). 
         [0035]    In  FIGS. 2   a - 2   c  are represented in principle how the fluid of the antenna substrate, which comprises added magnetic particles, can be modified for changing the resonant frequency of the antenna. 
         [0036]      FIG. 2   a  illustrates an undisturbed fluid  210  comprising added magnetic particles  220  having sub-micron physical dimensions, in other words said particles  220  have a largest dimension that is less than one micron. So, these magnetic particles can be called as nanoparticles. These nanoparticles  220  have a refractive index different to the refractive index of the fluid  210  and the particles  220  are extended throughout the fluid  210 . The particles  220  can comprise metallic and/or ceramic particles. The metallic particles can comprise e.g. cobalt, iron, manganese, nickel, niobium, tungsten, vanadium, or rare earth metal particles. Furthermore, the particles can be composite particles having metallic cores surrounded by electrically insulating coatings or electrically insulating cores surrounded by metallic coatings [5]. 
         [0037]    An ultrasonic transducer  230  is installed in close contact with the fluid  210 . Between the transducer  230  and the fluid  210  it is possible to use a suitable medium (not shown in the figure) in order to enable a fluent propagation for an ultrasonic signal. 
         [0038]    The magnetic nanoparticles  220  in the fluid  210  are re-arranged by means of an acoustic standing wave produced by the ultrasonic transducer  230  in a known manner. 
         [0039]    The acoustic standing wave in a fluid has a varying energy density in its nodal planes, which locate normal to the axis of the propagation of the standing wave. The particles of the fluid, which are responsive to an acoustic energy, will concentrate in the nodal planes and this affects a particle distribution in the fluid [6]. 
         [0040]    Thus, the antenna tuning method according to the invention utilises the above-mentioned standing wave by applying an ultrasonic field to the fluid  210  and establishing the standing wave for piling up (concentrating) the magnetic nanoparticles  220  at nodal planes. 
         [0041]    Next, in  FIG. 2   b , is illustrated a situation, wherein the ultrasonic transducer  230  produces the ultrasonic field into the fluid  210  (turning on the ultrasonic field). A box  240  on the right side of the figure depicts the pressure fluctuations of the ultrasonic field so that dark sections  250  represent the areas of the high pressure in the fluid  210  and white sections  260 , for one, represent the areas of the low pressure in the fluid  210 . 
         [0042]    Once the ultrasonic field is applied into the fluid  210 , the magnetic nanoparticles  220  concentrate to the areas of the high pressure  250  as layers  270 , if the fluid  210  supports a standing wave at the ultrasonic frequency and the refractive index of the nanoparticles  220  is different from that of the antenna substrate material  210 . 
         [0043]    Generally speaking, switching the ultrasonic field on will lead to the periodic structure of the magnetic properties of the medium and this, in turn, will lead to the different tuning frequency of the antenna, particularly if the RF magnetic field distribution in the active space is non-uniform, which is normally the case. 
         [0044]      FIG. 2   c  illustrates how the controlling of the frequency of the ultrasonic excitation allows controlling number of nanoparticle nodal planes  270 . As one can see from the figure, the number of nanoparticle nodal planes  270  is increased by increasing the frequency of the ultrasonic excitation. 
         [0045]    When the ultrasonic excitation is turned off, the nanoparticles  220  distribute again uniformly in the fluid  210 . 
         [0046]    The re-arranging of the magnetic nanoparticles  220  in a fluid  210  changes the properties of the fluid  210 . For example, the relative magnetic permeability can alter by a factor of two or more. When the modified fluid  210  is placed on or near an antenna element, and a property that has been modified is either a magnetic permeability or a dielectric constant, the resonant frequency of the antenna will change. 
         [0047]      FIG. 3  represents a flowchart according to the method in discussion. In first step  300 , an ultrasonic transducer is installed in touch with a fluid, which comprises magnetic particles, so that it can provide an ultrasonic field into said fluid. 
         [0048]    Then, according to step  320 , the transducer is turned on for producing the ultrasonic field into said fluid. The magnetic particles arrange to layers as shown in  FIG. 2   b  since a standing wave establishes in the fluid. 
         [0049]    In step  340  the frequency of the ultrasonic can be adjusted in order to control the number of the layers of the magnetic particles. If the frequency is increased, the number of the particle layers (nodal planes) increases. 
         [0050]    Since the ultrasonic field is turned off in step  360 , the magnetic particles spread out again uniformly in the fluid. As a result from the above-presented particle manipulation, the properties of the fluid, preferably a magnetic permeability or a dielectric constant, have changed, and if the modified fluid is placed on or near an antenna element, it will present a change in the resonant frequency of the antenna. 
         [0051]    An antenna having an antenna substrate, which is modified by the tuning method according to the invention, can be applied to various kind of devices such as mobile phones, laptops, GPS devices, and so on. 
         [0052]    The invention has been now explained above with reference to the aforesaid embodiments and the several advantages of the invention have been demonstrated. It is clear that the invention is not only restricted to these embodiments, but comprises all possible embodiments within the spirit and scope of the invention thought and the following patent claims. 
       REFERENCES 
       [0000]    
       
         [1] J. Ollikainen,  Design and implementation techniques of wideband mobile communications antennas,  Ph.D. Dissertation, TKK Helsinki University of Technology, 2004 
         [2] http://www.semiconductor.net/article/CA6436113.html 
         [3]  0 . Kivekäs, J. Ollikainen, and P. Vainikainen, “ Frequency - tunable internal antenna for mobile phones”, Proc.  13 th IEEE International Symposium on Personal, indoor and Mobile Radio Communications  ( PIMRC  2002), Lisbon, Portugal, 15-18 Sep. 2002, pp. 1882-1887, (CD-ROM, ISBN 0-7803-7590-4, paper: crl1593.pdf) 
         [4] Patent publication U.S. Pat. No. 6,437,747 B1 
         [5] Patent publication U.S. Pat. No. 6,842,140 B2 
         [6] Patent publication U.S. Pat. No. 4,877,516 A