Sound transmission through the human body with digital weaver modulation (DWM) method

An innovative sound transmission system which transmits sound wirelessly to ears without making any other noise outside is suggested. The system utilizes the human body as a sound transmission medium. The human body is a nonlinear medium and the nonlinear characteristic is the basis of the theorem for the system. When two ultrasonic waves with different frequencies are transmitted into the body, the difference frequency signal between the two original ultrasonic waves is generated during the propagation process and audible to a user. In this paper, single sideband amplitude modulation (SSB AM) method is used as a modulation scheme. SSB AM method can minimize the noise which occurs in the process of generating audible sound. To make a SSB AM modulator with a higher degree of accuracy, digital weaver modulation (DWM) method is adopted. DWM method enables a sharp cutoff filter to be implemented without increasing computational complexity in the DSP. An Equalizer filter which compensates the distortions in the ultrasonic transducer is also designed. The developed system was evaluated with a loaf of beef instead of the human body, and generation of full-bandwidth music sound in the beef was demonstrated. If the proposed system is applied to the human body, sound transmission may be possible without cable line required in conventional earphones.