Patent Publication Number: US-2016248276-A1

Title: Wireless power transmission apparatus, wireless power transmission system including the same and wireless power transmission method thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This U.S. non-provisional patent application claims priority under 35 U.S.C. §119 of Korean Patent Application No. 10-2015-0025286, filed on Feb. 23, 2015, the entire contents of which are hereby incorporated by reference. 
    
    
     BACKGROUND 
     The present disclosure herein relates to a wireless power transmission apparatus for an implantable medical device, a wireless power transmission system including the same, and a wireless power transmission method thereof, and more particularly, to a wireless power transmission apparatus for measuring an exposure level of a human body to electromagnetic fields during power transmission and controlling a transmission power level, a wireless power transmission system including the same, and a wireless power transmission method thereof. 
     The market of implantable medical device is rapidly growing with population aging and welfare activation. Application of the implantable medical device is extending to various disease treatment fields in order to assist in vulnerable function of human, and a power module thereof becomes essential to active treatment through the device. In order to use this smoothly, an additional cost and suffering are necessary. In order to address this, products using a wireless power transmission technique are being actively developed. 
     During power transmission by using a human body as a medium, the electromagnetic field (EMF) is absorbed to human tissues and the absorbed power increases a temperature of the human tissues to a certain level or greater. When this increase in temperature continues for a certain time or longer, corresponding tissues may be damaged. Like this, absorption of the EMF to the human tissues influences safety of human body, 
     Accordingly, an apparatus and method are required which are capable of observing variation in human body due to exposure to the EMF that occurs when power is supplied to a device inserted into the human body, and of enabling safe use of the device. 
     SUMMARY 
     The present disclosure provides a wireless power transmission apparatus capable of measuring an exposure level of a human body exposed to an EMF that occurs when power is wirelessly transmitted to an implantable medical device, and controlling a power transmission level using the measure result, a wireless power transmission system including the same, and a wireless power transmission method thereof. 
     An embodiment of the inventive concept provides a wireless power transmission apparatus that wirelessly transmits power to an implantable medical device. The wireless power transmission apparatus includes: a power supplying unit configured to output external power as a power signal having a set frequency; a power transmitting unit configured to output the power signal from the power supplying unit as a wireless power signal of an electromagnetic field (EMF) type; and a controller configured to output a power control signal for controlling an output level of the wireless power signal, wherein the controller calculates a specific absorption rate (SAR) and inner body temperature variation amount by using EMF and temperature measurement data transmitted from the implantable medical device in the power transmission process, and outputs the power control signal according to a result of comparing the calculated SAR and inner body temperature variation amount with a reference value. 
     In an embodiment, when the SAR or inner body temperature variation amount is greater than the reference value, the controller may control the power transmitting unit to reduce an output level of the wireless power signal. 
     In an embodiment, when the SAR or inner body temperature variation amount is equal to or smaller than the reference value, the controller may control the power transmitting unit to maintain an output level of the wireless power signal. 
     In an embodiment, the wireless power transmission apparatus may further include a display or an LED display configured to display the SAR and inner body temperature variation amount. 
     In an embodiment, the power transmission unit may include: a transmission coil configured to output the power signal of the power supplying unit as the wireless power signal of the EMF type; and a transmission antenna configured to receive the EMF and temperature measurement data transmitted from the implantable medical device. 
     In an embodiment, the power may be transmitted to the implantable medical device in a magnetic resonance type. 
     In an embodiments of the inventive concept, a wireless power transmission system includes a wireless power transmission device; and a wireless power receiving device, wherein the wireless power receiving device receives a wireless power signal transmitted from the wireless power transmission device, converts the received wireless power signal to a DC voltage to supply the DC voltage to a load, and measures an EMF intensity of the received wireless power signal to transmit the EMF intensity to the wireless power transmission device, and the wireless power transmission device calculates a SAR and inner body temperature variation amount by using the EMF intensity and inner body temperature measured by the wireless power receiving device, and controls an output level of the wireless power signal transmitted according to a result of comparing the calculated SAR and inner body temperature variation with reference values. 
     In an embodiment, the wireless power receiving device may include a receiving coil configured to receive the wireless power signal, and a receiving antenna configured to transmit the measured data of the EMF intensity of the wireless power signal and inner body temperature to the wireless power transmission device, and the wireless power transmission device may include a transmission coil configured to transmit the wireless power signal and a transmission antenna configured to receive the data. 
     In an embodiment, the wireless power transmission system may further include a matching circuit configured to match a resonance frequency of the receiving coil with a resonance frequency of the transmission coil in a wireless power transmitting process. 
     In an embodiment, when the SAR or inner body temperature variation amount is greater than the reference value, the wireless power transmission device may reduce an output level of the wireless power signal. 
     In an embodiment, when the SAR or inner body temperature variation amount is equal to or smaller than the reference value, the wireless power transmission device may maintain an output level of the wireless power signal. 
     In an embodiment, the wireless power transmission device may include a display or an LED display configured to display the SAR and inner body temperature variation amount. 
     In an embodiment, the wireless power receiving device may be located in an implantable medical device to supply power to a power supplying unit of the implantable medical device. 
     In an embodiments of the inventive concept, a method for wirelessly transmitting power by a wireless power transmission device includes: transmitting a wireless power signal of an EMF type to a wireless power receiving device; receiving measurement data for an EMF intensity of the wireless power signal and inner body temperature from the wireless power receiving device; and controlling an output level of the wireless power signal by using the measurement data, wherein the controlling of the output level is performed by calculating the SAR and inner body temperature variation amount by using the measurement data, and using the calculated SAR and inner body temperature variation amount. 
     In an embodiment, the controlling of the output level may include reducing an output level of the wireless power signal, when the SAR or inner body temperature variation amount is greater than a reference value. 
     In an embodiment, the controlling of the output level may include maintaining an output level of the wireless power signal, when the SAR or inner body temperature variation amount is equal to or smaller than a reference value. 
     In an embodiment, the method may further include displaying the calculated SAR and inner body temperature variation amount on a display. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The accompanying drawings are included to provide a further understanding of the inventive concept, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the inventive concept and, together with the description, serve to explain principles of the inventive concept. In the drawings: 
         FIG. 1  illustrates a state where an implantable medical device according to an embodiment of the inventive concept is implanted in a human body; 
         FIG. 2  is a block diagram exemplarily illustrating a wireless power transmission apparatus and an implantable medical device that wirelessly receives power from the wireless power transmission apparatus; 
         FIG. 3  is a detailed block diagram of a wireless power transmission apparatus according to an embodiment of the inventive concept; 
         FIG. 4  is a detailed block diagram of a wireless power receiver according to an embodiment of the inventive concept; 
         FIG. 5  exemplarily illustrates power transmission and data transmission by a wireless power transmission system according to an embodiment of the inventive concept; 
         FIG. 6  is an exemplary flowchart of a wireless power transmission method of a wireless power transmission system; and 
         FIG. 7  is an exemplary flowchart of a method of adjusting, by a wireless power transmission apparatus, an output level of a wireless power signal. 
     
    
    
     DETAILED DESCRIPTION 
     Exemplary embodiments of the inventive concept will be described below in more detail with reference to the accompanying drawings. The inventive concept may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive concept to those skilled in the art. 
     Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that the present invention can be easily realized by those skilled in the art. 
       FIG. 1  illustrates a state where an implantable medical device  100  according to an embodiment of the inventive concept is implanted in a human body. The implantable medical device means a medical device implanted in a user&#39;s body to collect physiological/pathological state information on a user, or closely connected to organs of the user to perform treatment such as control operations for the organs. 
     Referring to  FIG. 1 , the implantable medical device  100  according to an embodiment of the inventive concept may be implanted in a body to perform set functions. For example, the implantable medical device  100  may be an implanted artificial pacemaker, implanted external defibrillator, implanted medical electric stimulator, implanted electrical urinary continence, or implanted medicine supplying pump. However, the implantable medical device  100  according to an embodiment of the inventive concept is not limited thereto and includes all medical devices that are implanted in a body to be used for medical purposes. 
     The implantable medical device  100  according to an embodiment of the inventive concept may include, as a power supply, a battery for performing a function set therein. The implantable medical device  100  according to an embodiment of the inventive concept may include a power receiving means for wirelessly charging the battery. The power receiving means may receive power transmitted in a wireless signal type to charge the battery through processes such as rectification, DC level conversion, and the like. 
     A description will be provided about a detailed configuration and operation of the implantable medical device  100  according to an embodiment of the inventive concept for wirelessly receiving power with reference to  FIGS. 2 to 5 . 
       FIG. 2  is a block diagram exemplarily illustrating a wireless power transmission apparatus  200  and the implantable medical device  100  that wirelessly receives power from the wireless power transmission apparatus  200 . Referring to  FIG. 2 , the implantable medical device  100  according to an embodiment of the inventive concept may include a wireless power receiver  300  and a battery  110 . 
     Hereinafter, a power transmission process will be described in detail between the wireless power transmission apparatus  200  and the implantable medical device  100  according to an embodiment of the inventive concept with reference to  FIG. 2 . 
     The battery  110  of the implantable medical device  100  supplies operation power of the implantable medical device  100 . The battery  110  may be a rechargeable battery such as a Lithium-ion battery. The battery  110  may be discharged due to continuous use and accordingly require to be charged periodically or when necessary. The battery  110  according to an embodiment of the inventive concept may be wirelessly charged through the wireless power transmission apparatus  200 . 
     The wireless power transmission apparatus  200  may wirelessly deliver power to the implantable medical device  100 . In other words, the wireless power transmission apparatus  200  may transmit power in an EMF signal type to the wireless power receiver  300  of the implantable medical device  100 . For example, the wireless power transmission apparatus  200  may transmit power in a magnetic induction type or magnetic resonance type to the wireless power receiver  300 . 
     The wireless power receiver  300  may receive power in the EMF signal type from the wireless power transmission apparatus  200 , convert the power to DC signal through a rectifying process, amplify and convert the DC signal to a voltage-signal, and then charge the battery  110 . 
     The wireless power receiver  300  may measure an intensity and temperature of the EMF signal transmitted from the wireless power transmission apparatus  200 . When the power in the EMF signal type is transmitted to the implantable medical device  100 , a body part in which the implantable medical device  100  is implanted becomes exposed to the EMF. The wireless power receiver  300  may measure an exposure level of the body in the wireless power transmission process. 
     The wireless power transmission apparatus  200  may calculate a specific absorption rate (SAR) and a variation amount of inner body temperature by using the EMF exposure level and temperature measured by the wireless power receiver  300 . In addition, the wireless power transmission apparatus  200  may adjust a transmission power level by using the calculated SAR and variation amount of inner body temperature. For example, when the calculated SAR and variation amount of inner body temperature respectively exceed set values, the transmission power level may be reduced. For example, when the calculated SAR and variation amount of inner body temperature are respectively equal to or smaller than set values, the transmission power level may be reduced. 
     As described above, the wireless power transmission apparatus  200  according to an embodiment of the invention may wirelessly deliver power to the implantable medical device  100 . In addition, the transmission power level may be adjusted by using the exposure level of the body in the wireless power transmission process. Accordingly, the wireless power transmission apparatus  200  according to an embodiment of the inventive concept may reduce harmfulness to the body in the wireless power transmission process. 
       FIG. 3  is a detailed block diagram of the wireless power transmission apparatus  200  according to an embodiment of the inventive concept. Referring to  FIG. 3 , the wireless power transmission apparatus  200  may include a power supplying unit  210 , a power transmitting unit  220 , a controller  230 , and a notifying unit  240 . The power supplying unit  210  may include a power supplying unit  212 , a signal generating unit  214 , and a power amplifying unit  216 . The power transmitting unit  220  may include a transmission matching circuit  222 , a transmission coil  224 , and a transmission antenna  226 . The controller  230  may include a power controller  232 , a signal processing unit  234 , and a alarm controller  236 . The notifying unit  240  may include a display unit  242 , an LED display unit  244 , and a speaker  246 . 
     Hereinafter, an operation of the wireless power transmission apparatus  200  will be described in detail with reference to  FIG. 3 . 
     The power supplying unit  210  converts external power supplied through the power supplying unit  212  to an EMF signal, and outputs the EMF signal to the power transmitting unit  220 . 
     The power supplying unit  212  receives power from the outside thereof. For example, such external power may be AC power of 220 v/60 Hz. The power supplying unit  212  may rectify the input external power to output a DC voltage. 
     The signal generating unit  214  may generate a signal having a frequency that the wireless power transmission apparatus  200  requires. A frequency band of the generated signal may be, for example, several MHz to several tens of MHz. 
     The power amplifying unit  216  converts the DC voltage having a certain level output from the power supplying unit to a signal type having a predetermined frequency by using a signal generated from the signal generating unit  214 . In other words, a power signal SIG_PW for wirelessly transmitting the DC voltage may be generated. In addition, the power amplifying unit  216  may adjust an output level of the power signal SIG_PW. The power amplifying unit  216  may further include a protection circuit for preventing performance degradation and malfunction thereof. 
     The power transmitting unit  220  may transmit the power signal SIG_PW received from the power supplying unit  210  to the wireless power receiver  300  of the implantable medical device  100  through the transmission coil  224 . In other words, the power transmitting unit  220  receives the power signal SIG_PW to radiate the wireless power signal in the EMF signal type to the wireless power receiver  300 . In addition, the power transmitting unit  220  may receive EMF and temperature measurement data transmitted from the wireless power receiver  300  of the implantable medical device  100 . 
     The transmission matching circuit  222  may change a resonance frequency of the transmission coil  224 . To this end, the transmission matching circuit  222  may include a variable capacitor. The transmission matching circuit  222  may be located at a rear end of the transmission coil  224  and match impedance between the transmission coil  224  and the power supplying unit  210 . 
     The transmission coil  224  may transmit the power signal SIG_PW received from the power supplying unit  210  to the wireless power receiver  300  of the implantable medical device  100 . In other words, the transmission coil  224  may radiate the power signal SIG_PW as a wireless power signal of the EMF signal type. The wireless power supplying apparatus  200  and the transmission coil  224  of the wireless power receiver  300  according to an embodiment of the inventive concept may be configured with a loop antenna, not in a coil type. 
     The transmission antenna  226  may receive the EMF and temperature measurement data transmitted from the wireless power receiver  300  of the implantable medical device  100 . The EMF measurement data may be data measured by an EMF and temperature measuring unit  332  (see  FIG. 4 ) of the wireless power receiver  300 , and data for an inner body EMF exposure level in the wireless power transmission process. 
     In other words, the transmission coil  224  is used for transmitting power to the implantable medical device  100 , and the transmission antenna  226  is used for communicating with the implantable medical device  100 . The transmission antenna  226  may be used for transmitting power to the implantable medical device  100  instead of the transmission coil  224 . 
     The controller  230  may calculate the SAR and inner body temperature variation amount by using the EMF and temperature measurement data received through the transmission antenna  226 . The controller  230  may control the transmission power level according to the calculated SAR and inner body temperature variation amount. The controller  230  may control the notifying unit  240  to display the calculated SAR and inner body temperature variation amount as visual or auditory information. 
     The signal processing unit  234  may process a transmission signal SIG_TRN for the EMF exposure level received from the transmission antenna  226  to calculate the SAR and inner body temperature variation amount. For example, the SAR may be calculated according to the following Equations (1) and (2). 
     
       
         
           
             
               
                 
                   
                     S 
                      
                     
                         
                     
                      
                     A 
                      
                     
                         
                     
                      
                     R 
                   
                   = 
                   
                     
                       σ 
                        
                       
                           
                       
                        
                       
                         E 
                         2 
                       
                     
                     ρ 
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
     where σ denotes a conductivity (S/m) of a tissue, ρ denotes a density (kg/m 3 ) of a tissue, and E denotes an intensity (V/m) of electric field. 
     
       
         
           
             
               
                 
                   
                     S 
                      
                     
                         
                     
                      
                     A 
                      
                     
                         
                     
                      
                     R 
                   
                   = 
                   
                     ci 
                      
                     
                       
                         Δ 
                          
                         
                             
                         
                          
                         t 
                       
                       
                         Δ 
                          
                         
                             
                         
                          
                         T 
                       
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
     where ci denotes a specific heat capacity J/kg ° C., Δt denotes an exposure time, and ΔT denotes a temperature variation rate. 
     The calculated SAR and inner body temperature variation amount may be transmitted to the power controller  232  and alarm controller  236 . 
     The power controller  232  compares the calculated SAR and inner body temperature variation amount with reference values to output a power control signal CTR_PW capable of controlling the power transmission level according to the comparison result. For example, when the calculated SAR is greater than the reference value, the signal processing unit  234  may output the power control signal CTR_PW for controlling the transmission power level to be lowered. For example, when the calculated inner body temperature variation amount is greater than the reference value, the signal processing unit  234  may output the power control signal CTR_PW for controlling the transmission power level to be lowered. The power amplifying unit  216  may adjust an output level of the wireless power signal SIG_PW in response to the generated power control signal CTR_PW. 
     The alarm controller  236  may output a notification control signal CTR_ARM for controlling the notifying unit  240  so that information on the input SAR and inner body temperature variation amount are displayed on the notifying unit  240 . The notification control signal CTR_ARM may control the notifying unit  240  so that the SAR and inner body temperature variation amount are displayed as visual information through the display unit  242 . Alternatively, the notification control signal CTR_ARM may control the notifying unit  240  so that the SAR and inner body temperature variation amount are displayed through the LED display unit  244  and speaker  246 . For example, when the SAR and inner body temperature variation amount exceed the reference values, the alarm controller  236  may generate the notification control signal CTR_ARM to warn a user visually or acoustically through the LED display unit  244  or the speaker  246 . 
     The notifying unit  240  may visually display information on the SAR and inner body temperature variation amount. When the SAR and inner body temperature variation amount exceed the reference values, the alarm controller  236  may warn the user through the LED display unit  244  or the speaker  246 . 
     The display unit  242  may be a liquid crystal display device, touch screen, or the like capable of visually displaying the SAR and inner body temperature variation amount. 
     The LED display unit  244  may be configured with one or a plurality of LED elements to display the SAR and inner body temperature variation amount or the foregoing warning display by an operation of turning on/ turning off the LED elements. 
     The speaker  246  may warn the user in a sound type. 
     As described above, the wireless power transmission apparatus  200  according to an embodiment of the invention may wirelessly transmit power to the implantable medical device  100 . In addition, the wireless power transmission apparatus  200  may calculate the SAR and inner body temperature variation amount by using the EMF measured in the power transmission process and adjust the transmission power level by using the calculated result. Accordingly, the wireless power transmission apparatus  200  according to an embodiment of the inventive concept may secure body safety for exposure to the EMF by measuring the EMF exposure level in real time and adjusting the transmission power level using the EMF this. 
       FIG. 4  is a detailed block diagram of a wireless power receiver  300  according to an embodiment of the inventive concept. 
     Referring to  FIG. 4 , the wireless power transmission apparatus  200  may include a power receiving unit  310 , a voltage output unit  320 , a sensing unit  230 , and a sensing signal processing unit  340 . The power receiving unit  310  may include a receiving matching circuit  312 , a receiving coil  314 , and a receiving antenna  316 . The voltage output unit  320  may include a rectifying unit  322 , a DC-DC converting unit  324 , and a charging unit  326 . The sensing unit  330  may include an EMF and temperature measuring unit  332 , and an RF unit  334 . 
     Hereinafter, an operation of the wireless power transmission device  300  will be described in detail with reference to  FIG. 4 . 
     The power receiving unit  310  may receive power transmitted from the wireless power transmission apparatus  200 . The power receiving unit  310  may transmit sensed EMF data to the wireless power transmission apparatus  200 . 
     The receiving matching circuit  312  may change a resonance frequency of the receiving coil  314 . To this end, the receiving matching circuit  312  may include a variable capacitor. For example, the receiving matching circuit  312  may change a resonance frequency of the receiving coil  314  to be matched with the resonance frequency of the transmission coil  224 . When the resonance frequency of the receiving coil  314  matches with the resonance frequency of the transmission coil  224 , maximum power may be delivered. 
     The receiving coil  314  may receive power transmitted in the EMF signal type by the transmission coil  224 . When the wireless power supplying apparatus  200  and the transmission coil  224  of the wireless power receiver  300  according to an embodiment of the inventive concept deliver power in a magnetic induction type, the receiving coil  224  may be configured with a loop antenna, not in a coil type. The receiving coil  214  may output the received power signal SIG_RF of the EMF signal type to the rectifying unit  322 . The receiving antenna  316  may transmit the EMF and temperature data sensed by the sensing unit  330  to the wireless power transmission apparatus  200 . 
     The voltage output unit  320  may convert the power received by the receiving coil  312  to a DC voltage to charge the battery  110  (see  FIG. 2 ). 
     The rectifying unit  322  may rectify the power of the EMF type received by the receiving coil  312  to convert to the DC voltage. 
     The DC-DC converting unit  324  may convert the DC voltage converted by the rectifying unit  322  to a DC voltage having a level suitable for charging the battery  110 . 
     The charging unit  326  may charge the battery  110  by using the DC voltage converted by the DC-DC converting unit  324 . The charging unit  326  may further include an overcharge prevention circuit for preventing overcharging the battery  110 . 
     The sensing unit  330  may measure a magnitude of the EMF and a temperature absorbed to the body in the wireless power transmission process. 
     The EMF and temperature measuring unit  332  may receive the exposure level of EMF occurring during power transmission from the wireless power transmission apparatus  200  to the wireless power receiver  300 . The EMF and temperature measuring unit  332  may be configured with an antenna or in a coil type capable of measuring the exposure level of EMF or a temperature sensor capable of measuring the temperature. 
     The RF unit  334  may remove noise from the EMF signal received by the EMF and temperature measuring unit  332  to amplify or attenuate a signal level. Alternatively, the RF unit  334  may convert the measure temperature to an analog signal. 
     The sensing signal processing device  340  may perform a function for processing a signal so that a sensing signal SIG_GEN transmitted from the sensing unit  330  is transmitted through the receiving state antenna  316 . The processed sensing signal SIG_PSEN may be transmitted to the wireless power transmission apparatus  200  through the receiving antenna  316 . 
     The wireless power receiver  300  according to an embodiment of the inventive concept may be located inside the implantable medical device  100 . The wireless power receiver  300  according to an embodiment of the inventive concept may receive power from the wireless power transmission apparatus  200  to charge the battery  110  of the implantable medical device  100 . In addition, the wireless power receiver  300  according to an embodiment of the inventive concept may measure the exposure level of the body to the EMF to transmit the exposure level to the wireless power transmission apparatus  200 . 
       FIG. 5  exemplarily illustrates power transmission and data transmission by a wireless power transmission system  1000  according to an embodiment of the inventive concept. The wireless power transmission system  1000  according to an embodiment of the inventive concept may include the wireless power transmission apparatus  200  and the wireless power receiver  300 . 
     Referring to  FIG. 5 , the wireless power transmission system  1000  according to an embodiment of the inventive concept may transmit power in a magnetic resonance type between the transmission coil  224  and the receiving coil  312 . 
     In addition, the wireless power system  1000  according to an embodiment of the inventive concept may transmit EMF data sensed by the wireless power receiver  300  to the wireless power transmission apparatus  200  through the receiving state antenna  316 . The wireless power transmission apparatus  200  may receive the sensed EMF data through the transmission antenna  316  and then calculate the SAR and inner body temperature variation amount using this. The wireless power transmission apparatus  200  may adjust a transmission power level by using the calculated SAR and variation amount of inner body temperature. 
       FIG. 6  is an exemplary flowchart of a wireless power transmission method of a wireless power transmission system  1000 . Referring to  FIG. 6 , in the wireless power system  1000  according to an embodiment of the inventive concept, power is transmitted from the wireless power transmission apparatus  200  to the wireless power receiver  300 . The wireless power receiver  300  may be located inside the implantable medical device  100 . 
     Hereinafter, an operation of the wireless power transmission device  1000  will be described in detail with reference to  FIG. 6 . 
     The wireless power transmission apparatus  200  transmits a wireless power signal to the wireless power receiver  300  (operation S 110 ). The wireless power transmission apparatus  200 , as described above, receives external power to transmit a wireless power signal of the EMF signal type to the wireless power receiver  300  through the transmission coil  224 . 
     The wireless power receiver  300  may receive the wireless power signal transmitted from the wireless power transmission apparatus  200  and convert the wireless power signal to a DC voltage to charge the battery  100 . In addition, the wireless power receiver  300  may measure an EMF of the wireless power signal transmitted from the wireless power transmission apparatus  200  (operation S 210 ). The measured EMF may be an intensity of an electric field of the wireless power signal. 
     The power receiver  300  may transmit the measured EMF data to the wireless power transmission apparatus  200  (operation S 220 ). The measured EMF data may be transmitted through the receiving antenna  316  of the wireless power receiver  300 . 
     The wireless power transmission apparatus  200  may receive the EMF and temperature data transmitted from the wireless power receiver  300  and calculate the SAR and inner body temperature variation amount by using the received EMF and temperature data (operation S 120 ). The SAR may be calculated by using Equation (1) or (2) as described above. 
     The wireless power transmission apparatus  200  compares the calculated SAR and inner body temperature variation amount with the reference values and adjusts an output level of the wireless power signal (operation S 130 ). For example, when the calculated SAR is greater than the reference value, the wireless power transmission apparatus  200  may reduce the output level of the transmitted wireless power signal. For example, when the calculated inner body temperature variation amount is greater than the reference value, the wireless power transmission apparatus  200  may reduce the output level of the transmitted wireless power signal. For example, when the calculated SAR is smaller than the reference value, the wireless power transmission apparatus  200  may maintain the output level of the transmitted wireless power signal. 
     The wireless power transmission device  200  may output the wireless power signal whose output level is adjusted to the wireless power receiver  300 . 
     As described above, according to the wireless power transmission device  1000  according to an embodiment of the invention, the power may be delivered to the wireless power receiver  300  embedded in the body. In addition, the wireless power transmission system  1000  according to an embodiment of the inventive concept may measure the intensity of EMF influencing on the human body to adjust the transmission power level. In other words, the wireless power transmission system  1000  according to an embodiment of the inventive concept may prevent damage on the human body due to the EMF occurring in the wireless power transmission process. 
       FIG. 7  is an exemplary flowchart of a method of adjusting, by a wireless power transmission device, an output level of a wireless power signal. Hereinafter, a method for adjusting, by the wireless power transmission apparatus  200 , the output level of the wireless power signal will be described in detail with reference to  FIG. 7 . 
     Firstly, the wireless power transmission apparatus  200  may receive the EMF and temperature data measured for the body exposed to the EMF in the power transmission process. 
     Then, the wireless power transmission apparatus  200  calculates the SAR by using the received EMF and temperature data through Equation (1) or (2) (operation S 310 ). 
     The wireless power transmission apparatus  200  compares the calculated SAR and inner body temperature variation amount with the prereference values (operation S 320 ). 
     As the comparison result, when the calculated SAR or inner body temperature variation is greater than the reference value, the wireless power transmission apparatus  200  may reduce the output level of the transmitted wireless power signal. 
     As the comparison result, when the calculated SAR or inner body temperature variation amount is smaller than the reference value, the wireless power transmission apparatus  200  may maintain the output level of the transmitted wireless power signal (operation S 340 ). 
     As described above, the wireless power transmission apparatus  200  according to an embodiment of the inventive concept adjusts the output level of the wireless power signal by using the SAR and inner body temperature variation amount calculated by using the EMF data measured by the wireless power receiver  300 . Consequently, the wireless power transmission apparatus  200  according to an embodiment of the inventive concept may secure safety of a human body exposed to the EMF in the wireless power transmission process. 
     According to an embodiment of the inventive concept, power may be more easily supplied by wirelessly supplying power to an implantable medical device. 
     According to an embodiment of the inventive concept, safety may be secured by measuring an exposure level of a human body to an EMF during power transmission and controlling an output level of transmission power using the exposure level. 
     Thee above-disclosed subject matter is to be considered illustrative and not restrictive, and the appended claims are intended to cover all such modifications, enhancements, and other embodiments, which fall within the true spirit and scope of the inventive concept. Thus, to the maximum extent allowed by law, the scope of the inventive concept is to be determined by the broadest permissible interpretation of the following claims and their equivalents, and shall not be restricted or limited by the foregoing detailed description.