Abstract:
Disclosed is a wireless power transmitter. The wireless power transmitter for transmitting power to a wireless power receiver in a wireless scheme, includes a transmission circuit unit converting power supplied from a power supply unit into power having a frequency for resonance; a transmission induction coil coupling the converted power; and a transmission resonance coil disposed adjacent to the transmission induction coil to transfer the coupled power from the transmission induction coil to the wireless power receiver using the resonance, wherein the transmission circuit unit is vertically spaced apart from the transmission resonance coil.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit under 35 U.S.C. §119 of Korean Patent Application Nos. 10-2012-0027979, filed Mar. 19, 2012 and 10-2012-0060781, filed Jun. 7, 2012, which are hereby incorporated by reference in their entirety. 
     BACKGROUND 
     The disclosure relates to a wireless power transmitting technology. More particularly, the embodiment relates to a wireless power transmitter capable of increasing power transmission efficiency by improving a structure of the wireless power transmitter, and a wireless power transmission system. 
     A wireless power transmission or a wireless energy transfer refers to a technology of wirelessly transferring electric energy to desired devices. In the 1800&#39;s, an electric motor or a transformer employing the principle of electromagnetic induction has been extensively used and then a method of transmitting electrical energy by irradiating electromagnetic waves, such as radio waves or lasers, has been suggested. Actually, electrical toothbrushes or electrical razors, which are frequently used in daily life, are charged based on the principle of electromagnetic induction. The electromagnetic induction refers to the generation of an electric current through induction of a voltage when a magnetic field is changed around a conductor. The electromagnetic induction scheme has been successfully commercialized for electronic appliances having small sizes, but represents a problem in that the transmission distance of power is too short. 
     Besides the electromagnetic induction scheme, the long-distance transmission using the resonance and the short-wavelength radio frequency has been suggested as the wireless energy transfer scheme. 
     Recently, among wireless power transmitting technologies, an energy transmitting scheme employing resonance has been widely used. 
     Since an electric signal generated between the wireless power transmitter and the wireless power receiver is wirelessly transferred through coils in a wireless power transmitting system using resonance, a user may easily charge electronic appliances such as a portable device. 
     However, according to the related art, there is limitation to increase a Quality factor (Q) and power transmission efficiency between a transmitter side and a receiver side. 
     BRIEF SUMMARY 
     The embodiment provides a wireless power transmitter capable of maximizing power transmission efficiency between the wireless power transmitter and a wireless power receiver, and a wireless power transmission system. 
     The embodiment provides a wireless power transmitter capable of maximizing power transmission efficiency by adjusting disposal intervals between constituent elements of the wireless power transmitter, and a wireless power transmission system. 
     The embodiment provides a wireless power transmitter capable of maximizing power transmission efficiency by disposing a first substrate and a second substrate of the wireless power transmitter, and a wireless power transmission system. 
     The embodiment provides a wireless power transmitter capable of increasing power transmission efficiency by disposing a transmission resonance coil to have a predetermined angle, and a wireless power transmitting system. 
     According to the embodiment, there is provided a wireless power transmitter for transmitting power to a wireless power receiver in a wireless scheme, the wireless power transmitter including: a transmission circuit unit converting power supplied from a power supply unit into power having a frequency for resonance; a transmission induction coil coupling the converted power; and a transmission resonance coil disposed adjacent to the transmission induction coil to transfer the coupled power from the transmission induction coil to the wireless power receiver using the resonance, wherein the transmission circuit unit is vertically spaced apart from the transmission resonance coil. 
     According to the embodiment, there is provided a wireless power transmitter for transmitting power to a wireless power receiver in a wireless scheme, the wireless power transmitter including: a transmission induction coil transmitting power from a power supply unit; a transmission resonance coil induction-coupled with the transmission induction coil transmitting the power from the transmission induction coil to the wireless power receiver, and the transmission resonance coil is inclined at a predetermined angle with respect to a horizontal plane. 
     According to the embodiments, following effects can be achieved. 
     First, power transmission efficiency can be maximized by adjusting disposal intervals between constituent elements of the wireless power transmitter. 
     Second, the power transmission efficiency can be maximized through the arrangement of a transmission resonance coil and a second substrate of the wireless power transmitter. 
     Third, the power transmission efficiency to a receiver side can be increased by disposing the wireless power transmitter to have a predetermined angle. 
     Meanwhile, other various effects may be directly or indirectly disclosed in the following description of the embodiment of the disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram illustrating a wireless power transmission system according to an embodiment; 
         FIG. 2  is a circuit diagram showing an equivalent circuit of a transmitting induction coil according to an embodiment; 
         FIG. 3  is a circuit diagram showing an equivalent circuit of a power source and a wireless power transmitter according to an embodiment; 
         FIG. 4  is a circuit diagram showing an equivalent circuit of a wireless power receiver according to an embodiment; 
         FIG. 5  is a view illustrating a structure of a wireless power transmission system according to a first embodiment; 
         FIG. 6  is a front view illustrating the wireless power transmission system according to a first embodiment; 
         FIG. 7  is a view illustrating a structure of a wireless power transmission system according to a second embodiment; 
         FIG. 8  is a table illustrating variations in a Q value and power transmission efficiency as a function of a vertical distance between a transmission resonance coil and a second substrate of a wireless power transmitter according to the first embodiment; 
         FIG. 9  is a view illustrating a structure of a wireless power transmitter according to a third embodiment; 
         FIG. 10  is a diagram illustrating a wireless power transmission procedure of a wireless power transmitter according to the first embodiment; 
         FIGS. 11 and 12  are diagrams illustrating a wireless power transmission procedure of a wireless power transmitter according to the third embodiment; and 
         FIG. 13  is a table illustrating power transmission efficiency when the wireless power transmitter according to the third embodiment is used. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, embodiments will be described in detail with reference to accompanying drawings so that those skilled in the art can easily work with the embodiments. 
       FIG. 1  is a diagram illustrating a wireless power transmission system according to an embodiment. 
     Referring to  FIG. 1 , the wireless power transmission system may include a power source  100 , a wireless power transmitter  200 , and a wireless power receiver  300 . 
     The wireless power transmitter  200  may include a transmission induction coil  210  and a transmission resonance coil  220 . 
     The wireless power receiver  300  may include a reception resonance coil  310 , a reception induction coil  320 , a rectifier circuit  330 , and a load  340 . 
     Both terminals of the power source  100  are connected to both terminal of the transmission induction coil  210 , respectively. 
     The transmission resonance coil  220  may be spaced apart from the transmission induction coil  210  by a predetermined distance. 
     The reception resonance coil  310  may be spaced apart from the reception induction coil  320  by a predetermined distance. 
     Both terminals of the reception induction coil  320  are connected to both terminal of the rectifier circuit  330 , respectively. Both terminals of the load  340  are connected to both terminal of the rectifier circuit  330 , respectively. In the embodiment, the load  340  may be not included in the wireless power receiver  300 , but may be provided separately. 
     The power generated from a power source  100  is provided to the wireless power transmitter  200 , such that the power is transferred by resonance to the wireless power receiver  300  which is resonant with the wireless power transmitter  200 , that is, which has the same resonant frequency value as that of the wireless power transmitter  200 . 
     Hereinafter, a procedure of transmitting power will be described in detail. 
     The power source  100  is an AC power source for supplying AC power of a predetermined frequency. 
     AC current flows through the transmission induction coil  210  by the AC current from the power source  100 . When the AC current flows through the transmission induction coil  210 , the AC current may be induced to the transmission resonance coil  220  physically spaced apart from the transmission induction coil  210  using electromagnetic induction. The power transferred to the transmission resonance coil  220  is transmitted using resonance to the wireless power receiver  300  which forms a resonance circuit with the wireless power transmitter  200 . 
     Power may be transferred using resonance between two LC circuits which are impedance-matched with each other. The power transfer using resonance is able to transfer power at higher efficiency to a longer distance than those by electromagnetic induction. 
     The reception resonance coil  310  receives power using resonance from the transmission resonance coil  220 . The AC current flows through the reception resonance coil  310  by the received power. The power transmitted to the reception resonance coil  310  is transferred by electromagnetic induction to the reception induction coil  320 . The power transferred to the reception induction coil  320  is transferred through the rectifier circuit  330  to the load  340 . 
       FIG. 2  is a circuit diagram showing an equivalent circuit of a transmitting induction coil  210  according to an embodiment. 
     As shown in  FIG. 2 , the transmission induction coil  210  may include an inductor L 1  and a capacitor C 1 , and form a circuit having a suitable inductance value and a suitable capacitance value. 
     The transmission induction coil  210  may be constructed as an equivalent circuit in which both terminals of the inductor L 1  are connected to both terminals of the capacitor C 1 . In other words, the transmission induction coil  210  may be constructed as an equivalent circuit in which the inductor L 1  is connected to the capacitor C 1  in parallel. 
     The capacitor C 1  may include a variable capacitor, and impedance matching may be performed by adjusting the variable capacitor. The equivalent circuit of the transmission resonance coil  220 , the reception resonance coil  310 , and the reception induction coil  320  may be the same as those depicted in  FIG. 2 . 
       FIG. 3  is a circuit diagram showing an equivalent circuit of a power source  100  and a wireless power transmitter  200  according to an embodiment. 
     As shown in  FIG. 3 , each of the transmission induction coil  210  and the transmission resonance coil  220  may include an inductor L 1  or L 2  having predetermined inductance and a capacitor C 1  or C 2  having predetermined capacitance. 
       FIG. 4  is a circuit diagram showing an equivalent circuit of a wireless power receiver  300  according to an embodiment. 
     As shown in  FIG. 4 , each of the reception resonance coil  310  and the reception induction coil  320  may include an inductor L 3  or L 4  having a predetermined inductance value and a capacitor C 3  or C 4  having a predetermined capacitance value. 
     The rectifier circuit  330  may include a diode D 1  and a rectifying capacitor C 5  such that the rectifier circuit  330  converts alternating current (AC) power into direct current (DC) power and outputs the DC power. The rectifying unit  330  may include a rectifier and a smoothing circuit. The rectifier may include a silicon rectifier as a rectifying element. The smoothing circuit smoothes the output of the rectifier. 
     Although the load  340  is denoted as 1.3 V DC power, the load  340  may be a battery or other devices requiring DC power. The embodiment is not limited to 1.3 V. 
       FIG. 5  is a view illustrating a structure of a wireless power transmission system  400  according to a first embodiment. 
     The wireless power transmitter  400  according to the embodiment may efficiently transmit power when a receiver side is located at the lateral side rather than the upper side of the wireless power transmitter  400 . 
     Referring to  FIG. 5 , the wireless power transmitter  400  includes a power connecting unit  401 , a first substrate  403 , a transmission induction coil  405 , a transmission resonance coil  407 , a second substrate  409 , a shielding unit  411 , a transmission circuit unit  413 , a receiving unit  415 , and a support member  417 . 
     A power supplying unit  10  may supply DC power to the wireless power transmitter  400 . 
     The power supplying unit  10  may be included in the wireless power transmitter  400 . 
     The power connecting unit  401  may transfer the power supplied from the power supplying unit  10  to the transmission induction coil  405 . In the embodiment, the power connecting unit  401  may be disposed adjacent to one side of a transmission resonance coil  407  to be described later. The power supplied from the power supplying unit  10  may be DC power. 
     In the embodiment, the power connecting unit  401  may be disposed on the first substrate  403 , which will be described with reference to  FIG. 7  in detail. 
     The first substrate  403  may include a printed circuit board (PCB). 
     The transmission induction coil  405  may be disposed on the first substrate  403 . In one embodiment, when the first substrate  403  has a circular shape, the transmission induction coil  405  may be disposed along an outer contour line of the first substrate  403 . The first substrate having the circular shape is illustrative purpose only and the first substrate  403  may have a polygonal shape such as a rectangular shape. A shape of the transmission induction coil  405  disposed on the first substrate  403  may be changed according to the shape of the first substrate  403 . 
     The transmission induction coil  405  may be provided by winding a conductive wire several times, and may be disposed by forming a predetermined pattern on the first substrate  403 . In the embodiment, the transmission induction coil  405  may have a spiral structure or a helical structure, but the embodiment is not limited thereto. 
     The transmission induction coil  405  may transfer power supplied from the power supplying unit  10  to the transmission resonance coil  407  physically spaced apart from the transmission induction coil  405  using electromagnetic induction. 
     The transmission induction coil  405  may be connected to a capacitor  408  of the transmission resonance coil  407  through a feeding line on the first substrate  403 . 
     The transmission resonance coil  407  may receive power from the transmission induction coil  405  using electromagnetic induction. 
     The transmission resonance coil  407  may be disposed vertical to the transmission induction coil  405 . In the embodiment, the transmission resonance coil  407  and the transmission induction coil  405  may be spaced apart from each other by a predetermined vertical distance. 
     As shown in  FIG. 5 , in the embodiment, the transmission induction coil  407  may be laminated by winding a conductive wire several times. The transmission resonance coil  407  may have various shapes such as a spiral shape or a helical shape with a predetermined diameter. 
     The transmission resonance coil  407  may transmit power to a reception resonance coil (not shown) of a wireless power receiver (not shown) using resonance. 
     The shielding unit  411 , the second substrate  409 , and the transmission circuit unit  413  may be sequentially disposed on the receiving unit  415  in the upward direction. 
     The transmission circuit unit  413  may convert the power supplied from the power supplying unit  10  into power having a frequency for resonance. 
     The transmission circuit unit  413  may include a DC-DC converter, an oscillator, and an AC power generating unit. 
     The DC-DC may convert the power from the power supplying unit  10  into desired output power. 
     The oscillator may generate an AC signal having a resonance frequency. 
     The AC power generating unit outputs amplified AC power using the AC power received from the DC-DC converter and the AC signal received from the oscillator. The amplified AC power may be transferred to the transmission induction coil  405 . 
     The transmission circuit unit  413  may be disposed on the second substrate  409 . The transmission circuit unit  413  may be the form of a chip, and may include a plurality of chips. The second substrate  409  may include a PCB. In the embodiment, the second substrate  409  may have a circular shape, but the embodiment is not limited thereto. 
     When the second substrate  409  has the circular shape, the transmission circuit unit  413  may be on the second substrate  409 . 
     Hereinafter, a second substrate  409  having a circular shape will be described as one example. 
     The ratio of a diameter of the second substrate  409  to a diameter of the transmission resonance coil  407  may have a predetermined value. In the embodiment, the ratio of a diameter of the second substrate  409  to a diameter of the transmission resonance coil  407  may be 3.8 or less. It is preferable that the ratio of a diameter of the second substrate  409  to a diameter of the transmission resonance coil  407  may be 3.8. When the transmission resonance coil  407  has a coaxial spiral type helical structure, the diameter of the transmission resonance coil  407  may signify a distance between one point of an outermost wire passing through a center of the transmission resonance coil  407  and an opposite point of the outermost wire. 
     The second substrate  409  may be spaced apart from the transmission resonance coil  407  by a predetermined vertical distance. In the embodiment, it may be preferable that the vertical distance is in the range of 5 mm to 25 mm or less. 
     The ratio of a diameter of the second substrate  409  to a diameter of the transmission resonance coil  407  and the vertical distance between the second substrate  409  are associated with a quality factor Q and power transmission efficiency. The quality factor Q is a reciprocal of energy loss per unit time of the wireless power transmission system. The performance of the power transmission system can be gradually improved as the value of the quality factor Q is increased. The power transmission efficiency may signify the ratio of power received by the wireless power receiver to power transmitted from the wireless power transmitter  400 . 
     In the embodiment, the quality factor Q and the power transmission efficiency may be changed according to variation in the vertical distance between the second substrate  409  and the transmission resonance coil  407 . 
     In another embodiment, the quality factor Q and the power transmission efficiency may be changed if the vertical distance between the second substrate  409  and the transmission resonance coil  407  is changed in a state that the ratio of a diameter of the second substrate  409  to a diameter of the transmission resonance coil  407  is 3:8. A detailed description thereof will be given later. 
     The receiving unit  415  may receive a shielding unit  411 , a second substrate  409 , and a transmission circuit unit  413 . In the embodiment, the receiving unit  415  may have a cylindrical shape including an open top surface and a bottom surface with a predetermined diameter. 
     The shielding unit  411  may change a direction of a magnetic flux formed in the transmission resonance coil  407 . The shielding unit  411  will be described in detail below. 
     At least one support member  417  may vertically connect the receiving unit  415  to the first substrate  403 . 
     Hereinafter, the following is the arrangement between constituent elements of the wireless power transmitter  400  according to the embodiment. 
       FIG. 6  is a front view illustrating the wireless power transmission system  400  according to a first embodiment. 
     Referring to  FIG. 6 , the wireless power transmitter  400  may include a power connecting unit  401 , a first substrate  403 , a transmission induction coil  405 , a transmission resonance coil  407 , a second substrate  409 , a shielding unit  411 , a transmission circuit unit  413 , and a support member  417 . 
     Constituent elements of the wireless power transmitter  400  have the same functions as those of the constituent elements of the wireless power transmitter shown in  FIG. 5  described above, and thus the detailed description thereof is omitted. The following description will be made while focusing on the arrangement of respective constituent elements. 
     The first substrate  403  is disposed at the lowermost end of the wireless power transmitter  400 . 
     The transmission induction coil  405  may be disposed on the first substrate  403 . 
     The transmission resonance coil  407  may be spaced apart from the transmission induction coil  405  by a predetermined vertical distance. 
     The transmission induction coil  405  may be provided by winding a conductive wire several times while being laminated. 
     A height of the transmission resonance coil  407  may be 10 mm, but the embodiment is not limited thereto. 
     The power connecting unit  401  is provided at one terminal of the transmission resonance coil  407 . A height of the power connecting unit  401  may be 10 mm, but the embodiment is not limited thereto. 
     The second substrate  409  may be spaced apart from the transmission resonance coil  407  by a predetermined vertical distance. The vertical distance between the second substrate  409  and the transmission resonance coil  407  may be in the range of 5 mm to 25 mm, preferably, be 15 mm. The embodiment is not limited to 15 mm. 
     The transmission circuit unit  413  including a plurality of chips may be disposed on the second substrate  409 . 
     The second substrate  409  may have a circular shape. 
     The shielding unit  411  may have a cylindrical shape including an open top surface capable of the second substrate  409 . 
     The receiving unit  415  is disposed adjacent to a lower side of the shielding unit  411 , and may have a cylindrical shape including an open top surface. 
     The shielding unit  411  may change a direction of a magnetic flux formed in the transmission resonance coil  407  to a location at which the wireless power receiver is provided. Accordingly, the magnetic flux formed in the transmission resonance coil  407  may be more concentrated onto the wireless power receiver side. Preferably, when the wireless power receiver is disposed at a lateral side of the wireless power transmitter  400 , the shielding unit  411  may transfer the magnetic flux to the wireless power receiver side by changing a direction of the magnetic flux formed in the transmission resonance coil  407 . 
     Further, the shielding unit  411  may change the direction of the magnetic flux formed in the transmission resonance coil  407  to inhibit the malfunction of the transmission circuit unit  413 . Since the magnetic flux formed in the transmission resonance coil  407  may exert influence upon the transmission circuit unit  413  when the magnetic flux is transmitted to the transmission circuit unit  413 , the shielding unit  411  may inhibit the magnetic flux from being transmitted to the transmission circuit unit  413  to protect the transmission circuit unit  413 . Particularly, the shielding unit  411  has a cylindrical structure including an open top surface to minimize the influence of the transmission circuit unit  413  caused by a magnetic field formed in the transmission resonance coil  407 , thereby inhibiting the malfunction of the transmission circuit unit  413 . 
     The receiving unit  415  may be connected to the first substrate  403  through a plurality of support members  417 . 
     The support members  417  serve to connect and support the first substrate  403  and the receiving unit  415 . 
     When the second substrate  409  has a circular shape, a diameter of the second substrate  409  may be 30 mm and a diameter of the transmission resonance coil  407  may be 80 mm, but the embodiment is not limited thereto. The diameter of the second substrate  409  and the diameter of the transmission resonance coil  407  may be variously set if the ratio of the diameter of the second substrate  409  to the diameter of the transmission resonance coil  407  is kept as 3:8. 
       FIG. 7  is a view illustrating a structure of a wireless power transmission system  400  according to a second embodiment. 
     Referring to  FIG. 7 , the wireless power transmitter  400  according to the second embodiment includes a power connecting unit  401 , a first substrate  403 , a transmission induction coil  405 , a transmission resonance coil  407 , and a second substrate  409 . The wireless power transmitter  400  may further include the constituent elements illustrated in  FIG. 5 . 
     When compared with the embodiment shown in  FIG. 5 , a location of the power connecting unit  401  is changed in the wireless power transmitter  400  according to the second embodiment. 
     In detail, the power connecting unit  401  of the wireless power transmitter  400  of  FIG. 5  is disposed at a lateral side of the first substrate  403  of the transmission resonance coil  407 , but the power connecting unit  401  of the wireless power transmitter  400  according to the second embodiment is disposed at a top surface of the first substrate  403 . 
     When the power connecting unit  401  is disposed at the lateral side of the first substrate  403 , some magnetic flux formed from the transmission resonance coil  407  and transferred to a receiver side may be absorbed or blocked by the power connecting unit  401 , exerting influence upon the power transmission efficiency. 
     When the power connecting unit  401  is disposed at the top surface of the first substrate  403 , the magnetic flux formed from the transmission resonance coil  407  and transferred to the receiver side may not be absorbed or blocked by the power connecting unit  401 . That is, due to the arrangement of the power connecting unit  401  as illustrated in  FIG. 7 , the power transmission efficiency may be increased. 
     In detail, power transmission efficiency in the arrangement of the power connecting unit  401  of the wireless power transmitter  400  shown in  FIG. 7  is increased by 3% and the quality factor is increased by  120  as compared with the arrangement of the power connecting unit  401  of the wireless power transmitter  400  shown in  FIG. 5 . 
       FIG. 8  is a table illustrating variations in the Q value and power transmission efficiency as a function of a vertical distance between a transmission resonance coil  407  and a second substrate  409  of a wireless power transmitter  400  according to the embodiment. 
     It is assumed that a diameter of the second substrate  409  is 30 mm and a diameter of the transmission resonance coil  407  is 80 mm. 
     Further, it is assumed that the wireless power receiver is disposed at a side of the wireless power transmitter  400  other than an upper side and a lower side the wireless power transmitter  400 . 
     Referring to  FIG. 8 , when the vertical distance between the transmission resonance coil  407  and the second substrate  409  is 0 mm, the quality factor Q is 560. As the vertical distance is increased, the quality factor Q is increased. 
     When the vertical distance between the transmission resonance coil  407  and the second substrate  409  is 15 mm, the quality factor Q is 700. When the vertical distance is 20 mm, the quality factor Q is 710. When the vertical distance is 25 mm, the quality factor Q is 712. After that, as the vertical distance is increased, the quality factor Q may become constant. In addition, if the transmission efficiency of power transferred to the receiver side is 18% when the vertical distance between the transmission resonance coil  407  and the second substrate  409  is 0 mm, as the vertical distance is increased, the power transmission efficiency is increased. 
     When the vertical distance between the transmission resonance coil  407  and the second substrate  409  is 15 mm, the transmission efficiency of power transferred to the receiver side becomes 22%. When the vertical distance is 25 mm, the transmission efficiency of power transferred to the receiver side becomes 23%. When the vertical distance between the transmission resonance coil  407  and the second substrate  409  is equal to or greater than 25 mm, the transmission efficiency of power transferred to the receiver side may not be increased any more. 
     Meanwhile, if the vertical distance between the transmission resonance coil  407  and the second substrate  409  exceeds 25 mm, it is not preferable in view of the size of the wireless power transmitter  400 , so the vertical distance between the transmission resonance coil  407  and the second substrate  409  is preferably set to 25 mm or less. 
     In this manner, as the vertical distance between the transmission resonance coil  407  and the second substrate  409  is increased, the quality factor Q and the power transmission efficiency may be increased within a predetermined range. 
     Hereinafter, the wireless power transmitter  400  and the power transmission efficiency according to the third embodiment will be described with reference to  FIGS. 9 to 13 . 
       FIG. 9  is a view illustrating a structure of a wireless power transmitter  400  according to a third embodiment,  FIG. 10  is a diagram illustrating a wireless power transmission procedure of a wireless power transmitter  400  according to the first embodiment,  FIGS. 11 and 12  are diagrams illustrating a wireless power transmission procedure of a wireless power transmitter  400  according to the third embodiment, and  FIG. 13  is a table illustrating power transmission efficiency when the wireless power transmitter  400  according to the third embodiment is used. 
     First, referring to  FIG. 9 , the wireless power transmitter  400  includes a power connecting unit  401 , a first substrate  403 , a transmission induction coil  405 , a transmission resonance coil  407 , a second substrate  409 , a shielding unit  411 , a transmission circuit unit  413 , a receiving unit  415 , and a support member  417 . The constituent elements are substantially the same as those of  FIG. 5 . 
     The transmission resonance coil  407  may be inclined at a predetermined angle with respect to a horizontal line of a horizontal plane. In detail, the transmission resonance coil  407  may be inclined at a predetermined angle with respect to the horizontal line of a plane where the wireless power transmitter  400  is placed. It may be preferable that an angle between the transmission resonance coil  407  and the horizontal line is in the range of 0° to 30°. 
     One lateral side of the transmission resonance coil  407  may be inclined to have a preset angle with respect to a charging region to be used. If the transmission resonance coil  407  is inclined at the preset angle with respect to the horizontal line, the power can be transmitted with high efficiency to the wireless power receiver  300  placed at the charging region. 
       FIG. 10  illustrates a magnetic force line of a magnetic field generated from the transmission resonance coil  407  when the angle between the transmission resonance coil  407  and the horizontal line is 0°.  FIG. 11  illustrates a magnetic force line of a magnetic field generated from the transmission resonance coil  407  when the angle between the transmission resonance coil  407  and the horizontal line is 10°.  FIG. 12  illustrates a magnetic force line of a magnetic field generated from the transmission resonance coil  407  when the angle between the transmission resonance coil  407  and the horizontal line is 20°. 
     An electronic device  600  in  FIGS. 10 to 12  may include the wireless power receiver  300  described in  FIGS. 1 to 4 , and may receive power using a magnetic field from the transmission resonance coil  407 . The electronic device  600  may include a portable phone, a notebook computer, and a mouse, but the embodiment is not limited thereto. The electronic device  600  may include may include all devices capable of receiving the power from the wireless power transmitter  400 . 
     Further, it is assumed in  FIGS. 10 to 12  that a distance d between the transmission resonance coil  407  and the electronic device  600  is constant and the electronic device  600  is placed at a right side of the transmission resonance coil  407  in order to compare respective power transmission efficiencies with each other. In addition, in  FIGS. 10 to 12 , when the magnetic force line generated from the transmission resonance coil  407  passes through the electronic device  600 , the power may be transmitted to the electronic device  600 . When the magnetic force line generated from the transmission resonance coil  407  does not pass through the electronic device  600 , the power may not be transmitted to the electronic device  600 . 
     Referring to  FIG. 10 , the angle between the transmission resonance coil  407  and the horizontal line is 0°. In this case, some of a plurality of magnetic force lines generated from the transmission resonance coil  407  pass through the electronic device  600 , but remaining magnetic force lines may not pass through the electronic device  600 . That is, as shown in  FIG. 10 , a magnetic force line A and a magnetic force line B do not pass through the electronic device  600 . 
     To the contrary, referring to  FIG. 11 , the angle between the transmission resonance coil  407  and the electronic device  600  is 10°. In this case, the magnetic force line A which does not pass through the electronic device  600  in  FIG. 10  passes through the electronic device  600 . That is, as the transmission resonance coil  407  is inclined toward the electronic device  600 , the number of magnetic force lines directed to the electronic device  600  from among the magnetic force lines generated from the transmission resonance coil  407  is increased. 
     Moreover, referring to  FIG. 12 , the angle between the transmission resonance coil  407  and the electronic device  600  is 20°. In this case, the magnetic force line B which does not pass through the electronic device  600  in  FIGS. 10 and 11  passes through the electronic device  600 . That is because more magnetic force lines among the magnetic force lines generated from the transmission resonance coil  407  are directed to the electronic device  600  as the transmission resonance coil  407  is inclined toward the electronic device  600  as compared with a case of  FIG. 11 . 
       FIG. 13  is a table illustrating variations in the quality factor Q, a coupling coefficient, and power transmission efficiency when the angel of the transmission resonance coil  407  is changed from 0° to 39°. It is assumed that the electronic device  600  is placed at one lateral side of the transmission resonance coil  407 , and an angle the transmission resonance coil  407  is changed while one lateral side of the transmission resonance coil  407  is inclined toward a charging region to be used, that is, the electronic device  600 . 
     The quality factor Q may refer to an index of energy that may be stored in the vicinity of the wireless power transmitter or the wireless power receiver. The coupling coefficient represents the degree of inductive magnetic coupling between a transmission coil and a reception coil, and has a value of 0 to 1. The coupling coefficient may vary according to the relative position and the distance between the transmission coil and the reception coil. 
     The power transmission efficiency may refer to a ratio of power received by the wireless power receiver  300  mounted in the electronic device  600  to power transmitted from the wireless power transmitter  400 . The power transmission efficiency depends on the quality factor Q and the coupling coefficient, and can be gradually improved as the values of the quality factor and the coupling coefficient between the transmission resonance coil  407  and the reception resonance coil  310  are increased. 
     As shown in  FIGS. 10 to 12 , power transmission efficiency at a front side corresponds to power transmission efficiency when the electronic device  600  is placed at a front side of the wireless power transmitter  400 , power transmission efficiency at a side corresponds to power transmission efficiency when the electronic device  600  is placed at a right side or a left side of the wireless power transmitter  400 , and power transmission efficiency at a back side corresponds to power transmission efficiency when the electronic device  600  is placed at a back side of the wireless power transmitter  400 . 
     It is assumed that the same distance is set between the transmission resonance coil  407  and the electronic device  600  regardless of the position of the electronic device  600  at the front side, the lateral side, and the back side of the transmission resonance coil  407 . Referring to  FIG. 13 , when the electronic device  600  is placed at the front side of the transmission resonance coil  407 , as the angle between the transmission resonance coil  407  and the horizontal line is increased, the power transmission efficiency and the coupling coefficient may be increased but the quality factor Q may be reduced. 
     The coupling coefficient may be increased as the angle between the transmission resonance coil  407  and the horizontal line is increased because a greater amount of magnetic field formed in the transmission resonance coil  407  is transferred to the reception resonance coil  310  mounted in the electronic device  600 . In addition, the quality factor Q may be reduced because a magnetic field formed in the transmission resonance coil  407  is absorbed in a metal under the influence of a metal component of the electronic device. 
     If the angle between the transmission resonance coil  407  and the horizontal line exceeds 30°, power transmission efficiency to the electronic device  600  placed at the front side of the wireless power transmitter  400  may be reduced under the influence of the quality factor Q rather than the coupling coefficient. In particular, if the angle between the transmission resonance coil  407  and the horizontal line exceeds 30°, the whole power transmission efficiency may be deteriorated due to the power transmission efficiency to the electronic device  600  placed at the lateral side and the back side may be reduced 
     Meanwhile, if the angle between the transmission resonance coil  407  and the horizontal line is 3°, power transmission efficiency to the front side may be less than that of a case where the angle between the transmission resonance coil  407  and the horizontal line exceeds 30°. However, when taking into consideration the whole power transmission efficiency in the lateral side and the back side, the power transmission efficiency may be improved more than that of a case where the angle between the transmission resonance coil  407  and the horizontal line exceeds 30°. 
     Accordingly, it may be preferable in the embodiment that the angle between the transmission resonance coil  407  and the horizontal plane is in the range of 3° to 30°. 
     Although embodiments have been described with reference to a number of illustrative embodiments thereof, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the spirit and scope of the principles of this disclosure.