An Intuitive Sound Transmission Service based on a User's Touch Interface

An intuitive sound transmission service based on a user's touch interface is suggested. By touching a sound transmitting device, a user can hear sound wirelessly without making any other noise outside. The device utilizes the human body as a sound transmission medium. There is a large difference in acoustic impedance between the air and the human body. The acoustic impedance mismatch between air and the body allows the human body to become an acoustic wave guide. The transmitting sound in the body cannot be heard outside, and the device generates no noise outside. However, it is impossible to penetrate audible sound into the body without reflection. Some portion of sound should be reflected before transmitting into the body, and the reflected sound is heard to others around the user. In this paper, two ultrasonic waves are transmitted into the body to prevent the reflected sound to be heard outside. Two transmitted ultrasonic waves with different frequencies interact in the body due to the nonlinearity of the body, and the difference frequency signal between the two original ultrasonic waves is generated. To minimize the noise which can occur in the process of generating audible sound, single sideband amplitude modulation (SSB AM) method is adopted as a modulation method. If the proposed service is developed, a user may enjoy the music alone by touching a device without transmission line required in conventional earphones.