Patent Publication Number: US-2010119080-A1

Title: Human body sound transmission system and method using single sound source

Description:
TECHNICAL FIELD 
     The present invention relates to a human body sound transmission system using a human body as a transmission channel and a method thereof; and, more particularly, to a human body sound transmission system and method using a single sound source which can make users listen without a separate reception apparatus, simplify a sound system structure, and reduce cost of the sound system by transmitting a first high frequency signal carrying a sound signal in one transmission apparatus, transmitting a second high frequency signal having the same frequency as the first high frequency signal in the other transmission apparatus, and recovering the sound signal by a destructive interference between the first high frequency signal and the second high frequency signal in ear region of a user. 
     This work was supported by the Information Technology (IT) research and development program of the Korean Ministry of Information and Communication (MIC) and the Korean Institute for Information Technology Advancement (IITA) [2006-S-072-01, “Controller SoC for Human Body Communications”]. 
     BACKGROUND ART 
     A “Human body communication” eliminates ‘line’ of electrical appliances based on a principle that an electrical signal flows through a human body, and transmits a signal through changing electrical energy of the signal by using the human body as a cable. 
     A “Sound transmission system” disclosed in U.S. publication No. 2006/0143004 published in Jun. 29, 2006, which was filed claiming priority of the KR Patent Application Nos. 10-2004-0103036 and 10-2005-0100624, suggests a high frequency sound transmission system using the human body as the communication channel. In the high frequency sound transmission system, each of two sound transmission apparatuses has a corresponding sound source. 
     That is, in the above conventional sound transmission system, each sound transmission apparatus generates a sound signal, combines the generated sound signal and a high frequency signal, and transmits the combined signal through the human body. However, since each transmission apparatus includes the sound source, a structure of the conventional sound transmission system is complex, and thus manufacturing cost is expensive. 
     DISCLOSURE OF INVENTION 
     Technical Problem 
     An embodiment of the present invention is directed to provide a human body sound transmission system and method using a single sound source which can make users listen without a separate reception apparatus, simplify a sound system structure, and reduce manufacturing cost by transmitting a first high frequency signal carrying a sound signal in one transmission apparatus, transmitting a second high frequency signal having the same frequency as the first high frequency signal in other transmission apparatus, and recovering the sound signal by a destructive interference between the first high frequency signal and the second high frequency signal in ear region of a user. 
     Other objects and advantages of the present invention can be understood by the following description, and become apparent with reference to the embodiments of the present invention. Also, it is obvious to those skilled in the art of the present invention that the objects and advantages of the present invention can be realized by the means as claimed and combinations thereof. 
     Technical Solution 
     In accordance with an aspect of the present invention, there is provided a human body sound transmission system, including: a first transmission block for transmitting a combined signal of a first high frequency signal and a sound signal through a human body; and a second transmission block for transmitting a second high frequency signal having the same frequency as the first high frequency signal through the human body, to thereby recover the sound signal by destructing interference in a ear region of a user. 
     In accordance with another aspect of the present invention, there is provided a human body sound transmission method using a single sound source, comprising: transmitting a first high frequency signal carrying a sound signal through a human body; and transmitting a second high frequency signal having the same frequency as the first high frequency signal through the human body, to thereby recover the sound signal by destructive interference between the first high frequency signal and the second high frequency signal in a ear region of a user. 
     ADVANTAGEOUS EFFECTS 
     In the above present invention, since a human body sound transmission system includes a single sound source, it can be easily implemented. Also, a user contacted to a transmission apparatus can listen to a transmitted sound signal without a separate reception apparatus. 
     In addition, the human body sound transmission system can make only the user doing a human body communication to receive transmitted sound signal. The user can receive the sound signal without the separate reception apparatus, and thus, behaviors of the user may be free. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram illustrating a human body sound transmission system in accordance with an embodiment of the present invention. 
         FIG. 2  is a block diagram illustrating a first transmission apparatus having a sound source in accordance with an embodiment of the present invention. 
         FIG. 3  is a block diagram illustrating a second transmission apparatus without a sound source in accordance with an embodiment of the present invention. 
         FIGS. 4 to 8  are waveforms showing a destructive interference and a constructive interference between two signals transmitted from a human body sound transmission system in accordance with the present invention. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     The advantages, features and aspects of the invention will become apparent from the following description of the embodiments with reference to the accompanying drawings, which is set forth hereinafter, and thus the invention will be easily carried out by those skilled in the art to which the invention pertains. Also, when it is considered that detailed description on a related art may obscure the points of the present invention unnecessarily in describing the present invention, the description will not be provided herein. Hereinafter, specific embodiments of the present invention will be described with reference to the accompanying drawings. 
       FIG. 1  is a diagram illustrating a human body sound transmission system in accordance with an embodiment of the present invention. Hereinafter, a human body sound transmission method using a single sound source in accordance with the present invention will be described together without an additional flowchart. 
     As shown in  FIG. 1 , the human body sound transmission system includes a first transmission apparatus  10  and a second transmission apparatus  20  directly connected to the human body  30 . The first and second transmission apparatuses  10  and  20  are contacted to the human body apart from the same distance from each ear, respectively. Here, the first transmission apparatus  10  has a sound source, and the second transmission apparatus  20  has no sound source. Detailed description will be described referring to  FIGS. 2 and 3 . 
     A user can directly receive only sound signals based on a destructive interference between signals transmitted from each transmission apparatuses  10  and  20  without data processing for demodulating signals transmitted through the human body  30  as a communication signal. 
     The first transmission apparatus  10  generates a combined signal by combining the sound signal and a first high frequency signal, and transmits the combined signal through the human body  30 . Also, the second transmission apparatus  20  generates the second high frequency signal having the same frequency as the first high frequency signal generated in the first transmission apparatus  10  and transmits the second high frequency signal through the human body  30 . 
     In the ear region of the user, the destructive interference and a constructive interference occur by overlapping two signals transmitted from each of transmission apparatuses  10  and  20 . Since a signal generated by the constructive interference is over an audio frequency band of human, the user cannot detect the signal. Hereinafter, only the destructive interference will be described. 
       FIG. 2  is a block diagram illustrating a first transmission apparatus having a sound source in accordance with an embodiment of the present invention; and  FIG. 3  is a block diagram illustrating a second transmission apparatus without a sound source in accordance with an embodiment of the present invention. 
     As shown in  FIG. 2 , the first transmission apparatus  10  having the sound source includes a control unit  101 , a sound generating unit  102 , a high frequency signal generating unit  103 , a signal combining unit  104 , a phase shifter  105 , an amplifier  106 , a calibration unit  107 , a transmitting unit  108  and a distance measurement unit  109 . Herein, the first transmission apparatus  10  may be a hand-held type. 
     On the contrary, as shown in  FIG. 3 , the second transmission apparatus  20  without the sound source includes a control unit  201 , a high frequency signal generating unit  203 , a phase shifter  205 , an amplifier  206 , a calibration unit  207 , a transmitting unit  208  and a distance measurement unit  209 . Herein, the second transmission apparatus  20  may be the hand-held type. 
     The first transmission apparatus  10  transmits the sound signal though the human body  30 . 
     The control units  101  and  201  receive distances between the ear and the first and second transmission apparatuses  10  and  20 , respectively, and adjust frequency and phase of the signal generated in the sound generating unit  102  and the high frequency signal generating units  103  and  203 . That is, the control unit  101  eliminates the high frequency signal included in the combined signal outputted from the first transmission apparatus  10  by the destructive interference in the ear region, allows only sound signals of audio frequency band to be transmitted to the ear of the human, and thus the user can listen sound signals without the separate reception apparatus. 
     The control unit  101  of the first transmission apparatus  10  contacted to the human body  30  sets the frequency of the high frequency signal identically to that of a output signal from the second transmission apparatus  20  based on a distance from the ear to the transmission apparatus and a distance from other transmission apparatus  20  contacted to the same human body  30 . The control unit  201  is operated identically to the control unit  101 . When the two transmission apparatuses  10  and  20  are symmetrically contacted to the human body  30  with the same distance from the each ear, the control units  101  and  201  control the frequency and the phase of the corresponding high frequency signal transmitted through the human body in order to have the same frequency and phase. 
     In other words, the control units  101  and  102  adjust frequencies of output signals generated in the sound generating unit  102  and the high frequency signal generating units  103  and  203 , respectively, to recover only sound signal of audio frequency band based on destructive of the high frequency signals by overlapping of signals outputted from the first and second transmission apparatuses  10  and  20  around the ears. Here, the control units  101  and  201  of the two transmission apparatuses  10  and  20  can control a occurrence part and occurrence time of the destructive interference in the human body  30  by adjusting output speed of signals outputted from the high frequency signal generating units  103  and  203  and the transmitting units  108  and  109  so that a stereophonic sound effect can be provided. 
     Also, the control units  101  and  201  can change phases of output signals by controlling the phase shifters  105  and  205 , respectively, and adjust phases and frequencies of output signals by considering impedance matching between the human body  30  and the transmission apparatuses  10  and  20 . In addition, the control units  101  and  201  transmit pre-stored clock information and impedance matching information of the human body  30  to the calibration units  107  and  207 , respectively, and thus the clock information and the impedance matching information are used to calibrate transmitted signals through the human body  30 . 
     When the clock information and the impedance matching information of the human body  30  are stored in a separate memory of the transmission apparatuses  10  and  20 , the control units  101  and  201  extract the clock information and the impedance matching information from the corresponding memory and transmit them to the calibration units  107  and  207 , respectively, and thus the clock information and the impedance matching information can be used to calibrate transmitted signals through the human body  30 . 
     The sound generating unit  102  of the first transmission apparatus  10  having the sound source extracts sound data from the memory according to the control signal of the control unit  101 , and generates sound signals of audio frequency band corresponding to the extracted sound data in order to transmit the sound signals through the human body  30 . The sound generating unit  102  generates the sound signals based on the sound data stored in the memory of the first transmission apparatus  10 , or generates the sound signals by receiving sound data from an outer communication apparatus. 
     Then, the high frequency signal generating unit  103  of the first transmission apparatus  10  generates a first high frequency signal to be combined and transmitted with the sound signal outputted from the sound generating unit  102 . 
     The high frequency signal generating unit  203  of the second transmission apparatus  20  generates a second high frequency signal having the same phase with the first high frequency signal transmitted from the first transmission apparatus  10 . When the phases of two high frequency signals outputted form the transmission apparatuses  10  and  20  are identical to each other, the phases of the two high frequency signals, i.e., one is a simple high frequency signal and the other is a high frequency signal carrying the sound signal, become out-of phase in the ear region, and thus two high frequency signals are canceled. 
     The frequency of the high frequency signals generated in the high frequency signal generating units  103  and  203  can vary according to the frequency of the sound signal and the impedance of the human body  30 . 
     High frequency signals generated in the two transmission apparatuses  10  and  20  are controlled to have the same phase in order to be canceled by the destructive interference in the ear region of the human body  30 . The signals outputted from the high frequency signal generating units  103  and  203  can be ultrasonic signals having a higher frequency than that of the audio frequency band, i.e., 20 Hz to 20,000 Hz. 
     The sound signal generated in the sound generating unit  102  of the first transmission apparatus  10  and the high frequency signal generated in the high frequency signal generating unit  103  are combined in the signal combining unit  104 , and the combined signal is transmitted through the human body. The signal combining unit  104  combines the sound signal and the high frequency signal in order to minimize attenuation of sound wave during transmission of the sound signal through the human body  30  due to the impedance characteristics of the human body. 
     The phase shifter  105  of the first transmission apparatus  10  changes the output phase of the combined signal outputted from the signal combining unit  104  according to the control signal of the control unit  101 . Also, the phase shifter  205  of the second transmission apparatus  20  changes the phase of the second high frequency signal outputted from the high frequency signal generating unit  203  according to the control signal of the control unit  201 . 
     The phase shifter  105  adjusts the phase of the signal outputted from the first transmission apparatus  10 . Also, the phase shifter  205  adjusts the phase of the signal outputted from the second transmission apparatus  20 . Accordingly, the high frequency signals are canceled when the two high frequency signals are overlapped. When the first distance between the first transmission apparatus  10  contacted to the right side of the human body  30  and the right ear is extremely different from the second distance between the second transmission apparatus  20  contacted to the left side of the human body  30  and the left ear, the phase shifters  105  and  205  adjust the phases of two signals by delaying one of the signals in order that two signals are overlapped and interference occurs in the head of the human body  30 . 
     In addition, the phase shifter  105  changes the phase of the signal outputted from the first transmission apparatus  10  by controlling delay so that an interference occurrence part of the human body  30  is controlled. Likely, the phase shifter  205  changes the phase of the signal outputted from the second transmission apparatus  20  by controlling delay, so that the interference occurrence part of the human body  30  is controlled. 
     The phase shifters  105  and  205  can change the phase of signal based on a general phase shifting method, e.g., an electrical method or a mechanical method, such as a phase shifting method through a line switching. 
     The amplifiers  106  and  206  amplify output level of the phase shifted signals of the two transmission apparatuses in order to prevent attenuation of signals due to added noise during transmission through the human body  30 . 
     Since the control units  101  controls amplification ratio of the amplifier  106  and the control units  201  controls amplification ratio of the amplifier  206 , flexible handling can be achieved due to communication channel environment variation according to skin condition and health condition of the user. 
     In the first transmission apparatus  10  transmitting the combined signal of the sound signal and the high frequency signal, the calibration unit  107  solves sound quality problem i.e., difficult problem of controlling the sound quality, due to signal distortion. The signal distortion is caused by the impedance characteristics of the human body  30 . Since the impedance characteristics of the human body is varied according to the change of contact portions of transmission apparatuses  10  and  20 , and variation of health condition, the calibration considering the impedance characteristics should to be performed. 
     The transmitting units  108  and  208  are directly contacted to the human body  30  in the transmission apparatuses  10  and  20 , and output the combined signal of the sound signal and the high frequency signal, or the high frequency signal, respectively. The transmitting units  108  and  208  perform acoustically coupling between the transmission apparatuses  10  and  20 , and the human body  30 . That is, each of the transmitting units  108  and  208  is a kind of transducer, and transforms and outputs the signal to a vibration signal or an electrical signal which can be transmitted and recovered in the human body. 
     As shown in  FIG. 2 , the calibration unit  107  is located after the amplifier  106  in the first transmission apparatus  10 , and improves frequency characteristic and input/output characteristics by correcting the combined signal outputted from the signal combining unit  104 . However, in another embodiment, the calibration unit  107  may be located before the signal combining unit  104 , and can correct input signals before being combined. 
     Also, the transmission apparatuses  10  and  20  in accordance with the present invention may additionally include the distance measurement units  109  and  209  which measure distances between the contact portion corresponding to each transmission apparatus  10  or  20  and right ear or left ear based on sensing function. Then, the control units  101  and  201  control the phase shifters  105  and  205  based on the distances measured in the measurement units  109  and  209  to recover only the sound signal through destructive interference in the ear region of the user. 
       FIGS. 4 to 8  are waveforms showing a destructive interference and a constructive interference between two signals transmitted from a human body sound transmission system in accordance with the present invention. Hereinafter, transmission of the sound signal in the human body sound transmission system will be described referring to  FIGS. 4 to 8 . 
       FIGS. 5 and 6  represent waveforms of two signals transmitted from the transmission apparatuses  10  and  20 ;  FIG. 7  represents waveform showing the destructive interference between the two signals; and  FIG. 8  represents waveform showing the constructive interference between the two signals. 
       FIG. 4  shows waveforms of a sound signal  301  and a first high frequency signal  302  generated in the first transmission apparatus  10  contacted to the human body  30 ;  FIG. 5  shows waveform representing a signal  303  generated in the signal combining unit  104  by combining the sound signal  301  and the first high frequency signal  302 . Also,  FIG. 6  shows waveform of a second high frequency signal  304  generated in the second transmission apparatus  20  contacted to the same human body  30 . 
     The second high frequency signal  304  shown in  FIG. 6  precedes half-period than the first high frequency signal  302  shown in  FIG. 4 . That is, the first high frequency signal  302  and the second high frequency signal are out-of phase. 
       FIG. 7  shows waveform  305  generated by the destructive interference between the two signals  303  and  304 , which are outputted from the first transmission apparatus  10  and the second transmission apparatus  20  and have different phases to each other; and  FIG. 8  shows waveform  306  generated by the constructive interference between the two signals  303  and  304 . 
     When the destructive interference occurs as shown in  FIG. 7 , the high frequency signals are canceled, and the sound signal is transmitted into the ear region. On the other hand, when the constructive interference occurs as shown in  FIG. 8 , since the high frequency signal, which is higher than the audio frequency band of the human, still remains, user cannot detect the signal generated by the constructive interference. That is, only a signal generated by the destructive interference can be effectively transmitted through the human body, and can be detected by the user. 
     While the signals outputted from the two transmission apparatuses  10  and  20  are continuously transmitted through the medium of the human body, parts of the constructive interference change into the destructive interference, parts of the destructive interference change into the constructive interference in signal transmission. Thus, the sound signal can be detected in all regions overlaying two high frequency signals. 
     As described above, the present invention induces the destructive interference in the ear region by adjusting phases of the high frequency signals. However, the control unit  101  makes only the sound signal to arrive in the ear region of the human body by controlling frequencies of the sound signal outputted from the sound generating unit  102  and the high frequency signal outputted from the high frequency signal generating unit  103 . 
     For example, in case that the sound signal to be transmitted has f 0  frequency, the control unit  101  controls the sound generating unit  102  to generate the sound signal having f 0  frequency and the high frequency generating unit  103  to generate the high frequency signal having f 1  frequency. Also, the control unit  201  controls the high frequency generating unit  203  to generate the high frequency signal having f 1  frequency. Finally, the first transmission apparatus  10  outputs the signal having f 0 +f 1  frequency, and the second transmission apparatus  20  outputs the signal having f 1  frequency. 
     The output signals are combined into a signal having f 0  frequency in the ear region, and the signal is transmitted through the human body. As described above, if the sound signal having a predetermined frequency can be acquired by combining the signals outputted from the two transmission apparatuses  10  and  20  contacted to the human body  30 , any combination of all frequencies can be used. 
     The above described method according to the present invention can be embodied as a program and be stored on a computer readable recording medium. The computer readable recording medium is any data storage device that can store data which can be read by the computer system. The computer readable recording medium includes a read-only memory (ROM), a random-access memory (RAM), a CD-ROM, a floppy disk, a hard disk and an optical magnetic disk. 
     The present application contains subject matter related to Korean Patent Application No. 2007-0042677, filed in the Korean Intellectual Property Office on May 2, 2007, the entire contents of which are incorporated herein by reference. 
     While the present invention has been described with respect to certain preferred embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the scope of the invention as defined in the following claims.