Ultrasonic intra-body communication using semi-guided waves through human body tissues

Abstract

Body Area Network (BAN) demands a secure and low-power technology. Traditionally, RF signals were used, which suffer from high losses and lack of security. Recently, electro-quasistatic human body communication has emerged, enabling low-power communication, but somewhat susceptible to leakage. Ultrasound is presented as a promising alternative owing to its ability of propagating in water-dominated media, like the human body, besides being safe. Existing studies employ ultrasound devices for powering or communicating across tissues; either through transmitter-receiver aligned configurations (not suitable for non-line-of-sight communication) or using omnidirectional transducers, hence limiting the communication distance to only a few centimeters. This paper presents a theoretical study on confining ultrasound waves inside the human tissues (muscle, fat and skin). Through oblique incidence on the bone/muscle interface, the waves can bypass the bone (highly attenuative tissue) through total internal reflection, and be guided through water-rich body tissues. In addition, the high reflection at the skin/air interface (∼99.9%) confines most of the signal inside the body, ensuring secure communication. Simulations are performed on a simplified cylindrical-shaped human body model at 100 kHz, demonstrating the possibility of transmitting a signal over a distance of ∼1 m with losses <50 dB and leaked signal attenuation of additional >20 dB.